A sigma-delta modulator includes an N-bit quantization circuit that generates a stream of N-bit code words and a feedback signal path with an N-bit DAC circuit, having a non-ideal operation due to mismatch error, that converts the stream of N-bit code words to generate a feedback signal. A digital DAC copy circuit provides a digital replication of the N-bit DAC circuit. The digital replication accounts for the non-ideal operation of the N-bit DAC circuit 126 due to mismatch error, and converts the stream of N-bit code words to generate a stream of P-bit code words, where P>N, that are functionally equivalent to the feedback signal output from the N-bit DAC circuit.

Circuits and methods for converting digital input signals into the analog domain are described. Such circuits may perform the conversion in a segmented fashion. For example, a circuit may include a most significant bit (MSB) path and a least significant bit (LSB) path. The MSB path may include a first delta-sigma modulator having first and second outputs and a first digital-to-analog converter coupled to the first output of the first delta-sigma modulator. The LSB path comprises a second delta-sigma modulator comprising a loop filter and a quantizer. The quantizer may have an input coupled to the loop filter and to the digital filter. The LSB path may further include a second digital-to-analog converter coupled to an output of the quantizer. The circuit may further include a digital filter and/or a gain stage interposed between the MSB path and the LSB path.

A signal processor and a method for processing an input signal are presented. The signal processor is adapted to clip an oversampled input signal without introducing noise in the frequency band of interest. For instance, the signal processor may be used for clipping an acoustic signal. The signal processor includes a summer coupled to a limiter and to a feedback circuit. The summer is adapted to sum the input signal with at least one feedback signal to provide an adjusted signal. The limiter is adapted to compare the adjusted signal with a first threshold value and a second threshold value to provide a limited signal. The feedback circuit is adapted to calculate a difference between the limited signal and the adjusted signal, and to generate at least one feedback signal based on the difference.

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 sigma-delta analog-to-digital converter includes: a subtractor for subtracting a feedback signal from an analog input signal; a loop filter for processing the output signal from the subtractor to generate a filtered signal; a signal comparing circuit for selectively operating in an offset detection mode or a signal comparison mode, wherein the signal comparing circuit generates an error signal irrelevant to the relative magnitude between the filtered signal and a reference signal in the offset detection mode, and generates a comparison signal corresponding to the relative magnitude between the filtered signal and the reference signal in the signal comparison mode; an offset calibration control circuit for calibrating the offset of the signal comparing circuit and for controlling the signal comparing circuit to alternately switch between the offset detection mode and the signal comparison mode; and a digital-to-analog converter for generating the feedback signal according to the comparison signal.

The present invention provides a delta-sigma modulator and associated signal processing method, wherein the signal processing method includes: generating a first difference signal according to a difference between an input signal and a first feedback signal; filtering the first difference signal to generate a filtered signal; generating a second difference signal according to a difference between the filtered signal and a second feedback signal; quantizing the second difference signal to generate an output signal; using a first DAC to generate the first feedback signal according to the output signal; using a second DAC to generate a first analog signal according to the output signal; delaying the output signal to generate a first delayed output signal; using a third DAC to generate a second analog signal according to the first delayed output signal; and generating the second feedback signal according to the first analog signal and the second analog signal.

An apparatus for a signal processor for Wide-Band Applications is provided. The signal processor includes a plurality of parallel branches. Each parallel branch includes a frequency shifter, a sigma-delta-modulator, and a filter. The output signal of each branch is combined via a signal recombiner. The signal processor is suitable for wide-band applications due to centering the zeros of the sigma-delta-modulator's noise transfer function and filter's noise transfer function at the frequency of the frequency shifter in the same branch of the signal processor. Centering these zeros at the frequency of the frequency shifter shapes the quantization noise added by the sigma-delta-modulator away from the input signal frequency to make it easier to remove the quantization noise. This wideband performance is also achieved due to the design of the embodiment's filters. The embodiments of this invention use filters with symmetric transition bands and a pass-band that is wide enough for use in wireless applications.

Circuits and methods for converting digital input signals into the analog domain are described. Such circuits may perform the conversion in a segmented fashion. For example, a circuit may include a most significant bit (MSB) path and a least significant bit (LSB) path. The MSB path may include a first delta-sigma modulator having first and second outputs and a first digital-to-analog converter coupled to the first output of the first delta-sigma modulator. The LSB path comprises a second delta-sigma modulator comprising a loop filter and a quantizer. The quantizer may have an input coupled to the loop filter and to the digital filter. The LSB path may further include a second digital-to-analog converter coupled to an output of the quantizer. The circuit may further include a digital filter and/or a gain stage interposed between the MSB path and the LSB path.

An A/D converter includes an adder that calculates a difference between an analog input signal and a predicted value, a quantizer that quantizes the difference output from the adder to convert the analog input signal to a digital signal, a prediction filter that generates a predicted value from the digital signal output from the quantizer, and a D/A converter that converts the predicted value from a digital signal to an analog signal and output the predicted value to the adder. The predicted value before being subjected to conversion to the analog signal by the D/A converter defines and functions as an A/D converted output of the analog input signal input to the adder.

A continuous-time delta-sigma modulator includes a loop filter, a quantizer, a finite impulse response (FIR) filter, and a digital to analog converter. The loop filter integrates a difference between an input signal and a feedback signal. The quantizer quantizes a signal output from the loop filter to convert the quantized signal into a digital signal. The FIR filter performs an FIR filtering process on the digital signal output from the quantizer. The digital to analog converter converts a signal output from the FIR filter into an analog signal and outputs the converted analog signal as a feedback signal.