Abstract: A method and apparatus for compensating optical dispersion over an optical fiber are provided in fiber optic communications to increase a transmission distance by overcoming the optical dispersion caused by wavelength changes of light sources and dispersion effects of a fiber. In one implementation, the present technology may be implemented in the form of a RLC passive microwave filter with no extra power consumption. By way of example, an optical receiver may include a photodiode operable to receive an optical signal and produce an electrical signal, a transimpedance amplifier (TIA) operable to receive the electrical signal and produce a first amplified signal, and an electronic dispersion compensation (EDC) device operable to receive the first amplifier signal from the TIA and compensate or reduce the effects of optical dispersion on the received electrical signal.

Abstract: A calibration system may be provided for calibrating wireless communications circuitry in an electronic device during manufacturing. The calibration system may include data acquisition equipment for receiving an amplitude-modulated calibration signal from the electronic device. The calibration system may include calibration computing equipment for extracting pre-distortion coefficients from the amplitude-modulated calibration signal. The calibration computing equipment may be configured to detect a bulk phase drift in the amplitude-modulated calibration signal. The calibration computing equipment may be configured to remove the bulk phase drift from the amplitude-modulated calibration signal. The wireless communications circuitry may include a power amplifier that distorts a signal generated by the wireless communications circuitry. The wireless communications circuitry may include a pre-distortion compensator for countering the distortion.

Abstract: Signal modulation apparatus for applying a modulation signal to a carrier signal, the apparatus comprising: an amplitude modulator for modulating the amplitude of the carrier signal in accordance with a control signal; first mixing means for mixing together fractions of the carrier signal before and after action of the amplitude modulator to produce a first detection signal indicative of the amplitude modulation applied by the amplitude modulator; and detection means for comparing the control signal with a first detection signal to evaluate distortion in the first detection signal as compared with the control signal.

Abstract: The present disclosure relates to using windowing to reduce the bandwidth of an amplitude modulation (AM) power supply input signal (PSIS), which is fed to an AM power supply to provide envelope power to an RF power amplifier stage via an AM power supply output signal. By reducing the bandwidth, noise levels from the AM power supply may be reduced. However, although the bandwidth of the AM PSIS is reduced, the AM power supply output signal may track the AM of the RF power amplifier stage closely enough to meet linearity requirements and to provide high efficiency. The windowing may be based on dividing a stream of AM input samples into a stream of input windows, from which a stream of output windows is created to provide a stream of windowed AM input samples that are used to provide a windowed AM PSIS to the AM power supply.

Abstract: A semiconductor integrated circuit includes a first input terminal configured to input a baseband signal, a second input terminal configured to input a local oscillation signal, an output terminal configured to output a modulating signal, a first amplifier circuit configured to receive the baseband signal through the first input terminal and to output a first amplified signal of the baseband signal, a 2-multiplying circuit configured to receive the local oscillation signal through the second input terminal and to output a 2-multiplied signal of the local oscillation signal, an adder configured to add the 2-multiplied signal and the first amplified signal and to output an addition signal, a second amplifier circuit configured to receive the addition signal and to output a second amplified signal of the addition signal, and a mixer configured to multiply the second amplified signal and the local oscillation signal and to output the modulating signal to the output terminal.

Abstract: There is a need for effectively compensating distortion when a predistortion transmitter is subject to not only a memory effect due to nonlinearity of an amplifier, but also a modulator's DC offset, IQ unbalance, or local quadrature error. A predistortor to be used is a polynomial predistortor including a polynomial basis generation portion and an inner product calculation portion. The polynomial basis generation portion delays a real part and an imaginary part of a complex input signal Sx=Ix+jQx for up to M samples to generate 2(M+1) signals, duplicately combines these signals to generate monomials having maximum degree N, and outputs, as a basis vector, all or part of the monomials depending or needs. The inner product calculation portion performs an inner product calculation using a coefficient vector, i.e., a set of complex numbers sized equally to the basis vector to find a polynomial value and outputs the value as a complex signal.

Abstract: Embodiments of the present invention include amplitude-modulated or polar-modulated radio frequency (RF) power amplifier circuitry, in which an envelope power supply input to an RF power amplifier is powered by a pre-distorted amplitude modulation (AM) power supply. The pre-distorted AM power supply receives an AM signal, which is then pre-distorted and amplified to provide an AM power supply signal to the RF power amplifier. The pre-distortion of the AM signal is used to improve the linearity, the efficiency, or both, of the RF power amplifier. The pre-distortion provides a feed-forward system, which may allow use of a reduced bandwidth pre-distorted AM signal to an AM power supply and a reduced bandwidth AM power supply, which may increase efficiency.

Abstract: A timing adjusting method detects a phase error between a main signal path from which a transmitting signal is obtained and a control signal path from which a voltage control signal is obtained, based on a to-be-amplified signal that is to be amplified and represents an amplitude or a power of the transmitting signal prior to amplification and a feedback signal that represents an amplitude or a power of the transmitting signal after the amplification, adjusts an amount of delay of at least one of the main signal path and the control signal path so as to mutually cancel the phase error, and amplifies the transmitting signal from the main signal path depending on the voltage control signal from the control signal path. The detecting the phase error may include detecting polarity transition points of a slope of a waveform of the to-be-amplified signal or the feedback signal, and measuring the phase error using the detected polarity transition points.

Abstract: A power management device providing a power amplifier with power supply voltage is provided. The power management unit includes a parallel-hybrid amplitude modulator apparatus having a linear part configured to track frequency components of an input signal above a determined threshold frequency and a switching part arranged in parallel with the linear part and configured to track frequency components of the input signal below the determined threshold frequency. Additionally, the power management unit includes a current sensing and controlling part configured to determine the level of a direct current component at an output of the linear part and control the switching part to produce an output signal compensating for the direct current component at the output of the linear part to decrease the absolute level of the direct current at the output of the linear part.

Abstract: A fixed wireless access communications system comprises an access point and a plurality of subscriber units. Each subscriber unit (502) contends for access to a communications channel to the access point by transmitting a contention word to the access point during a contention time slot. The contention word is predistorted to compensate for the channel impulse response of the transmission channel so that the access point can decode the contention words without using equalisation. A control unit (512), which may comprise a microprocessor, loads the predistorted contention word (a) into a memory (520) and causes the stored predistorted contention word (a) to be applied to a transmitter (508) during a contention time slot when the subscriber unit (502) wishes to request a transmission channel to transmit data to the access point.

Abstract: The present apparatus includes: distortion amount detector which detects the amount of distortion of an output signal of the amplifier; parameter holder; parameter corrector which corrects a parameter held in the parameter holder in such a manner that the distortion amount detected by the distortion amount detector is improved; controller which controls frequency components to be subjected to distortion amount detection that is performed by the distortion amount detector, based on the distortion amounts of a plurality of different frequency components of the output signal of the amplifier and on specification values relating to the distortion amounts. This arrangement makes it possible to set (control) appropriate distortion data measurement point (frequency component to be detected) according to multiple specification values (for example, ACLR specification values) relating to the distortion amount.

Abstract: A method and device for reducing error components of a multi-channel modulator. The method comprises the steps of inverting substantially half of the channels of a modulator, and reducing error components between said inverted channels and said non inverted channels by inductive and/or capacitive summing. The method is especially suitable for synchronized pulses and similar signals to be modulated.

Abstract: A predistorer configured for use with an RF power amplifier having an input loop configured to be coupled to the input of the RF power amplifier and peak control circuit. Such an input loop includes a look-up table containing predistortion values to be applied to an input signal, in response to the power in the input signal, for forming a predistorted input signal. The predistorter may further include an output loop, such an output loop configured to measure an intermodulation distortion product of the RF power amplifier output resulting from the predistorted input signal, and operable to update the predistortion values in the look-up table. Such a peak control circuit configured to select a power supply voltage for the RF power amplifier in response to the power in the input signal.

Abstract: A bank of complex gain elements is used to provide a step-wise approximation of an arbitrary complex-gain predistortion function for a nonlinear transmitter. The bank of gain elements is in an adaptive loop realizing adaptive control. The adaptive loop is closed between an Input of the gain bank and an output of the transmitter through a linear receiver at an adaptive controller composed of a bank of proportional-integral (PI) controllers. The real and imaginary parts of each predistortion gain element are controlled by a corresponding adaptive PI controller. The signals processed by the adaptive controller are represented in orthogonal coordinates in terms of real and imaginary number pairs of complex numbers. The adaptive controller achieves unconditionally stable operation independently from the arbitrary phase rotation in the input signal or the adaptive loop.

Abstract: A phase-amplitude modulator for mobile communications employs a phase lock loop as an input to a nonlinear power amplifier providing phase information with amplitude information used to modulate the power amplifier output to synthesize phase-amplitude for the RF transmission signal.

Abstract: First, a digital section constituting a linearizer is activated. Then, a feedback loop for updating a distortion compensation coefficient is opened. Then, the analog section on the antenna side is activated from an ADC, including a PA, etc., or a DAC. Then, both the ATT value of an ATT installed in a feedback route for updating the distortion compensation coefficient and the signal delay amount of a signal delay unit are adjusted to make a state such that the distortion compensation coefficient can be accurately updated. Then, the feedback loop is closed, a distortion compensation table having the distortion compensation coefficient as an entry is generated and after the generation is completed, the operation shifts to the normal operation.

Abstract: A nonlinear compensator comprising a signal processing section, a distortion detecting section, and a distortion correcting section. The signal processing section detects the time difference and phase difference between two signals by calculating correlation, synchronizes the two signals with each other, and causes the phase of one signal to coincide with that of the other. The distortion detecting section determines an amplitude error and a phase error in the two signals and inputs the errors as distortion components to a distortion correcting section. The distortion correcting section sequentially selects the amplitude, the phase, and the amount of compensation corresponding to the value of the amplitude from the amounts of compensation registered at the initial stage and updated adaptively, and adds the amount of compensation to the digital base band signal obtained at the input demodulation section to compensate for the distortion components.

Abstract: An amplitude modulated source signal (102) is received, where this signal has a source frequency bandwidth and a source envelope. A dummy envelope is computed that would yield a constant if the dummy envelope and source envelope were to be combined. An amplitude modulated dummy signal (105) is generated, where this dummy signal exhibits the computed, dummy signal envelope and has a prescribed frequency bandwidth different than the source frequency bandwidth. The source and dummy signals are added to form a combined signal (113), which is directed to an input (114a) of a nonlinear circuit (114), that is, one that exhibits amplitude dependent nonlinearity. Signals of the dummy frequency bandwidth and any intermodulation products are filtered from the output, thereby providing a linearized output (118) corresponding to the original, source signal.

Abstract: An amplitude modulated source signal (102) is received, where this signal has a source frequency bandwidth and a source envelope. A dummy envelope is computed that would yield a constant if the dummy envelope and source envelope were to be combined. An amplitude modulated dummy signal (105) is generated, where this dummy signal exhibits the computed, dummy signal envelope and has a prescribed frequency bandwidth different than the source frequency bandwidth. The source and dummy signals are added to form a combined signal (113), which is directed to an input (114a) of a nonlinear circuit (114), that is, one that exhibits amplitude dependent nonlinearity. Signals of the dummy frequency bandwidth and any intermodulation products are filtered from the output, thereby providing a linearized output (118) corresponding to the original, source signal.

Abstract: A system and method for predistorting a signal which is to be amplified by a non-linear amplifier. The system and method uses additional predistortion circuits to eliminate the predistortion caused by amplifier input circuits and amplifier output circuits. In one aspect of the invention, the system and method uses a frequency response and phase corrector circuit to modify the amplitude versus frequency of the signal independent of phase.

Abstract: A quadrature modulator with set-and-forget carrier leakage compensation. The quadrature modulator comprises an in-phase and a quadrature branch. In the in-phase and quadrature branches, real-time digital signals are converted to analog signals, the analog signals are filtered, and the filtered analog signals are modulated with a carrier signal and a ninety degrees phase shifted version of the carrier, respectively. The modulated in-phase and quadrature signals are added so as to form a quadrature amplitude modulated signal. Preferably upon powering up of the quadrature modulator, in the in-phase and quadrature branches, carrier leakage is measured. The measured carrier leakage is supplied to comparators, which toggle, when carrier leakage is minimal in the respective in-phase and quadrature branches.

Abstract: A band limited Amplitude Shift Keyed (ASK) modulator employing linear modulation and an efficient Class C power amplifier. Band-limited operation is provided by filtering a digital baseband input signal prior to modulation. Closed loop feedback is employed around the amplifier to assure linear modulation over a wide modulation range which preserves the frequency characteristics of the baseband signal on the modulation envelope. Further filtering is accomplished by exploiting the closed loop system response, incorporating it in the filter characteristic as an added filter pole.

Abstract: An electronic circuit provides a linear output from a nonlinear transmission device such as a laser. Second and higher order distortion of the nonlinear device is compensated by applying a predistorted signal equal in magnitude and opposite in sign to the real and imaginary components of distortion produced by the nonlinear device. The input signal for the nonlinear device is applied to an in-line electrical path coupled to the nonlinear device. The in-line path contains at least one component for generating primarily real components of distortion. In some applications, at least one component for generating imaginary components of distortion is located on the in-line path. Filter stages are used to provide frequency dependent predistortion. In a preferred embodiment, an attenuator, a MMIC amplifier, a CATV hybrid amplifier, and a varactor in line with a semiconductor laser, provide the predistorted signal.

Abstract: In a high-power transmitter, an input complex signal is multiplied in a complex multiplier by control signals. The output complex signal from the multiplier is converted to a high frequency signal and amplified by a power amplifier for transmission. The amplitude of the input complex signal is detected to access a memory where amplitude and phase correction values are stored. During a read mode of the memory, a set of amplitude and phase correction values is specified by the detected amplitude and supplied to the complex amplifier as the control signals. During a write mode of the memory, a set of amplitude and phase correction values is specified by a delayed version of the detected amplitude and rewritten with a set of new amplitude and phase correction values. The amplified high frequency signal is down-converted to a low frequency complex signal.

Abstract: A postdistortion network for a receiver at a receiver location in an optical transmission system is disclosed. The receiver converts an optical signal carried over an optical transmission link to an RF signal. The postdistortion network includes an input terminal for receiving the RF signal and a distortion generator for generating a distortion signal from the RF signal. An adjusting circuit for adjusts the phase and amplitude of the distortion signal based on distortion at said receiver location. The adjusted distortion signal is combined with the RF signal in order to cancel or substantially suppress distortion in the RF input signal. The present invention permits individual receivers in an optical transmission system to be compensated for distortion which may be unique to that receiver location. A communications system including a predistortion network and a postdistortion network is also disclosed.

Abstract: A pulse step modulator (PSM) is presented herein for use in an AM transmitter. The modulator includes a plurality of unit step modules connected together in series with each module including a DC voltage source together with an associated actuatable switch for, when actuated, turning on the associated module to provide a unit step voltage. An output circuit is connected to the series connected modules for providing an output voltage to a load wherein the magnitude of the output voltage is equal to the sum of all of the voltage sources of the modules that are turned on. A plurality of module turn on signals are provided with each turn on signal serving to actuate one of the switches in one of the modules with the number of turn on signals being provided being dependent upon the magnitude of an input signal.

Abstract: In a modulated signal transmission system operable in response to an input digital signal of a baseband to produce a modulated signal through a nonlinear amplifier, a nonlinear converter is controlled by a control signal generator to compensate for not only a nonlinear distortion but also a linear distortion. The control signal generator is given a difference signal between a linearly detected signal and the input digital signal to which an estimated linear distortion is added by a linear filter having filter coefficients controlled by a filter coefficient estimator. An additional nonlinear converter is located prior to the linear filter. Alternatively, the linear filter may be located after the nonlinear converter.

Abstract: A feed-forward predistortion circuit to provide improved linear response in optic modulators. The circuit includes a non-linear element, an amplifier/delay means and a power combiner. The non-linear element generates a first signal sin(X), where (X) is the input signal. The amplifier/delay means generates a second signal 2(X). The first and second signals are combined in the power combiner to produce a modulating signal 2(X)-sin(X) which is fed to an optic modulator. The modulating signal 2(X)-sin(X) compensates for the transfer function of the optic modulator which has a transfer function sin(X), thereby producing a linear output.

Abstract: A control voltage generator in a transmitter arrangement for, e.g., QAM signals comprising a class C output amplifier (AMP). The control voltage generator (CVG) comprises a memory with a look up table (ROM), whereby the I,Q-signals (I,Q) of the modulating signal (DM) address a cell in the look-up table (ROM), the information of which is used as a control signal (CS) to control the amplifier output level (RF). The information is modified to compensate for temperature variations and other non-linearities.

Abstract: An adaptive predistortion circuit for a digital transmission system includes a predistortion circuit (52.sub.1, 52.sub.2, 52.sub.3) for predistorting the input data before they pass through a modulator (56) and then through an amplifier (57), and an adaptation circuit (61.sub.1, 61.sub.2, 61.sub.3) for continuously adapting the predistortion circuit to the stream of input data in response to a demodulation of the stream of transmitted data. The predistortion circuit further includes an encoder (51) which, on a first path, in response to digital data a.sub.k, generates digital data b.sub.k which leave a first predistortion circuit (52.sub.1) in a predistorted manner in-phase with the symbol clock, on a second path, digital data c.sub.k which leave a second distortion circuit (52.sub.2) in a predistorted manner phase-shifted by T/3 relative to the symbol clock and on a third path, digital data d.sub.k which leave a third predistortion circuit (52.sub.

Abstract: The invention provide a digital method of correcting non-linearity in a transmission chain, in which the effects of amplifier non-linearities are compensated by applying predistortion in baseband prior to modulation, with the signal being processed digitally in real time. The invention also provides apparatus for implementing the method. The invention is particularly applicable to radio beams for conveying digital signals.

Abstract: A radio transmitter arrangement for e.g. QAM signals comprising a class C output transistor amplifier (AMP). The control voltage generator (CVG) comprises a memory, whereby the I,Q-signals (I,Q) of the modulating signal (DM) address the control voltage generator (GEN), the information of which is used as a control signal (CS) acting as the collector voltage to control the amplifier output level (RF). The information can be modified to compensate for temperature variations and other non-linearities.

Abstract: A method of linearizing an amplifier to produce an amplified output sample v.sub.a in response to a predistorted input sample v.sub.d derived from an input modulation sample v.sub.m, such that v.sub.a .perspectiveto.Kv.sub.m, where K is the amplifier's desired constant amplitude gain. The squared magnitude x.sub.m of the input modulation sample v.sub.m is first derived. A table entry F.sub.i is then selected from a table containing N.sub.t values F.sub.i where i=0, 1, . . . N.sub.t -1. Each table entry corresponds to a squared magnitude value x.sub.mi ; and, for each table entry, F.sub.i G(x.sub.mi .vertline.F.sub.i .vertline..sup.2).perspectiveto.K, where G(x) is the complex gain of the amplifier. The table entry selected is the one for which the absolute value .vertline.x.sub.m -x.sub.mi .vertline. is minimized with respect to the table index i. The predistorted sample v.sub.d is then derived, in rectangular coordinates, as v.sub.d =v.sub.m F.sub.i, viz:Re(v.sub.d)=Re(v.sub.m)Re(F.sub.i)-Im(V.sub.m)Im(F.

Abstract: A microwave amplitude modulation system maintains constant amplitude attenuation at very high modulation rates over a broad range of microwave frequencies in response to voltage driving signals derived from modulation signals. In the system, the video input of a shunt-type PIN diode microwave amplitude modulation system is driven by a logarithmic voltage amplifier circuit which receives the modulation signals as an input.