Provided are, among other things, systems, apparatuses, methods and techniques for converting a discrete-time quantized signal into a continuous-time, continuously variable signal. An exemplary converter preferably includes: (1) multiple oversampling converters, each processing a different frequency band, operated in parallel; (2) multirate (i.e., polyphase) delta-sigma modulators (preferably second-order or higher); (3) multi-bit quantizers; (4) multi-bit-to-variable-level signal converters, such as resistor ladder networks or current source networks; (5) adaptive nonlinear, bit-mapping to compensate for mismatches in the multi-bit-to-variable-level signal converters (e.g., by mimicking such mismatches and then shifting the resulting noise to a frequently range where it will be filtered out by a corresponding bandpass (reconstruction) filter); (6) multi-band (e.g., programmable noise-transfer-function response) bandpass delta-sigma modulators; and/or (7) a digital pre-distortion linearizer (DPL) for canceling noise and distortion introduced by an analog signal bandpass (reconstruction) filter bank.

Provided are, among other things, systems, apparatuses, methods and techniques for converting a discrete-time quantized signal into a continuous-time, continuously variable signal. An exemplary converter preferably includes: (1) multiple oversampling converters, each processing a different frequency band, operated in parallel; (2) multirate (i.e., polyphase) delta-sigma modulators (preferably second-order or higher); (3) multi-bit quantizers; (4) multi-bit-to-variable-level signal converters, such as resistor ladder networks or current source networks; (5) adaptive nonlinear, bit-mapping to compensate for mismatches in the multi-bit-to-variable-level signal converters (e.g., by mimicking such mismatches and then shifting the resulting noise to a frequently range where it will be filtered out by a corresponding bandpass (reconstruction) filter); (6) multi-band (e.g., programmable noise-transfer-function response) bandpass delta-sigma modulators; and/or (7) a digital pre-distortion linearizer (DPL) for canceling noise and distortion introduced by an analog signal bandpass (reconstruction) filter bank.

A device includes a local oscillator, an all-digital phase-locked loop, a digital signal generator, sampling circuitry, and an interface. The local oscillator generates a local clock signal. The all-digital phase locked loop generates a sampling control signal. The ADPLL includes a phase-error detector, a digital filter and a sigma-delta modulator. The phase detector generates a phase error signal based on a loop clock signal and a received reference signal. The digital filter generates a signal indicative of a frequency ratio between a frequency of the reference clock signal and the local clock frequency based on the phase error signal. The sigma-delta modulator generates a modulated signal based on the signal indicative of the frequency ratio. The sampling control signal is based on the modulated signal. The sampling circuitry samples digital signals generated by the digital signal generator at a sampling frequency, which is a function of the sampling control signal.

To correct for non-linearities in the response of a microphone as a function of sound pressure level incident upon the microphone, a displacement non-linearity function is applied to the signal path of the microphone, wherein the displacement non-linearity function is a function of the digital audio output signal and has a response modeling non-linearities of the displacement as a function of a sound pressure level incident upon the microphone.

A digital delta-sigma modulator (DDSM) is disclosed with an input signal x[n], an output signal y[n], a quantization error signal e[n] and a dither signal d[n], having an equation described in the z-domain by
Y(z)=STF(z)X(z)+DTF(z)D(z)NTF(z)E(z), wherein Y(z), X(z), D(z) and E(z) are z-transforms of the output signal, the input signal, the dither signal, and the quantization error signal, and wherein STF(z), DTF(z) and NTF(z) correspond to a transfer function of the input signal, a transfer function of the dither signal, and a transfer function of the quantization error signal, and wherein the transfer function of the quantization error signal is of the form: $\mathrm{NTF}\left(z\right)=A{z}^{-Q}\left(1-z^{-1}\right)\left(1+\underset{i=1}{\overset{K}{.Math.}}{c}_i{z}^{-i}\right),$ A, Q and K are constants, coefficients c.sub.i are real valued and c.sub.K0 and wherein at least one of the zeroes z.sub.j of $\left(1+\underset{i=1}{\overset{K}{.Math.}}{c}_i{z}^{-i}\right)$

A system and method of digital to analog conversion including modulating a digital value D.sub.N-K with an oversampling delta sigma modulator to provide an M-bit coarse quantized value DM, in which D.sub.N-K comprises N-K least significant bits of an N-bit digital input value D.sub.N and in which quantization error may be shaped to a higher frequency above a signal band of interest, adding D.sub.M to a value D.sub.K to provide a select value D.sub.KM in which D.sub.K includes the K remaining most significant bits of D.sub.N, and applying mismatch shaping of a total of at least P=2.sup.K elements of a P-element DAC per cycle based on D.sub.KM to provide an analog output value. The analog output value may be filtered with a low-pass filter to provide a filtered analog output value. An order of low-pass filtering may be one more than an order of modulating.

Embodiments of circuits and methods are described below that may provide a modulator that has an enhanced signal-to-quantization-noise ratio (SQNR) for a given sampling frequency and bandwidth or that may enable a reduced sampling frequency for a target SQNR and bandwidth. In one or more embodiments, a modulator circuit may include a first modulator including an input and a first output, and including one or more feed-forward components; an output circuit including an input coupled to the first output and including an output, the output circuit including one of a noise-shaping circuit, a noise-shaped quantizer circuit, or an integrator and feed-forward component; and coefficients of the one or more feed-forward components of the first modulator and a transfer function of the output circuit provide a higher-order modulator with a first-order roll-off at high out-of-band frequencies.