This disclosure is directed to, among other things, techniques to decouple the number of bits in a quantizer from the number of bits in the feedback digital-to-analog converter (DAC). A delta-sigma analog-to-digital converter circuit can include a first quantizer to generate an output having a first number of bits and then emulate a second quantizer, such as by using a bit truncation technique, to generate an output having a second number of bits. The feedback DAC can be coupled to receive the second number of bits, where the output of the feedback digital-to-analog converter circuit has the second number of bits. These techniques can reduce the area of the feedback DAC, e.g., 4 or 5 bits, and the techniques can achieve a higher maximum stable amplitude (MSA) because it is effectively a second order loop.

Systems and method for improving stability and performance in class-D modulators. In particular, a multi-cycle feedback network is positioned around a quantizer of a digital class-D amplifier. The multi-cycle feedback network allows the main class-D feedback loop to have multiple clock cycles of delay.

A MASH type sigma delta AD converter includes a modulator, an analog filter filtering an extraction signal obtained by extracting a probe signal and an quantization error generated in a quantizer within a sigma delta modulator, a low speed AD converter performing an AD conversion of an output signal of the analog filter, a first adaptive filter searching for a transfer function of the sigma delta modulator, a second adaptive filter searching for a transfer function from an output of the modulator to the low speed AD converter via the analog filter, and a noise cancellation circuit cancelling the probe signal and the quantization error included in an output signal of the quantizer using the search results by the first and second adaptive filters.

An audio activity detector device is disclosed. The audio activity detector device comprises a closed loop feedback regulating circuit that supplies an input signal representative of a time-varying voltage signal to a quantizer circuit, wherein the quantizer circuit, as a function of the input signal, converts the input signal to a quantizer discrete-time signal; a first circuit that, as a function of the discrete-time signal, determines a key quantizer statistic value for the quantizer discrete-time signal; and a second circuit that, as a function of the key quantizer statistic value, determines a signal statistic value for the input signal and a gain control value.

An audio activity detector device is disclosed. The audio activity detector device comprises a closed loop feedback regulating circuit that supplies an input signal representative of a time-varying voltage signal to a quantizer circuit, wherein the quantizer circuit, as a function of the input signal, converts the input signal to a quantizer discrete-time signal; a first circuit that, as a function of the discrete-time signal, determines a key quantizer statistic value for the quantizer discrete-time signal; and a second circuit that, as a function of the key quantizer statistic value, determines a signal statistic value for the input signal and a gain control value.

A digital delta-sigma modulator may include a loop filter having a loop filter input configured to receive an input signal and generate an intermediate signal responsive to the input signal and a multi-bit quantizer configured to quantize the intermediate signal into a quantized output signal which is fed back as an input to the loop filter. The multi-bit quantizer may further be configured to operate in at least two modes comprising: (a) a normal mode in which, for each sample of the intermediate signal, the multi-bit quantizer generates a corresponding sample having a value selected from a set of a plurality of quantization levels; and (b) a code suppression mode in which, for each sample of the intermediate signal, the multi-bit quantizer generates a corresponding sample having a value selected from a subset of the set of a plurality of quantization levels.

A MASH type sigma delta AD converter includes a modulator, an analog filter filtering an extraction signal obtained by extracting a probe signal and an quantization error generated in a quantizer within a sigma delta modulator, a low speed AD converter performing an AD conversion of an output signal of the analog filter, a first adaptive filter searching for a transfer function of the sigma delta modulator, a second adaptive filter searching for a transfer function from an output of the modulator to the low speed AD converter via the analog filter, and a noise cancellation circuit cancelling the probe signal and the quantization error included in an output signal of the quantizer using the search results by the first and second adaptive filters.

A partitioned delta-sigma modulator for high-speed applications includes a plurality of modulation stages arranged in parallel to input and output terminals of the modulator and interconnected to one another in series. In some aspects, each of the plurality of modulation stages is configured to combine a first error signal from a prior modulation stage of the plurality of modulation stages with a first digital signal to produce an adder signal. In some aspects, the first error signal includes a delay from the prior modulation stage. Each of the plurality of modulation stages is also configured to convert the adder signal having a first bit width into a quantized signal having a second bit width smaller than the first bit width. Each of the modulation stages is also configured to provide a second error signal based on the quantized signal to a subsequent modulation stage of the plurality of modulation stages.

To effectively suppress an idle tone in a delta-sigma modulator that generates a feedback signal by a digital-to-analog converter. A filter integrates a difference between an input analog signal and a feedback signal, and outputs the integrated difference as an integrated signal. A preceding-stage quantizer quantizes an integrated signal into a digital signal, and outputs the resulting digital signal as a preceding-stage output signal. An adder adds a predetermined dithering signal to a preceding-stage output signal, and outputs the resulting signal as a subsequent-stage input signal. A subsequent-stage quantizer configured to quantize the subsequent-stage input signal into a digital signal of a shorter number of bits than a preceding-stage output signal, and outputs the resulting digital signal as a subsequent-stage output signal. A digital-to-analog converter configured to convert a subsequent-stage output signal into an analog signal, and outputs the resulting analog signal to a filter as a feedback signal.

An audio activity detector device is disclosed. The audio activity detector device comprises a closed loop feedback regulating circuit that supplies an input signal representative of a time-varying voltage signal to a quantizer circuit, wherein the quantizer circuit, as a function of the input signal, converts the input signal to a quantizer discrete-time signal; a first circuit that, as a function of the discrete-time signal, determines a key quantizer statistic value for the quantizer discrete-time signal; and a second circuit that, as a function of the key quantizer statistic value, determines a signal statistic value for the input signal and a gain control value.