CA2083536A1 - Power-conserving automatic bias control for linear amplifier in radio-telephone transmitter - Google Patents
Power-conserving automatic bias control for linear amplifier in radio-telephone transmitterInfo
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- CA2083536A1 CA2083536A1 CA 2083536 CA2083536A CA2083536A1 CA 2083536 A1 CA2083536 A1 CA 2083536A1 CA 2083536 CA2083536 CA 2083536 CA 2083536 A CA2083536 A CA 2083536A CA 2083536 A1 CA2083536 A1 CA 2083536A1
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Abstract
ABSTRACT OF THE DISCLOSURE
An automatic bias control ("ABC") circuit reduces the source current, e.g., collector-bias current, drawn by a power amplifier in order to minimize power consumption, without significantly affecting the amplifier's gain. The ABC circuit accomplishes this by regulating the control current supplied to a power amplifier in response to a sensor signal indicative of the amplitude of the source signal and a computer-controlled reference signal. The invention can be practiced advantageously in a terminal amplifier of a transmitter of a dual-mode mobile cellular radio-telephone. The sensor signal is used to take into account variations in the collector-bias current required to achieve a pre-determined amplifier gain under, for example, changing ambient (e.g., temperature) conditions. The reference signal is used to indicate, e.g., the mode of operation of the radio-telephone (i.e., whether digital or analog), the mode of operation of the amplifier (i.e., whether linear or non-linear), and the power level of the radio-frequency signal being supplied to the power amplifier. Accordingly, in each case, the bias currents can be set to lower values than in conventional linear amplifiers used in digital radio-telephones or non-linear amplifiers used in analog radio-telephones operating under the same conditions, thereby reducing power consumption.
An automatic bias control ("ABC") circuit reduces the source current, e.g., collector-bias current, drawn by a power amplifier in order to minimize power consumption, without significantly affecting the amplifier's gain. The ABC circuit accomplishes this by regulating the control current supplied to a power amplifier in response to a sensor signal indicative of the amplitude of the source signal and a computer-controlled reference signal. The invention can be practiced advantageously in a terminal amplifier of a transmitter of a dual-mode mobile cellular radio-telephone. The sensor signal is used to take into account variations in the collector-bias current required to achieve a pre-determined amplifier gain under, for example, changing ambient (e.g., temperature) conditions. The reference signal is used to indicate, e.g., the mode of operation of the radio-telephone (i.e., whether digital or analog), the mode of operation of the amplifier (i.e., whether linear or non-linear), and the power level of the radio-frequency signal being supplied to the power amplifier. Accordingly, in each case, the bias currents can be set to lower values than in conventional linear amplifiers used in digital radio-telephones or non-linear amplifiers used in analog radio-telephones operating under the same conditions, thereby reducing power consumption.
Description
POWE~-CONSERVING AUTOM~TIC BIAS CONTROL
FOR LINEAR ~MPLIFIER
IN RADIO-TELEP~ONE TR~NSMITTER
Field of the Inv~ntion The invention relates to telecommunication, and more particularly to automatic bias control techniques for improving the energy efficiency of radio-frequency ("RF") power amplifiers used in, e.g., transmitters of radio-telephones.
Background of the Invention Conventional radio-telephones typically employ controlled-gain RF power amplifiers to amplify modulated RF signals immediately prior to transmission. Since such amplifiers are employed in the final stages of the transmitters, they are sometimes called "terminal amplifiers."
Known digital radio-telephones adapted `for use in certain cellular communication systems employ "linear" terminal amplifiers in order to preserve the envelope of the RF signals.
In a linear amplifier, the amplitude and phase of the output are linearly related to those of the input so long as the amplifier is operated in the linear range of operating characteristics.
Preserving the RF signal envelope is important since known digital radio-telephones employ linear modulation techniques (e.g., quadrature phase-shift keying) that produce modulated RF
signals having time-varying RF envelopes. Distortions in the time-varying envelopes could give rise to errors when the signals are demodulated in a radio-telephone receiver. Also, envelope distortions can produce interference in adjacent communication channels in the cellular system due to growth of spectral sidebands.
Linear amplifiers are generally satisfactory in eliminating problematic signal distortions. Unfortunately, `? "
linear amplifiers are typically less efficient than non-linear amplifiers used typically in conventional analog radio-telephones.
Consider, for example, a conventional self-biasing Class AB, linear, RF power amplifier implemented using a pair of bipolar transistors in a common-emitter, push-pull configuration. The transistors receive RF signals for amplification and a bias current at their control terminals, i.e., their base electrodes. A source current is applied to the RF power output terminals of the transistors, i.e., their collector electrodes, and is usually called the "collector-bias current." The RF signals vary the flow of the instantaneous source current through the transistors in such manner that the RF output of the amplifier is a faithful reproduction of the input RF signal, but amplified with a gain "beta."
The current gain "beta" is the ratio of the collector-bias to base-bias currents. For a beta of 100, for example, the collector-bias current is 100 times larger`than the base-bias current. It follows that the amplifier must draw large collector-bias currents in order to amplify with a high gain, and thus produce RF signals for transmission at the high power levels often required in cellular communication. Of course, the higher the collector-bias currents drawn by the amplifier, the larger the amount of power consumed by the amplifier.
In addition, as input signals to a conventional amplifier increase in amplitude, bias currents must also increase. Thus terminal amplifiers require more power than amplifiers used in earlier stages of radio-telephone transmitters.
Moreover, a conventional linear amplifier typically requires higher collector-bias currents than non-linear amplifiers in order to remain in the linear range of its operating characteristics. Consequently, digital radio-telephones employing linear amplifiers usually consume more power than do typical analog radio-telephones employing non-linear amplifiers.
3 ~ 3 'j Even when not amplifying RF signals, a conventional linear power amplifier draws significant collector-bias current. When used in applications such as radio-telephones that transmit intermittently, and thus require RF signal amplification only some of the time, the amplifier wastes power by continuously providing bias even when not amplifying.
Even more power is wasted in digital radio-telephones than one might suspect at first blush, because of the way digital cellular systems operate. Standards for digital cellular systems mandate a form of multi-user spectrum sharing called "Time Division Multiple Access" or "TDMA." This approach employs time-division multiplexing to allow multiple (e.g., three) mobile units to use simultaneously the same RF channel that would normally accommodate only one user in a conventional analog cellular system. In TDMA systems, the users transmit sequentially; each user taking a turn in rotation. Since the channel is shared equally, each user transmits one-third of the time, during what is called the "transmit time slot," and does not transmit during the balance of the time. Consequently, the bias currents drawn by the transmitters' linear amplifiers during two thirds of the time of the operation of the transmitter represent wasted power.
The increased power consumption due to linear operation of conventional amplifiers and the wasted power due to TDMA
operation translate into a number of significant drawbacks for digital radio-telephone operation. For instance, the power consumed by a conventional amplifier which is not used for amplification is given off as heat, and can give rise to thermal dissipation problems and even, in severe cases, to thermal runaway. Furthermore, in applications in which the radio-telephones are energized by batteries, the increased power consumption and the power wasted by conventional digital radio-telephones can translate into shortened "talktime" (i.e., less acoustic-data transmission time) per battery charge.
An obvious solution that might come to mind is simply to 3 3 r~
decrease RF power levels of transmissions, and therefore the amplifier's gain, so as to require less collector-bias current from the power source. Unfor-tunately, RF power output levels for transmitters of mobile radio telephones used in cellular systems can not be set arbitrarily; they are dictated by operating conditions, and typically must comply with applicable standards. For instance, the Telecommunications Industry Association Interim Standards 54, 55 and S6 provide a plurality of successively decreasing power level ranges for example, eight nominal power levels, each within a tolerance range)~
In conventional cellular systems, base stations command the mobile units to use certain power level ranges at particular times, and the mobile units automatically follow the commands of the base stations in accordance with the standards.
Normally, conventional amplifiers are operated to produce output RF signals at approximately the nominal power levels in the ranges specified by the base-stations.
Accordingly, reducing arbitrarily the RF power output levels of transmissions from mobile radio-telephones in order to conserve power is not a practical solution. A more sophisticated solution is required.
SummarY of the Invention The invention resides in an automatic bias control ("ABC") circuit for reducing the source current drawn by the amplifier in order to minimize the amplifier's power consumption without significantly affecting the amplifier's gain. This is accomplished by regulating the control current (i.e., bias) supplied to a power amplifier in response to a sensor signal indicative of the amplitude of the source signal and a computer-generated reference signal.
The invention can be practiced advantageously in a linear terminal amplifier of a transmitter of a dual-mode digital/analog mobile cellular radio-telephone. The sensor signal is used to take into account variations in the source current required to achieve a pre-determined amplifier gain, for example, under changing ambient (e.g., temperature) conditions. The reference signal is used to indicate a characteristic of the operation of the amplifier, e.g., the mode of operation of the radio-telephone (i.e., whether digital or analog), the mode of the operation of the amplifier (i.e., whether linear or non-linear), and the power level of the RF
signal being supplied to the power amplifier. (When the input RF signal is higher, a larger source current is typically required, and its larger amplitude is taken into account automatically by the invention in controlling the power amplifier.) For instance, when the radio-telephone operates in the "digital" linear mode, the ABC circuit of the invention regulates the control current so as to provide linear amplification. Moreover, when the transmitter is not transmitting, e.g., when the transmitter is not in the TRANSMIT
time slot, the control current and, consequently, the source current, is reduced (e.g., to zero) so as to significantly reduce or eliminate power consumption when amplification is not needed.
In both "digital" and "analog" modes of operation, the invention adjusts the control current so-that the source current drawn by the amplifier is just sufficient to produce an RF output signal at a power level which is within the power level range specified by a base station, but preferably below the nominal power level provided by the standards. Moreover, in both modes, when the cellular base-station commands the mobile unit to decrease its RF output power, the invention permits the bias currents to be reduced to meet the lower levels efficiently.
In the "analog" mode of operation, on the other hand, the bias currents can be reduced to near the minimum power level within the specified range without regard to linearity of the ~ r~3 ~ t~
output.
Accordingly, in each case, the bias currents can be set to lower values than in conventional linear amplifiers used in digital radio-telephones or non-linear amplifiers used in analog radio-telephones operating under the same conditions, thereby reducing the time-averaged power consumption of radio-telephones.
In a illustrative embodiment, the ABC circuit can be used to control a linear RF power amplifier having at least one common-emitter bipolar transistor. The ABC circuit has a current sensor preferably incorporating a current mirror connecting to a bias supply for generating the collector-bias current for th~ transistor and a sensor signal indicative of the amplitude of the collector-bias current. The current mirror is particularly advantageous since it provides a low resistance between the bias supply and the collector electrode of the transistor, and thus consumes minimum power in deriving the sensor signal. Also, the sensor signal produced by the current mirror has only a small common-mode component.
The ABC circuit also has an error amplifier preferably incorporating a differential integrator fcr comparing the sensor signal from the current mirror with a reference signal controlled by a computer (e.g., a processor or microcomputer).
The differential inte~rator is particularly advantageous since the integration it performs can be used to eliminate transient responses of the ABC circuit that would otherwise tend to remove wanted modulation in the RF signal in the digital mode of operation.
Thus, the error amplifier supplies a base-bias current to the transistor, which is responsive to the integrated difference between a sensor signal indicative of the "actual"
collector-bias current drawn by the transistor, and a reference signal indicative of a "target" collector current, with a view towards minimizing the collector current and thus power consumption in the amplifier while not significantly affecting o~;7 ~ S ~; 3 ~
amplifier gain. As a result, the invention can, e.g., increase talktime in the radio-telephone, while permit-ting compliance with applicable standards. Moreover, the invention can, e.g., reduce thermal power loss by up to 65% and eliminate the likelihood of thermal runaway.
Brief De~criDtion of the Drawinqs The aforementioned and other aspects, features and advantages of the invention are explained in the following description, taken in connection with the accompanying drawings, wherein:
FIGURE 1 is a block diagram of a radio-telephone having an automatic bias control loop in accordance with the invention;
FIGURE 2 is a block diagram of the processor and modulator circuitry Of the digital branch of the transmitter of FIGURE 1;
and FIGURE 3 is a schematic diagram, partially in block diagram form, of an illustrative implementation of the RF power amplifier and bias control circuit of FIGURE 1.
DescriPtion of Preferred Embodiment FIGURE 1 shows a dual-mode analog/digital radio-telephone 10 in accordance with a preferred embodiment of the invention.
As the name implies, the illustrated radio-telephone can employ either digital or analog encoding/decoding of communication signals.
The radio-telephone 10 has a handset 12, a receiver 14, a transmitter 16, and a central processing unit ("CPU") 18 for controlling the operation of the telephone. The latter three components are often called a "transceiver." Additionally, the radio-telephone 10 includes a conventional power supply 20 and ~ ~Ç3~
a conventional antenna 21.
The handset 12 includes a microphone 22 and a speaker 24.
The microphone 12 converts sounds, e.g., messages spoken by a user, into electrical signals (called "TRANSMIT AUDIo signals") representing the spoken sounds. The speaker 24 converts electrical signals (called "RECEIVE AUDIO signals") representing audio data into sound intelligible to the user.
As is known in the art, the receiver 14 demodulates radio-frequency ("RF") signals received from the antenna, thereby producing the RECEIVE AUDIO signals, which are provided to the speaker 24.
The transmitter 16 processes the TRANSMIT AUDIo signal preparatory for broadcast by the antenna. To accomplish this, the transmitter 16 includes a processing and modulating ("P&M") circuit 26 for producing a signal called RF_IN by modulating an RF carrier with a digital signal derived from the TRANSMIT
AUDIO signal, and amplifying the resulting signal to a pre-selected power level under the control of the CPU 18.
The P&M circuit 26 illustrated in FIGURE 1 can be switched between digital and analog modes of operation, thus rendering the transmitter 16 capable of dual-mode digital/analog operation. This is accomplished by a pair of jointly operated, dual-pole/ single-throw, electronic switches 32, which connect the TRANSMIT AUDIO signal either to digital branch circuitry 34 for digital mode, or to analog branch circuitry 36 for analog mode of operation.
As shown in FIGURE 2, the digital branch circuitry 34 has a digitizer 34a for converting analog TRANSMIT AUDIO signals from the microphone 32 into digital signals, an encoder 34b for encoding (e.g., for error protection) the digitized signals, a modulator 34c for modulating an RF carrier with the encoded signals using, e.g., quadrature phase-shift keying, and an amplifier 34d for boosting the modulated signals to a pre-selected power level (e.g., one of eight power levels) and thus producing RF_IN.
The analog branch circuitry 36 contains conventional components for modulating the RF carrier with a filtered, amplified version of the TRANSMIT AUDIO signal, e.g., using conventional frequency modulation techniques, and then for amplifying the resulting signal.
The transmitter 16 also includes a linear, variable-gain RF terminal power amplifier 30 for boosting the power of RF_IN
by a constant gain. The transmitter 16 then supplies the resulting signal, called RF_OUT, to the antenna 21 for broadcast.
Owing to the amplification in the P&M circuit 26 and the terminal amplifier 30, the RF_OUT signal from the transmitter 16, when in its digital or analog mode of operation, has a power level falling within one of the, eOg., eight ranges specified by the above-referenced standards. It should be emphasized that the terminal amplifier 30 preferably amplifies RF_IN with a constant current gain, e.g., 100. The gradations in power required to comply with the standàrds are preferably provided in the P&M circuit 26.
The transmitter 16 also has an automatic bias control loop ("ABC") circuit 40 for controlling the gain of the power amplifier 30. In accordance with the invention, the ABC
circuit 40 is adapted specifically to reduce the DC power required by the power amplifier 28 without significantly affecting its current gain or in any way adversely affecting its operation.
The ABC circuit 40 includes a current sensor 42, a bias supply 44, an error amplifier 46, a reference generator 48, and a filter 50. The current sensing circuit 42 receives a supply current from the bias supply 44, and delivers a portion thereof as a source current to a source terminal 3Oa of the power amplifier 30. The current sensing circuit 42 also generates a sensor signal indicative of the amplitude of the supplied source current, and feeds the sensor signal to the error amplifier 46.
?,~ 3 ~
The reference generator 48 preferably is a digital-to-analog converter that converts digital control signals supplied over lines "x" and "y" (for a two-bit signal) by the CPU 18 into "reference signals," which are supplied to the error amplifier 48. The reference signals serve to indicate "target"
bias currents to be supplied to the power amplifier 30 to minimize or at least reduce DC power consumption by the amplifier.
The error amplifier 46 derives a bias-control signal based on a comparison of the sensor and reference signals, i.e., based on the "actual" and "target" source currents. The error amplifier 46 provides the bias-control signal to a low-pass filter 50.
The low-pass filter 50 passes the low-frequency component of the bias control signal as the control current to a control terminal of the amplifier 30, and controls the dynamic response of the ABC circuit 40. The amplitude of the control current determines the amplitude of the current flowing through the power amplifier. This determines the amount of the source current drawn by the amplifier 30, and thus its power requirements.
It will be apparent that the ABC circuit 40 virtually defines a feedback loop for automatically controlling the bias current. The feedback loop can be traced in FIGURE 1 from the current sensor 42 (which detects the amplitude of source current drawn by the amplifier 30), to the error amplifier 46, to the filter 50, and then to the power amplifier 30.
FIGURE 3 shows the RF power amplifier 30 and the ABC
circuit 40 in greater detail. Each of the depicted circuits will be described, starting with the power amplifier 30.
The power amplifier 30 includes a series-to-parallel or single-ended-to-balanced converter 52, which, in RF
terminology, is also called a front-end balun. The front-end balun 52 splits RF_IN into first and second balanced signals that are 180 degrees out of phase with one another and of the 3 ?~
same amplitude. The balun 52 supplies the first and second balanced signals to respective pairs 54, 56 of parallel capacitors for impedance matching. The outputs of the capacitors 54, 56 are interconnected by an inductor 62 for base-bias injection (as will further described shortly), and a capacitor 64 again for impedance matching. The outputs of the capacitors 54, 56 are coupled to an amplifier integrated circuit ("AMP IC") 66.
More specifically, the capacitors 54, 56 are connected to respective base terminals 68a, 70a of respective bipolar transistors 68, 70 forming the AMP IC 66. The transistors 68, 70 are connected for linear operation in a common-emitter arrangement or grounded-emitter arrangement. As the name implies, the emitters 68b, 70b of the transistors 68, 70 are tied to ground. The collectors 68c, 70c of transistors 68, 70 are interconnected by an inductors 71 for collector-bias injection, and a capacitor 72 for impedance matching. The collectors 68c, 70c are also connected to respective first and second pairs 78, 80 of parallel capacitors for impedance matching.
The outputs of the capacitors 78, 80 are connected to a parallel-to-series or balanced-to-single-ended converter or output balun 82. The output balun 82 combines the balanced signals from the capacitors 78, 80 into a signal RF_OUT, which is the output from the RF amplifier 30.
The power amplifier 30 also has a base-bias circuit 86 connected to the base 70a, and a collector-bias circuit 88 connected to the collector 70c. The base and collector-bias circuits 86, 88 de-couple the bias currents from the RF signal.
The base-bias circuit 86 has parallel capacitors 90 connected between the base 70a and ground, and a series inductor 92 connected between the base 70a and the filter 50. The collector-bias circuit 88 has a capacitor 94 connected between collector 70c and ground, and a series inductor 96 connected between the collector 70c and the current sensor 42.
c~ ti The current sensor ~2 receives a DC supply current "IDc"
from a bias supply 44 (FIGURE 1). The current sensor 42 serves as a current divider, feeding most of IDC to the power amplifier 30 as the collector-bias current, and supplying a small portion of this current to the error amplifier 46 over line 98 as the sensor signal. The sensor signal, as noted above, indicates the magnitude of the collector-bias current.
More specifically, the current sensor 42 is configured as a current mirror formed by first and second matched transistors 120, 122. The transistors 120, 122 have common base electrodes 120a, 122a that are connected to the collector 122b of transistor 122.
IDC is supplied to the emitter electrode 120c of transistor 120, and, via a resistor 124, to the emitter electrode 122c of transistor 122. Most of the IDC flows through transistor 120 and to the collector-bias circuit 88. A
small portion of IDC flows through transistor 122, where the current is impressed upon resistor 126 yielding a voltage that is supplied to the error amplifier 46.
It will be apparent that the fraction of IDC flowing through transistor 120 is determined by the resistive value of resistor 124, and that the voltage that is supplied to the error amplifier 46 as the sensor signal is determined by the resistive value of resistor 126. (The input impedance of the error amplifier 46 is much larger than the impedance of the resistor 126.) Moreover, the magnitude of the sensor signal is proportional to that of the current supplied to the collector-bias circuit 88, and thus indicative of the magnitude of the supplied collector-bias current.
The current mirror 42 also has a capacitive decoupling network 127 connected between the collector electrode 120b and ground for decoupling radio-frequency signals in the power amplifier 30 from the collector-bias current supplied by the current mirror 42.
The error amplifier 46 includes a comparator 130, ~ 1 ~ 3 ~ ~ 3 13 -13~
preferably, a differential integrator formed by an operational amplifier ("op amp") 132 and a capacitive/resistive feedback arrangement 13~. A first input 130a of the integrator 130 receives the sensor signal via a resistor 136 connec-ted to line 98, and a second input 130b receives a reference voltage from the reference generator 48. The output of the integrator 130 represents the integrated difference between the signals applied to the inputs 130a, 130b.
The comparator 130 performs integration in order to eliminate transient responses, so that, e.g., the ABC circuit 40 does not remove the wanted modulation from the signal (i.e., RF_IN) being amplified by the power amplifier 30. This is accomplished by providing the comparator 130 with appropriate integration time constants during circuit design.
An amplifying transistor 138 boosts the signal level of the output of the comparator 130, and provides the amplified signal to the filter 50. The filter 50 includes a series resistor 142 connected between the transistor 138 and both a capacitive shunt 144 to ground and the base-bias circuit 86 of the power amplifier 30. Thus, as noted above, the filter 50 provides the base-bias current, i.e., the control current, to the power amplifier 30.
As described hereinabove, the ABC circuit 40 uses the sensor signal and the reference signal in adjusting control current so as to minimize the collector-bias current, i.e., the source current, with a view to reducing the power consumed by the amplifier 30. The dissipated DC power (IlPdcll) for the power amplifier 30 shown in FIGURE 3 is given by the following equation:
Pdc ~Ic x Vc) - Prf where "Ic" is the collector-bias current, "Vc" is the collector-bias voltage, and "Prfll is the transmitted RF power.
Thus, it can be readily seen that reducing Ic causes PdC to 3 ~
decrease.
Key to successfully reducing the source current without adversely affecting the operation of the transmitter 16 is the reference voltage or signal, which is derived from the digital control signals from the CPU 18. The digital control signal preferably is an m-bit digital signal (where "m" is a positive integer) representing a number of desired operating conditions of the amplifier 30. For example, where "m" equals one, i.e., the digital control signal has a single bit, a LOW value for the signal could correspond to full bias, so that the amplifier 30 is turned ON and produces RF_OUT. A HIGH value of the digital control signal, on the other hand, could correspond to zero bias, so that the amplifier 30 is turned OFF and does not amplify, e.g., during periods of time when the radio-telephone 10 is not transmitting.
Alternatively, the digital control signal can have two bits, i.e., "m" equals two, which finds particular utility in TDMA systems. For example, the various values of a two-bit digital control signal can have the following results:
1) HIGH-HIGH: linear mode of operation of amplifier for higher power levels mandated by - standards applicable to digital radio-telephones;
FOR LINEAR ~MPLIFIER
IN RADIO-TELEP~ONE TR~NSMITTER
Field of the Inv~ntion The invention relates to telecommunication, and more particularly to automatic bias control techniques for improving the energy efficiency of radio-frequency ("RF") power amplifiers used in, e.g., transmitters of radio-telephones.
Background of the Invention Conventional radio-telephones typically employ controlled-gain RF power amplifiers to amplify modulated RF signals immediately prior to transmission. Since such amplifiers are employed in the final stages of the transmitters, they are sometimes called "terminal amplifiers."
Known digital radio-telephones adapted `for use in certain cellular communication systems employ "linear" terminal amplifiers in order to preserve the envelope of the RF signals.
In a linear amplifier, the amplitude and phase of the output are linearly related to those of the input so long as the amplifier is operated in the linear range of operating characteristics.
Preserving the RF signal envelope is important since known digital radio-telephones employ linear modulation techniques (e.g., quadrature phase-shift keying) that produce modulated RF
signals having time-varying RF envelopes. Distortions in the time-varying envelopes could give rise to errors when the signals are demodulated in a radio-telephone receiver. Also, envelope distortions can produce interference in adjacent communication channels in the cellular system due to growth of spectral sidebands.
Linear amplifiers are generally satisfactory in eliminating problematic signal distortions. Unfortunately, `? "
linear amplifiers are typically less efficient than non-linear amplifiers used typically in conventional analog radio-telephones.
Consider, for example, a conventional self-biasing Class AB, linear, RF power amplifier implemented using a pair of bipolar transistors in a common-emitter, push-pull configuration. The transistors receive RF signals for amplification and a bias current at their control terminals, i.e., their base electrodes. A source current is applied to the RF power output terminals of the transistors, i.e., their collector electrodes, and is usually called the "collector-bias current." The RF signals vary the flow of the instantaneous source current through the transistors in such manner that the RF output of the amplifier is a faithful reproduction of the input RF signal, but amplified with a gain "beta."
The current gain "beta" is the ratio of the collector-bias to base-bias currents. For a beta of 100, for example, the collector-bias current is 100 times larger`than the base-bias current. It follows that the amplifier must draw large collector-bias currents in order to amplify with a high gain, and thus produce RF signals for transmission at the high power levels often required in cellular communication. Of course, the higher the collector-bias currents drawn by the amplifier, the larger the amount of power consumed by the amplifier.
In addition, as input signals to a conventional amplifier increase in amplitude, bias currents must also increase. Thus terminal amplifiers require more power than amplifiers used in earlier stages of radio-telephone transmitters.
Moreover, a conventional linear amplifier typically requires higher collector-bias currents than non-linear amplifiers in order to remain in the linear range of its operating characteristics. Consequently, digital radio-telephones employing linear amplifiers usually consume more power than do typical analog radio-telephones employing non-linear amplifiers.
3 ~ 3 'j Even when not amplifying RF signals, a conventional linear power amplifier draws significant collector-bias current. When used in applications such as radio-telephones that transmit intermittently, and thus require RF signal amplification only some of the time, the amplifier wastes power by continuously providing bias even when not amplifying.
Even more power is wasted in digital radio-telephones than one might suspect at first blush, because of the way digital cellular systems operate. Standards for digital cellular systems mandate a form of multi-user spectrum sharing called "Time Division Multiple Access" or "TDMA." This approach employs time-division multiplexing to allow multiple (e.g., three) mobile units to use simultaneously the same RF channel that would normally accommodate only one user in a conventional analog cellular system. In TDMA systems, the users transmit sequentially; each user taking a turn in rotation. Since the channel is shared equally, each user transmits one-third of the time, during what is called the "transmit time slot," and does not transmit during the balance of the time. Consequently, the bias currents drawn by the transmitters' linear amplifiers during two thirds of the time of the operation of the transmitter represent wasted power.
The increased power consumption due to linear operation of conventional amplifiers and the wasted power due to TDMA
operation translate into a number of significant drawbacks for digital radio-telephone operation. For instance, the power consumed by a conventional amplifier which is not used for amplification is given off as heat, and can give rise to thermal dissipation problems and even, in severe cases, to thermal runaway. Furthermore, in applications in which the radio-telephones are energized by batteries, the increased power consumption and the power wasted by conventional digital radio-telephones can translate into shortened "talktime" (i.e., less acoustic-data transmission time) per battery charge.
An obvious solution that might come to mind is simply to 3 3 r~
decrease RF power levels of transmissions, and therefore the amplifier's gain, so as to require less collector-bias current from the power source. Unfor-tunately, RF power output levels for transmitters of mobile radio telephones used in cellular systems can not be set arbitrarily; they are dictated by operating conditions, and typically must comply with applicable standards. For instance, the Telecommunications Industry Association Interim Standards 54, 55 and S6 provide a plurality of successively decreasing power level ranges for example, eight nominal power levels, each within a tolerance range)~
In conventional cellular systems, base stations command the mobile units to use certain power level ranges at particular times, and the mobile units automatically follow the commands of the base stations in accordance with the standards.
Normally, conventional amplifiers are operated to produce output RF signals at approximately the nominal power levels in the ranges specified by the base-stations.
Accordingly, reducing arbitrarily the RF power output levels of transmissions from mobile radio-telephones in order to conserve power is not a practical solution. A more sophisticated solution is required.
SummarY of the Invention The invention resides in an automatic bias control ("ABC") circuit for reducing the source current drawn by the amplifier in order to minimize the amplifier's power consumption without significantly affecting the amplifier's gain. This is accomplished by regulating the control current (i.e., bias) supplied to a power amplifier in response to a sensor signal indicative of the amplitude of the source signal and a computer-generated reference signal.
The invention can be practiced advantageously in a linear terminal amplifier of a transmitter of a dual-mode digital/analog mobile cellular radio-telephone. The sensor signal is used to take into account variations in the source current required to achieve a pre-determined amplifier gain, for example, under changing ambient (e.g., temperature) conditions. The reference signal is used to indicate a characteristic of the operation of the amplifier, e.g., the mode of operation of the radio-telephone (i.e., whether digital or analog), the mode of the operation of the amplifier (i.e., whether linear or non-linear), and the power level of the RF
signal being supplied to the power amplifier. (When the input RF signal is higher, a larger source current is typically required, and its larger amplitude is taken into account automatically by the invention in controlling the power amplifier.) For instance, when the radio-telephone operates in the "digital" linear mode, the ABC circuit of the invention regulates the control current so as to provide linear amplification. Moreover, when the transmitter is not transmitting, e.g., when the transmitter is not in the TRANSMIT
time slot, the control current and, consequently, the source current, is reduced (e.g., to zero) so as to significantly reduce or eliminate power consumption when amplification is not needed.
In both "digital" and "analog" modes of operation, the invention adjusts the control current so-that the source current drawn by the amplifier is just sufficient to produce an RF output signal at a power level which is within the power level range specified by a base station, but preferably below the nominal power level provided by the standards. Moreover, in both modes, when the cellular base-station commands the mobile unit to decrease its RF output power, the invention permits the bias currents to be reduced to meet the lower levels efficiently.
In the "analog" mode of operation, on the other hand, the bias currents can be reduced to near the minimum power level within the specified range without regard to linearity of the ~ r~3 ~ t~
output.
Accordingly, in each case, the bias currents can be set to lower values than in conventional linear amplifiers used in digital radio-telephones or non-linear amplifiers used in analog radio-telephones operating under the same conditions, thereby reducing the time-averaged power consumption of radio-telephones.
In a illustrative embodiment, the ABC circuit can be used to control a linear RF power amplifier having at least one common-emitter bipolar transistor. The ABC circuit has a current sensor preferably incorporating a current mirror connecting to a bias supply for generating the collector-bias current for th~ transistor and a sensor signal indicative of the amplitude of the collector-bias current. The current mirror is particularly advantageous since it provides a low resistance between the bias supply and the collector electrode of the transistor, and thus consumes minimum power in deriving the sensor signal. Also, the sensor signal produced by the current mirror has only a small common-mode component.
The ABC circuit also has an error amplifier preferably incorporating a differential integrator fcr comparing the sensor signal from the current mirror with a reference signal controlled by a computer (e.g., a processor or microcomputer).
The differential inte~rator is particularly advantageous since the integration it performs can be used to eliminate transient responses of the ABC circuit that would otherwise tend to remove wanted modulation in the RF signal in the digital mode of operation.
Thus, the error amplifier supplies a base-bias current to the transistor, which is responsive to the integrated difference between a sensor signal indicative of the "actual"
collector-bias current drawn by the transistor, and a reference signal indicative of a "target" collector current, with a view towards minimizing the collector current and thus power consumption in the amplifier while not significantly affecting o~;7 ~ S ~; 3 ~
amplifier gain. As a result, the invention can, e.g., increase talktime in the radio-telephone, while permit-ting compliance with applicable standards. Moreover, the invention can, e.g., reduce thermal power loss by up to 65% and eliminate the likelihood of thermal runaway.
Brief De~criDtion of the Drawinqs The aforementioned and other aspects, features and advantages of the invention are explained in the following description, taken in connection with the accompanying drawings, wherein:
FIGURE 1 is a block diagram of a radio-telephone having an automatic bias control loop in accordance with the invention;
FIGURE 2 is a block diagram of the processor and modulator circuitry Of the digital branch of the transmitter of FIGURE 1;
and FIGURE 3 is a schematic diagram, partially in block diagram form, of an illustrative implementation of the RF power amplifier and bias control circuit of FIGURE 1.
DescriPtion of Preferred Embodiment FIGURE 1 shows a dual-mode analog/digital radio-telephone 10 in accordance with a preferred embodiment of the invention.
As the name implies, the illustrated radio-telephone can employ either digital or analog encoding/decoding of communication signals.
The radio-telephone 10 has a handset 12, a receiver 14, a transmitter 16, and a central processing unit ("CPU") 18 for controlling the operation of the telephone. The latter three components are often called a "transceiver." Additionally, the radio-telephone 10 includes a conventional power supply 20 and ~ ~Ç3~
a conventional antenna 21.
The handset 12 includes a microphone 22 and a speaker 24.
The microphone 12 converts sounds, e.g., messages spoken by a user, into electrical signals (called "TRANSMIT AUDIo signals") representing the spoken sounds. The speaker 24 converts electrical signals (called "RECEIVE AUDIO signals") representing audio data into sound intelligible to the user.
As is known in the art, the receiver 14 demodulates radio-frequency ("RF") signals received from the antenna, thereby producing the RECEIVE AUDIO signals, which are provided to the speaker 24.
The transmitter 16 processes the TRANSMIT AUDIo signal preparatory for broadcast by the antenna. To accomplish this, the transmitter 16 includes a processing and modulating ("P&M") circuit 26 for producing a signal called RF_IN by modulating an RF carrier with a digital signal derived from the TRANSMIT
AUDIO signal, and amplifying the resulting signal to a pre-selected power level under the control of the CPU 18.
The P&M circuit 26 illustrated in FIGURE 1 can be switched between digital and analog modes of operation, thus rendering the transmitter 16 capable of dual-mode digital/analog operation. This is accomplished by a pair of jointly operated, dual-pole/ single-throw, electronic switches 32, which connect the TRANSMIT AUDIO signal either to digital branch circuitry 34 for digital mode, or to analog branch circuitry 36 for analog mode of operation.
As shown in FIGURE 2, the digital branch circuitry 34 has a digitizer 34a for converting analog TRANSMIT AUDIO signals from the microphone 32 into digital signals, an encoder 34b for encoding (e.g., for error protection) the digitized signals, a modulator 34c for modulating an RF carrier with the encoded signals using, e.g., quadrature phase-shift keying, and an amplifier 34d for boosting the modulated signals to a pre-selected power level (e.g., one of eight power levels) and thus producing RF_IN.
The analog branch circuitry 36 contains conventional components for modulating the RF carrier with a filtered, amplified version of the TRANSMIT AUDIO signal, e.g., using conventional frequency modulation techniques, and then for amplifying the resulting signal.
The transmitter 16 also includes a linear, variable-gain RF terminal power amplifier 30 for boosting the power of RF_IN
by a constant gain. The transmitter 16 then supplies the resulting signal, called RF_OUT, to the antenna 21 for broadcast.
Owing to the amplification in the P&M circuit 26 and the terminal amplifier 30, the RF_OUT signal from the transmitter 16, when in its digital or analog mode of operation, has a power level falling within one of the, eOg., eight ranges specified by the above-referenced standards. It should be emphasized that the terminal amplifier 30 preferably amplifies RF_IN with a constant current gain, e.g., 100. The gradations in power required to comply with the standàrds are preferably provided in the P&M circuit 26.
The transmitter 16 also has an automatic bias control loop ("ABC") circuit 40 for controlling the gain of the power amplifier 30. In accordance with the invention, the ABC
circuit 40 is adapted specifically to reduce the DC power required by the power amplifier 28 without significantly affecting its current gain or in any way adversely affecting its operation.
The ABC circuit 40 includes a current sensor 42, a bias supply 44, an error amplifier 46, a reference generator 48, and a filter 50. The current sensing circuit 42 receives a supply current from the bias supply 44, and delivers a portion thereof as a source current to a source terminal 3Oa of the power amplifier 30. The current sensing circuit 42 also generates a sensor signal indicative of the amplitude of the supplied source current, and feeds the sensor signal to the error amplifier 46.
?,~ 3 ~
The reference generator 48 preferably is a digital-to-analog converter that converts digital control signals supplied over lines "x" and "y" (for a two-bit signal) by the CPU 18 into "reference signals," which are supplied to the error amplifier 48. The reference signals serve to indicate "target"
bias currents to be supplied to the power amplifier 30 to minimize or at least reduce DC power consumption by the amplifier.
The error amplifier 46 derives a bias-control signal based on a comparison of the sensor and reference signals, i.e., based on the "actual" and "target" source currents. The error amplifier 46 provides the bias-control signal to a low-pass filter 50.
The low-pass filter 50 passes the low-frequency component of the bias control signal as the control current to a control terminal of the amplifier 30, and controls the dynamic response of the ABC circuit 40. The amplitude of the control current determines the amplitude of the current flowing through the power amplifier. This determines the amount of the source current drawn by the amplifier 30, and thus its power requirements.
It will be apparent that the ABC circuit 40 virtually defines a feedback loop for automatically controlling the bias current. The feedback loop can be traced in FIGURE 1 from the current sensor 42 (which detects the amplitude of source current drawn by the amplifier 30), to the error amplifier 46, to the filter 50, and then to the power amplifier 30.
FIGURE 3 shows the RF power amplifier 30 and the ABC
circuit 40 in greater detail. Each of the depicted circuits will be described, starting with the power amplifier 30.
The power amplifier 30 includes a series-to-parallel or single-ended-to-balanced converter 52, which, in RF
terminology, is also called a front-end balun. The front-end balun 52 splits RF_IN into first and second balanced signals that are 180 degrees out of phase with one another and of the 3 ?~
same amplitude. The balun 52 supplies the first and second balanced signals to respective pairs 54, 56 of parallel capacitors for impedance matching. The outputs of the capacitors 54, 56 are interconnected by an inductor 62 for base-bias injection (as will further described shortly), and a capacitor 64 again for impedance matching. The outputs of the capacitors 54, 56 are coupled to an amplifier integrated circuit ("AMP IC") 66.
More specifically, the capacitors 54, 56 are connected to respective base terminals 68a, 70a of respective bipolar transistors 68, 70 forming the AMP IC 66. The transistors 68, 70 are connected for linear operation in a common-emitter arrangement or grounded-emitter arrangement. As the name implies, the emitters 68b, 70b of the transistors 68, 70 are tied to ground. The collectors 68c, 70c of transistors 68, 70 are interconnected by an inductors 71 for collector-bias injection, and a capacitor 72 for impedance matching. The collectors 68c, 70c are also connected to respective first and second pairs 78, 80 of parallel capacitors for impedance matching.
The outputs of the capacitors 78, 80 are connected to a parallel-to-series or balanced-to-single-ended converter or output balun 82. The output balun 82 combines the balanced signals from the capacitors 78, 80 into a signal RF_OUT, which is the output from the RF amplifier 30.
The power amplifier 30 also has a base-bias circuit 86 connected to the base 70a, and a collector-bias circuit 88 connected to the collector 70c. The base and collector-bias circuits 86, 88 de-couple the bias currents from the RF signal.
The base-bias circuit 86 has parallel capacitors 90 connected between the base 70a and ground, and a series inductor 92 connected between the base 70a and the filter 50. The collector-bias circuit 88 has a capacitor 94 connected between collector 70c and ground, and a series inductor 96 connected between the collector 70c and the current sensor 42.
c~ ti The current sensor ~2 receives a DC supply current "IDc"
from a bias supply 44 (FIGURE 1). The current sensor 42 serves as a current divider, feeding most of IDC to the power amplifier 30 as the collector-bias current, and supplying a small portion of this current to the error amplifier 46 over line 98 as the sensor signal. The sensor signal, as noted above, indicates the magnitude of the collector-bias current.
More specifically, the current sensor 42 is configured as a current mirror formed by first and second matched transistors 120, 122. The transistors 120, 122 have common base electrodes 120a, 122a that are connected to the collector 122b of transistor 122.
IDC is supplied to the emitter electrode 120c of transistor 120, and, via a resistor 124, to the emitter electrode 122c of transistor 122. Most of the IDC flows through transistor 120 and to the collector-bias circuit 88. A
small portion of IDC flows through transistor 122, where the current is impressed upon resistor 126 yielding a voltage that is supplied to the error amplifier 46.
It will be apparent that the fraction of IDC flowing through transistor 120 is determined by the resistive value of resistor 124, and that the voltage that is supplied to the error amplifier 46 as the sensor signal is determined by the resistive value of resistor 126. (The input impedance of the error amplifier 46 is much larger than the impedance of the resistor 126.) Moreover, the magnitude of the sensor signal is proportional to that of the current supplied to the collector-bias circuit 88, and thus indicative of the magnitude of the supplied collector-bias current.
The current mirror 42 also has a capacitive decoupling network 127 connected between the collector electrode 120b and ground for decoupling radio-frequency signals in the power amplifier 30 from the collector-bias current supplied by the current mirror 42.
The error amplifier 46 includes a comparator 130, ~ 1 ~ 3 ~ ~ 3 13 -13~
preferably, a differential integrator formed by an operational amplifier ("op amp") 132 and a capacitive/resistive feedback arrangement 13~. A first input 130a of the integrator 130 receives the sensor signal via a resistor 136 connec-ted to line 98, and a second input 130b receives a reference voltage from the reference generator 48. The output of the integrator 130 represents the integrated difference between the signals applied to the inputs 130a, 130b.
The comparator 130 performs integration in order to eliminate transient responses, so that, e.g., the ABC circuit 40 does not remove the wanted modulation from the signal (i.e., RF_IN) being amplified by the power amplifier 30. This is accomplished by providing the comparator 130 with appropriate integration time constants during circuit design.
An amplifying transistor 138 boosts the signal level of the output of the comparator 130, and provides the amplified signal to the filter 50. The filter 50 includes a series resistor 142 connected between the transistor 138 and both a capacitive shunt 144 to ground and the base-bias circuit 86 of the power amplifier 30. Thus, as noted above, the filter 50 provides the base-bias current, i.e., the control current, to the power amplifier 30.
As described hereinabove, the ABC circuit 40 uses the sensor signal and the reference signal in adjusting control current so as to minimize the collector-bias current, i.e., the source current, with a view to reducing the power consumed by the amplifier 30. The dissipated DC power (IlPdcll) for the power amplifier 30 shown in FIGURE 3 is given by the following equation:
Pdc ~Ic x Vc) - Prf where "Ic" is the collector-bias current, "Vc" is the collector-bias voltage, and "Prfll is the transmitted RF power.
Thus, it can be readily seen that reducing Ic causes PdC to 3 ~
decrease.
Key to successfully reducing the source current without adversely affecting the operation of the transmitter 16 is the reference voltage or signal, which is derived from the digital control signals from the CPU 18. The digital control signal preferably is an m-bit digital signal (where "m" is a positive integer) representing a number of desired operating conditions of the amplifier 30. For example, where "m" equals one, i.e., the digital control signal has a single bit, a LOW value for the signal could correspond to full bias, so that the amplifier 30 is turned ON and produces RF_OUT. A HIGH value of the digital control signal, on the other hand, could correspond to zero bias, so that the amplifier 30 is turned OFF and does not amplify, e.g., during periods of time when the radio-telephone 10 is not transmitting.
Alternatively, the digital control signal can have two bits, i.e., "m" equals two, which finds particular utility in TDMA systems. For example, the various values of a two-bit digital control signal can have the following results:
1) HIGH-HIGH: linear mode of operation of amplifier for higher power levels mandated by - standards applicable to digital radio-telephones;
2) HIGH-LOW: linear mode of operation of amplifier for lower power levels mandated by standards applicable to digital radio-telephones, and non-linear mode of operation of amplifier for higher power levels mandated by standards applicable to analog radio-telephones;
3) LOW-HIGH: non-linear mode of operation of amplifier for lower power levels mandated by standards applicable to analog radio-telephones; and 4) LOW-LOW: OFF
$~3 ~
In yet another alternative, the digital control signals can have five bits, with one specifying digital (linear) operation or analog operation, another specifying ON or OFF
(i.e., transmission or no transmission), and the remaining three specifying each of eight power levels.
The foregoing description has been limited to a specific embodiment of this invention. It will be apparent, however, that variations and modifications may be made to the disclosed embodiment with the attainment of some or all of the advantages of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the inventicn.
$~3 ~
In yet another alternative, the digital control signals can have five bits, with one specifying digital (linear) operation or analog operation, another specifying ON or OFF
(i.e., transmission or no transmission), and the remaining three specifying each of eight power levels.
The foregoing description has been limited to a specific embodiment of this invention. It will be apparent, however, that variations and modifications may be made to the disclosed embodiment with the attainment of some or all of the advantages of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the inventicn.
Claims (24)
1. A control circuit for adjusting a source current drawn by a power amplifier to minimize the amplifier's power consumption without significantly affecting the amplifier's gain, said control circuit comprising:
A) reference means for providing a reference signal;
B) sensor means for supplying the source current to said power amplifier, and for generating a sensor signal corresponding to the amplitude of the source current; and C) means responsive to said reference signal and said sensor signal for regulating the control current supplied to the power amplifier in response to the sensor signal and a computer-generated reference signal.
A) reference means for providing a reference signal;
B) sensor means for supplying the source current to said power amplifier, and for generating a sensor signal corresponding to the amplitude of the source current; and C) means responsive to said reference signal and said sensor signal for regulating the control current supplied to the power amplifier in response to the sensor signal and a computer-generated reference signal.
2. The control circuit in accordance with claim 1, in combinations with a terminal amplifier of a transmitter of a dual-mode mobile cellular radio-telephone.
3. The control circuit in accordance with claim 2, wherein the reference signal is indicative of whether the radio-telephone is operating in a digital mode of operation, and the amplifier is operating linearly, and of the power level of a radio-frequency signal being supplied to the power amplifier for amplification.
4. The control circuit in accordance with claim 3, wherein, when the reference signal indicates a digital mode and linear operation, the regulating means regulates the control current so as to provide linear amplification.
5. The control circuit in accordance with claim 3, wherein, when the transmitter is not transmitting, the regulating means reduces the control current to about zero so as to minimize power consumption when amplification is not needed.
6. The control circuit in accordance with claim 3, wherein, when said reference signal indicates an analog mode of operation, the regulating means adjusts the control current to near the minimum power level within a pre-selected power level range.
7. The control circuit in accordance with claim 2, wherein the regulating means adjusts the control current so that the source current drawn by the amplifier is just sufficient to produce a radio-frequency output signal at a power level which is within a pre-selected power level range, but preferably below a nominal power level within the range.
8. The control circuit in accordance with claim 1, wherein said sensor means includes a current mirror connected between a current supply and both said amplifier and said regulating means for supplying said source current to said amplifier and said sensor current to said regulating means.
9. The control circuit in accordance with claim 1, wherein said sensor means includes a pair of transistors connected as a current mirror, means for providing a supply current to said transistors, means for supplying a source current to a control terminal of said amplifier from said transistors, means for supplying a sensor signal to said regulating means from said transistors, and resistor means for causing said sensor signal to be proportional to said source current.
10. The control circuit in accordance with claim 8, wherein said regulating means includes an error amplifier comprising a differential integrator for comparing the sensor signal from the current mirror with the reference signal supplied by a computer.
11. The control circuit in accordance with claim 9, wherein said differential integrating means includes A) a differential integrator including said first and second inputs, and for integrating the difference between the reference signal and the sensor signal, thereby generating an integrator output;
D) amplifier means coupled to the differential integrator for amplifying the integrator output; and E) filter means coupled to the amplifier means for filtering the amplified integrator output, and supplying the filtered signal to the amplifier as the control signal.
D) amplifier means coupled to the differential integrator for amplifying the integrator output; and E) filter means coupled to the amplifier means for filtering the amplified integrator output, and supplying the filtered signal to the amplifier as the control signal.
12. The control circuit in accordance with claim 1, wherein said regulating means includes an error amplifier comprising a differential integrator for comparing the sensor signal with the reference signal supplied by a computer.
13. For use with a power amplifier receiving a source current and a control current for controlling the flow of the source current through the amplifier, said amplifier having a pre-selected gain, a power-conserving control circuit for reducing the source current required by the power amplifier in order to minimize the amplifier's power consumption without significantly affecting the amplifier's gain, said control circuit comprising:
A) means for providing a sensor signal indicative of an actual amplitude of the source current supplied to the amplifier at a particular instance of time;
B) means for providing a reference signal indicative of a target amplitude for the source current at the particular instance of time; and C) error amplifier means responsive to the integrated difference between the sensor signal and reference signal for generating a control signal that minimizes the source current without significantly affecting amplifier gain.
A) means for providing a sensor signal indicative of an actual amplitude of the source current supplied to the amplifier at a particular instance of time;
B) means for providing a reference signal indicative of a target amplitude for the source current at the particular instance of time; and C) error amplifier means responsive to the integrated difference between the sensor signal and reference signal for generating a control signal that minimizes the source current without significantly affecting amplifier gain.
14. A terminal power amplifier circuit for a radio-telephone transmitter comprising:
A) a power amplifier, which receives a radio-frequency input signal at a first terminal, a source current at a second terminal, and a control current at said first terminal for regulating the flow of the source current through the power amplifier, for generating an output radio-frequency signal at said second terminal that is an amplified replica of said radio-frequency input signal, the amplification corresponding to a pre-selected gain; and B) a control circuit for controlling the source current required by the power amplifier in order to minimize the amplifier's power consumption without significantly affecting the pre-selected gain, said automatic bias control circuit comprising i) reference means coupled to a computer for providing a reference signal indicative of at least one characteristic of the operation of the amplifier;
ii) a current mirror circuit for supplying the source current to said power amplifier, and for generating a sensor signal corresponding to the amplitude of the source current; and iii) an error amplifier coupled to receive the reference signal at one input thereof and the sensor signal at a second input thereof for integrating the difference therebetween to generate the control signal.
A) a power amplifier, which receives a radio-frequency input signal at a first terminal, a source current at a second terminal, and a control current at said first terminal for regulating the flow of the source current through the power amplifier, for generating an output radio-frequency signal at said second terminal that is an amplified replica of said radio-frequency input signal, the amplification corresponding to a pre-selected gain; and B) a control circuit for controlling the source current required by the power amplifier in order to minimize the amplifier's power consumption without significantly affecting the pre-selected gain, said automatic bias control circuit comprising i) reference means coupled to a computer for providing a reference signal indicative of at least one characteristic of the operation of the amplifier;
ii) a current mirror circuit for supplying the source current to said power amplifier, and for generating a sensor signal corresponding to the amplitude of the source current; and iii) an error amplifier coupled to receive the reference signal at one input thereof and the sensor signal at a second input thereof for integrating the difference therebetween to generate the control signal.
15. The terminal power amplifier circuit in accordance with claim 14, wherein the reference signal is indicative of a any of a plurality of characteristics of the operation of the amplifier, including whether the amplifier is to operate linearly.
16. The terminal power amplifier circuit in accordance with claim 15, wherein, when the reference signal indicates linear operation, the regulating means regulates the control current so as to provide linear amplification.
17. For use with a power amplifier receiving a source current and a control current for controlling the flow of the source current through the amplifier, said amplifier having a pre-selected gain, a method of automatically controlling the control signal for reducing the source current required by the power amplifier, thereby reducing the amplifier's power consumption without significantly affecting the amplifier's gain, the method comprising the steps of:
A) providing a reference signal to a control-signal regulator;
B) generating a sensor signal corresponding to the amplitude of the source current supplied to the amplifier; and C) integrating the difference between the reference signal and the sensor signal to generate the control signal.
A) providing a reference signal to a control-signal regulator;
B) generating a sensor signal corresponding to the amplitude of the source current supplied to the amplifier; and C) integrating the difference between the reference signal and the sensor signal to generate the control signal.
18. The method in accordance with claim 16, further comprising the steps of amplifying and filtering the integrated difference.
19. The method in accordance with claim 17, wherein the reference signal is indicative of whether the radio-telephone is operating in a digital mode of operation, whether the amplifier is operating linearly, and the power level of a radio-frequency signal being supplied to the power amplifier for amplification.
20. The method in accordance with claim 17, wherein, when the reference signal indicates a digital mode and linear operation, the regulating means regulates the control current so as to provide linear amplification.
21. The method in accordance with claim 17, wherein, when the reference signal indicates that the transmitter is not transmitting, the control signal is reduces the control current to about zero so as to significantly minimize power consumption when amplification is not needed.
22. The method in accordance with claim 17, wherein the control signal causes the source current to be just sufficient to produce a power amplifier output signal at a power level which is within a pre-selected power level range, but preferably below a nominal power level within the range.
23. The method in accordance with claim 17, wherein, when said reference signal indicates an analog mode of operation, the control signal is adjusted to near the minimum power level within a pre-selected power level range.
24. A method of generating an amplified replica of an radio-frequency input signal in a terminal power amplifier circuit for a radio-telephone transmitter, comprising the steps of:
A) receiving a radio-frequency input signal at a first terminal of said power amplifier, a source current at a second terminal thereof, and a control current at said first terminal for regulating the flow of the source current through the amplifier, thereby generating an output radio-frequency signal at said second terminal that is an amplified replica of said radio-frequency input signal, the amplification corresponding to a pre-selected gain; and B) controlling the source current required by the power amplifier in order to minimize the amplifier's power consumption without significantly affecting the pre-selected gain, said controlling step comprising the steps of i) providing a reference signal indicative of at least one characteristic of the operation of the amplifier;
ii) generating a sensor signal corresponding to the amplitude of the source current supplied to the power amplifier; and iii) integrating the difference between the reference and sensor signals to generate the control signal.
A) receiving a radio-frequency input signal at a first terminal of said power amplifier, a source current at a second terminal thereof, and a control current at said first terminal for regulating the flow of the source current through the amplifier, thereby generating an output radio-frequency signal at said second terminal that is an amplified replica of said radio-frequency input signal, the amplification corresponding to a pre-selected gain; and B) controlling the source current required by the power amplifier in order to minimize the amplifier's power consumption without significantly affecting the pre-selected gain, said controlling step comprising the steps of i) providing a reference signal indicative of at least one characteristic of the operation of the amplifier;
ii) generating a sensor signal corresponding to the amplitude of the source current supplied to the power amplifier; and iii) integrating the difference between the reference and sensor signals to generate the control signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US82736392A | 1992-01-29 | 1992-01-29 | |
| US07/827,363 | 1992-01-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2083536A1 true CA2083536A1 (en) | 1993-07-30 |
Family
ID=25249028
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2083536 Abandoned CA2083536A1 (en) | 1992-01-29 | 1992-11-23 | Power-conserving automatic bias control for linear amplifier in radio-telephone transmitter |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2083536A1 (en) |
-
1992
- 1992-11-23 CA CA 2083536 patent/CA2083536A1/en not_active Abandoned
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