International Business Machines Corporation

Ernest L Walker

William K Stelzenmuller

An improvement over an analog-to-digital converter in which a phase-locked loop (including a voltage controlled oscillator, a feedback path, and a phase discriminator) supplies clocking signals to a counter. The clocking signals are gated to the counter by a circuit which energizes a gate in response to a known reference signal and deenergizes an gate in response to the unknown source signal. The resultant count in a measure of the phase difference between the source and reference signals. Accuracy and stability derive from maintenance of a predetermined phase-locked relationship between a signal derived through frequency division of the loop output signal and the cyclic reference signal which is the reference for gating the counts to the counter. The loop output frequency is a harmonic of the frequency of the reference signal. Feedback phase control is developed through interaction of the frequency divided loop output signal with the reference signal in the phase discriminator circuit. The present invention improves the accuracy of the phase-locked loop by making the voltage controlled oscillator ripple waveform linear. This is accomplished by placing a frequency divider in series with the loop, another identical frequency divider in the feedback path, and using an integrator to filter the phase discriminator output.

Analog-to-digital conversion apparatus

A surface acoustic wave filter is provided having an input and an output transducer, each consisting of a pair of comb-like structures, wherein the electrodes or teeth are interleaved and are varied in length in accordance with a weighting function determined by the Fourier transformation of the respective transducer characteristic frequency response so as to each produce a pair of frequency passbands symmetrical about their characteristic frequency. The latter frequency passband of the input transducer has the same passband center frequency as the first frequency passband of the output transducer. The coincident passbands of said input and output transducers resulting in an output from the output transducer having the center frequency of the coincident passbands.

Surface acoustic wave device

An acoustical wave filter is formed by depositing a pattern of interdigitated conductors which form a coding arrangement on a piezeoelectric crystal. Multiplex communication through the crystal is achieved by depositing input filters of differing configuration on the crystals, which separate channels by autocorrelation of a pulse code. A single output filter is provided to respond to the waves set up in the crystal by the input filters to transmit these waves to a single common conductor. Demultiplex is similarly done on a second crystal.

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Wappingers Falls, NY, United States of America

Ernest L Walker