Low-power conversion between analog and digital signals using adjustable feedback filter
A system to convert between analog and digital signals, in some embodiments, comprises: a differentiator to produce a differentiated signal based on an input signal and a feedback signal; an integrator, coupled to the differentiator, to integrate the differentiated signal; a quantizer, coupled to the integrator, to quantize the integrated signal; and a low-pass feedback filter, coupled between an output of the quantizer and an input of the differentiator, to generate said feedback signal using the quantized signal, wherein the low-pass feedback filter pushes at least some noise of the quantized signal downward in the frequency spectrum.
1. A system to convert between analog and digital signals, comprising:
a differentiator to produce a differentiated signal based on an input signal and a feedback signal;
an integrator, coupled to the differentiator, to integrate the differentiated signal to generate an integrated signal;
a quantizer, coupled to the integrator, to quantize the integrated signal to generate a quantized signal; and
a low-pass feedback filter, coupled between an output of the quantizer and an input of the differentiator, to generate said feedback signal using the quantized signal,
wherein the low-pass feedback filter pushes at least some noise of the quantized signal downward in a frequency spectrum, and wherein the low-pass feedback filter has a roll-off region corresponding to a frequency range of 100 Hz to 20 kHz, inclusive.
2. The system of claim 1 , wherein the integrator and the low-pass feedback filter perform a second-order noise shaping on a signal as the signal passes through said system.
3. The system of claim 1 , further comprising digital filtering circuitry, coupled to the quantizer, that includes a low-pass filter to push at least some noise of the quantized signal downward in the frequency spectrum, and that further includes a high-pass filter to attenuate said at least some noise.
4. The system of claim 1 , further comprising digital filtering circuitry, coupled to the quantizer, that includes a low-pass filter that implements the transfer function of said low-pass feedback filter.
5. The system of claim 1 , further comprising digital filtering circuitry, coupled to the quantizer, that includes a decimator to decimate a digital signal.
6. The system of claim 1 , wherein the low-pass feedback filter has a dynamically adjustable cutoff frequency.
7. The system of claim 6 , wherein said dynamically adjustable cutoff frequency is adjusted based at least in part on an amplitude of the input signal.
8. The system of claim 7 , wherein the dynamically adjustable cutoff frequency is less than or equal to 20 Hz when an amplitude of the input signal is below a predetermined threshold.
9. The system of claim 6 , wherein the dynamically adjustable cutoff frequency is a function of a clock frequency provided to the system.
10. The system of claim 1 , wherein the low-pass feedback filter comprises multiple capacitors, each of the multiple capacitors capable of being coupled or uncoupled from a voltage supply based on the states of at least a first group of switches, and the multiple capacitors capable of being coupled in multiple serial configurations based on the states of at least a second group of switches.
11. The system of claim 10 , wherein the low-pass feedback filter applies a signal gain that is a function of the number of said multiple capacitors.
12. The system of claim 1 , wherein the differentiator and integrator are implemented with a single operational transconductance amplifier (OTA).
13. The system of claim 12 , wherein the integrator is a time-continuous integrator.
14. The system of claim 1 , wherein the system comprises an analog-to-digital converter or a digital-to-analog converter.
15. A method for converting between analog and digital signals, comprising:
combining an input signal and a feedback signal to produce a differentiated signal;
integrating the differentiated signal to produce an integrated signal;
quantizing the integrated signal to produce a quantized signal; and
low-pass filtering the quantized signal to produce said feedback signal, wherein said low-pass filtering pushes noise in the quantized signal downward in a frequency spectrum, and wherein said low-pass filtering applies a roll-off region corresponding to a frequency range of 100 Hz to 20 kHz, inclusive.
16. The method of claim 15 , further comprising:
low-pass filtering the quantized signal to produce a filtered signal having noise pushed downward in the frequency spectrum; and
high-pass filtering the filtered signal to attenuate said noise.
17. The method of claim 15 , further comprising dynamically adjusting a cutoff frequency used in said low-pass filtering of the quantized signal.
18. The method of claim 17 , wherein dynamically adjusting the cutoff frequency comprises using an amplitude of the input signal.
19. A system to convert between analog and digital signals, comprising:
a differentiator to produce a differentiated signal based on an input signal and a feedback signal;
an integrator, coupled to the differentiator, to integrate the differentiated signal to generate an integrated signal;
a quantizer, coupled to the integrator, to quantize the integrated signal to generate a quantized signal; and
a low-pass feedback filter, coupled between an output of the quantizer and an input of the differentiator, to generate said feedback signal using the quantized signal,
wherein the low-pass feedback filter pushes at least some noise of the quantized signal downward in a frequency spectrum, wherein the low-pass feedback filter has a dynamically adjustable cutoff frequency that is a function of a clock frequency provided to the system.
20. A system to convert between analog and digital signals, comprising:
a differentiator to produce a differentiated signal based on an input signal and a feedback signal;
an integrator, coupled to the differentiator, to integrate the differentiated signal to generate an integrated signal;
a quantizer, coupled to the integrator, to quantize the integrated signal to generate a quantized signal; and
a low-pass feedback filter, coupled between an output of the quantizer and an input of the differentiator, to generate said feedback signal using the quantized signal, wherein the low-pass feedback filter comprises multiple capacitors, each of the multiple capacitors capable of being coupled or uncoupled from a voltage supply based on the states of at least a first group of switches, and the multiple capacitors capable of being coupled in multiple serial configurations based on the states of at least a second group of switches.