Exact Evaluation of Delta Modulator Performance in Sonar Signal Processors

Abstract

Single-bit delta modulation is increasingly being used or suggested for telemetry and beam-forming in sonar receiving systems. To evaluate its performance in these applications, an exact time-domain analysis appropriate for logic circuits practically used was formulated, which served as the basis for the development of a computer program for the simulation of the codec (coder-decoder). The essence of this formulation lies in a more rigorous calculation of the local decoder output voltage corresponding to an arbitrary coder output bit pattern in terms of the pole locations of the integrating network. The difference between the local decoder output and the analog input signal represents the quantization noise. Utilizing an 800-Hz sinusoidal signal as the analog input to the codec, local decoder output waveforms for a number of cases were calculated and displayed to show the decrease of quantization noise with increasing clock frequency and the improvement of codec performance with double integrating network. The average quantization noise power was also calculated from samples of noise waveform to illustrate the quantitative determination of the output SNR and the dynamic range of the codec. Further work directed specifically at sonar beamforming applications is being planned.