US20100194476A1 - Amplifier compression adjustment circuit - Google Patents
Amplifier compression adjustment circuit Download PDFInfo
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- US20100194476A1 US20100194476A1 US12/366,143 US36614309A US2010194476A1 US 20100194476 A1 US20100194476 A1 US 20100194476A1 US 36614309 A US36614309 A US 36614309A US 2010194476 A1 US2010194476 A1 US 2010194476A1
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- H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
- H03F3/24—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers of transmitter output stages
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- H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
- H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
- H03F1/0211—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the supply voltage or current
- H03F1/0216—Continuous control
- H03F1/0222—Continuous control by using a signal derived from the input signal
- H03F1/0227—Continuous control by using a signal derived from the input signal using supply converters
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- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
- H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
- H03F1/0211—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the supply voltage or current
- H03F1/0216—Continuous control
- H03F1/0233—Continuous control by using a signal derived from the output signal, e.g. bootstrapping the voltage supply
- H03F1/0238—Continuous control by using a signal derived from the output signal, e.g. bootstrapping the voltage supply using supply converters
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- H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
- H03F1/0261—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the polarisation voltage or current, e.g. gliding Class A
- H03F1/0266—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the polarisation voltage or current, e.g. gliding Class A by using a signal derived from the input signal
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- H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
- H03F1/0261—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the polarisation voltage or current, e.g. gliding Class A
- H03F1/0272—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the polarisation voltage or current, e.g. gliding Class A by using a signal derived from the output signal
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- H03F3/189—High-frequency amplifiers, e.g. radio frequency amplifiers
- H03F3/19—High-frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only
- H03F3/195—High-frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only in integrated circuits
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Definitions
- the present invention relates to a circuit for controlling RF PAs (Radio Frequency Power Amplifiers), and more specifically, to an RF PA controller circuit that controls the supply voltage of a PA using a closed amplitude control loop with an amplitude correction signal.
- RF PAs Radio Frequency Power Amplifiers
- RF (Radio Frequency) transmitters and RF power amplifiers are widely used in portable electronic devices such as cellular phones, laptop computers, and other electronic devices. RF transmitters and RF power amplifiers are used in these devices to amplify and transmit the RF signals remotely.
- RF PAs are one of the most significant sources of power consumption in these electronic devices, and their efficiency has a significant impact on the battery life on these portable electronic devices. For example, cellular telephone makers make great efforts to increase the efficiency of the RF PA systems, because the efficiency of the RF PAs is one of the most critical factors determining the battery life of the cellular telephone and its talk time.
- FIG. 1 illustrates a conventional RF transmitter circuit, including a transmitter integrated circuit (TXIC) 102 and an external power amplifier (PA) 104 .
- the RF transmitter circuit may be included in a cellular telephone device using one or more cellular telephone standards (modulation techniques) such as UMTS (Universal Mobile Telephony System) or CDMA (Code Division Multiple Access), although the RF transmitter circuit may be included in any other type of RF electronic device.
- UMTS Universal Mobile Telephony System
- CDMA Code Division Multiple Access
- the RF transmitter circuit will be described herein as a part of a cellular telephone device.
- the TXIC 102 generates the RF signal 106 to be amplified by the PA 104 and transmitted 110 remotely by an antenna (not shown).
- the RF signal 106 may be an RF signal modulated by the TXIC 102 according to the UMTS or CDMA standard.
- the RF power amplifier 104 in general includes an output transistor (not shown) for its last amplification stage.
- the output transistor tends to distort the RF modulated signal 106 , resulting in a wider spectral occupancy at the output signal 110 than at the input signal 106 .
- cellular telephone standards typically regulate the amount of acceptable distortion, thereby requiring that the output transistor fulfill high linearity requirements.
- the output transistor of the PA 104 needs to be biased in such a way that it remains linear at the peak power transmitted. This typically results in power being wasted during the off-peak of the amplitude of the RF input signal 106 , as the biasing remains fixed for the acceptable distortion at the peak power level.
- Certain RF modulation techniques have evolved to require even more spectral efficiency, and thereby forcing the RF PA 104 to sacrifice more efficiency. For instance, while the efficiency at peak power of an output transistor of the PA 104 can be above 60%, when a modulation format such as WCDMA is used, with certain types of coding, the efficiency of the RF PA 104 falls to below 30%. This change in performance is due to the fact that the RF transistor(s) in the RF PA 104 is maintained at an almost fixed bias during the off-peak of the amplitude of the RF input signal 106 .
- EER envelope Elimination and Restoration
- the EER technique applies the amplitude signal (not shown in FIG. 1 ) and the phase signal (not shown in FIG. 1 ) of the RF input signal 106 separately to 2 ports of the power amplifier 104 , i.e., its supply voltage port (Vcc) 108 and its RF input port 107 , respectively.
- Vcc supply voltage port
- the EER technique often fails to provide significant efficiency gains, because the supply voltage 108 cannot be varied in an energy-efficient way to accommodate the large variations in the amplitude signal of the RF input signal 106 and thus it fails to provide a substantial energy efficiency gain while maintaining the required linear amplification of the RF signal in the RF PA 104 .
- This is mainly due to the difficulty in realizing a fast, accurate, wide range, and energy efficient voltage converter to drive the supply voltage of the RF PA 104 .
- variable power supply which is typically comprised of a linear regulator (not shown in FIG. 1 ) that varies its output voltage on a fixed current load such as the PA in linear mode, by principle reduces the supply voltage at constant current and by itself consumes the power resulting from its current multiplied by the voltage drop across the linear regulator when there is a large drop in the amplitude signal of the RF input signal 106 .
- the conventional methods of controlling a PA fail to address the amplitude-to-phase re-modulation (AM-to-PM) which occurs in a non-frequency linear device such as a PA.
- AM-to-PM amplitude-to-phase re-modulation
- PA non-frequency linear device
- the conventional methods are not suitable for the common types of PAs for use in common mobile telephony or mobile data systems because the required spectral occupancy performance is compromised by the AM to PM distortion.
- PAs are typically used in conjunction with band pass filters that have a high electric coefficient of quality.
- These filters are typically of the SAW (surface acoustic wave) type. Due to their high coefficient of quality, the filters exhibit a relatively high group delay. The group delay makes it very difficult for a correction loop to work around the arrangement of the SAW filter and the PA while still meeting the high bandwidth requirements needed for the correction of the AM-to-PM.
- SAW surface acoustic wave
- One embodiment of the present invention disclosed is a power amplifier controller circuit for controlling a power amplifier based upon an amplitude correction signal or amplitude error signal.
- the power amplifier receives and amplifies an input signal to the power amplifier and generates an output signal, and the power amplifier controller circuit controls the power amplifier so that it operates in an efficient manner.
- the PA controller circuit comprises an amplitude control loop and a phase control loop.
- the amplitude control loop determines the amplitude correction signal (also referred to herein as the amplitude error signal), which is indicative of the amplitude difference between the amplitude of the input signal and the attenuated amplitude of the output signal, and adjusts the supply voltage to the power amplifier based upon the amplitude correction signal.
- the phase control loop determines a phase error signal, which indicates a phase difference between phases of the input signal and the output signal, and adjusts the phase of the input signal based upon the phase error signal to match the phase of the output signal.
- the phase control loop corrects for unwanted phase modulation introduced by the AM to PM non-ideality of the power amplifier and thus reduces phase distortion generated by the power amplifier.
- the amplitude control loop comprises an amplitude comparator comparing the amplitude of the input signal with an attenuated amplitude of the output signal to generate an amplitude correction signal, and a power supply coupled to receive the amplitude correction signal and generating the adjusted supply voltage provided to the power amplifier based upon the amplitude correction signal.
- the power supply can be a switched mode power supply.
- a high-efficiency yet low-bandwidth power supply such as the switched mode power supply may be used to provide the adjusted supply voltage to the power amplifier.
- the amplitude correction signal is split into two or more signals with different frequency ranges and provided respectively to different types of power supplies with different levels of efficiency to generate the adjusted supply voltage provided to the power amplifier.
- the power supplies include a first power supply with a first efficiency and a second power supply with a second efficiency higher than the first efficiency.
- the first power supply receives a first portion of the amplitude correction signal in a first frequency range and generates a first adjusted supply output based upon the first portion of the amplitude correction signal
- the second power supply receives a second portion of the amplitude correction signal in a second frequency range lower than the first frequency range and generates a second adjusted supply output based upon the second portion of the amplitude correction signal.
- the first and second adjusted supply outputs are combined to form the adjusted supply voltage provided to the power amplifier.
- the first power supply can be a linear regulator, and the second power supply can be a switched mode power supply.
- the second embodiment of the present invention has the additional advantage that the switched mode power supply may be implemented with even narrower bandwidth as compared to the first embodiment without significantly sacrificing efficiency.
- a narrower bandwidth power supply or a variable power supply with a smaller range of voltage variation is easier to implement.
- the amplitude control loop further comprises a gain control module receiving the amplitude correction signal to generate a gain control signal, and a variable gain amplifier adjusting the amplitude of the input signal according to the gain control signal.
- the third embodiment has the advantage that it is possible to operate the power amplifier at any given depth beyond its compression point, resulting in an extra degree of freedom in designing the PA circuit. This is useful in optimizing the efficiency gain versus spectral occupancy performance.
- the variable gain amplifier By adding the variable gain amplifier, the amplitude of variation of the Vcc or bias voltage to the PA is further reduced, resulting in further significant efficiency gains.
- the amplitude control loop includes a variable gain amplifier (VGA) adjusting the amplitude of the input signal, as in the third embodiment, thus providing a second means of adjusting the amplitude of the output of the PA.
- VGA variable gain amplifier
- the DC components of the amplitude correction signal are blocked from controlling the VGA.
- the DC gain of the VGA is controlled separately by a compression control signal, which sets the average gain of the VGA and thus the drive into the PA.
- the compression control signal provides a means to control the power amplifier's depth beyond its compression point, allowing control of the tradeoff between efficiency and spectral occupancy performance of the PA.
- the amplitude control loop includes a variable gain amplifier (VGA) adjusting the amplitude of the input signal, as in the third embodiment.
- VGA variable gain amplifier
- the DC components of the amplitude correction signal are blocked from controlling the power supply.
- the DC voltage supplied by the power supply is controlled separately by a compression control signal, which sets the average output voltage of the power supply, affecting the compression level of the PA.
- the compression control signal provides a means to control the power amplifier's depth beyond its compression point, allowing control of the tradeoff between efficiency and spectral occupancy performance of the PA.
- the amplitude control loop includes a variable gain amplifier (VGA) adjusting the amplitude of the input signal, as in the third embodiment.
- VGA variable gain amplifier
- the overall loop gain is controlled by a compression control signal, affecting the compression level of the PA.
- the compression control signal provides a means to control the power amplifier's depth beyond its compression point, allowing control of the tradeoff between efficiency and spectral occupancy performance of the PA.
- FIG. 1 illustrates a conventional RF transmitter circuit.
- FIG. 2 illustrates an RF transmitter circuit including the PA controller in accordance with the present invention.
- FIG. 3A illustrates an RF power amplifier system, in accordance with a first embodiment of the present invention.
- FIG. 3B illustrates a method of controlling the amplitude control loop of a RF PA system, in accordance with the first embodiment of the present invention.
- FIG. 4A illustrates an RF power amplifier system, in accordance with a second embodiment of the present invention.
- FIG. 4B illustrates a method of controlling the amplitude control loop of a RF PA system, in accordance with the second embodiment of the present invention.
- FIG. 5A illustrates an RF power amplifier system, in accordance with a third embodiment of the present invention.
- FIG. 5B illustrates a method of controlling the amplitude control loop of a RF PA system, in accordance with the third embodiment of the present invention.
- FIG. 6 illustrates a method of controlling the phase control loop of a RF power amplifier system in accordance with the present invention.
- FIG. 7 illustrates simulation results of the changes in the waveform of the supply voltage 208 to the PA 104 corresponding to the conventional polar control method, the first embodiment of FIG. 3A , and the third embodiment of FIG. 5A , for a typical commercial WCDMA PA with 3.4 V nominal supply voltage and WCDMA modulation using 3.84 Mchips per second.
- FIG. 8 illustrates the simulation results of an example of a time domain waveform present at the node 509 of FIG. 5A for a typical commercial WCDMA PA with 3.4 V nominal supply voltage and WCDMA modulation using 3.84 Mchips per second.
- FIG. 9 illustrates the simulation results of an example of a time domain waveform present at nodes 401 and 403 of FIG. 5A for a typical commercial WCDMA PA with 3.4 V nominal supply voltage and WCDMA modulation using 3.84 Mchips per second.
- FIG. 10A illustrates an RF power amplifier system, in accordance with a fourth embodiment of the present invention.
- FIG. 10B illustrates an implementation example of the RF power amplifier system of FIG. 10A , in accordance with the fourth embodiment of the present invention.
- FIG. 10C illustrates an RF power amplifier system, in accordance with a fifth embodiment of the present invention.
- FIG. 10D illustrates an implementation example of the RF power amplifier system of FIG. 10C , in accordance with the fifth embodiment of the present invention.
- FIG. 10E illustrates an implementation example of generating the compression control signal used in FIGS. 10A , 10 B, 10 C, and 10 D.
- FIG. 10F illustrates an RF power amplifier system, in accordance with a sixth embodiment of the present invention.
- FIG. 11 illustrates how the RF power amplifier systems of FIGS. 10A , 10 B, 10 C, 10 D, and 10 F control the operation point of the RF PA.
- FIG. 2 illustrates an RF transmitter circuit including the PA controller 202 in accordance with the present invention.
- the PA controller 202 is placed between the transmitter IC 102 and the PA 104 to receive the RF signal 204 from the TXIC 102 and provide the RF signal 206 to the PA 104 , while controlling the PA 104 by way of an adjusted supply voltage 208 .
- the PA controller 202 is also placed between the power supply line (Vcc) 210 and the PA 104 .
- the PA 104 amplifies the RF signal 206 to output the amplified RF output signal 110 , which is also provided as a feedback signal back to the PA controller 202 .
- Vcc power supply line
- the adjusted supply voltage 208 is generated by the PA controller 202 based on an amplitude correction signal (not shown in FIG. 2 ) indicative of the difference between the attenuated amplitude of the feedback RF output signal 110 and the amplitude of the RF input signal 204 .
- amplitude correction signal is used herein synonymously with the term “amplitude error signal.”
- the PA controller 202 adjusts the supply voltage (Vcc) 210 based upon the amplitude correction signal to generate the adjusted supply voltage 208 provided to the PA 104 , to optimize the efficiency of the PA 104 .
- An advantage of the PA controller 202 is that existing signal connections to the PA 104 and the TXIC 102 need not change when the PA controller 202 is inserted between the TXIC 102 , the PA 104 , and the supply voltage (Vcc) 210 .
- the PA controller circuit 202 may also adjust the phase and amplitude of the signal 204 to allow for power control and PA ramping, in accordance with information received through the configuration signals 209 . Since the PA controller circuit 202 is aware of the voltage at the output and the current in the power amplifier 104 , it can also adjust for load variations at an antenna (not shown herein) that may be used with the PA. If a directional coupler (not shown) is used to feed the attenuated amplitude of the signal 204 , the PA controller 202 can adjust the forward power while controlling the PA operation point as it is aware of the voltage and current at node 208 .
- FIG. 3A illustrates an RF PA system, according to a first embodiment of the present invention.
- the RF PA system includes the PA 104 , and the PA controller 202 including a closed amplitude control loop and a closed phase control loop.
- the phase control loop includes two limiters 312 , 314 , a phase comparator 316 , a loop filter (PLF (Phase Loop Filter)) 318 , and a phase shifter 320 .
- the phase comparator 316 is of an adequate type with a capture range greater than 2*PI.
- a combination of adjustable delay elements and frequency dividers may be used.
- a phase sub-ranging system can be used since the dynamic phase variations that the phase correction loop processes are limited in amplitude.
- a sub-ranging phase control block (not shown) could be one of the constituents of the phase comparator 316 used with this system. Advantages of using sub-ranging in the phase comparator 316 are stability and good noise.
- the amplitude control loop includes an adjusted variable attenuator (RFFA (RF Feedback Attenuator)) 306 , two matched amplitude detectors 302 , 304 , a comparator 308 , and a switched mode power supply (SMPS) 310 .
- RFFA RF Feedback Attenuator
- SMPS switched mode power supply
- the phase control loop monitors the RF input signal 204 from the transmitter IC 102 (not shown in FIG. 3A ) and compares the phase of the RF input signal 204 with the phase of the output signal 110 of the PA 104 attenuated 326 by the adjusted variable attenuator (RFFA) 306 , resulting in a control signal 319 that varies the phase of the RF signal 206 coming out of the phase shifter 320 .
- the limiter 312 receives the RF input signal 204 from the TXIC 102 and outputs to the comparator 316 an amplitude limited signal 324 mathematically representative of the phase of its input signal.
- the limiter 314 also receives the output signal 110 of the PA 104 as attenuated 326 by the adjusted variable attenuator (RFFA) 306 , and outputs its phase signal 325 to the comparator 316 .
- the comparator 316 compares the phases of the output signals 324 , 325 of the two limiters 312 , 314 , and generates a phase error signal 317 .
- phase error signal is used herein synonymously with the term “phase correction signal.”
- the phase error signal 317 is filtered by the loop filter (PLF) 318 to generate the phase control signal 319 .
- the loop filter 318 completes the phase loop and provides the necessary gain, bandwidth limitation, and loop stability required for the phase loop to function properly.
- the particular loop filter used here can be of any type, and can include multiple integration and derivation stages so as to satisfy the best loop performance.
- the types of the loop filter may include classical types I, II, and the like.
- a particularity of this phase loop design is that the group delay through the PA 104 must be taken into account for stability reasons. This is achieved by choosing the proper pole-zero placement in the loop filter and may include delay compensation.
- the phase control signal 319 is input to the phase shifter 320 to control the shifting of the phase of the input RF signal 206 so that the phase of the output signal 110 dynamically matches the phase of the transmitter signal 204 .
- phase control loop The function of the phase control loop is to counteract the AM (Amplitude Modulation) to PM (Phase Modulation) characteristics of the PA 104 , which is part of the normal distortion characteristics of transistor-based amplifiers, allowing for the phase of the RF signal to be held constant at the output 110 of the PA 104 compared with the input 204 of the phase shifter 320 and thus reducing phase distortion generated by the PA 104 .
- This phase control loop contributes to linearizing the PA 104 as the AM to PM phase shift of the PA 104 tends to become higher at higher power levels.
- the phase control loop allows the PA 104 to function at higher power levels with less distortion for the output signal 110 , thus allowing the use of the PA 104 in more favorable efficiency conditions.
- the phase control loop also helps in correcting any additional AM to PM characteristics that the amplitude control loop (described below) may cause. While FIG. 3A shows the phase shifter circuit 320 controlling the input to the PA 104 , it is also possible to place the phase shifter 320 at the output of the PA 104 with the same benefits.
- phase control loop is of the error correction only type.
- the phase control loop does not modify the phase of the input signal 204 to the PA 104 unless the PA 104 or the amplitude control loop introduces a phase error. Since the noise contributions of the feedback loops affect the overall signal quality of the RF transmitter, an error correction only loop such as the phase control loop shown in FIG. 3A by definition introduces only a small correction, hence has a low noise contribution.
- the amplitude control loop is also of the error correction only type, and thus is referred to herein as the amplitude correction loop.
- amplitude control loop and amplitude correction loop are used synonymously herein.
- the amplitude of the RF input signal 204 is monitored through the amplitude detector 302 and compared by the comparator 308 with the amplitude at the output 110 of the PA 104 as attenuated 326 by the adjusted variable attenuator (RFFA) 306 , seen through a matched amplitude detector 304 .
- the attenuator 306 is adjusted such that the output 110 of the PA 104 is at a desired level.
- variable attenuator (RFFA) 306 This can be achieved though programming 321 the variable attenuator (RFFA) 306 by either a digital input to the PA controller 202 or by analog control of the variable attenuator (RFFA) 306 .
- the comparator 308 generates an error signal 309 indicating the difference between the amplitude of the input RF signal 204 and the attenuated amplitude 326 of the output RF signal 110 , referred to herein as the “amplitude correction signal” 309 .
- the amplitude correction signal 309 is fed into power supply 310 , which is a switch mode power supply (SMPS).
- the SMPS 310 generates an adjusted supply voltage 208 provided to one or more supply voltage pins of the PA 104 based upon the amplitude correction signal 309 .
- the adjusted supply voltage 208 in essence operates as a bias control signal that controls the operating point of the PA 104 .
- adjusting the supply voltage 208 of the PA 104 has the effect of varying its gain, as well as changing its efficiency. For a given output power, lowering the supply voltage 208 to the PA 104 provides better efficiency for the PA 104 .
- the adjusted supply voltage 208 of the PA 104 is adjusted to ensure that the PA 104 stays in its most efficient amplification zone. Because adjusting the supply voltage 208 of the PA 104 does make a change to the gain of the PA 104 , the output amplitude of the PA 104 changes with the supply voltage 208 from the SMPS 310 , and the amplitude control loop can be closed. The principles of such operation can be explained as follows.
- the amplitude control loop will detect this error between the output and input of the PA 104 , and raise the supply voltage to the PA 104 such that the initially-desired output power is delivered, resulting in linear operation of the system, even with a non-linear PA 104 .
- the PA 104 will be fully or partially saturated from its Vcc, for example, the highest 10 dB of its output power range, and as the RF modulation of the RF signal 104 forces the amplitude to vary, the amplitude control loop will only be actively controlling the supply voltage 208 to the PA 104 when the highest powers are required. For lower input power, the amplitude control loop will leave the supply voltage 208 at a fixed level because it detects no gain error, resulting in a fixed gain for the PA 104 .
- the depth beyond compression can be adjusted by setting the level of the input signal 204 and the level of the attenuator 306 , as well as the default supply voltage Vcc (not shown in FIG. 3A ) to the PA 104 .
- FIG. 7 This behavior is illustrated in FIG. 7 where simulation results compare the behavior of the conventional polar architecture (with no feedback) where the supply voltage to the PA swings between 0.1 V and 2.9 V and reaches a minimum value around 0.1 V as shown with curve 701 , while the supply voltage 208 to the PA 104 in the first embodiment of FIG. 3A using the amplitude correction signal 309 does not drop below 0.5 V as shown with curve labeled 702 .
- the amplitude swing in the dual gain control method is clearly further reduced as indicated by curve 703 , as will be explained in detail below with respect to the third embodiment of the present invention with reference to FIGS. 5A and 5B .
- Varying the supply voltage to the PA 104 also results in a phase change.
- the phase control loop described above operates in conjunction with the amplitude control loop to maintain the accuracy of RF modulation at the output signal of the PA 104 .
- the phase control loop is also an error correction loop only, and therefore minimally contributes to noise.
- the amplitude correction loop has the advantage that an SMPS 310 , which does not consume any significant power by itself and thus actually increases the efficiency of the overall RF power amplifier system, can be used to generate the adjusted supply voltage 208 to the PA 104 .
- An SMPS 310 is easier to implement to follow the amplitude correction signal 309 with a narrow range of variation, but would be more difficult to implement if it had to follow the unmodified amplitude of the RF input signal 204 .
- This is related to the fact that the amplitude signal itself has its fastest variations when the amplitude itself is low.
- the amplitude correction loop does not need to make any changes to its output when the PA is operating in linear mode.
- the amplitude correction signal 309 may be only active for the highest 10 dB of the actual output power variation.
- the amplitude signal itself may vary by 40 dB, and varies much faster between ⁇ 10 dBc to ⁇ 40 dBc than it does between 0 dBc to ⁇ 10 dBc.
- the bandwidth requirements on the SMPS 310 which are coupled with the rate of change of the voltage, are reduced when an amplitude correction signal 309 rather than the amplitude signal itself is used to control the supply of the PA 104 .
- the SMPS 310 does not consume any significant power by itself, and thus does not significantly contribute to usage of the battery power, and actually increases the efficiency of the RF power amplifier system.
- a conventional polar modulation technique typically utilizes the amplitude signal itself to adjust the supply voltage to the PA 104 , which prevents the use of an SMPS 310 for wideband RF signals because of the higher bandwidth requirements. Therefore, conventional RF power amplifier control systems typically use linear regulators (rather than an SMPS) to adjust the supply voltage to the PA 104 .
- linear regulators rather than an SMPS
- Such a linear regulator by itself consumes power resulting from its current multiplied by the voltage drop across the linear regulator. When there is a large drop in the amplitude signal, this can result in significant power being lost and results in none or little reduction in the overall battery power being consumed by the RF transmitter. This is because any efficiency gained in the RF PA is mostly lost in the linear regulator itself.
- FIG. 3B illustrates a method of controlling the amplitude control loop of a RF PA 104 in an RF PA system, according to the first embodiment of the present invention.
- the comparator 308 compares 354 the amplitude 323 of the RF input signal 204 with the attenuated amplitude 322 of the RF output signal 110 from the PA 104 to generate an amplitude correction signal 309 .
- the SMPS 310 generates 358 an adjusted supply voltage 208 provided to the PA 104 based upon the amplitude correction signal 309 , and the process ends 360 .
- FIG. 4A illustrates an RF PA system, according to a second embodiment of the present invention.
- the RF PA system illustrated in FIG. 4A is substantially the same as the RF transmitter circuit illustrated in FIG. 3A , except that (i) the amplitude correction signal 309 is split into two signals, a high frequency amplitude correction signal 401 that is fed into a high frequency path including a linear regulator 402 and a low frequency amplitude correction signal 403 that is fed into a low frequency path including an SMPS 404 and that (ii) the outputs of the linear regulator 402 and the SMPS 404 are combined in the adder block 406 to generate the adjusted supply voltage 208 to the PA 104 .
- a simple current adding node, a small, high frequency transformer or other types of active electronic solutions can be used as the adder block 406 .
- Any other types of power combiner circuits may be used as the adder block 406 .
- the high frequency amplitude correction signal 401 is input to the linear regulator 402 , which generates the high frequency part 405 of the adjusted supply voltage 208 .
- the low frequency amplitude correction signal 403 is input to the SMPS 404 , which generates the low frequency part 407 of the adjusted supply voltage 208 .
- the adder block 406 combines the high frequency part 405 and the low frequency part 407 to generate the adjusted supply voltage 208 to the PA 104 in order to keep the PA 104 in an efficient operation range.
- the amplitude correction signal 309 is split into the high frequency amplitude correction signal 401 and the low frequency amplitude correction signal 403 using the high pass filter 410 and the low pass filter 411 , respectively.
- the high frequency amplitude correction signal 401 comprised of components of the amplitude correction signal 309 higher than a predetermined frequency
- the low frequency amplitude correction signal 403 is comprised of components of the amplitude correction signal 309 lower than the predetermined frequency.
- the predetermined frequency used to split the amplitude correction signal 309 can be set at any frequency, but is preferably set at an optimum point where the efficiency of the overall RF transmitter system becomes sufficiently improved.
- the predetermined frequency can be as low as 1/20 th of the spectrally occupied bandwidth for the RF signal.
- the predetermined frequency may not be fixed but may be adjusted dynamically to achieve optimum performance of the RF transmitter system.
- Power consumed by the linear regulator 401 from a power source such as a battery (not shown) for a given control voltage 208 on the PA 104 can be approximated as follows:
- the SMPS 404 achieves much lower power consumption. While the linear regulator 402 is generally less efficient than the SMPS 404 , the linear regulator 402 processing the high frequency part 401 of the amplitude correction signal 309 does not make the overall RF PA system inefficient in any significant way, because most of the energy of the amplitude correction signal 309 is contained in the low frequency part 403 rather than the high frequency part 401 . This is explained below with reference to FIGS. 8 and 9 .
- both a high efficiency path comprised of the SMPS 404 carrying the low frequency portion 403 of the amplitude correction signal 309 and a low efficiency path comprised of the linear regulator 402 carrying the high frequency portion 401 of the amplitude correction signal 309 has the advantage that it is possible to use an SMPS 404 with a limited frequency response.
- the SMPS 404 need not accommodate for very high frequencies but just accommodates for a limited range of lower frequencies of the amplitude correction signal 309 , making the SMPS 404 much easier and more cost-effective to implement.
- Combining the SMPS 404 with the linear regulator 402 enables high bandwidths of operation accommodating for full frequency ranges of the amplitude correction signal 309 without sacrificing the overall efficiency of the RF PA system in any significant way, since most of the energy of the amplitude correction signal 309 that is contained in the low frequency part 403 of the amplitude correction signal 309 is processed by the more efficient SMPS 404 rather than the less efficient linear regulator 402 .
- Table 1 illustrates the percentage of energy contained in the various frequency ranges in a hypothetical simple 4QAM (Quadrature Amplitude Modulation) signal used in WCDMA cellular telephones and the overall efficiency that can be expected to be achieved by the RF transmitter according to the embodiment of FIG. 4A with the assumptions of the particular operating conditions as illustrated in Table 1.
- the combined amplitude and phase spectrum is 4 MHz wide.
- FIG. 4B illustrates a method of controlling the amplitude control loop of a RF PA in an RF PA system, in accordance with the second embodiment of the present invention.
- FIG. 4B is explained in conjunction with FIG. 4A .
- the comparator 308 compares 454 the amplitude 323 of the RF input signal 204 with the attenuated amplitude 322 of the RF output signal 110 from the PA 104 to generate an amplitude correction signal 309 .
- the low frequency part 403 of the amplitude correction signal 309 is applied 456 to the high efficiency SMPS 404 while the high frequency part 401 of the amplitude correction signal 309 is applied 456 to the low efficiency linear regulator 402 .
- the supply voltage 208 to the PA 104 is adjusted 460 based upon the combination of the outputs 407 , 405 of the high efficiency SMPS 404 and the low efficiency linear regulator 402 , and the process ends 462 .
- FIG. 5A illustrates an RF PA system, according to a third embodiment of the present invention.
- the RF transmitter system illustrated in FIG. 5A is substantially the same as the RF transmitter system illustrated in FIG. 4A , except that the gain control block 506 and the variable gain amplifier 502 are added to provide an additional means to control the efficiency of the PA 104 and the overall RF transmitter system.
- the third embodiment of FIG. 5A is illustrated herein as an improvement to the second embodiment of FIG. 4A , note that the same concepts of the third embodiment of FIG. 5A can also be used to improve the first embodiment of FIG. 3A .
- the gain control block 506 receives the amplitude correction signal 309 and adjusts the gain of the variable gain amplifier 502 based upon the amplitude correction signal 309 , as well as passing the low frequency and high frequency parts 403 , 401 of the amplitude correction signal 309 to the SMPS 404 and the linear regulator 402 , respectively, to generate the adjusted supply voltage 208 as explained above with reference to FIG. 4A .
- a control signal 504 is created to further compensate the gain of the variable gain amplifier 502 before the PA 104 .
- This arrangement allows the use of even lower bandwidth for the PA controller system as compared to that of the second embodiment described in FIG. 4A above. Also the programmability of the output power can now be entirely left to the PA controller 202 , while in the embodiment of FIG. 4A changing the output power required a change in gain in the transmitter IC 102 .
- variable gain amplifier 502 and the gain control block 506 it is possible to use the PA 104 at any given depth beyond its compression point.
- depth beyond compression is used herein to refer to the difference between the averaged input compression level of the PA 104 and the actual averaged input power at the PA 104 .
- the input to the PA 104 can be overdriven by 10 dB beyond the 1 dB compression point of the PA 104 .
- a dynamic adjustment of both the input level and the supply voltage allows this loop system to reduce significantly further the amplitude of the control voltage 208 .
- the independent programming of gain and compression point by the closed amplitude control loop also makes it possible to reduce the amount of high frequency energy that the power supply system (linear regulator) has to deliver to the PA 104 .
- This can be done by having the variable gain amplifier 502 correct for some of the gain error at a higher speed than the Vcc control loop (closed on node 208 ) can do, thus reducing the amount of correction that is to be done by the low efficiency, high frequency branch (linear regulator 401 ).
- the bandwidth of the signals at nodes 208 and 504 can be made to be significantly different.
- the gain control block 506 adjusts the compression point while the gain loop remains closed through the variable gain amplifier 502 . This allows the RF controller system to search an optimum depth beyond compression (as measured by the absolute value of the amplitude correction signal 309 or alternatively by the averaged value of the gain control 504 ) and efficiency with less effect on the resulting signal quality.
- the search for the optimum depth beyond compression can be made by a slow control loop which monitors the absolute value of the amplitude correction signal 309 , as well as its derivative. Another alternative is to monitor the averaged value of the gain control signal 504 .
- a control system for the compression level of the variable gain amplifier 502 can be implemented. Because in the embodiment of FIG. 5A both the supply voltage 208 to the PA 104 and the input 508 to the PA 104 can be adjusted, this embodiment inherently offers greater flexibility in design by exploiting two sources of signal information for control. This allows to further reduce the amplitude of the variation of the voltage control signal 208 , as shown on FIG. 7 , where the voltage with the smallest variation is the signal labeled 703 , corresponding to this third embodiment of FIG. 5A .
- the third embodiment of FIG. 5A is also well suited to process directly a polar representation of the RF signal.
- an amplitude signal from the TXIC 102 would couple to the amplitude detector 302 and a phase only signal from the TXIC 102 would be coupled to the variable gain amplifier 502 and the limiter 312 .
- FIG. 5B illustrates a method of controlling the amplitude control loop of a RF PA in an RF transmitter system, in accordance with the third embodiment of the present invention.
- the method illustrated in FIG. 5B is substantially the same as the method illustrated in FIG. 4B , except that step 512 is added.
- step 512 the input signal 508 to the PA 104 is adjusted, by use of a variable gain amplifier 502 , based upon the amplitude correction signal 309 . Therefore, the method of FIG. 5B is provided with an additional means for controlling the efficiency of the PA 104 and the overall RF PA system.
- FIG. 6 illustrates a method of controlling the phase control loop of a RF PA in an RF PA system in accordance with the present invention.
- the phase control method of FIG. 6 can be used with any one of the methods of controlling the amplitude correction loops described in FIGS. 3B , 4 B, and 5 B, as shown in FIGS. 3A , 4 A, and 5 A.
- the method of FIG. 6 will be explained in conjunction with FIGS. 3A , 4 A, and 5 A.
- the comparator 316 compares 604 the phase of the RF input signal 204 with the phase of the attenuated RF output signal 326 from the PA 104 to generate the phase error signal 317 .
- the phase error signal 316 is filtered 606 by the loop filter (PLF) 318 to generate the phase control signal 319 .
- the phase of the input RF signal 204 is shifted 608 based upon the phase control signal 319 so that the difference between the phase of the input signal 204 and the phase of the output RF signal 110 is held constant, and the process ends 610 .
- FIG. 7 illustrates simulation results of the changes in the waveform of the supply voltage 208 to the PA corresponding to the conventional polar control method, the first embodiment of FIG. 3A , and the third embodiment of FIG. 5A , for a typical commercial WCDMA PA with 3.4 V nominal supply voltage and WCDMA modulation using 3.84 Mchips per second.
- the adjusted supply voltage 208 generated by a conventional polar system as indicated by curve 701 varies the most with wide fluctuations
- the adjusted supply voltage 208 generated by the first embodiment of FIG. 3A as indicated by curve 702 varies less than the curve 701
- the adjusted supply voltage 703 generated by the third embodiment of FIG. 5A varies the least with only a little fluctuation.
- FIG. 8 illustrates the simulation results of an example of a time domain waveform present at node 509 (which voltage would be the same as the voltage at node 309 ) of FIG. 5A
- FIG. 9 illustrates the simulation results of an example of a time domain waveform present at nodes 401 and 403 of FIG. 5A , both for a typical commercial WCDMA PA with 3.4 V nominal supply voltage and WCDMA modulation using 3.84 Mchips per second.
- the loop voltage versus time on FIG. 8 shows that the loops maintain a voltage much lower than 2.5 V most of the time, except for some short instants. This is due to the signal's amplitude characteristics which require high peaks but a much lower average.
- the voltages 401 and 403 are shown.
- the low pass filtered signal 403 is almost a DC signal of value 1.9 V
- FIG. 10A illustrates an RF power amplifier system, in accordance with a fourth embodiment of the present invention.
- the RF PA system illustrated in FIG. 10A is substantially the same as the RF PA system illustrated in FIG. 5A , except that it additionally includes a DC blocking module 1002 and a summing module 1004 , and additionally receives a compression control signal 1001 .
- the DC blocking module 1002 is added in series with the VGA gain control signal 504 and filters out (blocks) DC components of the VGA gain control signal 504 to output primarily the AC components 1006 of the VGA control signal 504 .
- the compression control signal 1001 is a DC or low frequency signal that is used to set the average gain of the VGA 502 .
- the AC components 1006 of the VGA control signal 504 and the compression control signal 1001 are summed in the summing module 1004 to generate a modified VGA control signal 1008 .
- the modified VGA control signal 1008 sets the gain of the VGA 502 .
- the gain control block 506 adjusts the gain of the VGA 502 with the VGA gain control line 1006 based upon only the AC components of the amplitude correction signal 309 .
- the AC components 1006 passed by the DC blocking module (also referred to herein as a frequency blocking module or frequency selection module) 1002 include sufficiently low frequencies to ensure that the VGA 502 contributes to correcting the amplitude error of the PA 104 even at low frequencies.
- the average gain of the VGA 502 is set by the compression control signal 1001 , which is added to the AC components 1006 of the VGA gain control signal 504 .
- the VGA 502 increases its average gain and thus increases its drive into the PA 104 . Increased drive into PA 104 results in the PA 104 operating in a higher depth beyond compression with improved power efficiency, with a tradeoff in spectral occupancy performance due to increased amplitude of the variation of the supply voltage 208 to the PA 104 .
- FIG. 10A is illustrated herein as an improvement to the third embodiment of FIG. 5A with multiple power supplies 402 , 404 generating the supply voltage 208 to the PA 104 , note that the concepts of the fourth embodiment of FIG. 10A can also be used to in a RF PA system with a single power supply controlling the supply voltage 208 to the PA 104 .
- FIG. 10B illustrates an implementation example of the RF power amplifier system of FIG. 10A , in accordance with the fourth embodiment of the present invention.
- the example circuitry of FIG. 10B is substantially the same as the RF PA system of FIG. 10A , except that the DC blocking module 1002 of FIG. 10A is implemented as a capacitor 1052 , a resistor 1056 is added in series to the compression control signal 1001 , and the summing block 1004 is implemented as a simple current summing node 1054 .
- the capacitor 1052 blocks the DC components of the VGA gain control signal 504 to output primarily the AC components 1006 of the VGA control signal 504 .
- the compression control signal 1001 imposes a DC level to control the average gain of the VGA 502 .
- the AC components 1006 above the frequency F of the VGA control signal 504 and the DC frequency components below the frequency F of the compression control signal 1001 are summed in the summing node 1054 to generate a modified VGA control signal 1008 .
- the modified VGA control signal 1008 sets the gain of the VGA 502 .
- the gain control block 506 adjusts the gain of the VGA 502 with the VGA gain control line 1006 based upon only the AC components of the amplitude correction signal 309 above frequency F.
- the average gain of the VGA 502 is set by the DC components of the compression control signal 1001 , which are superimposed on the AC components 1006 of the VGA gain control signal 504 .
- the VGA 502 increases its average gain and thus increases its drive into the PA 104 .
- FIG. 10C illustrates an RF power amplifier system, in accordance with a fifth embodiment of the present invention.
- the RF PA system illustrated in FIG. 10C is substantially the same as the RF PA system illustrated in FIG. 10A , except that DC blocking module 1062 is now in series with the amplitude correction signal 509 which controls power supply 1060 and filters out (blocks) DC components of the amplitude correction signal 509 from gain control block 506 to output primarily the AC components of the amplitude correction signal 509 .
- the compression control signal 1070 is a DC or low frequency signal that is used to set the average voltage 208 supplied to PA 104 by power supply 1060 .
- the AC components 1064 of the amplitude correction signal 509 and the compression control signal 1070 are summed in the summing module 1066 to generate a modified amplitude correction signal 1068 .
- the modified amplitude correction signal 1068 sets the voltage 208 supplied by power supply 1060 to the PA 104 .
- the amplitude correction loop adjusts the voltage 208 supplied by power supply 1060 based upon only the AC components 1064 of the amplitude correction signal 309 .
- the AC components 1064 passed by the DC blocking module (also referred to herein as a frequency blocking module or frequency selection module) 1062 include sufficiently low frequencies to ensure that the power supply 1060 contributes to correcting the amplitude error of the PA 104 even at low frequencies.
- the average voltage 208 supplied to PA 104 by power supply 1060 is set by the compression control signal 1070 , which is added to the AC components 1064 of the power supply control signal 509 .
- the control polarity is designed such that by increasing the level of the compression control signal 1070 , power supply 1060 decreases its average voltage 208 supplied to the PA 104 and thus decreases the headroom of PA 104 . Decreased headroom for PA 104 results in the PA 104 operating in a higher depth beyond compression with improved power efficiency, with a tradeoff in spectral occupancy performance due to increased amplitude of the variation of the supply voltage 208 to the PA 104 .
- FIG. 10C is illustrated herein as an improvement to the fourth embodiment of FIG. 5A with multiple power supplies 402 , 404 (within overall power supply block 1060 ) generating the supply voltage 208 to the PA 104
- the concepts of the fifth embodiment of FIG. 10C can also be used in a RF PA system with a single power supply controlling the supply voltage 208 to the PA 104 .
- FIG. 10D illustrates an implementation example of the RF power amplifier system of FIG. 10C in accordance with the fifth embodiment of the present invention.
- the example circuitry of FIG. 10D is substantially the same as the RF PA system of FIG. 10 C, except that the DC blocking module 1062 of FIG. 10C is implemented as a capacitor 1072 , a resistor 1078 is added in series to the compression control signal 1070 , and the summing block 1066 is implemented as a simple current summing node 1076 .
- the capacitor 1072 blocks the DC components of the amplitude correction signal 509 to output primarily the AC components 1064 of the amplitude correction signal 509 .
- the compression control signal 1070 imposes a DC level to control the average voltage 208 of power supply 1060 .
- the AC components 1064 above the frequency F of the amplitude correction signal 509 and the DC frequency components below the frequency F of the compression control signal 1070 are summed in the summing node 1076 to generate a modified amplitude correction signal 1068 .
- the modified amplitude correction signal 1068 sets the voltage 208 of power supply 1060 .
- the voltage 208 supplied by power supply 1060 is based upon only the AC components of the amplitude correction signal 509 above frequency F.
- the average voltage 208 to PA 104 is set by the DC components of the compression control signal 1070 , which are superimposed on the AC components 1064 of the amplitude correction signal 509 .
- the power supply 1060 decreases its average voltage 208 and thus increases the level of compression of the PA 104 .
- FIG. 10E illustrates an implementation example of generating the compression control signal used in FIGS. 10A , 10 B, 10 C, and 10 D, utilizing distortion control module 1080 .
- the distortion control module 1080 samples a signal at distortion measurement input 1094 (input) and provides a compression control signal 1095 (output) based on the difference between the distortion determined at input 1094 and target distortion level 1092 .
- Input 1094 is typically coupled to PA output signal 110 or 326 in the relevant embodiments.
- the compression control signal 1095 is equivalent to the compression control signal 1001 in FIG. 10A , and the compression control signal 1070 in FIG. 10C .
- Distortion measurement module 214 comprises a frequency down-conversion module 1084 , a pair of filters 1085 , 1086 , a pair of power detectors 1087 , 1088 , and a ratio calculation module 1089 .
- Input signal 1094 is down-converted through a frequency down-conversion module 1084 .
- the frequency down-conversion module 1084 comprises an I/Q demodulator (not shown).
- the frequency down-conversion module 1084 outputs the down-converted signal to two different filters: a desired channel filter 1085 and an outside desired channel filter 1086 .
- the filters 1085 , 1086 can be analog or digital filters.
- the desired channel filter 1085 is configured to pass frequencies within the desired channel and remove frequencies outside the desired channel.
- the outside desired channel filter 1086 is configured to pass frequencies within one or more ranges outside the range of the desired frequency channel.
- the frequency ranges passed by the outside desired channel filter 1086 can include frequencies in an adjacent channel, an alternate channel, a combination of an adjacent channel and an alternate channel, or any other combination of frequency ranges outside the desired channel.
- Each filter 1085 , 1086 outputs a filtered signal to a power detector 1087 , 1088 , respectively, for determining power levels of the filtered signals.
- the power detector 1087 determines and outputs a power level corresponding to the signal power in the desired channel.
- the power detector 1088 determines and outputs a power level corresponding to the signal power outside of the desired channel (e.g., adjacent channel power, alternate channel power, or a combination of the two).
- the outputs of the power detectors 1087 , 1088 are coupled to the ratio calculation module 1089 to determine the ratio of the outside desired channel power to the desired channel power.
- the ratio of these powers is a measure of distortion 1090 .
- the measure of distortion 1090 may be given by:
- the comparator 1093 compares this measured distortion level 1090 with a target distortion level 1092 . As the measured PA distortion level 1090 decreases lower than the target distortion level 1092 , the level of output 1095 increases. As the measured PA distortion level 1090 increases higher than the target distortion level 1092 , the level of output 1095 decreases. As mentioned previously, the target distortion level 1092 may be chosen to ensure adjacent- and alternate-channel power levels meet cellular telephone standards.
- the distortion control module 1080 may be part of a servo loop which attempts to target a specific acceptable distortion level 1092 . Filtering and gain adjustment elements required for loop stability are not shown, and are typically required to stabilize the loop.
- FIG. 10E describes a method of measurement of distortion
- other methods may be substituted.
- EVM Error Vector Magnitude
- Peak Amplitude Distortion or any other measurement that represents distortion may be used.
- output 1095 is connected to compression control signal 1001 and 1070 in FIGS. 10A and 10C , respectively.
- a decrease in the level of output 1095 indicates a level of distortion that is higher than the target distortion level 1092 .
- output 1095 is connected to the compression control signal 1001 or 1070 , a corresponding decrease in the compression of PA 104 results, which in turn results in a decrease in distortion at the output of PA 104 .
- a servo loop is created, with the system targeting the target distortion level 1092 .
- Such a control loop is desirable because it optimizes the efficiency of PA 104 by maintaining the maximum level of PA compression to enhance efficiency, while maintaining an acceptable level of distortion.
- FIG. 10E describes in detail a method for determining the level of distortion at the PA output, other methods may be substituted and are still within the spirit of the invention.
- FIG. 10F illustrates an RF power amplifier system, in accordance with a sixth embodiment of the present invention.
- the RF PA system illustrated in FIG. 10F is substantially the same as the RF PA system illustrated in FIG. 5A , except that compression control signal 1099 is used to control RFFA (RF Feedback Attenuator) 306 .
- RFFA RF Feedback Attenuator
- Reducing the attenuation at RFFA 306 has the effect of decreasing the overall amplitude closed loop gain, thus forcing PA 104 further into compression.
- increasing the attenuation at RFFA 306 increases overall amplitude closed loop gain, and reduces the level of compression of PA 104 .
- controlling RFFA 306 is an effective way to control the depth beyond compression of PA 104 .
- Gain control block 506 may include circuitry to block or modify the DC components of amplitude correction signal 309 before passing this signal to VGA control 504 . Note that while FIG. 10F describes in detail a technique for adjusting the overall amplitude closed loop gain, other methods may be substituted and are still within the spirit of the invention.
- FIG. 11 illustrates how the RF power amplifier system of FIGS. 10A , 10 B, 10 C, 10 D, and 10 F control the operation point of the RF PA.
- the graphs shown in FIG. 11 illustrate the relationship between the input power Pin to the PA 104 and the output power Pout of the PA 104 .
- the output power (Pout) of the PA 104 increases approximately linearly as the input power (Pin) is increased when the PA 104 operates in the region left of the compression line 1102 .
- the output power of the PA 104 does not increase significantly with input power and increases primarily as the supply voltage 208 to the PA 104 increases from Vin 1 to Vin 2 , to Vin 3 , and to Vin 4 , etc.
- the PA 104 When operating in the range 1108 beyond the compression line 1102 , the PA 104 operates in saturation. As operation of the PA 104 moves from line 1102 to 1104 , and further towards line 1106 , the PA 104 operates at an increased depth beyond compression.
- the compression control signal 1001 , 1070 , or 1099 may increase the depth beyond compression by increasing the average input power Pin to the PA 104 for a given output power Pout.
- the action of the amplitude control loop adjusts the PA power supply voltage 208 to maintain the expected gain relationship between RF input signal 204 and the RF output signal 110 , thus forcing PA 104 to operate with lower gain and deeper in saturation.
- FIGS. 4A , 5 A, and 10 A, 10 B, 10 C, 10 D, and 10 F split the amplitude correction signal 309 into two frequency ranges
- the power amplifier controller circuit can be used with any type of power amplifier for many different types of electronic devices, although the embodiments are described herein with respect to a RF PA controller used in cellular telephone applications. Examples of these applications include video signals and Manchester coded data transmissions.
- digital techniques can be used to process some of the signals of the PA system described herein. Whether a signal is represented in an analog form or a digital form will not change the functionality or principles of operation of the amplitude and phase control loops of the PA system according to various embodiments of the present invention. For instance, based on the observation of the amplitude error signal 309 , one could calculate a typical transfer function for the PA 104 and construct the signals that drive the PA at nodes 206 , 208 , which is still a form of closed loop control.
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Abstract
Description
- 1. Field of the Invention
- The present invention relates to a circuit for controlling RF PAs (Radio Frequency Power Amplifiers), and more specifically, to an RF PA controller circuit that controls the supply voltage of a PA using a closed amplitude control loop with an amplitude correction signal.
- 2. Description of the Related Art
- RF (Radio Frequency) transmitters and RF power amplifiers are widely used in portable electronic devices such as cellular phones, laptop computers, and other electronic devices. RF transmitters and RF power amplifiers are used in these devices to amplify and transmit the RF signals remotely. RF PAs are one of the most significant sources of power consumption in these electronic devices, and their efficiency has a significant impact on the battery life on these portable electronic devices. For example, cellular telephone makers make great efforts to increase the efficiency of the RF PA systems, because the efficiency of the RF PAs is one of the most critical factors determining the battery life of the cellular telephone and its talk time.
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FIG. 1 illustrates a conventional RF transmitter circuit, including a transmitter integrated circuit (TXIC) 102 and an external power amplifier (PA) 104. For example, the RF transmitter circuit may be included in a cellular telephone device using one or more cellular telephone standards (modulation techniques) such as UMTS (Universal Mobile Telephony System) or CDMA (Code Division Multiple Access), although the RF transmitter circuit may be included in any other type of RF electronic device. For purposes of illustration only, the RF transmitter circuit will be described herein as a part of a cellular telephone device. The TXIC 102 generates theRF signal 106 to be amplified by thePA 104 and transmitted 110 remotely by an antenna (not shown). For example, theRF signal 106 may be an RF signal modulated by theTXIC 102 according to the UMTS or CDMA standard. - The
RF power amplifier 104 in general includes an output transistor (not shown) for its last amplification stage. When an RF modulatedsignal 106 is amplified by theRF PA 104, the output transistor tends to distort the RF modulatedsignal 106, resulting in a wider spectral occupancy at theoutput signal 110 than at theinput signal 106. Since the RF spectrum is shared amongst users of the cellular telephone, a wide spectral occupancy is undesirable. Therefore, cellular telephone standards typically regulate the amount of acceptable distortion, thereby requiring that the output transistor fulfill high linearity requirements. In this regard, when theRF input signal 106 is amplitude-modulated, the output transistor of thePA 104 needs to be biased in such a way that it remains linear at the peak power transmitted. This typically results in power being wasted during the off-peak of the amplitude of theRF input signal 106, as the biasing remains fixed for the acceptable distortion at the peak power level. - Certain RF modulation techniques have evolved to require even more spectral efficiency, and thereby forcing the
RF PA 104 to sacrifice more efficiency. For instance, while the efficiency at peak power of an output transistor of thePA 104 can be above 60%, when a modulation format such as WCDMA is used, with certain types of coding, the efficiency of theRF PA 104 falls to below 30%. This change in performance is due to the fact that the RF transistor(s) in theRF PA 104 is maintained at an almost fixed bias during the off-peak of the amplitude of theRF input signal 106. - Certain conventional techniques exist to provide efficiency gains in the
RF PA 104. One conventional technique is EER (Envelope Elimination and Restoration). The EER technique applies the amplitude signal (not shown inFIG. 1 ) and the phase signal (not shown inFIG. 1 ) of theRF input signal 106 separately to 2 ports of thepower amplifier 104, i.e., its supply voltage port (Vcc) 108 and itsRF input port 107, respectively. However, the EER technique often fails to provide significant efficiency gains, because thesupply voltage 108 cannot be varied in an energy-efficient way to accommodate the large variations in the amplitude signal of theRF input signal 106 and thus it fails to provide a substantial energy efficiency gain while maintaining the required linear amplification of the RF signal in theRF PA 104. This is mainly due to the difficulty in realizing a fast, accurate, wide range, and energy efficient voltage converter to drive the supply voltage of theRF PA 104. - The conventional EER technique can function better only if a variable power supply with a very large variation range is used to adjust the supply voltage based on the amplitude signal of the
RF input signal 106, while not reducing the efficiency of the RF transmitter by power consumed by the power supply itself. However, the variable power supply, which is typically comprised of a linear regulator (not shown inFIG. 1 ) that varies its output voltage on a fixed current load such as the PA in linear mode, by principle reduces the supply voltage at constant current and by itself consumes the power resulting from its current multiplied by the voltage drop across the linear regulator when there is a large drop in the amplitude signal of theRF input signal 106. This results in no change in the overall battery power being consumed by the RF transmitter, because any efficiency gained in theRF PA 104 is mostly lost in the linear regulator itself. Variations of the EER technique, such as Envelope Following and other various types of polar modulation methods, likewise fails to result in any significant gain in efficiency in the RF transmitter, because the supply voltage is likewise adjusted based on the amplitude signal of theRF input signal 106 which inherently has large variations and thus has the same deficiencies as described above with respect to conventional EER techniques. - Quite often, the conventional methods of controlling a PA fail to address the amplitude-to-phase re-modulation (AM-to-PM) which occurs in a non-frequency linear device such as a PA. Thus, the conventional methods are not suitable for the common types of PAs for use in common mobile telephony or mobile data systems because the required spectral occupancy performance is compromised by the AM to PM distortion.
- Finally, PAs are typically used in conjunction with band pass filters that have a high electric coefficient of quality. These filters are typically of the SAW (surface acoustic wave) type. Due to their high coefficient of quality, the filters exhibit a relatively high group delay. The group delay makes it very difficult for a correction loop to work around the arrangement of the SAW filter and the PA while still meeting the high bandwidth requirements needed for the correction of the AM-to-PM.
- Thus, there is a need for an RF PA system that is efficient over a wide variety of modulation techniques and results in a significant net decrease in power consumption by the RF PA system. There is also a need for a PA controller that can correct the AM to PM effects, while not relying on a PA specially designed for low AM to PM at the expense of efficiency. In addition, there is a need for a PA controller that can exclude the use of SAW filters from the path of the correction loop in the PA circuitry.
- One embodiment of the present invention disclosed is a power amplifier controller circuit for controlling a power amplifier based upon an amplitude correction signal or amplitude error signal. The power amplifier receives and amplifies an input signal to the power amplifier and generates an output signal, and the power amplifier controller circuit controls the power amplifier so that it operates in an efficient manner.
- The PA controller circuit comprises an amplitude control loop and a phase control loop. The amplitude control loop determines the amplitude correction signal (also referred to herein as the amplitude error signal), which is indicative of the amplitude difference between the amplitude of the input signal and the attenuated amplitude of the output signal, and adjusts the supply voltage to the power amplifier based upon the amplitude correction signal. The phase control loop determines a phase error signal, which indicates a phase difference between phases of the input signal and the output signal, and adjusts the phase of the input signal based upon the phase error signal to match the phase of the output signal. Thus, the phase control loop corrects for unwanted phase modulation introduced by the AM to PM non-ideality of the power amplifier and thus reduces phase distortion generated by the power amplifier.
- In a first embodiment of the present invention, the amplitude control loop comprises an amplitude comparator comparing the amplitude of the input signal with an attenuated amplitude of the output signal to generate an amplitude correction signal, and a power supply coupled to receive the amplitude correction signal and generating the adjusted supply voltage provided to the power amplifier based upon the amplitude correction signal. The power supply can be a switched mode power supply. By using the amplitude correction signal to control the supply voltage to the power amplifier, a high-efficiency yet low-bandwidth power supply such as the switched mode power supply may be used to provide the adjusted supply voltage to the power amplifier.
- In a second embodiment of the present invention, the amplitude correction signal is split into two or more signals with different frequency ranges and provided respectively to different types of power supplies with different levels of efficiency to generate the adjusted supply voltage provided to the power amplifier. For example, in the second embodiment, the power supplies include a first power supply with a first efficiency and a second power supply with a second efficiency higher than the first efficiency. The first power supply receives a first portion of the amplitude correction signal in a first frequency range and generates a first adjusted supply output based upon the first portion of the amplitude correction signal, and the second power supply receives a second portion of the amplitude correction signal in a second frequency range lower than the first frequency range and generates a second adjusted supply output based upon the second portion of the amplitude correction signal. The first and second adjusted supply outputs are combined to form the adjusted supply voltage provided to the power amplifier. The first power supply can be a linear regulator, and the second power supply can be a switched mode power supply. By dividing the amplitude correction signal into two or more signals with different frequency ranges, the second embodiment of the present invention has the additional advantage that the switched mode power supply may be implemented with even narrower bandwidth as compared to the first embodiment without significantly sacrificing efficiency. A narrower bandwidth power supply or a variable power supply with a smaller range of voltage variation is easier to implement.
- In a third embodiment of the present invention, the amplitude control loop further comprises a gain control module receiving the amplitude correction signal to generate a gain control signal, and a variable gain amplifier adjusting the amplitude of the input signal according to the gain control signal. The third embodiment has the advantage that it is possible to operate the power amplifier at any given depth beyond its compression point, resulting in an extra degree of freedom in designing the PA circuit. This is useful in optimizing the efficiency gain versus spectral occupancy performance. By adding the variable gain amplifier, the amplitude of variation of the Vcc or bias voltage to the PA is further reduced, resulting in further significant efficiency gains.
- In a fourth embodiment of the present invention, the amplitude control loop includes a variable gain amplifier (VGA) adjusting the amplitude of the input signal, as in the third embodiment, thus providing a second means of adjusting the amplitude of the output of the PA. However, the DC components of the amplitude correction signal are blocked from controlling the VGA. The DC gain of the VGA is controlled separately by a compression control signal, which sets the average gain of the VGA and thus the drive into the PA. Thus, the compression control signal provides a means to control the power amplifier's depth beyond its compression point, allowing control of the tradeoff between efficiency and spectral occupancy performance of the PA.
- In a fifth embodiment of the present invention, the amplitude control loop includes a variable gain amplifier (VGA) adjusting the amplitude of the input signal, as in the third embodiment. However, the DC components of the amplitude correction signal are blocked from controlling the power supply. The DC voltage supplied by the power supply is controlled separately by a compression control signal, which sets the average output voltage of the power supply, affecting the compression level of the PA. Thus, in a manner similar to the fourth embodiment, the compression control signal provides a means to control the power amplifier's depth beyond its compression point, allowing control of the tradeoff between efficiency and spectral occupancy performance of the PA.
- In a sixth embodiment of the present invention, the amplitude control loop includes a variable gain amplifier (VGA) adjusting the amplitude of the input signal, as in the third embodiment. However, the overall loop gain is controlled by a compression control signal, affecting the compression level of the PA. Thus, in a manner similar to the fourth embodiment, the compression control signal provides a means to control the power amplifier's depth beyond its compression point, allowing control of the tradeoff between efficiency and spectral occupancy performance of the PA.
- The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter.
- The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings.
-
FIG. 1 illustrates a conventional RF transmitter circuit. -
FIG. 2 illustrates an RF transmitter circuit including the PA controller in accordance with the present invention. -
FIG. 3A illustrates an RF power amplifier system, in accordance with a first embodiment of the present invention. -
FIG. 3B illustrates a method of controlling the amplitude control loop of a RF PA system, in accordance with the first embodiment of the present invention. -
FIG. 4A illustrates an RF power amplifier system, in accordance with a second embodiment of the present invention. -
FIG. 4B illustrates a method of controlling the amplitude control loop of a RF PA system, in accordance with the second embodiment of the present invention. -
FIG. 5A illustrates an RF power amplifier system, in accordance with a third embodiment of the present invention. -
FIG. 5B illustrates a method of controlling the amplitude control loop of a RF PA system, in accordance with the third embodiment of the present invention. -
FIG. 6 illustrates a method of controlling the phase control loop of a RF power amplifier system in accordance with the present invention. -
FIG. 7 illustrates simulation results of the changes in the waveform of thesupply voltage 208 to thePA 104 corresponding to the conventional polar control method, the first embodiment ofFIG. 3A , and the third embodiment ofFIG. 5A , for a typical commercial WCDMA PA with 3.4 V nominal supply voltage and WCDMA modulation using 3.84 Mchips per second. -
FIG. 8 illustrates the simulation results of an example of a time domain waveform present at thenode 509 ofFIG. 5A for a typical commercial WCDMA PA with 3.4 V nominal supply voltage and WCDMA modulation using 3.84 Mchips per second. -
FIG. 9 illustrates the simulation results of an example of a time domain waveform present atnodes FIG. 5A for a typical commercial WCDMA PA with 3.4 V nominal supply voltage and WCDMA modulation using 3.84 Mchips per second. -
FIG. 10A illustrates an RF power amplifier system, in accordance with a fourth embodiment of the present invention. -
FIG. 10B illustrates an implementation example of the RF power amplifier system ofFIG. 10A , in accordance with the fourth embodiment of the present invention. -
FIG. 10C illustrates an RF power amplifier system, in accordance with a fifth embodiment of the present invention. -
FIG. 10D illustrates an implementation example of the RF power amplifier system ofFIG. 10C , in accordance with the fifth embodiment of the present invention. -
FIG. 10E illustrates an implementation example of generating the compression control signal used inFIGS. 10A , 10B, 10C, and 10D. -
FIG. 10F illustrates an RF power amplifier system, in accordance with a sixth embodiment of the present invention. -
FIG. 11 illustrates how the RF power amplifier systems ofFIGS. 10A , 10B, 10C, 10D, and 10F control the operation point of the RF PA. - The Figures (FIG.) and the following description relate to preferred embodiments of the present invention by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of the claimed invention.
- Reference will now be made to several embodiments of the present invention(s), examples of which are illustrated in the accompanying figures. Wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein.
-
FIG. 2 illustrates an RF transmitter circuit including thePA controller 202 in accordance with the present invention. ThePA controller 202 is placed between thetransmitter IC 102 and thePA 104 to receive the RF signal 204 from theTXIC 102 and provide the RF signal 206 to thePA 104, while controlling thePA 104 by way of an adjustedsupply voltage 208. ThePA controller 202 is also placed between the power supply line (Vcc) 210 and thePA 104. ThePA 104 amplifies the RF signal 206 to output the amplifiedRF output signal 110, which is also provided as a feedback signal back to thePA controller 202. As will be explained below with reference toFIGS. 3A , 3B, 4A, 4B, 5A, and 5B, the adjustedsupply voltage 208 is generated by thePA controller 202 based on an amplitude correction signal (not shown inFIG. 2 ) indicative of the difference between the attenuated amplitude of the feedbackRF output signal 110 and the amplitude of theRF input signal 204. Note that the term “amplitude correction signal” is used herein synonymously with the term “amplitude error signal.” ThePA controller 202 adjusts the supply voltage (Vcc) 210 based upon the amplitude correction signal to generate the adjustedsupply voltage 208 provided to thePA 104, to optimize the efficiency of thePA 104. An advantage of thePA controller 202 is that existing signal connections to thePA 104 and theTXIC 102 need not change when thePA controller 202 is inserted between theTXIC 102, thePA 104, and the supply voltage (Vcc) 210. - The
PA controller circuit 202 may also adjust the phase and amplitude of thesignal 204 to allow for power control and PA ramping, in accordance with information received through the configuration signals 209. Since thePA controller circuit 202 is aware of the voltage at the output and the current in thepower amplifier 104, it can also adjust for load variations at an antenna (not shown herein) that may be used with the PA. If a directional coupler (not shown) is used to feed the attenuated amplitude of thesignal 204, thePA controller 202 can adjust the forward power while controlling the PA operation point as it is aware of the voltage and current atnode 208. -
FIG. 3A illustrates an RF PA system, according to a first embodiment of the present invention. The RF PA system includes thePA 104, and thePA controller 202 including a closed amplitude control loop and a closed phase control loop. - The phase control loop includes two
limiters phase comparator 316, a loop filter (PLF (Phase Loop Filter)) 318, and aphase shifter 320. To achieve stability over all conditions, thephase comparator 316 is of an adequate type with a capture range greater than 2*PI. To achieve this, a combination of adjustable delay elements and frequency dividers may be used. Also a phase sub-ranging system can be used since the dynamic phase variations that the phase correction loop processes are limited in amplitude. A sub-ranging phase control block (not shown) could be one of the constituents of thephase comparator 316 used with this system. Advantages of using sub-ranging in thephase comparator 316 are stability and good noise. - The amplitude control loop includes an adjusted variable attenuator (RFFA (RF Feedback Attenuator)) 306, two matched
amplitude detectors comparator 308, and a switched mode power supply (SMPS) 310. Note that thelimiter 312 and thedetector 302, and thelimiter 314 and thedetector 304, can be combined into a single limiter/power detector blocks without altering the functionality of the system. - Referring to
FIG. 3A , the phase control loop monitors the RF input signal 204 from the transmitter IC 102 (not shown inFIG. 3A ) and compares the phase of theRF input signal 204 with the phase of theoutput signal 110 of thePA 104 attenuated 326 by the adjusted variable attenuator (RFFA) 306, resulting in acontrol signal 319 that varies the phase of the RF signal 206 coming out of thephase shifter 320. More specifically, thelimiter 312 receives the RF input signal 204 from theTXIC 102 and outputs to thecomparator 316 an amplitudelimited signal 324 mathematically representative of the phase of its input signal. Thelimiter 314 also receives theoutput signal 110 of thePA 104 as attenuated 326 by the adjusted variable attenuator (RFFA) 306, and outputs itsphase signal 325 to thecomparator 316. Thecomparator 316 compares the phases of the output signals 324, 325 of the twolimiters phase error signal 317. Note that the term “phase error signal” is used herein synonymously with the term “phase correction signal.” Thephase error signal 317 is filtered by the loop filter (PLF) 318 to generate thephase control signal 319. Theloop filter 318 completes the phase loop and provides the necessary gain, bandwidth limitation, and loop stability required for the phase loop to function properly. The particular loop filter used here can be of any type, and can include multiple integration and derivation stages so as to satisfy the best loop performance. The types of the loop filter may include classical types I, II, and the like. A particularity of this phase loop design is that the group delay through thePA 104 must be taken into account for stability reasons. This is achieved by choosing the proper pole-zero placement in the loop filter and may include delay compensation. Thephase control signal 319 is input to thephase shifter 320 to control the shifting of the phase of the input RF signal 206 so that the phase of theoutput signal 110 dynamically matches the phase of thetransmitter signal 204. - The function of the phase control loop is to counteract the AM (Amplitude Modulation) to PM (Phase Modulation) characteristics of the
PA 104, which is part of the normal distortion characteristics of transistor-based amplifiers, allowing for the phase of the RF signal to be held constant at theoutput 110 of thePA 104 compared with theinput 204 of thephase shifter 320 and thus reducing phase distortion generated by thePA 104. This phase control loop contributes to linearizing thePA 104 as the AM to PM phase shift of thePA 104 tends to become higher at higher power levels. By limiting the effects of AM to PM of thePA 104, the phase control loop allows thePA 104 to function at higher power levels with less distortion for theoutput signal 110, thus allowing the use of thePA 104 in more favorable efficiency conditions. In addition, the phase control loop also helps in correcting any additional AM to PM characteristics that the amplitude control loop (described below) may cause. WhileFIG. 3A shows thephase shifter circuit 320 controlling the input to thePA 104, it is also possible to place thephase shifter 320 at the output of thePA 104 with the same benefits. - Note that the phase control loop is of the error correction only type. In other words, the phase control loop does not modify the phase of the
input signal 204 to thePA 104 unless thePA 104 or the amplitude control loop introduces a phase error. Since the noise contributions of the feedback loops affect the overall signal quality of the RF transmitter, an error correction only loop such as the phase control loop shown inFIG. 3A by definition introduces only a small correction, hence has a low noise contribution. - The amplitude control loop is also of the error correction only type, and thus is referred to herein as the amplitude correction loop. Thus, amplitude control loop and amplitude correction loop are used synonymously herein. Referring to
FIG. 3A , the amplitude of theRF input signal 204 is monitored through theamplitude detector 302 and compared by thecomparator 308 with the amplitude at theoutput 110 of thePA 104 as attenuated 326 by the adjusted variable attenuator (RFFA) 306, seen through a matchedamplitude detector 304. Theattenuator 306 is adjusted such that theoutput 110 of thePA 104 is at a desired level. This can be achieved though programming 321 the variable attenuator (RFFA) 306 by either a digital input to thePA controller 202 or by analog control of the variable attenuator (RFFA) 306. Thecomparator 308 generates anerror signal 309 indicating the difference between the amplitude of theinput RF signal 204 and theattenuated amplitude 326 of theoutput RF signal 110, referred to herein as the “amplitude correction signal” 309. Theamplitude correction signal 309 is fed intopower supply 310, which is a switch mode power supply (SMPS). TheSMPS 310 generates an adjustedsupply voltage 208 provided to one or more supply voltage pins of thePA 104 based upon theamplitude correction signal 309. The adjustedsupply voltage 208 in essence operates as a bias control signal that controls the operating point of thePA 104. - For a given output power, adjusting the
supply voltage 208 of thePA 104 has the effect of varying its gain, as well as changing its efficiency. For a given output power, lowering thesupply voltage 208 to thePA 104 provides better efficiency for thePA 104. The adjustedsupply voltage 208 of thePA 104 is adjusted to ensure that thePA 104 stays in its most efficient amplification zone. Because adjusting thesupply voltage 208 of thePA 104 does make a change to the gain of thePA 104, the output amplitude of thePA 104 changes with thesupply voltage 208 from theSMPS 310, and the amplitude control loop can be closed. The principles of such operation can be explained as follows. - When the input to the
PA 104 increases, the output of thePA 104 also increases. As thePA 104 stays in its linear region of operation, which corresponds to small input signals, its output will increase linearly with its input. Thus, both inputs to thecomparator 308 will rise by the same amount, resulting in no error correction and no change to thesupply voltage 208. This is the case when the output power is relatively small and well below the saturation point. As the input power continues to rise at the input ofPA 104, there will be a point beyond which the output of thePA 104 will no longer be directly proportional with the input to thePA 104. The amplitude control loop will detect this error between the output and input of thePA 104, and raise the supply voltage to thePA 104 such that the initially-desired output power is delivered, resulting in linear operation of the system, even with anon-linear PA 104. - In a practical application, the
PA 104 will be fully or partially saturated from its Vcc, for example, the highest 10 dB of its output power range, and as the RF modulation of the RF signal 104 forces the amplitude to vary, the amplitude control loop will only be actively controlling thesupply voltage 208 to thePA 104 when the highest powers are required. For lower input power, the amplitude control loop will leave thesupply voltage 208 at a fixed level because it detects no gain error, resulting in a fixed gain for thePA 104. The depth beyond compression can be adjusted by setting the level of theinput signal 204 and the level of theattenuator 306, as well as the default supply voltage Vcc (not shown inFIG. 3A ) to thePA 104. This behavior is illustrated inFIG. 7 where simulation results compare the behavior of the conventional polar architecture (with no feedback) where the supply voltage to the PA swings between 0.1 V and 2.9 V and reaches a minimum value around 0.1 V as shown withcurve 701, while thesupply voltage 208 to thePA 104 in the first embodiment ofFIG. 3A using theamplitude correction signal 309 does not drop below 0.5 V as shown with curve labeled 702. The amplitude swing in the dual gain control method is clearly further reduced as indicated bycurve 703, as will be explained in detail below with respect to the third embodiment of the present invention with reference toFIGS. 5A and 5B . - Varying the supply voltage to the
PA 104 also results in a phase change. Thus, the phase control loop described above operates in conjunction with the amplitude control loop to maintain the accuracy of RF modulation at the output signal of thePA 104. Note that the phase control loop is also an error correction loop only, and therefore minimally contributes to noise. - Furthermore, the amplitude correction loop has the advantage that an
SMPS 310, which does not consume any significant power by itself and thus actually increases the efficiency of the overall RF power amplifier system, can be used to generate the adjustedsupply voltage 208 to thePA 104. This is possible because the adjustedsupply voltage 208 to thePA 104 is generated by theSMPS 310 based upon theamplitude correction signal 309 which by nature has a much narrower range of variation or fluctuation rather than the actual amplitude of theRF input signal 204 which by nature has a much wider range of variation or fluctuation. AnSMPS 310 is easier to implement to follow theamplitude correction signal 309 with a narrow range of variation, but would be more difficult to implement if it had to follow the unmodified amplitude of theRF input signal 204. This is related to the fact that the amplitude signal itself has its fastest variations when the amplitude itself is low. The amplitude correction loop does not need to make any changes to its output when the PA is operating in linear mode. For example, theamplitude correction signal 309 may be only active for the highest 10 dB of the actual output power variation. In contrast, the amplitude signal itself may vary by 40 dB, and varies much faster between −10 dBc to −40 dBc than it does between 0 dBc to −10 dBc. Thus the bandwidth requirements on theSMPS 310, which are coupled with the rate of change of the voltage, are reduced when anamplitude correction signal 309 rather than the amplitude signal itself is used to control the supply of thePA 104. TheSMPS 310 does not consume any significant power by itself, and thus does not significantly contribute to usage of the battery power, and actually increases the efficiency of the RF power amplifier system. In contrast, a conventional polar modulation technique typically utilizes the amplitude signal itself to adjust the supply voltage to thePA 104, which prevents the use of anSMPS 310 for wideband RF signals because of the higher bandwidth requirements. Therefore, conventional RF power amplifier control systems typically use linear regulators (rather than an SMPS) to adjust the supply voltage to thePA 104. Such a linear regulator by itself consumes power resulting from its current multiplied by the voltage drop across the linear regulator. When there is a large drop in the amplitude signal, this can result in significant power being lost and results in none or little reduction in the overall battery power being consumed by the RF transmitter. This is because any efficiency gained in the RF PA is mostly lost in the linear regulator itself. -
FIG. 3B illustrates a method of controlling the amplitude control loop of aRF PA 104 in an RF PA system, according to the first embodiment of the present invention. Referring to bothFIGS. 3A and 3B , as the process begins 352, thecomparator 308 compares 354 theamplitude 323 of theRF input signal 204 with theattenuated amplitude 322 of the RF output signal 110 from thePA 104 to generate anamplitude correction signal 309. TheSMPS 310 generates 358 an adjustedsupply voltage 208 provided to thePA 104 based upon theamplitude correction signal 309, and the process ends 360. -
FIG. 4A illustrates an RF PA system, according to a second embodiment of the present invention. The RF PA system illustrated inFIG. 4A is substantially the same as the RF transmitter circuit illustrated inFIG. 3A , except that (i) theamplitude correction signal 309 is split into two signals, a high frequencyamplitude correction signal 401 that is fed into a high frequency path including alinear regulator 402 and a low frequencyamplitude correction signal 403 that is fed into a low frequency path including anSMPS 404 and that (ii) the outputs of thelinear regulator 402 and theSMPS 404 are combined in theadder block 406 to generate the adjustedsupply voltage 208 to thePA 104. For example, a simple current adding node, a small, high frequency transformer or other types of active electronic solutions can be used as theadder block 406. Any other types of power combiner circuits may be used as theadder block 406. The high frequencyamplitude correction signal 401 is input to thelinear regulator 402, which generates thehigh frequency part 405 of the adjustedsupply voltage 208. The low frequencyamplitude correction signal 403 is input to theSMPS 404, which generates thelow frequency part 407 of the adjustedsupply voltage 208. Theadder block 406 combines thehigh frequency part 405 and thelow frequency part 407 to generate the adjustedsupply voltage 208 to thePA 104 in order to keep thePA 104 in an efficient operation range. - The
amplitude correction signal 309 is split into the high frequencyamplitude correction signal 401 and the low frequencyamplitude correction signal 403 using thehigh pass filter 410 and thelow pass filter 411, respectively. The high frequencyamplitude correction signal 401 comprised of components of theamplitude correction signal 309 higher than a predetermined frequency and the low frequencyamplitude correction signal 403 is comprised of components of theamplitude correction signal 309 lower than the predetermined frequency. The predetermined frequency used to split theamplitude correction signal 309 can be set at any frequency, but is preferably set at an optimum point where the efficiency of the overall RF transmitter system becomes sufficiently improved. For example, the predetermined frequency can be as low as 1/20th of the spectrally occupied bandwidth for the RF signal. In other embodiments, the predetermined frequency may not be fixed but may be adjusted dynamically to achieve optimum performance of the RF transmitter system. - Power consumed by the
linear regulator 401 from a power source such as a battery (not shown) for a givencontrol voltage 208 on thePA 104 can be approximated as follows: -
- with Effl=1.05, which is sufficiently close to 1 to allow for this approximation, where Pbat is the power from the battery, Ipa is the input current to the
PA 104, Vpa is the input supply voltage to thePA 104, and Vcc is the supply voltage of the battery. In addition, power consumed by theSMPS 404 from a power source such as a battery (not shown) for a givencontrol voltage 208 on thePA 104 can be approximated as follows: -
P bat =Effs*I pa *V pa - with Effs=1.1, and the efficiency of the switch (not shown) in the SMPS generally exceeding 90%.
- If the average input voltage Vpa to the
PA 104 is significantly lower than supply voltage Vcc of the battery, theSMPS 404 achieves much lower power consumption. While thelinear regulator 402 is generally less efficient than theSMPS 404, thelinear regulator 402 processing thehigh frequency part 401 of theamplitude correction signal 309 does not make the overall RF PA system inefficient in any significant way, because most of the energy of theamplitude correction signal 309 is contained in thelow frequency part 403 rather than thehigh frequency part 401. This is explained below with reference toFIGS. 8 and 9 . - Using both a high efficiency path comprised of the
SMPS 404 carrying thelow frequency portion 403 of theamplitude correction signal 309 and a low efficiency path comprised of thelinear regulator 402 carrying thehigh frequency portion 401 of theamplitude correction signal 309 has the advantage that it is possible to use anSMPS 404 with a limited frequency response. In other words, theSMPS 404 need not accommodate for very high frequencies but just accommodates for a limited range of lower frequencies of theamplitude correction signal 309, making theSMPS 404 much easier and more cost-effective to implement. Combining theSMPS 404 with thelinear regulator 402 enables high bandwidths of operation accommodating for full frequency ranges of theamplitude correction signal 309 without sacrificing the overall efficiency of the RF PA system in any significant way, since most of the energy of theamplitude correction signal 309 that is contained in thelow frequency part 403 of theamplitude correction signal 309 is processed by the moreefficient SMPS 404 rather than the less efficientlinear regulator 402. - For example, Table 1 below illustrates the percentage of energy contained in the various frequency ranges in a hypothetical simple 4QAM (Quadrature Amplitude Modulation) signal used in WCDMA cellular telephones and the overall efficiency that can be expected to be achieved by the RF transmitter according to the embodiment of
FIG. 4A with the assumptions of the particular operating conditions as illustrated in Table 1. The combined amplitude and phase spectrum is 4 MHz wide. -
TABLE 1 4QAM Signal Below Above PA current = 100 mA 100 KHz 100 KHz (up to Adjusted supply voltage (Through 40 MHz) 208 to PA = 60% of Vbat SMPS (Through Linear All on average 404) Regulator 402) Frequencies Percentage of energy in 83% 17% 100% adjusted supply voltage 208 to PA 104 indesignated bandwidth Efficiency of 90% 57% 71% conversion at 60% of Vbat Current from battery 66.66 mA 17.85 mA 84.51 mA Power supply system 71% efficiency using high and low bandwidth paths - Despite the extremely narrow bandwidth (100 KHz) of the
SMPS 404 shown in the example of Table 1, 71% efficiency in the RF power amplifier supply system according to the embodiment ofFIG. 4A can be expected under the above hypothetical conditions by using a 90%efficient SMPS 404 combined with a 57% efficientlinear regulator 402. This is a very significant improvement over conventional PA controller systems that would typically use only a linear regulator under the same operating conditions and thus would be only 57% efficient. By using anSMPS 404 with an increased bandwidth, it is possible to improve the efficiency of the RF power amplifier even further. -
FIG. 4B illustrates a method of controlling the amplitude control loop of a RF PA in an RF PA system, in accordance with the second embodiment of the present invention.FIG. 4B is explained in conjunction withFIG. 4A . Referring to bothFIGS. 4A and 4B , as the process begins 452, thecomparator 308 compares 454 theamplitude 323 of theRF input signal 204 with theattenuated amplitude 322 of the RF output signal 110 from thePA 104 to generate anamplitude correction signal 309. Thelow frequency part 403 of theamplitude correction signal 309 is applied 456 to thehigh efficiency SMPS 404 while thehigh frequency part 401 of theamplitude correction signal 309 is applied 456 to the low efficiencylinear regulator 402. Thesupply voltage 208 to thePA 104 is adjusted 460 based upon the combination of theoutputs high efficiency SMPS 404 and the low efficiencylinear regulator 402, and the process ends 462. -
FIG. 5A illustrates an RF PA system, according to a third embodiment of the present invention. The RF transmitter system illustrated inFIG. 5A is substantially the same as the RF transmitter system illustrated inFIG. 4A , except that thegain control block 506 and thevariable gain amplifier 502 are added to provide an additional means to control the efficiency of thePA 104 and the overall RF transmitter system. Although the third embodiment ofFIG. 5A is illustrated herein as an improvement to the second embodiment ofFIG. 4A , note that the same concepts of the third embodiment ofFIG. 5A can also be used to improve the first embodiment ofFIG. 3A . - More specifically, the
gain control block 506 receives theamplitude correction signal 309 and adjusts the gain of thevariable gain amplifier 502 based upon theamplitude correction signal 309, as well as passing the low frequency andhigh frequency parts amplitude correction signal 309 to theSMPS 404 and thelinear regulator 402, respectively, to generate the adjustedsupply voltage 208 as explained above with reference toFIG. 4A . By monitoring the amplitude of theamplitude correction signal 309 input to thegain control block 506, acontrol signal 504 is created to further compensate the gain of thevariable gain amplifier 502 before thePA 104. This arrangement allows the use of even lower bandwidth for the PA controller system as compared to that of the second embodiment described inFIG. 4A above. Also the programmability of the output power can now be entirely left to thePA controller 202, while in the embodiment ofFIG. 4A changing the output power required a change in gain in thetransmitter IC 102. - With the addition of the
variable gain amplifier 502 and thegain control block 506, it is possible to use thePA 104 at any given depth beyond its compression point. The term “depth beyond compression” is used herein to refer to the difference between the averaged input compression level of thePA 104 and the actual averaged input power at thePA 104. For instance, when the peak output power is required, the input to thePA 104 can be overdriven by 10 dB beyond the 1 dB compression point of thePA 104. It is also possible to adjust the supply voltage of thePA 104 at the instant when the peak power is required, such that the 1 dB compression point is set higher and it is only necessary to overdrive thePA 104 input by 3 dB to obtain the same output peak power. A dynamic adjustment of both the input level and the supply voltage allows this loop system to reduce significantly further the amplitude of thecontrol voltage 208. - In the embodiment of
FIG. 5A , the independent programming of gain and compression point by the closed amplitude control loop also makes it possible to reduce the amount of high frequency energy that the power supply system (linear regulator) has to deliver to thePA 104. This can be done by having thevariable gain amplifier 502 correct for some of the gain error at a higher speed than the Vcc control loop (closed on node 208) can do, thus reducing the amount of correction that is to be done by the low efficiency, high frequency branch (linear regulator 401). Thus, the bandwidth of the signals atnodes node 208 relative to the bandwidth atnode 504. The ratio of the two active bandwidths is part of the design trade-off for the whole system. Thegain control block 506 adjusts the compression point while the gain loop remains closed through thevariable gain amplifier 502. This allows the RF controller system to search an optimum depth beyond compression (as measured by the absolute value of theamplitude correction signal 309 or alternatively by the averaged value of the gain control 504) and efficiency with less effect on the resulting signal quality. The search for the optimum depth beyond compression can be made by a slow control loop which monitors the absolute value of theamplitude correction signal 309, as well as its derivative. Another alternative is to monitor the averaged value of thegain control signal 504. In order to control the relative action of both amplitude controls 504 and 208, and in particular control the maximum voltage atnode 208, a control system for the compression level of thevariable gain amplifier 502 can be implemented. Because in the embodiment ofFIG. 5A both thesupply voltage 208 to thePA 104 and theinput 508 to thePA 104 can be adjusted, this embodiment inherently offers greater flexibility in design by exploiting two sources of signal information for control. This allows to further reduce the amplitude of the variation of thevoltage control signal 208, as shown onFIG. 7 , where the voltage with the smallest variation is the signal labeled 703, corresponding to this third embodiment ofFIG. 5A . - In addition, the third embodiment of
FIG. 5A is also well suited to process directly a polar representation of the RF signal. In this case, an amplitude signal from theTXIC 102 would couple to theamplitude detector 302 and a phase only signal from theTXIC 102 would be coupled to thevariable gain amplifier 502 and thelimiter 312. -
FIG. 5B illustrates a method of controlling the amplitude control loop of a RF PA in an RF transmitter system, in accordance with the third embodiment of the present invention. The method illustrated inFIG. 5B is substantially the same as the method illustrated inFIG. 4B , except thatstep 512 is added. Instep 512, theinput signal 508 to thePA 104 is adjusted, by use of avariable gain amplifier 502, based upon theamplitude correction signal 309. Therefore, the method ofFIG. 5B is provided with an additional means for controlling the efficiency of thePA 104 and the overall RF PA system. -
FIG. 6 illustrates a method of controlling the phase control loop of a RF PA in an RF PA system in accordance with the present invention. The phase control method ofFIG. 6 can be used with any one of the methods of controlling the amplitude correction loops described inFIGS. 3B , 4B, and 5B, as shown inFIGS. 3A , 4A, and 5A. The method ofFIG. 6 will be explained in conjunction withFIGS. 3A , 4A, and 5A. As the process begins 602, thecomparator 316 compares 604 the phase of theRF input signal 204 with the phase of the attenuated RF output signal 326 from thePA 104 to generate thephase error signal 317. Thephase error signal 316 is filtered 606 by the loop filter (PLF) 318 to generate thephase control signal 319. The phase of theinput RF signal 204 is shifted 608 based upon thephase control signal 319 so that the difference between the phase of theinput signal 204 and the phase of theoutput RF signal 110 is held constant, and the process ends 610. -
FIG. 7 illustrates simulation results of the changes in the waveform of thesupply voltage 208 to the PA corresponding to the conventional polar control method, the first embodiment ofFIG. 3A , and the third embodiment ofFIG. 5A , for a typical commercial WCDMA PA with 3.4 V nominal supply voltage and WCDMA modulation using 3.84 Mchips per second. As explained previously, the adjustedsupply voltage 208 generated by a conventional polar system as indicated bycurve 701 varies the most with wide fluctuations, the adjustedsupply voltage 208 generated by the first embodiment ofFIG. 3A as indicated bycurve 702 varies less than thecurve 701, and the adjustedsupply voltage 703 generated by the third embodiment ofFIG. 5A varies the least with only a little fluctuation. -
FIG. 8 illustrates the simulation results of an example of a time domain waveform present at node 509 (which voltage would be the same as the voltage at node 309) ofFIG. 5A , andFIG. 9 illustrates the simulation results of an example of a time domain waveform present atnodes FIG. 5A , both for a typical commercial WCDMA PA with 3.4 V nominal supply voltage and WCDMA modulation using 3.84 Mchips per second. The loop voltage versus time onFIG. 8 shows that the loops maintain a voltage much lower than 2.5 V most of the time, except for some short instants. This is due to the signal's amplitude characteristics which require high peaks but a much lower average. InFIG. 9 , thevoltages high pass filter 410 and a 100 kHzlow pass filter 411, respectively. It can be seen that the low pass filteredsignal 403 is almost a DC signal of value 1.9 V, while the high pass filteredsignal 401 is a band limited waveform having a low DC value and an rms value of only 0.2V. If the 1.9V is generated with an efficiency of 90% by an easy-to-realize lowoutput bandwidth SMPS 404, and the 0.2V is generated with an efficiency of 60% using alinear amplifier 402, thesignal 309 can be generated with a combined efficiency of (1.9+0.2)/(1.9/0.9+0.2/0.6)=87.5%. This is much better than generating thesignal 309 using a linear regulator with an average efficiency of (1.9/3.4)/1.05=53%. While it should be understood that the calculations presented herein are engineering approximations, the potential benefit in battery life is clearly apparent through this example. -
FIG. 10A illustrates an RF power amplifier system, in accordance with a fourth embodiment of the present invention. The RF PA system illustrated inFIG. 10A is substantially the same as the RF PA system illustrated inFIG. 5A , except that it additionally includes aDC blocking module 1002 and a summingmodule 1004, and additionally receives acompression control signal 1001. - The
DC blocking module 1002 is added in series with the VGAgain control signal 504 and filters out (blocks) DC components of the VGAgain control signal 504 to output primarily theAC components 1006 of theVGA control signal 504. Thecompression control signal 1001 is a DC or low frequency signal that is used to set the average gain of theVGA 502. TheAC components 1006 of theVGA control signal 504 and thecompression control signal 1001 are summed in the summingmodule 1004 to generate a modifiedVGA control signal 1008. The modifiedVGA control signal 1008 sets the gain of theVGA 502. - Thus, the
gain control block 506 adjusts the gain of theVGA 502 with the VGAgain control line 1006 based upon only the AC components of theamplitude correction signal 309. TheAC components 1006 passed by the DC blocking module (also referred to herein as a frequency blocking module or frequency selection module)1002 include sufficiently low frequencies to ensure that theVGA 502 contributes to correcting the amplitude error of thePA 104 even at low frequencies. The average gain of theVGA 502 is set by thecompression control signal 1001, which is added to theAC components 1006 of the VGAgain control signal 504. By increasing the level of thecompression control signal 1001, theVGA 502 increases its average gain and thus increases its drive into thePA 104. Increased drive intoPA 104 results in thePA 104 operating in a higher depth beyond compression with improved power efficiency, with a tradeoff in spectral occupancy performance due to increased amplitude of the variation of thesupply voltage 208 to thePA 104. - Although the fourth embodiment of
FIG. 10A is illustrated herein as an improvement to the third embodiment ofFIG. 5A withmultiple power supplies supply voltage 208 to thePA 104, note that the concepts of the fourth embodiment ofFIG. 10A can also be used to in a RF PA system with a single power supply controlling thesupply voltage 208 to thePA 104. -
FIG. 10B illustrates an implementation example of the RF power amplifier system ofFIG. 10A , in accordance with the fourth embodiment of the present invention. The example circuitry ofFIG. 10B is substantially the same as the RF PA system ofFIG. 10A , except that theDC blocking module 1002 ofFIG. 10A is implemented as acapacitor 1052, aresistor 1056 is added in series to thecompression control signal 1001, and the summingblock 1004 is implemented as a simple current summingnode 1054. - The
capacitor 1052 blocks the DC components of the VGAgain control signal 504 to output primarily theAC components 1006 of theVGA control signal 504. Thecompression control signal 1001 imposes a DC level to control the average gain of theVGA 502. The combination ofresistor 1056 andcapacitor 1052 forms a frequency-selective network that passes frequencies above F=1/(2πRC) from the VGAgain control signal 504 and passes frequencies below F=1/(2πRC) from thecompression control signal 1001, where R is the resistance value of theresistor 1056 and C is the capacitance value of thecapacitor 1052. For example, the capacitance value C ofcapacitor 1052 may be 1 nF and the resistance value R ofresistor 1056 may be 5.3 KOhms, resulting in F=30 KHz. TheAC components 1006 above the frequency F of theVGA control signal 504 and the DC frequency components below the frequency F of thecompression control signal 1001 are summed in the summingnode 1054 to generate a modifiedVGA control signal 1008. The modifiedVGA control signal 1008 sets the gain of theVGA 502. - Thus, the
gain control block 506 adjusts the gain of theVGA 502 with the VGAgain control line 1006 based upon only the AC components of theamplitude correction signal 309 above frequency F. The average gain of theVGA 502 is set by the DC components of thecompression control signal 1001, which are superimposed on theAC components 1006 of the VGAgain control signal 504. By increasing the level of thecompression control signal 1001, theVGA 502 increases its average gain and thus increases its drive into thePA 104. -
FIG. 10C illustrates an RF power amplifier system, in accordance with a fifth embodiment of the present invention. The RF PA system illustrated inFIG. 10C is substantially the same as the RF PA system illustrated inFIG. 10A , except thatDC blocking module 1062 is now in series with theamplitude correction signal 509 which controlspower supply 1060 and filters out (blocks) DC components of theamplitude correction signal 509 from gain control block 506 to output primarily the AC components of theamplitude correction signal 509. Thecompression control signal 1070 is a DC or low frequency signal that is used to set theaverage voltage 208 supplied toPA 104 bypower supply 1060. TheAC components 1064 of theamplitude correction signal 509 and thecompression control signal 1070 are summed in the summingmodule 1066 to generate a modifiedamplitude correction signal 1068. The modifiedamplitude correction signal 1068 sets thevoltage 208 supplied bypower supply 1060 to thePA 104. - Thus, the amplitude correction loop adjusts the
voltage 208 supplied bypower supply 1060 based upon only theAC components 1064 of theamplitude correction signal 309. TheAC components 1064 passed by the DC blocking module (also referred to herein as a frequency blocking module or frequency selection module) 1062 include sufficiently low frequencies to ensure that thepower supply 1060 contributes to correcting the amplitude error of thePA 104 even at low frequencies. Theaverage voltage 208 supplied toPA 104 bypower supply 1060 is set by thecompression control signal 1070, which is added to theAC components 1064 of the powersupply control signal 509. The control polarity is designed such that by increasing the level of thecompression control signal 1070,power supply 1060 decreases itsaverage voltage 208 supplied to thePA 104 and thus decreases the headroom ofPA 104. Decreased headroom forPA 104 results in thePA 104 operating in a higher depth beyond compression with improved power efficiency, with a tradeoff in spectral occupancy performance due to increased amplitude of the variation of thesupply voltage 208 to thePA 104. - Although the fifth embodiment of
FIG. 10C is illustrated herein as an improvement to the fourth embodiment ofFIG. 5A withmultiple power supplies 402, 404 (within overall power supply block 1060) generating thesupply voltage 208 to thePA 104, note that the concepts of the fifth embodiment ofFIG. 10C can also be used in a RF PA system with a single power supply controlling thesupply voltage 208 to thePA 104. -
FIG. 10D illustrates an implementation example of the RF power amplifier system ofFIG. 10C in accordance with the fifth embodiment of the present invention. The example circuitry ofFIG. 10D is substantially the same as the RF PA system of FIG. 10C, except that theDC blocking module 1062 ofFIG. 10C is implemented as acapacitor 1072, aresistor 1078 is added in series to thecompression control signal 1070, and the summingblock 1066 is implemented as a simple current summingnode 1076. - The
capacitor 1072 blocks the DC components of theamplitude correction signal 509 to output primarily theAC components 1064 of theamplitude correction signal 509. Thecompression control signal 1070 imposes a DC level to control theaverage voltage 208 ofpower supply 1060. The combination ofresistor 1078 andcapacitor 1072 forms a frequency-selective network that passes frequencies above F=1/(2πRC) from theamplitude correction signal 509 and passes frequencies below F=1/(2πRC) from thecompression control signal 1070, where R is the resistance value of theresistor 1078 and C is the capacitance value of thecapacitor 1072. For example, the capacitance value C ofcapacitor 1072 may be 1 nF and the resistance value R ofresistor 1078 may be 5.3 KOhms, resulting in F=30 KHz. TheAC components 1064 above the frequency F of theamplitude correction signal 509 and the DC frequency components below the frequency F of thecompression control signal 1070 are summed in the summingnode 1076 to generate a modifiedamplitude correction signal 1068. The modifiedamplitude correction signal 1068 sets thevoltage 208 ofpower supply 1060. - Thus, the
voltage 208 supplied bypower supply 1060 is based upon only the AC components of theamplitude correction signal 509 above frequency F. Theaverage voltage 208 toPA 104 is set by the DC components of thecompression control signal 1070, which are superimposed on theAC components 1064 of theamplitude correction signal 509. By increasing the level of thecompression control signal 1070, thepower supply 1060 decreases itsaverage voltage 208 and thus increases the level of compression of thePA 104. -
FIG. 10E illustrates an implementation example of generating the compression control signal used inFIGS. 10A , 10B, 10C, and 10D, utilizingdistortion control module 1080. Thedistortion control module 1080 samples a signal at distortion measurement input 1094 (input) and provides a compression control signal 1095 (output) based on the difference between the distortion determined atinput 1094 and targetdistortion level 1092.Input 1094 is typically coupled toPA output signal compression control signal 1095 is equivalent to thecompression control signal 1001 inFIG. 10A , and thecompression control signal 1070 inFIG. 10C . - Returning to
FIG. 10E ,distortion measurement module 1082 is hereby described. Distortion measurement module 214 comprises a frequency down-conversion module 1084, a pair offilters power detectors ratio calculation module 1089.Input signal 1094 is down-converted through a frequency down-conversion module 1084. In one embodiment, the frequency down-conversion module 1084 comprises an I/Q demodulator (not shown). The frequency down-conversion module 1084 outputs the down-converted signal to two different filters: a desiredchannel filter 1085 and an outside desiredchannel filter 1086. Thefilters channel filter 1085 is configured to pass frequencies within the desired channel and remove frequencies outside the desired channel. The outside desiredchannel filter 1086 is configured to pass frequencies within one or more ranges outside the range of the desired frequency channel. According to various embodiments, the frequency ranges passed by the outside desiredchannel filter 1086 can include frequencies in an adjacent channel, an alternate channel, a combination of an adjacent channel and an alternate channel, or any other combination of frequency ranges outside the desired channel. Eachfilter power detector channel filter 1085, thepower detector 1087 determines and outputs a power level corresponding to the signal power in the desired channel. Thepower detector 1088 determines and outputs a power level corresponding to the signal power outside of the desired channel (e.g., adjacent channel power, alternate channel power, or a combination of the two). The outputs of thepower detectors ratio calculation module 1089 to determine the ratio of the outside desired channel power to the desired channel power. The ratio of these powers is a measure ofdistortion 1090. For example, the measure ofdistortion 1090 may be given by: -
Measure of distortion (1090)=output of power detector (1088)/output of power detector (1087). - It may be desirable to design
power detectors -
Measure of distortion (1090)=output of power detector (1088)−output of power detector (1087). - The
comparator 1093 compares this measureddistortion level 1090 with atarget distortion level 1092. As the measuredPA distortion level 1090 decreases lower than thetarget distortion level 1092, the level ofoutput 1095 increases. As the measuredPA distortion level 1090 increases higher than thetarget distortion level 1092, the level ofoutput 1095 decreases. As mentioned previously, thetarget distortion level 1092 may be chosen to ensure adjacent- and alternate-channel power levels meet cellular telephone standards. - Thus, the
distortion control module 1080 may be part of a servo loop which attempts to target a specificacceptable distortion level 1092. Filtering and gain adjustment elements required for loop stability are not shown, and are typically required to stabilize the loop. - Note that while
FIG. 10E describes a method of measurement of distortion, other methods may be substituted. For example, measurement of EVM (Error Vector Magnitude), Peak Amplitude Distortion, or any other measurement that represents distortion may be used. - With regards to
FIG. 10A andFIG. 10C , and also referring toFIG. 10E ,output 1095 is connected tocompression control signal FIGS. 10A and 10C , respectively. As previously described, a decrease in the level ofoutput 1095 indicates a level of distortion that is higher than thetarget distortion level 1092. Sinceoutput 1095 is connected to thecompression control signal PA 104 results, which in turn results in a decrease in distortion at the output ofPA 104. Thus, a servo loop is created, with the system targeting thetarget distortion level 1092. Such a control loop is desirable because it optimizes the efficiency ofPA 104 by maintaining the maximum level of PA compression to enhance efficiency, while maintaining an acceptable level of distortion. Note that whileFIG. 10E describes in detail a method for determining the level of distortion at the PA output, other methods may be substituted and are still within the spirit of the invention. -
FIG. 10F illustrates an RF power amplifier system, in accordance with a sixth embodiment of the present invention. The RF PA system illustrated inFIG. 10F is substantially the same as the RF PA system illustrated inFIG. 5A , except thatcompression control signal 1099 is used to control RFFA (RF Feedback Attenuator) 306. Reducing the attenuation atRFFA 306 has the effect of decreasing the overall amplitude closed loop gain, thus forcingPA 104 further into compression. Conversely, increasing the attenuation atRFFA 306 increases overall amplitude closed loop gain, and reduces the level of compression ofPA 104. Thus, controllingRFFA 306 is an effective way to control the depth beyond compression ofPA 104. - As mentioned previously, operating
PA 104 at a greater depth beyond compression offers improved power efficiency, with a tradeoff in spectral occupancy performance due to the increased amplitude of the variation of thesupply voltage 208 to thePA 104.Gain control block 506 may include circuitry to block or modify the DC components ofamplitude correction signal 309 before passing this signal toVGA control 504. Note that whileFIG. 10F describes in detail a technique for adjusting the overall amplitude closed loop gain, other methods may be substituted and are still within the spirit of the invention. -
FIG. 11 illustrates how the RF power amplifier system ofFIGS. 10A , 10B, 10C, 10D, and 10F control the operation point of the RF PA. The graphs shown inFIG. 11 illustrate the relationship between the input power Pin to thePA 104 and the output power Pout of thePA 104. As shown inFIG. 11 , the output power (Pout) of thePA 104 increases approximately linearly as the input power (Pin) is increased when thePA 104 operates in the region left of thecompression line 1102. To the right of thecompression line 1102, the output power of thePA 104 does not increase significantly with input power and increases primarily as thesupply voltage 208 to thePA 104 increases from Vin1 to Vin2, to Vin3, and to Vin4, etc. - When operating in the
range 1108 beyond thecompression line 1102, thePA 104 operates in saturation. As operation of thePA 104 moves fromline 1102 to 1104, and further towardsline 1106, thePA 104 operates at an increased depth beyond compression. According to the fourth embodiment ofFIGS. 10A and 10B , the fifth embodiment ofFIGS. 10C and 10D , and the sixth embodiment ofFIG. 10F , thecompression control signal PA 104 for a given output power Pout. The action of the amplitude control loop adjusts the PApower supply voltage 208 to maintain the expected gain relationship betweenRF input signal 204 and theRF output signal 110, thus forcingPA 104 to operate with lower gain and deeper in saturation. - As mentioned earlier, operating
PA 104 at a higher depth beyond compression results in improved power efficiency. With an increase in depth beyond compression, a larger range of theoutput 110 ofPA 104 is controlled bypower supply voltage 208, thus ensuring thatPA 104 remains in saturation through a larger portion of the amplitude signal swings—and therefore ensuring that thePA 104 operates with higher efficiency. However, the burden placed on the power supply circuitry, includinglinear regulator block 402 and SMPS block 404, due to a higher required variation of thesupply voltage 208 to thePA 104, may result in reduction in spectral occupancy performance. Further,VGA 502 must handle a larger gain change whenPA 104 transitions from saturation to linear operation if operating at a high depth beyond compression (this transition region is shown onFIG. 11 as thelines PA supply voltage 208 reaches its minimum output voltage). The bandwidth and slew rate limitations of the VGA control loop may adversely affect spectral occupancy performance. Thus, the ability to adjust the depth beyond compression using the technique described inFIGS. 10A , 10B, 10C, 10D, and 10F offers a useful means of trading efficiency for spectral occupancy performance. - Upon reading this disclosure, those of skill in the art will appreciate still additional alternative structural and functional designs for the RF power amplifier controller through the disclosed principles of the present invention. For example, although the embodiments in
FIGS. 4A , 5A, and 10A, 10B, 10C, 10D, and 10F split theamplitude correction signal 309 into two frequency ranges, it is possible to split theamplitude correction signal 309 into more than two different frequency ranges for separate processing by adjustable power supply components. The power amplifier controller circuit can be used with any type of power amplifier for many different types of electronic devices, although the embodiments are described herein with respect to a RF PA controller used in cellular telephone applications. Examples of these applications include video signals and Manchester coded data transmissions. For another example, digital techniques can be used to process some of the signals of the PA system described herein. Whether a signal is represented in an analog form or a digital form will not change the functionality or principles of operation of the amplitude and phase control loops of the PA system according to various embodiments of the present invention. For instance, based on the observation of theamplitude error signal 309, one could calculate a typical transfer function for thePA 104 and construct the signals that drive the PA atnodes - Thus, while particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and components disclosed herein and that various modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the method and apparatus of the present invention disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (22)
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US7777566B1 (en) | 2010-08-17 |
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WO2010090694A1 (en) | 2010-08-12 |
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