Ring oscillator delta sigma ADC modulator with replica path nonlinearity calibration
AssigneeThe Regents of the University of California
InventorsIan Galton, Gerry Taylor
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Abstract
An embodiment provides a continuous-time delta-sigma modulator for analog-to-digital conversion. The modulator includes a signal path generating including a ring voltage controlled oscillator driven by an analog input signal. The signal path produces digital values by sampling the ring voltage controlled oscillator. A calibration circuit measures nonlinear distortion coefficients in a replica of the signal path. A nonlinearity corrector corrects the digital values based upon determined nonlinear distortion coefficients. Preferred embodiment ADC ΔΣ modulators do not require any analog integrators, feedback DACs, comparators, or reference voltages, and do not require a low jitter clock.
Claims17
A continuous-time delta-sigma modulator for analog-to-digital conversion, comprising:
- an actual signal path including a converter that drives a ring voltage controlled oscillator, a ring sampler for sampling said voltage controlled oscillator, a phase decoder that maps values from the ring sampler into a phase number, a digital differentiator that differentiates the phase number and a nonlinearity corrector providing a corrected signal path output;
- and
- a calibration circuit including a replica signal path, the calibration circuit measuring a voltage controlled oscillator center frequency of said replica signal path, wherein said replica signal path is corrected with calibration sequences of independent, zero-mean, pseudo-random sequences, said calibration circuit using said center frequency to adjust current of said converter in said signal path, said calibration circuit further providing correction data generated from an output of said replica signal path to said nonlinearity corrector.
A continuous-time delta-sigma modulator for analog-to-digital conversion, comprising:
- a signal path generating including a ring voltage controlled oscillator driven by an analog input signal, the signal path producing digital values by sampling the ring voltage controlled oscillator;
- a calibration circuit that measures nonlinear distortion coefficients in a replica of said signal path;
- and
- a nonlinearity corrector correcting said digital values based upon said nonlinear distortion coefficients.
A continuous-time delta-sigma modulator for analog-to-digital conversion, comprising:
- a ring sampler that samples said ring voltage controlled oscillator;
- a phase decoder that maps digital values sampled by the ring sample onto a phase number that represents the phase of the ring voltage controlled oscillator as a quantized value to a fraction of cycle of the ring voltage controlled oscillator;
- and
- a digital background calibration circuit that conducts 1) digital background cancellation of ring voltage controlled oscillator-induced second-order and third-order distortion and 2) digital background tuning of the ring voltage controlled oscillator's center frequency to the ΔΣ modulator's sample rate, fs*, wherein the digital background cancellation is conducted in combination with a pseudo-differential architecture and the digital background tuning centers the input range of the ΔΣ modulator about the midscale input voltage to maximize dynamic range, and thereby provide reconfigurability by automatically retuning the ring voltage controlled oscillator's center frequency whenever fs is changed.
A method for analog-to-digital signal conversion, the method comprising:
- driving a ring oscillator with a current derived from an analog input signal;
- phase converting a signal determined from an output of the ring oscillator and generating an output signal;
- determining nonlinear distortion introduced by said ring oscillator with a replica path including a replica of said ring oscillator and said phase converter;
- and
- correcting said output signal based upon said nonlinear distortion determined in said step of determining.
Dependencies are inferred from the claim text.