Abstract: To reduce the size and power dissipation of a feed-forward amplifier, two identical high power amplifiers in a quadrature combined configuration function both as the main amplifier and as the error amplifier. The feed-forward amplifier has two control loops to increase amplifier linearity and reduce intermodulation distortion. A first loop is provided to subtract a properly scaled and delayed sample of the amplifier input spectrum from a scaled and phase shifted sample of its output spectrum which contains intermodulation distortion. The result of this subtraction (if the samples are maintained at the same amplitude and 180 degrees out of phase) is a signal rich in the intermodulation products of the amplifier.

Abstract: A method and apparatus is provided for amplifying electronic signals in a linear fashion while maintaining DC power efficiency. In one embodiment, the invention comprises a coupler receiving an input signal and connected to a non-linear amplifier. A tone generator is also connected to the coupler, and generates a tone signal at a selected frequency. The coupler combines the tone signal and an input signal and provides the combined signal to the amplifier. The combined signal is amplified and bandpass filtered to remove spectral by-products. The power of the tone wave generator signal is selected so as to cause the nonlinear amplifier to operate near its saturation point but in a linear region. The effect is to linearize the operation of the nonlinear amplifier, while simultaneously minimizing the presence of intermods and maintaining a relatively high level of DC power efficiency.

Abstract: An error corrected amplifier circuit (100) for use in a radio frequency system is provided. The error corrected amplifier circuit (100) includes a first pilot modulation stage (101) and a second pilot modulation stage (103). The first pilot modulation stage (101) creates a first amplified signal (129) having an error component and a first error signal (134) indicative of the error component. The second pilot modulation stage (103) receives the first amplified signal (129) and the error signal (134) and generates an error reduced amplified signal (158).

Abstract: The compensation range of feed-forward amplifiers is expanded. The peak value of the input or output of an auxiliary amplifier 15 is detected with a peak power measuring instrument 24, and the characteristic of a distortion detecting loop 100 is controlled with a vector adjuster 3 and a control circuit 9 so as to minimize this peak value. By controlling the characteristic of the distortion detecting loop by detecting the peak value, the range of linearity compensation is expanded compared with conventional control based on the average level.

Abstract: An adaptive control system and method is provided in a feed-forward linear amplifier, and in particular a multi-channel linear amplifier, wherein analyzed distortion or error detection of nonlinear distortion components of the output signal of a main amplifier element is used to correct distortion in amplification of an information signal using a two-stage distortion correction circuit. Analysis of the distortion is based on a sweep of the entire operating frequency band from which the distortion components are extracted. I.F. sampling (sub-harmonic sampling) may be used in analog-to-digital conversion of an I.F. signal to detect the distortion within a pass-band.

Abstract: The invention provides methods and apparatus for substituting a reference spread spectrum signal for a pilot tone or providing a reference spread spectrum signal where no pilot tone has been used. The invention has particular relevance when a large number of input channels are required for a broad band linear amplifier and when an omni-directional antenna is required for a repeater which may be prone to instability.

Abstract: A first pilot signal is superimposed onto an input signal thereto to distribute the signal as a first signal and a second signal to two destinations. The first signal is fed via an equalizer to a main amplifier for amplification thereof such that a second pilot signal is mixed with the amplified signal to attain a main amplification signal. Subtraction is conducted between the second signal and the main amplification signal to extract a distortion signal to be fed via an equalizer to an auxiliary amplifier so as to produce an auxiliary amplification signal. Between the main and auxiliary amplification signals, there is effected subtraction to attain a differential signal. The pilot signals are detected according to the differential and output signals. The equalizers are controlled to set the pilot signals to a minimum value. Consequently, there is achieved a linear amplifier obtaining a stable amplification signal with reduced distortion in a wide band.

Abstract: In a first step, a control circuit 61 turns a switch 63 to detect a frequency of an input signal input to an input terminal 1 and distortion generated by amplification of this input signal or mixed in and sets a frequency of a pilot signal output from a variable frequency oscillator 53 at a value other than the input signal frequency and a frequency of the distortion and close to an average value of the input signal. Thereafter, the control circuit 61 turns the switch 63 off and controls a distortion detecting loop 7 by using the pilot signal in a second step and controls a distortion removing loop 4 in a third step. In a fourth step, it succeeds the control of the distortion removing loop 4 in a normal state and controls the distortion detecting loop 7 again only when environment is changed largely.

Abstract: A bus leveling system for automatically monitoring and maintaining the amplitude of a radio frequency (RF) signal carded on a bus. A two-stage variable gain amplifier (64) is connected in series with the bus. Each stage of the variable gain amplifier is constructed with a PIN diode (84, 86) in a feedback path of the stage. The amplification of the variable gain amplifier is varied by the injection of current into the feedback path to adjust the resistance of the PIN diodes. A control circuit having an RE detector (78) is provided to monitor and adjust the gain generated by the variable gain amplifier. Preferably, the control circuit and the variable gain amplifier are incorporated into an Application Specific Integrated Circuit (ASIC) (62). The RF detector is constructed of two Gilbert multipliers (202, 204) to minimize errors caused by operating condition changes, including variations in power supply voltage, temperature, or process.

Abstract: A feedforward-type distortion compensation circuit which can compensate for a non-linear distortion component generated by a main amplifier.

Abstract: A first loop is provided to subtract a properly scaled and delayed sample of the amplifier's input spectrum from a scaled and phase shifted sample of its output spectrum which contains intermodulation distortion. The result of this subtraction (if the samples are maintained at the same amplitude and 180 degrees out of phase) is a signal rich in the intermodulation products of the amplifier. A feature of the invention is a differential phase-amplifier comparator which compares the signals prior to and after amplification and generates control signals for amplitude and phase trimmers for the signal prior to the amplifier and thus maintains the required equal amplitude and 180 degree phase relationship required for carrier cancellation. The signals before amplification and after amplification are subtracted leaving substantially the intermodulation products resulting from amplification.

Abstract: A feed-forward amplifier of a type preventing unwanted waves from being outputted in an initial operation suitable to a use in a radio transmitter-receiver in a radio communication system, aimed to reduce a loss in the course from an output of a main amplifier to an output of the apparatus by implementing an output control during the initial operation in the front stage of the main amplifier without switches having been heretofore used, further reducing a power consumption of the apparatus.

Abstract: A feed forward cancellation amplifier system for amplifying radio frequency telephony signals, including a main amplifier, an error correction circuit producing a message error signal, an error amplifier for producing an amplified message error signal that is then subtracted from the amplified and distorted message signal output of the main amplifier prior to a final output circuit, a negative feedback circuit responsive to a test signal for compensating and minimizing variation or drift in the operation of the error amplifier, the error correction circuit including a vector modulator responsive to modified quadrature vector components of the message error signal for producing a single voltage vector error signal, and the negative feedback circuit including an I & Q network for modifying the quadrature vector components of the error signal in the error correction circuit.The preferred form of the invention utilizes PIN diodes to provide voltage controlled attenuators in the vector modulator.

Abstract: A feedforward distortion compensation circuit includes a main amplification path, an auxiliary amplification path, first and second transmission paths, a signal attenuation path, a first signal injector, a first signal distributor, a second signal injector, a first signal synthesizer, a first phase difference detector, a first level detector, a second phase difference detector, a second signal synthesizer, a second level detector, and a control circuit.

Abstract: An adaptive control system and method for use with a feed-forward linear amplifier, and in particular a multi-channel linear amplifier wherein a distortion (error) detection circuit is used for detecting a nonlinear distortion component of a main amplifier output for using in correcting distortion in amplifying an information signal. The distortion correction can be extracted from a pilot signal, an analysis of distortion from a channel-by-channel sweep or from analysis of selected target channels. Analysis can be based on a single signal, an average of many signals, or a selection of maxima of one or many signals. Subharmonic sampling may be used in analog to digital conversion of an IF signal to detect for distortion within a passband.

Abstract: In a feed forward amplifier, an RF amplifier is supplied with an input RF signal at an input terminal for amplifying the same; a distortion extraction loop supplied with the input RF signal and further with the output RF signal from the RF amplifier is for extracting non-linear distortion components formed in the output RF signal as a result of amplification in the RF amplifier; a variable phase shifter is provided in the distortion extraction loop for varying a phase of the input RF signal; a variable attenuator is provided in the distortion extraction loop for attenuating an amplitude of the input RF signal that has been supplied to the distortion extraction loop; and a distortion extraction circuit is provided in the distortion extraction loop for producing a distortion output signal that includes non-linear components; further, a control circuit is supplied with the input signal and with the distortion output signal for extracting a main signal component contained in the distortion output signal.

Abstract: In a feed forward amplifier (100), a main amplifier (125) is coupled between an input (102) at which an input signal is received and an output (173) at which an output signal is provided. The output signal is an amplification of the input signal. A sample of the output signal is compared (144) with a sample of the input signal to produce a difference signal indicative of distortions introduced by the main amplifier (125). An error amplifier (165) provides a distortion signal which is an amplification of the difference signal, and the distortion signal is combined (169) with the output signal to compensate for main amplifier distortions. A random frequency, constant amplitude sine wave pilot signal is combined (117) with the input signal, and a correlation power detector (194,195,202,212,213) is provided to determine the magnitude of the pilot signal in the output signal. The gain and phase of the difference signal is then adjusted (155) to minimize the magnitude of the pilot signal in the output signal.

Abstract: A feedforward distortion minimization circuit includes a first loop with an input splitter and first and second signal paths, each signal path having an amplifier. An output combiner couples the two signal paths and has an output signal path and an output dump load path. A first signal detector on the dump load path detects a dump load signal, and in response a gain and phase controller operates to adjust the gain and phase of a first signal on one of two signal paths to minimize the power delivered to the dump load. The feedforward circuit also includes embodiments in which both amplifiers operate at around the same power amplification level, and in which a second loop has an error amplifier for further distortion correction.

Abstract: A device for testing an amplifier. A plurality of PN modulators are provided corresponding to a plurality of oscillators at stages preceding or following them, or fluctuation is given to division ratios at the oscillators. Since each of n carriers combined by a combiner contains phase fluctuation, the possibility that the peaks will overlap each other or that the carriers having opposite phases will negate each other is very low. The peak power in signals supplied to the amplifier to be tested is unlikely to vary, enabling accurate evaluation or testing.

Abstract: A method and apparatus for controlling a feed-forward compensated power amplifier system is disclosed which uses a spread spectrum technique to cover a control signal or signals and injects a composite signal at a suitable point into the feed-forward amplifier system to reduce distortion. The amount of bandwidth spread is governed by the amount of processing gain needed in the remapping process and the needed time response of the system. Control signals after remapping of the spread spectrum at the output of the system are correlated in a match filter correlator and the result is used to control, in either polar or cartesian coordinates, the injection, in anti-phase, of the extracted distortion into the feed forward amplifier output.

Abstract: A power amplifier having a gain factor of G for generating an output signal from a low power amplitude and phase modulated input signal. The power amplifier generates first and second constant envelope signals. Each constant envelope signal has the same frequency as said input signal. The first constant envelope signal has the same amplitude as the second constant envelope signal but differs in phase from the first constant envelope signal by an amount depending on the amplitude of the input signal. The output signal is generated by vectorially adding the first and second constant envelope signals. The amplifier has a feedback loop which operates by determining the difference in amplitude between the input signal and a signal having an amplitude 1/G times the amplitude of the output signal. The phase difference between the first and second constant envelope signals is altered so as to reduce the determined difference in amplitude.

Abstract: A control circuit for an automatically controlled feed forward nonlinear distortion compensation amplifier. The control circuit controls a distortion detection loop and a distortion removal loop. The distortion detection loop is a loop for feeding forward input to a main amplifier into a first directional coupler. The distortion removal loop is a loop for feeding forward distortion elements into a second directional coupler. The main amplifier is preceded by a variable attenuator and a variable phase shifter. A variable attenuator and a variable phase shifter are also located in a feed forward path to the second directional coupler. The control circuit controls the variable attenuator and the variable phase shifter preceding the main amplifier for detecting the distortion elements. The control circuit controls the variable attenuator and the variable phase shifter located in the feed forward path to the second directional coupler for removing the distortion elements.

Abstract: In a receiver comprising a receiver filter (12) with a frequency attenuation band and a pilot oscillator (25) for generating a pilot oscillation signal with a pilot frequency in the frequency attenuation band, a coupler (26) couples the pilot oscillation signal and a filtered receiver signal of the receiver filter to form a coupled signal. A low noise amplifier (13) amplifies the coupled signal into an amplified signal which comprises an amplified receiver signal component derived from the filtered receiver signal and an amplified pilot oscillation signal component derived from the pilot oscillation signal. A branching filter (27) branches the amplified signal into the amplified receiver signal component and the amplified pilot oscillation signal. A pilot signal component detector unit (28) detects the amplified pilot oscillation signal component to produce a direct pilot signal.

Abstract: Briefly described the present invention is a feed forward amplifier network (200) employing a frequency swept pilot tone signal (212) in order to reduce the distortion generated by the network's power amplifier (202). Initially a composite input signal (216) comprising either wide (520) and/or narrow (510) bandwidth modulation formats is input into the network (200). In addition, the frequency swept pilot tone (212), generated for example by a variable frequency oscillator (213), is injected into the input path of the power amplifier (202). Thereafter, distortion cancellation is employed to generate an amplified output signal (217) having output components (510,520) which replicate those within the input signal (216). Thereafter, pilot tone power is detected (by 215) within the amplifier passband where the output components (510,520) are absent, in order to ascertain the average pilot tone power remaining within the amplified output signal (217).

Abstract: A linear amplifier performing a continuous distortion compensation control without no line cut to prevent deterioration of intermodulation distortion and ensure talking quality including a power amplifier for amplifying a plurality of carriers and a distorter for generating an intermodulation distortion with an equal amplitude of an antiphase for negating an intermodulation distortion generated by the power amplifier. A processing unit outputs an attenuation value control voltage and a phase control voltage to the distorter depending on an ambient temperature information detected by a temperature sensor and control voltage data corresponding thereto, read out of a memory.

Abstract: An amplification system for amplifying an input signal at radio frequency comprises a linear power amplifier and a drive unit. In a test mode, the drive unit feeds two signal tones simultaneously to the amplifier input and a processing circuit analyse the output of the amplifier to identify distorting IMPs. A predistortion circuit operates in an amplification mode to apply a predistortion to a digital representation of the input signal to compensate for the effect of the distorting IMPs generated in the amplifier.

Abstract: In order to improve the distortion performance of a feed forward corrected amplifier, an amplifier arrangement includes a distortion generator (312) which is coupled between an input (15) and a main amplifier (1). The amplifier arrangement is such that the input signal passes to the distortion generator (312) via a coupler (307). The signal passes via a delay network (310) which compensates for the delay of the distortion generator (312) and is tapped by a coupler (308) to be combined by a coupler (313) with the distorted signal from the distortion generator (312). In this way the output of the distortion generator is subtracted from a sample of the input signal so that only the distortion remains to pass via phase (314) and amplitude (315) correction networks to be amplifier by a gain element (316) before being coupled back into the main signal path by a coupler (309). The correction is active over a portion of the main amplifier characteristics such as the compression region of the main amplifier.

Abstract: Briefly described the present invention is a feed forward amplifier network employing a frequency swept pilot tone signal in order to reduce the distortion generated by the network's power amplifier. A frequency swept pilot tone, generated for example by a variable frequency oscillator, is injected into the input path of the power amplifier's input signal. Thereafter, distortion cancellation employed to generate an amplified output signal, substantially free of both pilot tone and the distortion signals generated by the power amplifier. The amplified output signal is then detected by a detector, phase locked to the variable frequency oscillator, in order to ascertain the average pilot tone energy remaining within the amplified output signal. In response to a detection, various amplifier network characteristics are adjusted in order to reduce the amount of pilot tone at the amplifier network output.

Abstract: A feedforward distortion cancellation circuit active control of both cancellation loops and a pilot signal and using least means squared circuits in both cancellation loops is disclosed. According to the invention, by using a pilot signal as the reference signal in a least means squared cancellation circuit, the required level of cancellation is reduced and thus it is easier to fabricate the circuit and the circuit is more stable.

Abstract: A microwave power amplifier includes first and second circuits each having first, second, third and fourth terminals. Each of the first and second circuits has functions of distributing an input signal to the second and third terminals and generating first and second output signals 180.degree. out of phase with each other through the second and third terminals, respectively, adding a first pair of 180.degree. out-of-phase input signals to the second and third terminals and outputting a first resultant signal through the first terminal, and adding a second pair of in-phase input signals to the second and third terminals and outputting a second resultant signal through the fourth terminal.

Abstract: A feed forward circuit receives an input signal having at least one carrier therein in a prescribed frequency range. The input signal is applied to a first circuit path having a power amplifier that produces an output signal with a distortion component and to a second circuit path that delays the input signal without distortion. The output signal of the first circuit path is combined with the output signal of the second circuit path to form a signal representative of the distortion component of the first circuit path output signal and the distortion component representative signal is subtracted from the output signal of the first circuit path to cancel the distortion component therein. The prescribed frequency range of the first circuit path output is scanned to detect a carrier signal and the amplitude and phase of the signal in the first circuit path is modified to minimize the magnitude of the detected carrier in the distortion representative signal.

Abstract: A plurality of amplifier channels, wherein each channel is automatically gain controlled by a gain control signal and wherein the gain of each channel is a known function of a plurality of constants of corresponding to each amplifier and of the gain control signal, can be calibrated by the following method. The method comprising the steps of measuring each output of each amplifier at a corresponding plurality of gain control values and at a corresponding input to each amplifier. The number of the plurality of the constants equals the number of the plurality of the gain control values. The method continues by computing the gain of each amplifier at the step of measuring. The constants corresponding to each amplifier are then computed according to the function and computed gain. A corresponding changed gain control signal is applied to each amplifier according to the function to set the corresponding gain of each amplifier to a corresponding predetermined calibrated value.

Abstract: A distortion simulating pilot is injected at the input of an amplifier which uses feed forward distortion correction. The magnitude of the pilot signal in the amplifier output is used to control a decreasing step size circuit algorithm for adjusting the gain and phase of the feed forward distortion signal to eliminate substantially the pilot signal and the distortion introduced by the amplifier.

Abstract: A variable level converter comprising a first variable level converting unit, a second variable level converting unit and an amplifying transistor connected therebetween. Each of the first and second variable level converting units comprises an inverted L-type variable attenuator which includes a variable impedance element. Each variable impedance element is controlled by the same level control signal and has the same electric characteristics.

Abstract: A syllabic compandor using a pilot in the signal frequency band, with a compression ratio between approximately 2 and 20, including a frequency and delay equalizer in the negative-feedback loss-control circuits of the compressor and expandor, to permit high compression and expansion ratios without positive feedback at any frequency or signal level, the expansion ratio materially less than the compression ratio in some cases, and sampling at more than the Nyquist frequency for the signal band to remove any unwanted periodic wave such as the pilot wave, lying in the signal frequency band, from the output, without altering phase and amplitude of other waves in the signal frequency band.

Abstract: Apparatus for controlling the gains of a pair of gain-matched amplifiers includes means for applying to each amplifier a pilot tone in the form of an exponentially-decaying periodic signal. The apparatus also includes three control loops, one for comparing the output of one amplifier with a reference signal to derive an error signal used to control the amplifier gains when the pilot tone is absent, and a second for controlling the gains when the pilot tone is present. The third loop subtracts the outputs of the two amplifiers and uses the resulting error signal in conjunction with one or other of the signals from the other two loops to control the gain of one of the two amplifiers.

Abstract: Disclosed is a system for supervising the level of input applied to a level regulator using a pilot signal. According to the invention, an input level supervisory circuit is provided which utilizes a level adjusting variable element of the level regulator, or employs a particular variable element arranged to be driven by means of the control voltage for said level adjusting variable element simultaneously with the latter element and having characteristics equal thereto, and which has a transmission ratio in a reciprocal or inverse relationship to the alternating current transmission ratio of a main signal alternating current transmission line of the level regulator. The input level supervisory circuit is supplied with an input voltage or current from a direct current constant-voltage power source or a direct current constant-current power source to generate an output voltage by means of which supervision of the level of the pilot signal input to the level regulator is performed.

Abstract: The present invention concerns the transmission of information, and consists in a continuous regulator responsive to the amplitude of a pilot tone included in the signal whose level is to be regulated, including a variable-gain quadripole through which said signal is passed, an automatic gain control loop including a circuit controlling the gain of the quadripole, and an auxiliary feedback loop through which the control circuit also controls the automatic gain control loop. The regulator is applicable with advantage to transmission systems.

Abstract: The invention relates to transmission systems and in particular to level regulators controlled by a pilot tone and used in such systems to correct variations over a period of time in the attenuation of the transmission system.The subject of the invention is a level regulator governed by a pilot tone whose gain control circuit locks in a mean position where there is a very low or zero value detected for the pilot tone. This locking is achieved by modifying the supply voltage of the error amplifier of the loop providing automatic gain control for the regulator.The invention is of particular application to cable transmission systems with repeaters.

Abstract: An automatic phase and gain balance controller is incorporated in a typical baseband processor of a MTI radar system employing doppler processing techniques to effect balancing adjustments in the in-phase (I) and quadrature (Q) signal generation channels for substantially eliminating spurious image frequency component formations which may result from any unbalance therein. More specifically, the automatic controller provides two substantially non-interactive servo control loops to maintain balance between the I and Q signal generation channels by performing balancing adjustments on two adjustment parameters, namely phase and amplitude. Phase and amplitude imbalance errors between the I and Q channel are obtained in response to a pilot signal which is injected into the baseband processor of the MTI radar receiver, perferably during the dead times of the interpulse periods of pulsed reception.

Abstract: This invention is a device for measuring small differences between relatively high sound pressure levels at two different microphone sites. It provides electrical insertion voltages, "pilot" voltages, as a means for continuously monitoring the gains of two acoustical channels. The difference between two pilot voltages is utilized to force the gain of one channel to track the other channel.

Abstract: Audio frequency signalling, from a central location in a telephone system to a remote location serviced by a particular telephone set, is accomplished by connecting an audio frequency amplifier, having a predetermined a.c. threshold voltage level, and a predetermined d.c. voltage level, across the telephone line at said particular telephone set. By concurrently applying a low frequency a.c. pilot signal of an amplitude greater than the a.c. threshold voltage level of the audio frequency amplifier and an audio frequency signal voltage of a lesser amplitude to the telephone line at the central location, when said particular telephone set is on-hook, said audio frequency amplifier is enabled by the low frequency a.c. pilot signal and supplied with operating current from the telephone line. The audio frequency amplifier, thus enabled and energized, attenuates the low frequency a.c.

Abstract: An electronic circuit for automatically controlling gain and roll-off in wide-band amplifiers for use in tele-distribution systems including a feedback network with a negative temperature coefficient pure ohmic resistance feedback. When automatically controlling roll-off, a second negative temperature coefficient resistance is placed in series with an inductance.