Sampling/quantization converters
Provided are, among other things, systems, methods and techniques for converting a continuous-time, continuously variable signal into a sampled and quantized signal. According to one representative embodiment, an apparatus includes multiple quantization-noise-shaping continuous-time filters, each in a separate processing branch and having an adder that includes multiple inputs and an output; an input signal is coupled to one of the inputs of the adder; the output of the adder is coupled to one of the inputs of the adder through a first filter; and the output of a sampling/quantization circuit in the same processing branch is coupled to one of the inputs of the adder through a second filter, with the second filter having a different transfer function than the first filter.
1. An apparatus for converting a continuous-time, continuously variable signal into a sampled and quantized signal, comprising:
an input line for accepting an input signal that is continuous in time and continuously variable;
a plurality of processing branches coupled to the input line, each of said processing branches including: (a) a continuous-time quantization-noise-shaping circuit, (b) a sampling/quantization circuit coupled to an output of the continuous-time quantization-noise-shaping circuit, (c) a digital bandpass filter coupled to an output of the sampling/quantization circuit, and (d) a line coupling the output of the sampling/quantization circuit back into the continuous-time quantization-noise-shaping circuit; and
an adder coupled to outputs of the plurality of processing branches,
wherein a center frequency of the digital bandpass filter in each said processing branch corresponds to a minimum in the quantization noise transfer function for the continuous-time quantization-noise-shaping circuit in the same processing branch, and
wherein each of said digital bandpass filters includes: (a) a quadrature frequency downconverter that generates in-phase and quadrature outputs, using cosine and sine sequences with a frequency corresponding to the minimum in the quantization noise transfer function, (b) a first moving-average filter coupled to the in-phase output of the quadrature frequency downconverter, (c) a second moving-average filter coupled to the quadrature output of the quadrature frequency downconverter, and (d) a quadrature frequency upconverter that uses cosine and sine sequences with the frequency corresponding to the minimum in the quantization noise transfer function.
2. An apparatus according to claim 1 , wherein the digital bandpass filters in different ones of said processing branches select different frequency bands that collectively cover a desired frequency range.
3. An apparatus according to claim 1 , wherein the digital bandpass filters in at least one of said processing branches have evenly spaced center frequencies.
4. An apparatus according to claim 1 , wherein the digital bandpass filters in different ones of said processing branches have at least one of: (i) center frequencies that are spaced at non-equal intervals, and (ii) bandwidths that are not all equal to each other.
5. An apparatus according to claim 1 , wherein each of the first moving-average filter and the second moving-average filter within at least one of the digital bandpass filters is comprised of three cascaded moving-average functions.
6. An apparatus according to claim 1 , wherein the digital bandpass filter is comprised of cascaded moving-average operations that collectively provide spectral minima at frequencies other than multiples of an output data rate of said apparatus.
7. An apparatus according to claim 1 , wherein the digital bandpass filter is comprised of cascaded moving-average functions, wherein the number of moving-average functions is other than one plus an effective order of the noise transfer function associated with the continuous-time quantization-noise-shaping circuit in the same processing branch.
8. An apparatus according to claim 1 , wherein the digital bandpass filter comprises a moving-average operation that is implemented as a recursive structure.
9. An apparatus according to claim 1 , wherein at least one of the digital bandpass filters is implemented as a polyphase decomposition structure.
10. An apparatus according to claim 9 , wherein a polyphase decomposition factor, m, of the polyphase decomposition structure is a submultiple of the number of processing branches, M.
11. An apparatus according to claim 1 , wherein the sine and cosine sequences used by the quadrature frequency downconverter and the quadrature frequency upconverter for quadrature downconversion and upconversion, respectively, are generated through direct digital synthesis using digital accumulators and sinusoid lookup.
12. An apparatus according to claim 1 , wherein the sine and cosine sequences used by the quadrature frequency downconverter and the quadrature frequency upconverter for quadrature downconversion and upconversion, respectively, are generated using recursive functions.
13. An apparatus according to claim 1 , wherein the digital bandpass filter in each of a plurality of said processing branches introduces total distortion power limited to less than 40 dB below data converter signal level.
14. An apparatus according to claim 1 , wherein the digital bandpass filter in each of a plurality of said processing branches introduces total distortion power limited to less than 50 dB below data converter signal level.
15. An apparatus according to claim 1 , wherein the digital bandpass filter in each of a plurality of said processing branches attenuates shaped quantization noise by at least 40 dB.
16. An apparatus according to claim 1 , wherein the digital bandpass filter in each of a plurality of said processing branches attenuates shaped quantization noise by at least 60 dB.
17. An apparatus according to claim 1 , wherein the digital bandpass filter in each of a plurality of said processing branches attenuates shaped quantization noise by at least 80 dB.
18. An apparatus according to claim 1 , further comprising a tapped transmission line distribution structure for providing the input signal to a plurality of the continuous-time quantization-noise-shaping circuits.
19. An apparatus for converting a continuous-time, continuously variable signal into a sampled and quantized signal, comprising:
an input line for accepting an input signal that is continuous in time and continuously variable;
a continuous-time quantization-noise-shaping filter; and
a sampling/quantization circuit coupled to an output of the continuous-time quantization noise-shaping filter,
wherein the continuous-time quantization-noise-shaping filter comprises an adder that includes a plurality of inputs and an output, with the input signal being coupled to one of the inputs of the adder, the output of the adder being coupled to one of the inputs of the adder through a first filter, the output of the sampling/quantization circuit in the same processing branch being coupled to one of the inputs of the adder through a second filter, and the second filter having a different transfer function than the first filter, and
wherein the continuous-time quantization-noise-shaping filter has a noise transfer function with a minimum at a particular frequency.
20. An apparatus according to claim 19 , further comprising a digital bandpass filter coupled to an output of the sampling/quantization circuit, and wherein a center frequency of the digital bandpass filter corresponds to the particular frequency.
21. An apparatus according to claim 19 , wherein said continuous-time quantization noise-shaping filter comprises distributed-element components and monolithic microwave integrated circuits (MMICs).
22. An apparatus according to claim 19 , wherein said continuous-time quantization noise-shaping filter incorporates a delay element that provides a delay of at least ¼ of a sampling period used by the sampling/quantization circuit.
23. An apparatus according to claim 19 , wherein said continuous-time quantization noise-shaping filter incorporates a delay element that provides a delay of at least ½ of a sampling period used by the sampling/quantization circuit.
24. An apparatus according to claim 19 , wherein the continuous-time quantization noise-shaping filter is second-order.
25. An apparatus according to claim 19 , wherein the continuous-time quantization noise-shaping filter is fourth-order.
26. An apparatus according to claim 19 , further comprising an active calibration component that adjusts a parameter of at least one component of the continuous-time quantization-noise-shaping filter.