Abstract: A closed loop, active cancellation technique (ACT)-based RF power amplifier linearization architecture injects a pilot tone as a ‘pseudo distortion’ signal into signal paths through first and second matched RF amplifiers, and a set of power minimization loops are closed around the RF amplifier pair. The power minimizing control loops control a set of vector modulators such that both the injected pilot tone and intermodulation distortion products are canceled, while RF carrier components constructively sum in the composite output of the two RF amplifiers.

Abstract: A feed forward arrangement for linearizing a distorting element such as an amplifier. The arrangement has error correction means which produces an error correction signal that is combined with the output signal of the distorting element to produce a corrected output signal. A pilot signal is injected into the distorting element path so as to be processed by the error correction means and the presence of the pilot signal in the corrected output signal is monitored by comparison with the pilot signal so as to produce another error correction signal to adjust the error correction means. The pilot signal is advantageously derived from the distorting element input signal.

Abstract: High efficiency and high power output are attained in a multi-tone FF RF amplifier by eliminating fundamentals in a first loop and then operating on the IMD products only in a second loop. Since lower power tones are adjusted in the IMD product reduction, less complex, lower power processing circuitry is required and higher efficiency is realized since both amplifiers add in-phase and approximately equally at the RF output.

Abstract: A closed loop, active cancellation technique (ACT)-based RF power amplifier linearization architecture injects a pilot tone as a ‘pseudo distortion’ signal into signal paths through first and second matched RF amplifiers, and a set of power minimization loops are closed around the RF amplifier pair. The power minimizing control loops control a set of vector modulators such that both the injected pilot tone and intermodulation distortion products are canceled, while RF carrier components constructively sum in the composite output of the two RF amplifiers.

Abstract: A gain and phase control system performs a gain (or phase) adjustment based on the results of a previous gain (or phase) adjustment after an intervening phase (or gain) adjustment. A gain adjustment is based on the results of a previous gain adjustment rather than on the results of an intervening phase adjustment. A phase adjustment is based on the results of a previous phase adjustment rather than the results of an intervening gain adjustment. As such, the above-mentioned increase in error signal does not occur because a gain adjustment is based on the results of the previous gain adjustment, and a phase adjustment is based on the results of the previous phase adjustments.

Abstract: In a feedforward amplifier with a simplified circuit configuration, leakage signals are prevented between output terminals of a pilot oscillator and between input terminals of a detector circuit to remove distorted signals with almost ideal improvement. Each of an output change-over section of the pilot oscillator and an input change-over section of the detector includes a multistage change-over switch or an isolator, the pilot oscillator and the detector being shared between a distortion detecting loop and a distortion removing loop.

Abstract: A feedforward amplifier combines an input signal delayed by a delay circuit with an output signal by a combiner; down-converts the output of the combiner to a low frequency by a frequency converter; extracts a distortion component from the output of-the frequency converter; measures the distortion component by a power detector; and controls a second vector regulator of a distortion canceling loop by a controller such that the distortion component measured becomes minimum.

Abstract: A hybrid multicarrier RF power amplifier linearization architecture combines ACT and feed-forward amplifier stages to achieve high output distortion rejection and enhanced amplifier linearity. A carrier cancellation loop is coupled with a main RF power amplifier stage having parallel RF power amplifiers coupled via intermod-complementing predistortion paths. The carrier cancellation loop is coupled to a feed-forward loop containing a feed-forward RF power amplifier, to produce a composite amplified output signal having very reduced intermodulation products. Vector modulators in the main amplifier and feed-forward amplifier stages are controlled by a digital signal processor, using outputs from various monitoring subsystems, including pilot tone detection, correlator, distortion and power detector circuits.

Abstract: The present invention provides a novel feed forward amplifier (“FFA”) and a pilot tone generator-receiver therefor. In an embodiment of the invention, the feed forward amplifier only requires a single oscillator to operate both the pilot tone generator and pilot tone receiver used in conjunction with the amplifier circuitry of the FFA. In another embodiment of the invention, a method is provided of generating and detecting a pilot tone from a single oscillating signal.

Abstract: A circuit for processing an information signal in which is embedded pilot signal. The circuit is connectable to a configuration used for applying distortion correction to the output of an amplifier fed by the information signal. The information signal can be a CDMA signal or an FDMA signal in which one or more channels are pilot channels containing the pilot signal. The circuit includes first and second demodulators which are used for demodulating the embedded pilot signal at first and second points which are respectively located before and after the application of distortion correction by the configuration. Also described is a controller connected to the first and second demodulators, which varies the amount of distortion correction applied by the configuration as a function of the pilot signals demodulated by the first and second demodulators.

Abstract: In a distortion detecting loop, an inputted RF signal is branched into two input signals by a distributor, one of the branched input signals is amplified by a main amplifier whose output signal is branched by a directional coupler, the branched output signal from the amplifier and the other branched input signal are inverted relatively to each other and combined together to extract a distortion component signal produced by the main amplifier with a detector. If the amplitude of the distortion component signal is greater than a predetermined threshold, then a control circuit changes the distortion component signal to a substitute signal having an amplitude smaller than the predetermined threshold, and controls a vector adjuster based on the amplitudes of the detected distortion component signal and the substitute signal in order to reduce the amplitude of the detected distortion component signal.

Abstract: In a distortion injection path (15) wherein a detected distortion component of a main amplifier (23) becomes amplified, distortion by an auxiliary amplifier (29a) is detected by an auxiliary distortion detector (42) composed of a variable attenuator (27a), a variable phase shifter (28a), a first auxiliary amplifier (29a), a delay line (36) and a phase inverter (37), and the detected distortion is cancelled by an auxiliary distortion canceller (43) composed of a variable attenuator (27b), a variable phase shifter (28a), a second auxiliary amplifier (29b) and a delay line (39), thereby increasing the efficiency of the amplifier.

Abstract: A feedforward high power linear amplifier for wideband cellular applications uses slope compensation in combination with two modulated pilot signals to control intermodulation distortion cancellation stages in order to effect a much higher degree of linearity than can be achieved with conventional feed forward linear power amplifier designs.

Abstract: A feed-forward amplifier and a controller thereof. Two types of second pilot signals, sum frequency and difference frequency of a base pilot signal and a local oscillation signal, are generated by an injection-side mixer and injected into a distortion detection loop. Part of a signal appearing at an output terminal is branched, converted in frequency by a detection-side mixer using the local oscillation signal, filtered by a narrow-band filter, input to a synchronizing detector with the filtered output of the filter as error signals, and synchronizing detected with reference to the base pilot signal so as to generate control signals for a distortion rejection loop. The spectrums of the second pilot signals may be spread. A process to cancel the input signal component at the detection side may be performed. A simple circuit configuration enhances the distortion component rejection and suppression effect and shortens the time required until an optimum control state is established.

Abstract: An adaptive gain and/or phase control system adapts the gain and/or phase adjustment resolution to provide improved performance. For example, the adaptive gain and/or phase control system can dynamically adjust the adjustment resolution for gain and/or phase adjustments as a function of the error signal(s). In response to a large error signal(s) (far from the null), the adaptive gain/or phase control system decreases the adjustment resolution, resulting in a faster convergence rate. In a feed forward distortion reduction system, decreasing the adjustment resolution improves the transient response of the amplifier (for example, given any set of operating conditions, how quickly the amplifier responds to a changing input). As phase or gain adjustments are made to approach the null, the error signal reduces, and the adaptive distortion reduction system increases the adjustment resolution.

Abstract: The invention relates to an adaptation method and amplifier arrangement, which comprises feedforward amplifying means (10) which amplify a signal entering the arrangement, and adjusting means (20, 25, 50, 80) which use complex factors &agr; and &bgr;, which are adapted in order to adjust the phase and amplitude of the input signal to the amplifier arrangement. The amplifier arrangement also comprises attenuation means (40) which attenuate the signal amplified by the amplifier (10), means (60) which subtract the attenuated signal from the adapted signal, adjusting means (50, 80) which receive part of the signal entering the arrangement for adaptation by factor a, which is adapted partly by the signal obtained from the adapted signal.

Abstract: In the balance adjustment using a pilot signal in a distortion detector and a distortion canceller of a feed-forward amplifier for amplifying a CDMA transmission signal, a pilot code is spread by a long code different from that of the CDMA transmission signal to obtain the pilot signal. The pilot signal is converted to a signal of the transmission frequency band, and the converted signal is injected into the transmission signal at the input side of the amplifier. The pilot signal frequency band is detected from the output of an auxiliary amplifier of the distortion canceller and converted to the base band, thereafter being despread to detect the pilot signal (code).

Abstract: A multi-tone signal amplifier topology and an amplifying method in which a first amplifier outputs a first signal having at least one fundamental frequency signal and a first distortion signal. A second amplifier outputs a second signal that has a fundamental frequency signal corresponding to each fundamental frequency signal of the first signal and a second distortion signal. Each fundamental frequency signal of the second signal is substantially in-phase with the corresponding fundamental frequency signal of the first signal, while the second distortion signal is substantially 180° out-of-phase with the first distortion signal. An output coupler combines the first and second signals to form a third signal having the corresponding fundamental frequency signals of the first and second signals constructively combined and a third distortion signal that is a difference between the first distortion signal and the second distortion signal.

Abstract: The invention relates to a method and apparatus for reducing the distortion output of an amplifier used with an RF signal. The method and apparatus typically modify the distortion of the amplifier to reduce it, by detecting cross-modulation components modulated onto a continuous wave, low level, pilot signal injected at the input of the amplifier system. The circuitry detects the cross-modulation components and provides correction signals in response thereto.

Abstract: An amplifier with feedforward loops for rejecting non-linear distortion and control circuitry for such amplifier and employing a distortion compensation method. A signal from a dominant path is input into a synchronizing detector via an ALC circuit as a reference signal. Using this reference signal, an error signal output from a distortion rejection loop is subjected to synchronizing detection. An offset voltage of a mixer inside the synchronizing detector can be prevented from varying due to change in local level. Outputs from synchronizing detectors are used for control to optimize corresponding loops. As a pilot signal for a distortion detection loop can be eliminated, undesirable spurious effects due to such a pilot signal is avoided. The acquisition time of each of the loops can be shortened because an optimizing control using a step-by-step procedure under CPU control can be eliminated.

Abstract: The invention relates to a low cost feed forward RF power amplifier arrangement for amplifying an RF input signal using a main power amplifier operating as a Class AB amplifier. The method and apparatus modify the input signal to the main amplifier to compensate for the distortion added by the main power amplifier. The circuit provides for injecting a pilot signal prior to the Class AB amplifier and adjusting the correction circuitry of the amplifier based on a quadrature modulated, chopped derivative of the injected pilot signal.

Abstract: A feed-forward amplifier is provided, which can implement satisfactory linearity immediately after its activation. The amplifier has a high productivity and exhibits less long term fluctuations of its characteristics during the operation. In the feed-forward amplifier, the transfer function of a path from an input terminal to a directional coupler via a main amplifier and the transfer function of a path from the input terminal to the directional coupler via a first delay means are automatically controlled so as to be equal in amplitude but anti-phase relative to each other. The transfer function of a path from the main amplifier to an output terminal via a second delay means and the transfer function of a path from the main amplifier to the output terminal via an auxiliary amplifier are automatically controlled so as to be equal in amplitude but anti-phase relative to each other.

Abstract: A control system comprising an electrical circuit that produces distortion where the electrical circuit has a frequency band of operation. Double side band pilot signals are located slightly outside the boundaries of the frequency band of operation so as not to interfere with any signals within the frequency band of operation, but still provide information that the control system uses to substantially cancel the distortion.

Abstract: The present invention relates to a feed-forward amplifying device suitable for radio communication systems such as digital automobile telephone.

Abstract: A reception circuit for a cellular telephone according to the present invention shares the use of a code division multiple access system and a frequency division multiple access system, comprises: an amplifier circuit at the forefront stage; a bypass circuit connected to the amplifier circuit at the forefront in parallel therewith, having lower gain than the amplifier circuit at the forefront stage; and a common processing circuit connected to the latter stages of the amplifier circuit at the forefront and the bypass circuit, and when the level of a received signal is not higher than predetermined voltage, induces the received signal to the processing circuit through the amplifier circuit at the forefront while when the level of the received signal exceeds the predetermined voltage, the received signal is induced to the processing circuit through the bypass circuit.

Abstract: The present invention provides an improved pilot detection technique for a control system comprising an electrical circuit that produces distortion and which applies the pilot signal to the electrical circuit and uses information obtained from the pilot signal to cancel the distortion from the electrical circuit.

Abstract: A method and apparatus for amplifying a feedforward linear power using a pilot tone hopping are disclosed. The method in a feedforward linear power amplifier system first determines an operating frequency signal for amplification from a radio frequency (RF) signal applied to the linear amplifier system. A pilot frequency signal is determined from the previously determined operating frequency signal, and the decided pilot frequency signal is hopped into an upper sideband or lower sideband of the operational frequency bandwidth of the applied RF signal and the determined pilot frequency signal is output to an input port of a main amplifier. One typical advantage of the method is that distortion component suppression characteristics in the wide operating frequency bandwidth are obtained by only one pilot signal generator and use of a control/detect device leads to simplicity of the circuit.

Abstract: A feed foward amplifier including a first amplifier for amplifying a first input signal; an extraction unit for extracting a distortion element added to a second signal output from the first amplifier; a second amplifier for amplifying the distortion element; an adder for inverting the phase of either the second signal or of a third signal output from the amplifier and for adding these signals; and a controller for controlling the supply of power to the second amplifier based on a level of the first terminal. When the controller ascertains that the detected level is equal to or greater than the reference level, the controller unit powers on the second amplifier. When the detected level is lower than the reference level, the controller powers off the second amplifier. Thus, since the power to the second amplifier is switched off when the volume of traffic is low, the consumption of power is reduced.

Abstract: A calibration system for a feed forward distortion reduction system periodically uses a pilot signal to calibrate the pilotless feed forward reduction system. In calibrating the feed forward distortion reduction system, the calibration system periodically injects the pilot signal onto a signal path, for example, when no signal is present on the signal path. A portion of the pilot signal on the signal path is provided to a feed forward path of the feed forward distortion reduction system. The pilot signal on the feed forward path is combined with the pilot signal on the signal path, and the calibration system adjusts the relative phase and amplitude between the pilot signal on the feed forward path and the pilot signal on the signal path to achieve the desired combination of the pilot signals.

Abstract: An improved feedforward amplifier capable of enhancing accuracy of extraction of an error signal corresponding to a distortion component while preventing outflow of an pilot signal. A switch is disposed between a pilot signal oscillator and a third power combiner for superimposing the pilot signal on an output signal from a main amplifier, and third control means is connected with the switch so that the switch is opened at the time of error signal extraction and closed at the time of error signal elimination.

Abstract: A spread spectrum (SS) pilot extraction system clips the RF carriers before the SS pilot is de-spread and the RF carriers are spread. The clipping of the RF carriers raises the noise level in the spectrum. However, the small increase in the in-band noise level is more than offset by the reduction of the in-band RF noise from spreading the clipped carriers. As a result, the reduction in the in-band noise from spreading the clipped carriers expands the detection range of the de-spread pilot. In doing so, the control circuitry can achieve further cancellation of the pilot and the IMD components. Thus, the SS pilot extraction system for feed forward RF amplifiers improves the spread spectrum pilot extraction and detection at the final output coupler to achieve improved pilot and IMD cancellation.

Abstract: A pilot signal detection system uses a band reject filter to reject the frequency band of at least one carrier signal to improve pilot signal detection. For example, in a feed forward distortion reduction system, the carrier signal(s) is on a main signal path along with a pilot signal which is injected into the main signal path at a frequency adjacent to the frequency band of the carrier signal(s). The carrier signal(s) and the pilot signal are amplified on the main signal path, resulting in distortion on the main signal path. To reduce the distortion from the main signal path, the feed forward distortion reduction system detects and reduces the pilot signal. To improve detection of the pilot signal, the pilot signal detection system provides a signal representative of the carrier signal(s) and the pilot signal with distortion from the main signal path onto a pilot detection path.

Abstract: A feedforward amplifier system including a main amplifier and first and second error amplifiers, and wherein the first error amplifier is itself a feedforward amplifier whose operation is corrected by the second error amplifier. With appropriate selection of circuit components the operating power required by the amplifier system, and hence the size of the package in which it is contained, may be reduced up to one-third.

Abstract: The present invention provides for a gain control circuit (10) and method for providing gain control of a variable amplification circuit (16) using a pilot signal. A pilot signal is added to the received signal. The pilot signal has at least a minimum signal level which when added to the signal received insures the sampled input signal has a level above the point where offset or low power errors are experienced. Preferably the pilot signal will be a sinusoidal signal having a frequency within the operational bandwidth of the amplifier (16), but outside the frequency range of the input signal.

Abstract: Apparatus and methods that compensate for the effects of gain and phase variations of a high power amplifier in the presence of multicarrier traffic. The calibration system and method impose negligible degradation to the multicarrier traffic processed by the high power amplifier. A calibration signal generator is used to generate a plurality of nondisrupting calibration signals, such as pseudorandom numbers, which are also summed and combined with the multicarrier traffic signals. The plurality of nondisrupting calibration signals are also combined to produce a combined nondisrupting calibration signal. Each of the nondisrupting calibration signals is selectively output and is combined with sampled versions of the amplified multicarrier traffic signals produced by the high power amplifier to despread them.

Abstract: A dual loop feed forward amplifier and method of amplification. The dual loop feed forward amplifier contains at least two amplification stages that introduce unwanted intermodulation products into the output signal. A spreading tone is introduced to the RF signal in between the first and second amplification stages. The spreading tone is created by a bi-phase modulator that spreads an input tone in accordance with a spread PN-code. After the spreading tone is amplified by the subsequent stages of the feed forward amplifier, the spreading tone is despread by the same spread PN-code. The resulting output tone is mixed with the original input tone. The output of the mixer is then filtered to remove the unwanted spurious products produced by the mixer. The feed forward amplifier is then actively adjusted by a computer controller to reduce any difference between input tone and the output tone until a desired signal-to-interference ratio is obtained.

Abstract: A control system comprising an electrical circuit that produces distortion where the electrical circuit has a frequency band of operation. A pilot modulated carrier signal is generated and is cause to traverse across the frequency band of operation of the electrical circuit. Information obtained from the traversing pilot modulated carrier signal when it is determined that there is no interference between any signal applied to or generated by the electrical circuit. The information is used by the control system to substantially cancel the distortion.

Abstract: A feedforward amplifier network (42) generates a fixed offset frequency swept pilot tone (46) over at least the same frequency band as an input signal (40). The fixed offset frequency swept pilot tone (46) is a function of a variable frequency reference signal (52) and a fixed pilot tone clock signal (54). A mixer arrangement (66 and 70), as opposed to a phase lock loop arrangement, helps ensure that the fixed frequency offset can be generated over the swept range. In addition, the feedforward amplifier network (42) incorporates a delay (58) which is added to the variable frequency reference signal (52) and used by a pilot tone detector (57) so that the pilot tone generator (44) and pilot tone detector (57) are in synchronization over narrow bands to accommodate pilot tone detection in the presence of code division multiple access channels that are relatively close together.

Abstract: An improved feed-forward multi carrier power amplifier architecture is described along with a novel array antenna wherein the improved amplifier may be advantageously put to use. The improved amplifier provides for independent control of unwanted intermodulation products generated in the amplifier. When used in the novel array structure, a separate radiation lobe containing the unwanted intermodulation products may be steered independently from a main radiation lobe. In a cellular base station application, the radiation lobe containing the unwanted intermodulation products may be steered away from the main radiation lobe thereby providing spatial filtering of the unwanted signals. The radiation lobe containing the unwanted intermodulation products may be steered rapidly in time using, for example, a noise like function to provide statistical averaging of the interference in the direction of desired communications.

Abstract: An automatic control system for reducing distortion produced by electrical circuit where a pilot signal pulse is applied to the electrical circuit for a period of time during which the system determines the adjustments to be made to its circuitry to reduce the distortion.

Abstract: A method and apparatus in a feedforward amplifier (100) includes a summer (293) summing the desired signal (12) with a pair of tag signals (241, 242). An error signal (226) is coupled with a delayed version of the summed signal (48). The phase and amplitude of signals (226, 237) are adjusted according to a first and second gradient decent controllers (221, 231) output signal (225) which is based on the first DC signal (224) and output signal (235). The output signal (235) is based on the detected power level of a leaked signal at the output coupler (62). The adjustment of the input signal (237) to the second amplifier, when the detected power level fluctuation exceeds a predetermined threshold level, is repeated. The tag signals (241) are produced in phase lock with the sweeping detecting (222) function.

Abstract: A method and apparatus for controlling a feedforward amplifier, wherein a superior distortion compensation characteristic is maintained over a wide frequency range, with the influence due to temperature variation and weathering minimized. A pilot signal generated by a pilot signal generator circuit is injected into the output of the main amplifier of a feedforward amplifier, and then the signal is sampled at the output of a first circuit and a second circuit, which is then low-range converted by a frequency converter and demodulated into I and Q components by a quadrature demodulator, and amplified and shaped into a pilot monitor signal; and a control circuit controls the vector adjusters within the distortion suppression circuit of the first and the second circuits using the I and Q signal components as the error signal so that as the amplitude level of pilot monitor signal is mininized the control value is maintained.

Abstract: A broadband feed-forward amplifier configuration includes an amplifier having an input and an output. A comparison loop compares the signal output to the amplifier with a signal input to the amplifier to generate an error signal and this error signal is inverted, processed, and amplified to provide a correction signal at the output of the amplifier (the cancellation loop). In the cancellation loop and at the input of the main amplifier, the circuit includes gain and phase correction circuitry for correcting small variations in amplitude and phase. A quadrature modulated pilot signal is injected at the input to the main amplifier path and is cancelled in the output to generate control signals for controlling the gain and phase correction circuits within the cancellation loop and within the main amplification loop.

Abstract: A feedforward amplifier system comprises a main amplifier and an auxiliary amplifier. An input signal including one carrier signal used as a first pilot signal, is supplied to a main amplifier to produce an amplified output signal. A second pilot signal is injected into the amplified output signal. The amplified output signal from the main amplifier is supplied to an output of the amplifier system through a delay line. In each of a first loop associated to the main amplifier and a second loop including the auxiliary amplifier, two control signals with pilot signal components arc produced, discrete Fourier transforms of the pilot signal components of the two control signals are calculated, and the amplitude and phase of the input signal of the main or auxiliary amplifiers are adjusted to values making the two Fourier transforms substantially equal to each other. Alternatively, the first pilot signal is produced by a generator and is injected into the input signal.

Abstract: Complex additional feed-forward error sensor loops and error correction loops are replaced in a high-frequency multi-carrier signal amplifier system with simple signal predistortor structures. In addition, less costly error amplifiers are facilitated and system efficiency increased by the introduction of error predistortor structures.

Abstract: A control arrangement and method for controlling a gain and phase adjuster used for controlling the gain and phase of a compensation signal for compensating for the distortion produced by a power amplifier is disclosed. The control arrangement makes use of a reference signal, of known frequency, which is amplified along with the desired carrier signals. The reference signal component of the amplified signal is then isolated and a comparison is made, either with the actual reference signal, e.g., by a QAM demodulator, or alternatively with the known frequency of the reference signal, e.g., by a FM discriminator, in order to determine the differences in gain and in phase of the reference signal component of the amplified signal in comparison with the reference signal. For example, a QAM demodulator is used for producing a first difference signal indicative of the phase switch difference, and a second difference signal indicative of the gain switch difference.

Abstract: The automatic gain control circuit of the present invention improves upon conventional techniques using a pilot carrier for control by monitoring for the presence of the pilot carrier. If the pilot carrier level is at an undetectable level, it will switch control of the level control section of the automatic gain control circuit to the equivalent thermal setting by means of a switch. The switch connects the output of a temperature-sensing network to a Bode driving circuit that approximates attenuation of a given transmission medium over temperature. The gain setting will therefore be based on an approximation of what the cable losses should be at the detected temperature of the amplifier housing. The present invention provides dynamic gain adjustment, even in the event of pilot carrier signal loss.

Abstract: A bidirectional amplifier that compensates for signal attenuation in a transmission medium uses a first diplex filter for directing a first signal including a pilot signal and propagating in a first direction along a first section of the transmission medium onto a first path of the amplifier. A second diplex filter directs a second signal in a different frequency band than the first signal that is propagating in a second direction opposite to the first signal along a second section of the transmission medium onto a second path of the amplifier. The first and second paths interconnect separate sections of the first and second diplex filters. A compensating device is disposed in the first and second paths wherein a pilot detection circuit detects the pilot signal in the first signal and generates therefrom separate control signals to first and second Bode Slope Equalizers in the first and second paths, respectively.

Abstract: A system for substantially eliminating nonlinear distortion, such as intermodulation products, introduced when a signal is processed by a nonlinear device. The system adds an out-of-band signal to an input signal to produce a combined signal having a power that substantially equals a nominal operating point power for a nonlinear device. Preferably, the instantaneous power of the out-of-band signal is adjusted by an automatic gain amplifier. The combined signal is input to the nonlinear device to produce an output. A filter processes the output of the nonlinear device to recover the information content of the original signal after processing by the nonlinear device. For example, if the nonlinear device is a power amplifier, the filtered output is an amplification of the input signal.

Abstract: A feedforward amplifier comprises a first feedforward circuit and a second feedforward circuit. The first feedforward circuit detects the distortion component of the output of a main amplifier through a first distortion detection circuit, and inserts the detected distortion component into the output signal of the main amplifier in a first distortion cancellation circuit to cancel the distortion component. The second feedforward circuit detects the distortion component of the output of the first feedforward circuit through a second distortion detection circuit, and inserts the detected distortion component into the output signal of the first feedforward circuit in a second distortion cancellation circuit, to perform distortion cancellation over a wide range of frequencies.