Delta modulator having low-level random noise characteristic

Claim 1

A delta modulator, suitable for audio signal processing, which provides a subjectively tolerable low-level random idling noise in the demodulated output of the modulator, comprising: high-gain comparator amplifier means having two inputs and an output; input means for applying an initial analog signal to one input of the comparator amplifier means; a sampling gate comprising a flip-flop circuit having a main input, a sampling input, and first and second outputs, one of the gate outputs comprising the modulator output, the main input of the sampling gate being connected to the output of the comparator amplifier means; clock means for applying a high-frequency clock signal to the sampling input of the gate to control actuation of the gate between two alternate operating conditions and generate two output pulse signals of inverse polarity at the gate outputs; a principal integrating negative feedback circuit, having a short time constant, connected from one output of the sampling gate to one input of the comparator amplifier means, for integrating one pulse signal from the gate to develop a replica analog signal and for applying that replica signal to the comparator amplifier means in bucking relation to the initial analog signal; and a self-bias feedback circuit, comprising an integrating circuit having a long time constant, connected from one output of the sampling gate to one input of the comparator amplifier means, for applying a self-bias reference to the comparator amplifier means, the self-bias feedback circuit also transmitting a negative feedback A.C. signal of limited amplitude to introduce a limited broad-band noise content into the output signal of the modulator; one of the feedback circuits being connected to the other input of the comparator amplifier means.