MXPA00007176A - Power amplifying circuit with load adjust for control of adjacent and alternate channel power - Google Patents

Abstract

A power amplifying circuit with load adjust for control of adjacent and alternate channel power. A power amplifier amplifies an input signal to produce an amplified signal. A variable impedance network presents different impedances to the output of the power amplifier responsive to a load control signal. A peak-to-average detector provides an indication of a peak-to-average ratio of the amplified signal. A controller coupled to the peak-to-average detector and the variable impedance network produces the load control signal responsive to the indication of the peak-to-average ratio.

Description

POWER AMPLIFIER CIRCUIT WITH LOAD ADJUSTMENT FOR CHANNEL POWER CONTROL ADJACENT AND ALTERNATE Field of the Invention The present invention relates generally to power amplifiers. More specifically, the present invention relates to a power amplifier circuit for improving the efficiency and power of the adjacent channel.

Antecedents of the Invention. The power amplifier is a key technology in the design of portable radiotelephony in cell phones, the power amplifier has a great impact on the time available to talk. This is because the power amplifier originates a significant amount of power in relation to the other circuit systems within the cell phone. A parameter that defines how much power the power amplifier consumes is the efficiency of the power amplifier. Generally, power amplifiers are known whose direct current supply voltages vary continuously to match the requirements of the signal level to improve efficiency over a previously determined range of input signal levels. One such example is described in U.S. Patent No. 4,442,407. Titled "CONTROL OF AUTOMATIC N IVEL RCU ITOS FOR AMPLI FICADOR DE POTENCIA", issued to Thomas R. Apel, on June 1, 1982. In the '407 patent the power amplifier is operated with an improved efficiency by means of of the modulation of the RF amplifier of the direct current supply voltage in response to a comparison between a signal that corresponds to a weighted summation of the magnitude of the load current of the amplifier and the supply voltage, and the amplitude of the signal of modulation. However, the system described in '407 does not refer much to another important performance parameter of the power amplifiers used for cell phone systems of transmitted power of the adjacent and alternate channel. In cell phone systems, the power of the adjacent radiated channel can cause interference in the cellular channels, thus causing a degradation in the overall operation of the system. Adjacent and alternate channel power parameters are even more critical in cellular systems employing linear modulation schemes such as, Interim Standard (IS) -136 Time Division Multiple Access (TDMA) and IS-95 Division Multiple Access of Codes (CDMA). By optimizing the efficiency of the power amplifier, regardless of the operation of the adjacent and alternate channel power, the power amplifier could fail to the power specifications of the adjacent and alternate channel for a particular cellular system.

A system for simultaneously increasing the linearity and efficiency of power amplifiers is described in U.S. Patent No. 5, 101, 172. Entitled "LINEAR AMPLIFIER" issued to Yukio Ikeda and associates on December 1, 1990. Patent '172 drain voltage is controlled by a direct current / direct current converter to follow the amplitude level of the output signal. This increases the efficiency of the power amplifier but introduces the distortion of the amplitude modulation (AM) and the distortion of the phase modulation (PM). The input and output closing detectors are used in this way in conjunction with the phase and amplitude comparators in order to introduce a pre-distortion to counteract the distortion introduced by the power amplifier. This system requires the exact tracking of the distortion of the power amplifier, which can be difficult. In addition, multiple connectors and circuit that compare phase / amplitude, add size and cost when used in a portable cell phone. Another technique for minimizing distortion of the power amplifier is described in US Patent No. 4, 348,644. Titled "CI RCU ITO OF AMPLI FICACIÓN OF POWER WITH MEANS OF EXCHANGE FOR THE SUPPLY OF VOLTAGE" issued to Shingo Kamiya on March 24, 1980. In the '644 patent a power amplification circuit detects the crest factor (for example , the peak to average ratio) of the output signal of a power amplifier, when the peak factor is large, means that the voltage supply to the power amplifier was increased. On the contrary, when the crest factor is small, the supply voltage has been reduced. In this way, when more supply voltage is needed for the amplifier in order to handle the high peak-to-average ratio, the supply voltage is increased, on the contrary when there is a small proportion of peak to average, the supply voltage it is diminished. The high peaks are therefore faithfully reproduced by the raising of the supply voltage and the power loss is reduced by increasing and decreasing the supply voltage to the power amplifier, as necessary. The '644 patent technique is useful in electronic systems for amplifying musical signals. In this type of application, faithful reproduction of the musical signal is necessary in order to produce an acceptable fidelity. However, the '644 technique does not address the need to exchange fidelity versus efficiency in a manner necessary to produce portable radiotelephones of high efficiency and low cost.

Summary of the Invention Accordingly, there is a need for power amplifier with more accurate and understandable control of the adjacent and alternate channel power transmitted by the power amplifier, there is an additional need for the power amplifier to operate the linear schemes efficiently of modulation. A method for exchanging linearity and efficiency is necessary for the power amplifiers used in portable radiotelephones. There is also a need to control the power of the adjacent channel of the amplifier, the power of the alternating channel and the efficiency of operation by compensating the variations from part to part present in portable radiotelephones. There is also a need to control the average of the power amplifier that transmits the power while controlling the linearity and efficiency of the power amplifier.

Brief Description of the Drawings. Figure. 1 is a block diagram of a radiotelephone having a receiver and a transmitter; Figure 2 is a block diagram of a record used to conduct peak-to-average ratio experiments; Figure 3 is a graph of the peak power supply voltage, gain and peak to average ratio over a finite period of time, all against the input power, for the adaptation of the test of Figure 2; Figure 4 is a graph of the power of the adjacent channel, the power of the alternating channel, and the ratio of maximum power from peak to average over a finite period of time, all against the input power, for sample adaptation of the Figure 2; Figure 5 is a block diagram of a power amplifier circuit for use in the transmitter of Figure 1; Figure 6 is a block diagram of a peak to average difference detector for use in the power amplification circuit of Figure 5; Figure 7 illustrates an amplification method of an RF signal; Figure 8 shows a variable impedance network that can be used in the power amplification circuit of Figure 5; Figure 9 shows a second mode of the variable impedance network; and Figure 10 is a graph of the impedances for the variable impedance network.

Detailed Description of the Invention. Figure 1 is an illustration in a block diagram form of a radiotelephone communication system 100. The radiotelephone communication system 100 includes a remote transceiver 10 and one or more radiotelephones, such as portable radiotelephones 12. The transceiver remote 10 sends and receives RF signals to and from the portable radiotelephone 12 within a designated geographical area. The portable radiotelephone 12 includes an antenna 14, a transmitter 16, a receiver 18, a control block 20, a synthesizer 22, a duplexer 24, and an interface of the user 26. To receive the information, the portable radiotelephone 12 detects the RF signals that contain the data through the antenna 14 and produce the RF signals detected. The receiver 18 converts the detected RF signals into electrical baseband signals, demodulates the electrical band base signals, retrieves the data, including the automatic frequency control information, and the data outputs to the control block 20. control block 20, formats the data into recognizable voice or data information for use by the user interface 26. Generally the user interface 26 includes a microphone, a speaker, a display, and a keyboard. The user interface 26 is for receiving the user's input and presenting the received data that was transmitted by the remote transmitter 10. The receiver 18 includes a circuit system such as low noise amplifiers, filters, down-conversion mixers and quadrature mixers, and an automatic gain control circuit system, all known in the art. In order to transmit RF signals containing information from the radiotelephone 12 to the remote receiver 10 the user interface 26 directs the user's input data to the control block 20. The control block 20 generally includes any of a DSP core., a microcontroller core, memory, regulation generation circuit system, software, and an output power control circuit. The control block 20 formats the information obtained from the user interface 26 and transports it to the transmitter 16 for conversion into modulated RF signals. The transmitter 16 transports the modulated RF signals to the antenna 14 for transmission to the remote transceiver 10. In this way, the transmitter 16 is located to transmit a modulated information signal. The duplexer provides the isolation between the signals transmitted by the transmitter 16 and the signals received by the receiver 18. The portable radiotelephone 12 can be operated in a previously determined frequency band. The synthesizer 22 provides the receiver 18 and the transmitter 16 with the signals, tuned for the appropriate frequency, in order to allow the reception of the information signals. Control over the functions of the receiver 18 and the transmitter 16, such as the channel frequency is provided by the control block 20. So the control core 20 provides the synthesizer 22 with program instructions for the frequency synthesis. Experiments with a prototype power amplifier were initially performed to determine if the peak to average transmitted ratio of the signal produced by the transmitter 16 can be used to predict the adjacent channel power and the alternate channel power. The power of the adjacent channel is defined as the amount of power in a designated bandwidth transmitted on a channel immediately adjacent to the channel that is currently operating the transmitter d. Alternate channel power is defined as the amount of power in a designated transmitted bandwidth that is beyond the transmitter channel 16.

For example, in the IS-95 CDMA cell phone system, the transmitter may be operating at 836 MHz. The adjacent channel would be at 836 MHz +/- 885 KHz, and the alternate channel would be at 836 MHz +/- 1 .98 M Hz. Figure 2 is a block diagram of a test setting 200 used to perform peak-to-average ratio experiments. The test setting 200 includes a signal generator 40 connected through a bidirectional connector 42 to the input of the power amplifier apparatus being tested (DUT) 44. The output 46 of the DUT 44 is connected to the connector 46. The Signal generator 40 produces an RF input signal. A portion of the input signal is connected to port 48 and measured with the power meter 50. The rest of the input RF signal produced by the output of bidirectional connector 53 is applied to DUT 44. The portion of the RF signal of The input that is reflected in the input 43 of the DUT is connected to the port 52 where it is measured by means of the power meter 54. The measurements made with the power meter 54 allow the measurement of the return input loss of the DUT 44. The RF input signal is amplified by the DUT 44 to produce an amplified signal at the DUT 56 output, and the amplified signal is applied to the connector 46. A portion of the amplified signal is connected via port 58 to the spectrum analyzer. With the spectrum analyzer 60, the power of the adjacent channel and the power of the alternating channel of the amplified signal can be measured with respect to the power of the operating channel. The rest of the amplified signal is produced at the output of the connector 66 and the peak-to-average powers are measured by the power meter 68. The power supply 70 provides a controllable supply voltage to the supply port 72 of the DUT 44 For testing purposes the operating frequency is set to 836 MHz, and the signal generator 40 varies the power of the input RF signal from -9 dBm to +7 dBm in 1 dB increments. With the increase of the input power in 1 dB increments, the average power of the amplified signal produced at the output of the DUT 56 is kept constant by adjusting the supply voltage applied to the DUT 44 (for example, in this case the drain of the FET apparatus, of the DUT 44) in other words, the supply voltage of the DUT 44 is adjusted in order to adjust the gain of the DUT 44 thereby having a constant average output power for different input levels. The signal generator 40 produces an input signal having modulation to create a complex input signal characterized by an average power and a peak power that depends on the modulation scheme used. In the illustrated mode, the modulation scheme is the one used in the IS-95 CDMA which is a cell phone system with quadrature phase change compensation by means of the keyboard (OQPSK) with a base filter of band as is known in art. This modulation scheme produces an instantaneous peak-to-average ratio of 5.2 dB. Throughout the specification, the term peak-to-average ratio shall be understood to mean the ratio of peak to average power. However, the peak-to-average ratio of the voltage levels could be used, without using the power of the present invention. At each input power level, the adjacent and alternate channel power emissions are measured by means of the spectrum analyzer 60, the supply voltage to the DUT 44 is adjusted by changing the modulation of the burst width in a switch regulator (not shown as known in the art). Alternatively, the supply voltage could be adjusted using a linear regulator. Figure 3 is a graph of the supply voltage, the DUT gain 44 and the peak to maximum instantaneous average ratio in a finite time average all against the input power, the left vertical axis 90 is the gain in dB of the DUT44 which corresponds to the gain curve 92. The right vertical axis 94 is the supply voltage in volts of the DUT 44 which corresponds to the voltage supply curve 96. The axis vertical right 94 is also the maximum peak-to-average ratio in dB over a finite period of time and corresponds to the peak-to-average curve 98. The horizontal axis 102 is the input power in dBm.

Figure 3 shows that it is possible to vary the supply voltage of the DUT 44 in a range of input powers in order to maintain a constant output power. For a linear increase in the input power there is a linear decrease in the gain of the DUT 44 by varying the supply voltage to the DUT 44. The peak-to-average curve 98 is a plot of the maximum peak-to-average ratio over a range of specified time. The sustained peak measurement technique is used with the test equipment, in order to detect the maximum instantaneous peak-to-average ratio at each input power and supply voltage setting. For example, the signal generator 40 (Figure 2) produces an input signal having an OQPSK modulation similar to that used for the IS-95 CDMA cellular system. Therefore, the maximum instantaneous peak-to-average ratio of the input signal is 5.2 dB. When the DUT 44 is linear and does not introduce significant distortion, the maximum peak-to-average ratio measured should be close to 5.2 dB. For the low input power (for example, -9 dBm) and a supply voltage of 3.2V, the peak-to-average curve 98 shows that the DUT 44 is linear, this is proved by the fact that the maximum instantaneous proportion peak to average recorded at the -9 dBm input is approximately 5.2 dBm; the DUT 44 does not introduce distortion (for example, the clamping of the peak signal, at low levels of input power). In addition, the peak-to-average curve 98 shows that as the input power to the DUT 44 is increased and the supply voltage of the DUT 44 is adjusted to maintain a constant power output, the maximum instantaneous peak to average ratio over a period of Finite time decreases monotonically. That the peak-to-average ratio decreases monotonically here, shows that an operating difference in the control circuit could be used to adjust a maximum instantaneous peak-to-average ratio desired over a finite period of time while maintaining the stability of the circuit control. These results are applicable to various output powers, different power amplifier designs using an identical semiconductor device or even different power amplifier device technologies, such as field effect transistors (FETs) or bipolar transistor technology. Figure 4 is a graph of the adjacent channel power, the alternate channel power and the maximum instantaneous peak-to-average ratio over a finite period of time, all against the input power, once again, the output power is sustained constant at 20 dBM by means of the variation of the supply voltage. The left vertical axis 1 12 is the adjacent alternating channel power in dBc of the DUT 44. The horizontal axis 1 14 is the input power in dBr. The curve AdjCP_down 1 16 is the output power of the adjacent channel at the low site of the operating channel. For example, the operation input signal channel is set to 836 MHZ. The power of the adjacent channel on the low side is then the power in a bandwidth of 30kHz, 885kHz below 836MHz. Similarly, the curve AdjCP_alta 1 18 is the output power of the adjacent channel of 885kHz above 836MHz. The AltCP_low 120 curve is the output power of the alternate channel of 1.98MHz down to 836MHz. Similarly, the high AltCP_122 curve is the alternative channel output power of 1.98 MHz above 836MHz, the limit curve Adj_spec 124 is also illustrated in Figure 4, which corresponds to the power specification limit of the adjacent channel. (minus 42 dBc) and limit curve Alt_spec 126 corresponding to the power specification limit to the alternating channel (-54 dBc) both in accordance with the IS-95 CDMA specification. The limits of the specification vary for different cellular standards. The vertical right axis 128 is the maximum instantaneous peak-to-average ratio over a finite period of time expressed in dB that corresponds to the peak-to-average curve 130. The peak curve to average 1 30 is the same curve as the peak curve. to average 98 of Figure 3 because both curves represent the same data. As the input generation is increased and the output power is kept constant, the power of the adjacent channel and the power of the alternate channel increase. Note that for the powers of the adjacent channel and the alternate channel to be less than about -55dBc, the measurements are limited by the limitations of the test instrumentation (e.g., the dynamic range of the spectrum analyzer 60 of FIG. 2 and FIG. purity of the spectrum of the signal generator 40). However, the data points near where the powers of the adjacent and alternate channel cross their specification limits, the curves of the adjacent channel and the alternate channel are monotonic. Near region 136 of compliance with the specifications for adjacent channel power, region 138 of the compliance specification for the alternate channel power, the maximum instantaneous peak-to-average ratio over a finite period of time is proportionally inverse to both , the power of the adjacent channel and the power of the alternating channel. With this apparatus particularly 44, as the input power is increased, the specification limit of the adjacent channel is reached before the specification limit for the power of the alternating channel is reached. Therefore, for the particular power amplifier used as the DUT 44, the maximum instantaneous peak to average ratio over a finite period of time can be monitored for the purpose of adjusting the supply voltage in order to obtain a channel power. adjacent desired and that will also ensure that the specification meets the power of the alternate channel.

Because the maximum instantaneous peak-to-average ratio over a finite period of time can be controlled in a predictable manner, the power of the adjacent channel can also be controlled. By controlling the maximum instantaneous peak-to-average ratio over a finite period of time, the outputs of a power amplifier, the power of the adjacent channel and the power of the alternating channel are being controlled indirectly. This provides an efficient and predictable way to control the power of the adjacent channel and the alternate channel. As an example, in the IS-95 CDMS cellular system the specification limit for the adjacent channel power is -42dBc. crossing point 150 (Figure 4) where the power of the adjacent channel crosses the specification limit that corresponds to the maximum instantaneous peak-to-average ratio over a finite period of time is approximately 2.6dB as illustrated by the dotted line 152. Thus, for a transmitter using a power amplifier comprising the DU-T 44, the maximum instantaneous peak-to-average ratio over a finite period of time is maintained at approximately 2.6dB to maintain both the power of output of the input channel, as of the alternate within the specifications. In order to provide some margin, the power amplifier circuit can maintain the maximum instantaneous peak-to-average ratio over a finite period of time by 2.8dB or 3dB.

Figure 5 is a block diagram of a power amplification circuit 300 for use in the transmitter 16 (Figure 1). The power amplifier circuit 300 includes a power amplifier 172 connected to a variable impedance network 174. A latch detector 178 is connected to an output of the power amplifier 173. In the illustrated embodiment, the latch detector 178 is connected at the output of the variable impedance network 174. The latch detector 178 is connected to the peak detector at 180 average and the peak detector at 180 is connected to the controller 184. Alternatively, the controller may be inside the latch block. control 20 (Figure 1). The controller is connected to the variable impedance network 174. The peak to average detector includes a peak-to-average difference detector 182 connected to an analog to digital converter (ADC) 192 and a digital circuit 194. The difference detector of mean peak 182 includes a peak detector 183 and an average processing circuit 188, and a difference circuit 190. An RF input signal with lation is applied to the power amplifier 172 through the input 170, the amplifier power 172 produces an amplified signal at the output 174. A portion of the amplified signal is connected to the latch detector 178. The latch detector 178 serves to remove the signal from the RF carrier of the amplified signal. The resulting signal is applied to the average peak difference detector 182, the average peak difference detector 182 detects a peak level of the amplified signal and the average power of the amplified signal and provides an indication of the peak level and the average power during a predetermined period of time. The peak detector 186 determines a peak level and the average circuit system 188 determines the average power 188. The difference circuit system 190 determines the difference between the peak level and the average power to produce a difference signal. This sampling was carried out at a low index, since the sampling is of an average value during a previously determined time. For example, for the cellular system and IS-136 TDMA, sampling occurs in the order of approximately 150KHz, (for example, an average each burst), and for CDMA cellular systems, sampling occurs in the order of approximately 20KHz ( an average every 50 microseconds). The difference signal is applied to the ADC 192 for the conversion to digital samples referred to as digital word. The digital word is compared to a difference correlation table 196 within the digital circuit system 194. In this way, depending on the peak-to-average difference, the digital circuit system produced a resulting peak-to-average ratio 194. The digital circuit system contains a conventional logic circuit system and condition machines, as is known in the art. Alternatively, the comparison with the correlation table can be implemented with a digital signal processor (DSP) or a microprocessor. The resulting peak-to-average ratio is applied to the controller 184, the controller 184 produces a load control signal in response to the indication of the difference between the peak level and the average power of the amplified signal, which is applied to the variable impedance network 174. The variable impedance network 174 has different impedances at the output of the power amplifier 173 in response to the indication of the difference between the peak level and the average power of the amplified signal (e.g., in response to the load control signal). The impedance presented to the output of the power amplifier 173 is adjusted until the peak-to-average ratio of the amplified signal appearing at the output 176 is substantially equal to a previously determined level. In other words, the impedance is adjusted until the peak-to-average ratio is substantially equal to the peak-to-average ratio desired. By maintaining a peak-to-average ratio of the amplified signal, the power amplifier circuit system 300 also controls the power of the adjacent channel and the power of the alternating channel in the radiated emissions. The power amplifier circuit system 300 may optionally include a circuit system for controlling the average output power. The average output power of the transmitter 16 (Figure 1) varies according to the desired average changeable output power, and the controller causes the variable Impedance network 174 to present different impedances to the output of the power amplifier 173 over only a portion of a total dynamic range of the average output power. A variable gain circuit, in this case the variable gain amplifier 206, is connected to the input 170 at the input of the power amplifier 172. The average processing circuit 188 produces an indication on the line 191 of the average output power . The ADC 192 converts the indication of the average output power to a digital signal, and the digital circuit system 194 applies the digital signal to the controller 184. The controller 184 produces a control gain signal that is applied to the VGA 206 to control the gain of VGA 206 thus maintaining a desired average output power. Figure 6 is an example embodiment of a peak and difference detector 182 used in conjunction with the peak-to-average detector 180 (Figure 5) the peak and difference detector 182 includes an average processor circuit 188 a first op-amp 266, a difference circuit 190 a peak detector 186 and a second op-amp 272. The average processor circuit 188 includes a series resistor 276 connected to a bypass capacitor 278 and a bypass resistor 280. The peak detector 188 includes a diode detector 292 connected to a bypass capacitor 294 and a bypass resistor 296.

The difference circuit 190 has a first input 304 connected through a series resistor 282 to a negative input of an op-amp 284. A second output 306 is connected through a series resistor 286 and a bypass resistor 288 to a positive input of the op-amp 284. The output of op-amp 284 is the output of the peak and difference detector 262. The closing signal produced by the closure detector 178 (Figure 5) is applied to the detector input peak and difference 260. The closing signal is applied to the average processing circuit 168 and the peak detector 186, the peak of the closing signal is produced by the peak detector 186 while the average value of the closing signal , is produced by the average processor circuit 188. The first op-amp 272 and the second op-amp 272 are voltage trackers to produce an isolation between the average processor circuit 188 and the difference circuit 190 and between the detector peak 186 and the difference circuit 190. The stored average value is applied to the first input 304 and the detected detected peak of the signal is applied to the second input 306, the difference between the peak and average signal is produced at the output 262. In an alternative embodiment of the power amplifier circuit of Figure 5, the peak detector does not include the difference circuit 190. ' Instead, the peak detector 186 and the average processor circuit 188 are sampled directly by means of the ADC 192. Either the circuit of the digital circuit system 194 or the controller 188 then calculates a peak-to-average ratio. This alternative embodiment eliminates in this way the need for a correlation table 196 and a simplified circuit configuration. For the adequacy of the dynamic range in the order of 20dB using a single peak detector 186 and a single averaging circuit 188, the ADC 192 must have high resolution in the order of twelve bits. In yet another embodiment of the power amplifier circuit of Figure 5, the average peak detector 180 does not include a peak and difference detector 182. Instead, the closing signal produced by the closure detector 178 is applied directly by means of line 179 to ADC 172. The peak-to-average ratio is calculated by software. In the IS-136 TDMA cell phone system, the ADC 192 must sample the closing signal at approximately 50KHz. For the IS-95 CDMA cellular system, the ADC 192 must sample the closing signal at approximately 2.5MHz. When the ADC 192 directly samples the detected baseband signal produced by the latch detector 178, the power amplifier circuit may include an optional band-base digital peak detector 175 to eliminate the need for higher sampling rates. . The transmitter 16 (Figure 1) contains a digital band base circuit system for receiving an information signal and producing a digital current in L-Q (for example, via an encoder not shown, as is known in the art). The transmitter 16 (Figure 1) additionally includes a conventional transmitter circuit system (also not shown) for converting digital current to a radio frequency RF input signal as is known in the art. For example, the transmitting circuit system includes frequency conversion mixers, quadrature modulators, and filters. The digital peak detector 175 monitors via port 171 the digital current produced by the digital baseband circuit system (not shown) to determine when a peak will occur in the RF input signal. The digital peak detector 175 produces a peak indication signal which is applied to the delay block 181. The delay block is a digital delay circuit system responsible for the delay that the digital current will experience as it travels through the transmitter 16 (Figure 1) and is produced at the output 176 (Figure 5), the delayed signal is applied to the sample and stops the ADC 192 circuit system to detonate the ADC 192 to make the peak sample at an appropriate time. The ADC 192 then produces a digital peak value. The digital peak detector 175 comprises the digital logic that can be implemented in a specific application integrated circuit (ASIC). The digital peak detector 175 monitors the current and the bit IQs for an a priori known bit pattern in order to produce a peak amplitude in the closure produced in the latch detector 178. The function of the digital peak detector can be also implemented by means of software or can be carried out by means of the controller 184 (Figure 5). An example of the monitoring of the digital band base signal for the peaks is described in the pending North American patent application entitled "DIG ITAL MODULATOR WITH COMPENSATION", Series No. 08/694/004, filed August 8, 1996 , assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference. Figure 7 shows a flow chart illustrating a method for amplifying an RF signal. The method is started in block 350, and in block 352 portable radio telephone 12 (Figure 1) is turned on. The variable impedance network 174 (Figure 5) is set to an initial impedance in block 354. This can be done, for example, by sending the digital word 0000 to the variable impedance network 402 (Figure 9). This initial impedance is a starting point of the impedance that is known to cause the portable radiotelephone to pass the power specifications of the adjacent and alternate channels. In block 356 the desired average power is chosen and the gain of VGA 206 (Figure 5) is set to achieve the desired average power. The power output circuit is kept closed by constant monitoring of the average output power and adjusting the gain of VGA 206 (Figure 5) to maintain a desirable average output power.

In block 358, the peak-to-average ratio of the amplified signal is detected and determined in decision block 360, as if the peak-to-average ratio detected was within a predetermined level or limit. If the detected peak-to-average ratio is within a predetermined level, it will be determined whether the method has been done in the decision block 372 (for example, signal transmission is complete): if the method has been done, the method ends in block 374; or otherwise, the method continues in block 356. The previously determined level is a previously determined peak-to-average ratio which is known to correspond to any of a certain radiated power of the alternating channel and to a certain radiated power of the adjacent channel. For example, in a IS-95 CDMA portable radiotelephone, the previously determined peak-to-average ratio may be approximately 3 dB. If this is determined in decision block 360, the peak-to-average ratio is not close enough to the previously determined level (for example, within more or less a previously determined amount of the previously determined level, such as within +/- 0.5 dB), then a decision block 362 is determined if the peak-to-average ratio detected is greater than the previously determined level. If the detected peak-to-average ratio is greater than the previously determined level then this is determined in decision block 364, if the variable impedance network 174 (Figure 5) still has an adjustment range in any adjustment range of • Remaining impedance to present a different impedance to the output of the power amplifier 173 (Figure 5). If there is no more dynamic range available from the network of Variable impedance 174 (Figure 5), the existing setting of the variable impedance network 174 is maintained, and the process continues to block 356. For example, if the word of digital current is applied to the variable impedance network 402 ( Figure 9) is 1 1 1 1, there are no other conditions available to increase the variable impedance network 174 (Figure 5). If there is more dynamic range available (for example, the word of digital current is <1 1 1 1), then the load control signal is changed in block 366 to adjust the impedance network 174 (Figure 5). For example, to adjust the variable impedance network 402 (Figure 9), variable impedance network 402, comprises the increase of the digital control word (e.g., charge control signal), to a higher condition, such as from 1 1 10 to 1 1 1 1. The method then continues in block 356. If it has been determined in block 362 that the peak-to-average ratio is lower than the previously determined level, then in block 368 it is determined if any dynamic range still exists in the impedance network 174 (Figure 5). For example, if the load control signal to the variable impedance network 402 in Figure 9 is currently in OOOO, then the load control signal can not be further decreased. If there is no remaining dynamic range, the existing setting of the variable impedance network 174 (Figure 5) is maintained and the process continues in block 356. If there is more dynamic range available with the variable impedance network 174 (Figure 5), then the load control signal is changed in block 370 to adjust the variable impedance network 174. For example, for variable impedance network 402 (Figure 9), the adjustment of variable impedance network 402 comprises the decrease of the digital control word (e.g., charge control signal) to a lower condition, such as from 0001 to 0000. The method then continues in block 356. In Figure 8 a first mode of the network is shown.

Variable impedance 400 which can be used to present different impedances to power amplifier 172 (Figure 5). The variable impedance network 400 includes the first transmission line 408, the bypass capacitor 422 connected to the ground potential 416, a second transmission line 410, and at least one variable element 418 connected to the ground potential 416. The variable element 418 may be selected from the group consisting of a varactor diode and a variable voltage capacitor. The charge control signal is applied to the input 403 in the form of a voltage to vary the capacitance of the variable element 418.

The arrow 404 shows that the impedance presented at the input 406 is maintained to be substantially the optimum impedance for the power amplifier 172 (FIG. 5) for the different output power levels. The controller 184 (Figure 5) produces an analogous voltage as a load control signal. In this way, the controller can include a digital to analog converter (DAC) to produce the analog signal. Other configurations of the variable impedance network 400 may be displayed. For example, additional elements may be included, such as, charged element or distributed element inductors, additional transmission lines and capacitors, and additional variable elements. Figure 9 shows a second mode of the variable impedance network 402. The variable impedance network 402 includes the first transmission line 442, a fixed bypass capacitor 446 connected to the ground potential 448, a second transmission line 444 , and at least one variable element 452 connected to the ground potential 448, the at least one variable element 452 comprises a plurality of capacitors 454 connected alternately and disconnected at the output of the power amplifier 173 (Figure 5) using PIN diodes or micro-mechanical switches. The load control signal is applied to the input 450 to open and close a plurality of switches 456 which connect the plurality of capacitors 454 to the output of the power amplifier 173 (FIG. 5). Arrow 458 illustrates that the impedance presented at input 440 is maintained. In the illustrated mode, the controller 184 (Figure 5) produces a four-bit digital control signal to control the plurality of switches 456. The controller may include a change register (not shown) to convert the digital control word to a four-bit parallel word, like the load control signal. In another embodiment, the shift register may be a multiple chip module in conjunction with the power amplifier 173 (Figure 5). Therefore, '16 different impedances are possible for the variable impedance network 402. In this way, the variable impedance network has at least one variable element. The variable element may be selected from the group consisting of a varactor diode, a variable voltage capacitor and a plurality of capacitors alternately connected and disconnected at the output of the signal amplifier using micro-mechanical switches or PIN diodes. Other configurations of the variable impedance network 402 can be contemplated without the use of an inventive faculty. For example, additional elements may include, a charged element or distributed element inductors, additional distribution lines and capacitors, and additional variable elements. A combination of the variable impedance network 400 and the variable impedance network 402 could be used to increase the range of the impedances that can be obtained. In addition, the load control signal may comprise multiple signals to separately control different elements of variable impedance. The, Figure 10 is a Smith 470 plot showing the conditions of the impedance range corresponding, for example, to the variable impedance network 402 (Figure 9). The first impedance condition 472 which we also refer to as the impedance condition corresponds to a load control signal of 0000. The last impedance condition 474 corresponds to a load control signal 1 1 1 1. The above description of the preferred embodiments of the present invention is provided so that any person skilled in the art can use or construct a power amplifier circuit with load adjustment. Those skilled in the art will appreciate that various modifications of these embodiments may be made and the generic principles defined in the present invention may be applied to other modalities in the use of an inventive faculty. For example, the power amplifier circuit can be used with a transmitter that operates in more than one frequency band. The load will be adjusted based on the peak-to-average ratio in conjunction with the operating frequency band (eg, different peak-to-average ratios desired). The power amplifier circuit provides a highly effective way to improve the efficiency of a power amplifier, while maintaining the necessary power operation of the adjacent channel and the alternating channel. The power of the adjacent and alternate channel may result substantially from a power amplifier. Alternatively, the power of the adjacent and alternate channel may be the result of a transmitting circuit system that precedes the power amplifier in the transmission path. The power amplifier circuit also allows controlling the power of the adjacent and alternating channel in part-to-part variations present in portable radiotelephones.

Claims (14)

R E I N V I D A C I O N E S Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property.
1. A power amplifier circuit (300) characterized by: a power amplifier (172) for amplifying an input signal to produce an amplified signal; a variable impedance network (174) connected to an output of the power amplifier (174) to present different impedances to the output of the power amplifier (172) in response to the load control signal; a peak-to-average difference detector (180) connected to an output of the power amplifier (172), the peak-to-average difference detector (180) to detect a peak level of the amplified signal and an average signal power amplified and to produce an amplification of a difference between the peak level and the average power; and a controller (184) connected to the peak-to-average difference detector (180) and the variable impedance network (174), the controller (184) to produce the charge control signal in response to the indication of difference between the peak level and the average power of the amplified signal.
2. 2. - The power amplifier circuit (300) as described in Claim 1 further characterized in that the controller (184) causes the variable impedance network (174) to present different impedance at the output of the power amplifier (172). ) to maintain the difference between the peak level and the substantially equal average power at a previously determined level.
3. 3. - The power amplifier circuit (300) as described in Claim 2 further characterized in that the controller (184) determines a peak-to-average ratio of the amplified signal based on the indication of the difference between the peak level and the average power, for the controller (184) to produce the load control signal in response to the peak-to-average ratio.
4. 4. - The power amplifier circuit (300) as described in Claim 1 further characterized in that, the average output power varies according to a desired changeable average output power, said controller (184) causing the impedance network variable (174) present different impedances to the output of the power amplifier (172) only over a portion of a total dynamic range of the average output power.
5. 5. - The power amplifier circuit (300) as described in Claim 1 further characterized in that it has a variable gain circuit (206) connected to an input of the power amplifier (172), wherein the controller (184) adjust a gain of the variable gain circuit (206) in response to the average power indication to cause the average power to be substantially equal to the desired average power output.
6. 6. - The power amplifier circuit (300) as described in Claim 1 further characterized in that, the peak-to-average difference detector (180) detects the peak level and the average power of the amplified signal over a period of time previously determined.
7. A power amplifier circuit (300) characterized by; a power amplifier (172) for amplifying an input signal to produce an amplified signal; a variable impedance network (174) connected to an output of the power amplifier (172), the variable impedance network (174) to present different impedances to the output of the power amplifier (172) in response to a control signal of load; a peak-to-average detector (180) connected to an output of the power amplifier (172), so that the peak-to-average detector (180) produces an indication of a peak-to-average ratio of the amplified signal; and a controller (184) connected to the peak-to-average detector (180) and the variable impedance network (174), the controller (184) to produce the load control signal in response to the indication of the peak-to-peak ratio. average of the amplified signal.
8. 8. - The power amplifier circuit (300) as described in Claim 7 further characterized in that the controller (184) causes the variable impedance network (174) to present different impedances to the output of the power amplifier (172) to cause the peak-to-average ratio of the amplified signal to be substantially equal to a previously determined level.
9. 9. - The power amplifier circuit (300) as described in Claim 7 further characterized in that, the power of the average output varies according to a desired changeable average output power, causing the controller (184) that the network of Variable mpedance (174) present variable mpedances at the output of the power amplifier (172) over only a portion of the dynamic range of the average output power.
10. 10. - The power amplifier circuit (300) as described in Claim 7 further characterized in that, in a variable gain circuit (206) connected to an input of the power amplifier (172), wherein the peak detector at average (180) provides an indication of an average output power, and the controller (184) adjusts a gain of the variable gain circuit (206) in response to the indication of the average power to cause the average power to be substantially equal to the average desirable output power.
11. 1 .- The power amplifier circuit (300) as described in Claim 7 further characterized in that, the peak to average detector (180) detects the peak-to-average ratio of the amplified signal over a period of time previously determined.
12. 12. - A method for the amplification of a radio frequency (RF) signal characterized by said method by: amplifying the RF signal with a power amplifier (172) to produce an amplified signal; the detection of a peak-to-average line (358) of the amplified signal; the production of an indication in the peak-to-average ratio; and changing the impedances (366, 370) presented to an output of the power amplifier in response to the indication of the peak-to-average ratio.
13. 13. - the method as described in Claim 12 further characterized in that the impedances presented at the output of the power amplifier cause the peak-to-average ratio of the amplified signal to be substantially equal to a desired peak-to-average ratio.
14. 14. - the method as described in Claim 13 further characterized in that an average output power of the amplified signal varies according to a desired changeable average output power, the impedances presented at the output of the amplifier change only in a portion of a total dynamic range of the average output power. R E S U M E N A power amplifier circuit (300) with load adjustment to control the power of the adjacent channel and the alternating channel. A power amplifier (172) amplifies an input signal to produce an amplified signal. A variable impedance network (174) presents different impedances to the output of the power amplifier (172) in response to the load control signal. A peak-to-average detector (180) provides an indication of a peak-to-average ratio of the amplified signal. A controller (184) connected to the peak-to-average detector (180) and the variable impedance network (174) produces a load control signal in response to the indication of the peak-to-average ratio.