Communications Satellite Corporation

Vasil Uzunoglu

Chester J Wolejsza, Jr

William E Mattis, Jr

An adaptive equalizer performs equalization at IF, demodulates the input signal and then generates the equalization coefficients at baseband from the demodulated data. Coefficient updating can be done on a non-real time basis and coefficients for individual bursts stored in a coefficient memory for retrieval when the same burst occurs in the next frame, thus obtaining a pseudo-continuous equalization for each burst. The error signal is derived from demodulated equalized data and correlated with demodulated unequalized data to generate the correlation coefficients, and individual error signals from each channel can be combined into a single composite error signal for correlation purposes.

Digitally controlled transversal equalizer

A phase canceller for a carrier recovery network (CRN) to cancel phase shifts associated with the band pass filter in the network. The canceller is a semiconductor device receiving an input signal at one junction to cause emitted carriers to migrate to a collector at a controlled rate determined by an applied electric field between a pair of ohmic contacts located between emitter and collector junctions with the field control by a signal from a phase detector in the AFC loop of the CRN.

Phase canceller for carrier recovery network

A temperature stabilized semiconductor delay element is comprised of an emitter and collector separated on a substrate by distance l. A voltage applied to ohmic contacts on either side of the emitter and collector provides an electric field E, whereby the delay .tau. between the emitter and collector is given by .tau.=l.sup.2 /.mu.E, where .mu. is the semiconductor mobility which varies with temperature. A compensation device located on the same substrate as the delay device provides the delay device with an electric field E=K/.mu., where K is constant, such that .tau.=l.sup.2 /K. The time delay .tau. is thus independent of temperature.

Temperature stabilized semiconductor delay element

A synchronous oscillator is provided to divide the frequency of an input signal by a noninteger number, the noninteger number being expressed as the ratio of two whole integers X/Y. The oscillator is tuned to the desired output frequency, whereby every Yth cycle of the output signal is synchronized by every Xth cycle of the input signal at the negative (and possibly positive) peak of the output signal, thereby effecting a simultaneous multiplication and division of the input frequency of Y and X respectively. A pulse forming network provides the input signal in the form of pulses, whereby synchronization is effected at precise points in time. Pulse width and amplitude are adjustable to vary the input signal energy.

Division by noninteger numbers using synchronous oscillators

A carrier recovery network for QPSK modems employs a synchronous oscillator which may be used as a frequency multiplier, divider and tracking bandpass filter. A preferred embodiment of the carrier recovery network includes a multiply-by-four circuit to remove QPSK data modulation, and a synchronous oscillator tuned to one-fourth the input frequency to thereby act as a frequency divider and tracking bandpass filter to provide a recovered carrier signal.

Carrier recovery network for QPSK modems employing synchronized

A clock recovery network uses a voltage proportional to the incoming symbol rate as a coarse tuning signal to control the tuned center frequency of a voltage controlled oscillator. The incoming data is used to positively synchronize the oscillator to the incoming data stream.

Universal clock recovery network for QPSK modems

A surface acoustic wave device is used as a unique word detector and coherent demodulator for a digital code differential phase-shift signal. The device improves code word detection by providing a coherent reference with a correlation gain of 10 log M dB. M is the additional number of fingers introduced into the surface acoustic wave device, which determine the phase of the unique word. To achieve this result with higher reliability and higher correlation coefficient, use is made also of a few bits of the clock recovery which precede the unique word in a preamble as used in Time Division Multiple Access (TDMA) systems. The device requires two interdigital output transducers, one of which provides a maximum output in response to surface acoustic waves representing the unique word, and the other of which provides a maximum output in response to surface acoustic waves corresponding to a preassigned pattern of the unique word, such as a sequence of all zeros combined with a partial sequence of the clock recovery bits. The outputs of the two interdigital output transducers are maximized at the same instant to detect the auto-correlation peak of the unique word with performance equivalent to coherent demodulation. Also, clock and data are recovered in the second set of interdigital transducers.

Surface acoustic wave unique word detector and coherent demodulator

An operational amplifier uses p- and n-channel enhancement type MOSFETs as variable input resistors on the inverting and non-inverting legs, respectively, of the amplifier, and the sources and gates of the MOSFETs are tied together. By using V.sub.S, the source-to-ground voltage, and V.sub.GS, the gate-to-source voltage, as input signals, the device will perform 4-quadrant multiplication at operating frequencies as high as 400MHz.

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Ellicott City, MD, United States of America

Vasil Uzunoglu