Other

Dbx Corporation

Harris Corporation

Daniel B Talbot

David E Blackmer

Edwin Ray Twitchell

Spurious frequency components from the output signal of a direct digital synthesizer are reduced with minimum degradation of the fundamental frequency of the output signal. The synthesizer has a phase accumulator for receiving digital multibit modulation data words from a source, a periodic wave function converter for converting the modulation data words into digital waveform data words and a digital-to-analog converter for converting the digital waveform data words into an analog signal which serves as the output signal. The output signal has a frequency and waveform dictated by the modulation data words. Reduction of spurious frequency components is achieved by generating a dither waveform representing a band limited waveform. The dither waveform is summed with the modulation data words prior to application to the wave function converter to provide a dither modulated analog output signal. A sampled dither signal is combined with the dither modulated analog output signal in such a manner that the dither waveform is cancelled from the fundamental waveform of the analog output signal.

Apparatus for reducing spurious frequency components in the output

An improved substantially 'zero distortion' four quadrant modulator of the type including a pair of differential elements respectively coupled to the Y input port terminals of the modulator and exhibiting nonlinear amplitude transfer functions, includes the means for substantially linearizing the nonlinear transfer function. The means includes a pair of operational amplifiers, each having an input coupled to a respective terminal of the Y input port and an output coupled to the corresponding differential element so that the differential element is disposed in the feedback path of the operational amplifier.

Amplitude modulator having substantially zero modulation distortion

An improved substantially 'zero distortion' four quadrant modulator of the type including a pair of differential elements respectively coupled to the Y input port terminals of the modulator and exhibiting nonlinear amplitude transfer functions, includes the means for substantially linearizing the nonlinear transfer function. The means includes a pair of operational amplifiers, each having an input coupled to a respective terminal of the Y input port and an output coupled to the corresponding differential element so that the differential element is disposed in the feedback path of the operational amplifier. An improved demodulator is provided by detecting the amplitude modulated signal with a first detector and applying the detected signal to one input of a signal comparator. A feedback loop couples the output of the signal comparator to its other input. In particular the output is coupled to the Y input port of a substantially zero distortion modulator, which has the X input adapted to receive a continuous wave signal. The output of the modulator is detected by a second detector which in turn is coupled to the other input of the signal comparator. The first and second detectors are matched for their nonlinear amplitude transfer functions so that the output of the signal comparator is a substantially zero distorted representation of the envelope component of the amplitude modulated signal.

Closed loop amplitude demodulator

A multiplier circuit for controlling gain amplification of an electrical input signal responsively to a control signal comprises log conversion means for producing a log signal as a logarithmic function of the input signal, means for producing a multiplier signal as a function of the sum of the log signal and the control signal and antilog-conversion means for producing an antilog signal as an antilogarithmic function of the multiplied signal. The improvement is characterized by the log conversion means and antilog conversion means each including passive elements capable of exhibiting log-linear and antilog-linear transfer characteristics. The passive elements are preferably in the form of diode elements connected in a diode bridge.

Multiplier circuit

An improved signal expansion system and technique is disclosed. The system comprises a detector for sensing an input signal and for producing responsively thereto a D.C. control signal having an amplitude as a function of the input signal, and a gain control amplifier for amplifying the input signal, the amplifier including means for controlling the gain of the amplifier as a function of the amplitude of the control signal. The improvement comprises means for varying the amplitude of the D.C. signal at least in part as a function of the time derivative of that amplitude.

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Hudson, MA, United States of America

Daniel B Talbot