Sampling/quantization converters
Provided are, among other things, systems, apparatuses, methods and techniques for converting a continuous-time, continuously variable signal into a sampled and quantized signal. One such apparatus includes an input line for accepting an input signal that is continuous in time and continuously variable, multiple processing branches coupled to the input line, and an adder coupled to outputs of the processing branches. Each of the processing branches includes a continuous-time quantization-noise-shaping circuit, a sampling/quantization circuit coupled to an output of the continuous-time quantization-noise-shaping circuit, a digital bandpass filter coupled to an output of the sampling/quantization circuit, and a line coupling an output of the digital-to-analog converter circuit back into the continuous-time quantization-noise-shaping circuit. A center frequency of the digital bandpass filter in each the processing branch corresponds to a minimum in a quantization noise transfer function for the continuous-time quantization-noise-shaping circuit in the same processing branch.
1. An apparatus for converting a continuous-time, continuously variable signal into a sampled and quantized signal at a final sampling rate, comprising:
an input line for accepting an input signal that is continuous in time and continuously variable;
a plurality of sampling/quantization circuits coupled to the input line; and
an adder coupled to outputs of the plurality of sampling/quantization circuits,
wherein each of said sampling/quantization circuits operates at a subsampling rate which is less than said final sampling rate,
wherein each of said sampling/quantization circuits subsamples on a different phase of a subsampling clock, such that subsampling instants associated with each of said sampling/quantization circuits are offset in time by increments which are integer multiples of a period corresponding to said final sampling rate, and
wherein said adder sums the time-offset and subsampled outputs of said sampling/quantization circuits to produce, in combination with said sampling/quantization circuits, a filter response that has a magnitude that decreases with angular frequency co according to sin(ω)/ω.
2. An apparatus according to claim 1 , wherein said final sampling rate is at least twice a maximum frequency component associated with said continuous-time input signal.
3. An apparatus according to claim 1 , wherein said adder sums the outputs of said sampling/quantization circuits to produce a filter response which is at least approximately equal to that of a zero-order hold at said subsampling rate.
4. An apparatus according to claim 1 , wherein at least one of said sampling/quantization circuits is a single-bit quantizer.
5. An apparatus according to claim 1 , wherein at least one of said sampling/quantization circuits is a multi-bit quantizer.