Digital-to-analog converter with noise-free sigma-delta modulation

Abstract

The digital-to-analog converter utilizes a modulator for effecting sigma-delta modulation of multi-bit input data to form a pattern of quantized output data so as to produce a pulse signal corresponding to the input data. The converter is provided with a zero detecting circuit for detecting a silent condition when the input data is continuously held at a zero level. An injecting circuit operates when the silent condition is detected for effecting continuous injection of a fractional reset signal into the modulator to gradually change an internal state of the modulator. A control circuit is provided to detect when the modulator reaches an optimum internal state effective to stabilize a varying idling pattern of the quantized output data for stopping the injection of the fractional reset signal so as to effect convergence of the varying idling pattern into a fixed idling pattern which is substantially free of an audible frequency component under the silent condition.

Dependencies are inferred from the claim text.