A quantizer for a sigma-delta modulator, a sigma-delta modulator, and a method of shaping noise are provided. The quantizer includes: an integrator configured to generate, in a K.sup.th sampling period, a quantization error signal for a K.sup.th period according to an internal signal, a quantization error signal for a (K−1).sup.th period, a filtered quantization error signal for the (K−1).sup.th period and a filtered quantization error signal for a (K−2).sup.th period; an integrating capacitor configured to store the quantization error signal for the K.sup.th period, to weight the internal signal in a (K+1).sup.th sampling period; a passive low-pass filter configured to acquire the quantization error signal for the K.sup.th period in a K.sup.th discharge period, and feed back the filtered quantization error signal to the integrator in a (K+1).sup.th sampling period and a (K+2).sup.th sampling period; and a comparator configured to quantize the quantization error signal for the K.sup.th period.

A quantizer for a sigma-delta modulator, a sigma-delta modulator, and a method of shaping noise are provided. The quantizer includes: an integrator configured to generate, in a K.sup.th sampling period, a quantization error signal for a K.sup.th period according to an internal signal, a quantization error signal for a (K−1).sup.th period, a filtered quantization error signal for the (K−1).sup.th period and a filtered quantization error signal for a (K−2).sup.th period; an integrating capacitor configured to store the quantization error signal for the K.sup.th period, to weight the internal signal in a (K+1).sup.th sampling period; a passive low-pass filter configured to acquire the quantization error signal for the K.sup.th period in a K.sup.th discharge period, and feed back the filtered quantization error signal to the integrator in a (K+1).sup.th sampling period and a (K+2).sup.th sampling period; and a comparator configured to quantize the quantization error signal for the K.sup.th period.

The present disclosure relates generally to techniques for continuous-time sigma-delta analog-to-digital converter (ADC). The continuous-time sigma-delta ADC may include a feed-forward capacitor in parallel with a current-steering excess loop delay (ELD) digital-to-analog converter (DAC), and by creating a zero in a transfer function of a Gm cell, both an ELD feedback loop settling and a main feedback loop may be recovered. As a result, the performance and stability of the continuous-time sigma-delta ADC can be achieved. Additionally, a summation node in the continuous-time sigma-delta ADC may offer flexibility in the architecture design of the continuous-time sigma-delta ADC.

A quad signal generator circuit generates four 2.sup.N-1 bit control signals in response to a 2.sup.N-1 bit thermometer coded signal. A digital-to-analog converter (DAC) circuit has 2.sup.N-1 unit DAC elements, with each unit DAC element including four switching circuits controlled by corresponding bits of the four 2.sup.N-1 bit control signals. Outputs of the 2.sup.N-1 unit DAC elements are summed to generate an analog output signal. The quad signal generator circuit controls a time delay applied to clock signals relative to the 2.sup.N-1 bit thermometer coded signal and a time delay applied to the 2.sup.N-1 bit thermometer coded signal relative to the delayed clock signals in logically generating the four 2.sup.N-1 bit control signals. The analog output signal may be a feedback signal in a sigma-delta analog-to-digital converter (ADC) circuit that includes a multi-bit quantization circuit operating to quantize a filtered loop signal to generate the 2.sup.N-1 bit thermometer coded signal.

A quad signal generator circuit generates four 2.sup.N-1 bit control signals in response to a 2.sup.N-1 bit thermometer coded signal. A digital-to-analog converter (DAC) circuit has 2.sup.N-1 unit DAC elements, with each unit DAC element including four switching circuits controlled by corresponding bits of the four 2.sup.N-1 bit control signals. Outputs of the 2.sup.N-1 unit DAC elements are summed to generate an analog output signal. The quad signal generator circuit controls a time delay applied to clock signals relative to the 2.sup.N-1 bit thermometer coded signal and a time delay applied to the 2.sup.N-1 bit thermometer coded signal relative to the delayed clock signals in logically generating the four 2.sup.N-1 bit control signals. The analog output signal may be a feedback signal in a sigma-delta analog-to-digital converter (ADC) circuit that includes a multi-bit quantization circuit operating to quantize a filtered loop signal to generate the 2.sup.N-1 bit thermometer coded signal.

The present disclosure relates generally to techniques for continuous-time sigma-delta analog-to-digital converter (ADC). The continuous-time sigma-delta ADC may include a feed-forward capacitor in parallel with a current-steering excess loop delay (ELD) digital-to-analog converter (DAC), and by creating a zero in a transfer function of a Gm cell, both an ELD feedback loop settling and a main feedback loop may be recovered. As a result, the performance and stability of the continuous-time sigma-delta ADC can be achieved. Additionally, a summation node in the continuous-time sigma-delta ADC may offer flexibility in the architecture design of the continuous-time sigma-delta ADC.

Described herein is a modulator with improved metastability in which the control loop remains stable. In one embodiment, the modulator utilizes differently delayed feedback to successive integrators of the control loop to suppress metastability errors without compromising the stability of the control loop. This is accomplished by including one or more quantizers in the control loop. This technique may be applied to control loops of at least second order, i.e., having two or more integrator stages, where at least one feedback term after the first is non-zero.

In some embodiments, an analog-to-digital converter (ADC) comprises a loop filter configured to produce an error signal based on a difference between an analog input signal and a feedback signal. The ADC also comprises a main comparator set comprising one or more main comparators, the main comparator set configured to digitize the error signal and further configured to drive a main digital-to-analog converter (DAC). The ADC further comprises an auxiliary comparator set comprising a plurality of auxiliary comparators, the auxiliary comparator set configured to digitize the error signal when the ADC is in a runaway state and further configured to drive an auxiliary DAC to bring the error signal into a predetermined range.

Described herein is a modulator with improved metastability in which the control loop remains stable. In one embodiment, the modulator utilizes differently delayed feedback to successive integrators of the control loop to suppress metastability errors without compromising the stability of the control loop. This is accomplished by including one or more quantizers in the control loop. This technique may be applied to control loops of at least second order, i.e., having two or more integrator stages, where at least one feedback term after the first is non-zero.

In some embodiments, an analog-to-digital converter (ADC) comprises a loop filter configured to produce an error signal based on a difference between an analog input signal and a feedback signal. The ADC also comprises a main comparator set comprising one or more main comparators, the main comparator set configured to digitize the error signal and further configured to drive a main digital-to-analog converter (DAC). The ADC further comprises an auxiliary comparator set comprising a plurality of auxiliary comparators, the auxiliary comparator set configured to digitize the error signal when the ADC is in a runaway state and further configured to drive an auxiliary DAC to bring the error signal into a predetermined range.