Sigma-delta converter system and method
A sigma-delta converter may include a filter coupled to a first summation circuit and a second summation circuit. A multi bit quantizer may be coupled to the second summation circuit. A single bit digital-to-analog converter (DAC) may be included that defines a feedback path between the multi-bit quantizer and the first summation circuit. A feed-forward coefficient circuit defining a feed forward path between the first summation circuit and the second summation circuit may be included.
1. A method of controlling a feed-forward sigma-delta converter including a multi-bit quantizer and having a feed-forward coefficient, the method comprising:
multiplying an input signal to the sigma-delta converter by the feed-forward coefficient;
summing a product of the feed-forward coefficient and an input to the sigma-delta converter with at least one output of a filter;
converting the sum of the product and the output of the filter into a multi-bit-wide value; and
varying the feed-forward coefficient in response to at least one bit of the multi-bit-wide value.
2. The method of claim 1 , further comprising performing a single-bit digital-to-analog conversion on a most significant bit of the multi-bit-wide value.
3. The method of claim 1 , wherein varying the feed-forward coefficient includes linearly varying the feed-forward coefficient in response to the at least one bit of the multi-bit-wide value.
4. A method of controlling a feed-forward sigma-delta converter, comprising:
receiving an input voltage;
filtering the input voltage to generate a filtered output signal;
quantizing the filtered output signal to generate a multiple-bit-wide digital output;
adjusting the value of a feed-forward coefficient responsive to the multiple-bit-wide digital output; and
multiplying the input voltage times the feed-forward coefficient and supplying the value of the input voltage times the feed-forward coefficient to change the value of the filtered output signal.
5. The method of claim 4 , further comprising performing single-bit digital-to-analog conversion on a most significant bit of the multiple-bit-wide digital output.
6. The method of claim 4 , wherein the operation of filtering further comprises noise shaping.
7. A sigma-delta converter, comprising:
a filter coupled to a first summation circuit at an input, and a second summation circuit at an output;
a multi bit quantizer coupled to the second summation circuit;
a single bit digital-to-analog converter (DAC) defining a feedback path between the multi bit quantizer and the first summation circuit; and
a feed-forward coefficient circuit coupled between the first summation circuit and the second summation circuit, the feed-forward coefficient circuit comprising:
switched capacitor circuitry having an input node configured to receive an input voltage and having an output;
an operational amplifier having first and second inputs and having an output, the output of the switched capacitor circuit being coupled to a selected one of the first and second inputs; and
a feedback network coupled to the selected one of the first and second inputs of the operational amplifier and to the output of the operational amplifier.
8. The sigma-delta converter of claim 7 , wherein the feedback network comprises a capacitor and a bi-state device coupled in parallel between the selected first and second input and the output of the operational amplifier.
9. The sigma-delta converter of claim 8 , wherein the switched capacitor circuitry comprises a plurality of switched capacitor circuits, each of the plurality of switched capacitor circuit including,
a first bi-state device serially coupled to a capacitor and configured to receive the input voltage, and
a second bi-state device coupled to the first bi-state device and the capacitor, and coupled to a reference potential.
10. The sigma-delta converter of claim 7 , wherein the second summation circuit comprises a plurality of switched capacitor circuits configured to receive input voltages from the filter and coupled to an operational amplifier having a feedback network coupled to an output of the plurality of switched capacitor circuits.
11. The sigma-delta converter of claim 10 , wherein the plurality of switched capacitor circuits each includes a first bi-state device serially coupled to a capacitor and configured to receive the input voltage, and a second bi-state device coupled to the first bi-state device and the capacitor, and coupled to a ground potential.
12. The sigma-delta converter of claim 11 , wherein the first bi-state device is configurable in a high logic state and a low logic state, and the second bi-state device is configurable in a high logic state and a low logic state, such that when the first bi-state device is configured in the high logic state, the second bi-state device is configured in the low logic state, and when the second bi-state device is configured in the high logic state, the first bi-state device is configured in the low logic state.
13. The sigma-delta converter of claim 7 , wherein the first summation circuit comprises a first switched capacitor circuit and a second switched capacitor circuit coupled to an operational amplifier having a feedback capacitor.
14. The sigma-delta converter of claim 13 , wherein the first switched capacitor circuit comprises a first reference bi-state device and a second bi-state device coupled to a reference capacitor.
15. The sigma-delta converter of claim 14 , wherein the first reference bi-state device and the second bi-state device are responsive to a logic state that depends at least upon an output of the multi bit quantizer.
16. The sigma-delta converter of claim 13 , wherein the second switched capacitor circuit comprises a first bi-state device and a serially-coupled second bi-state device that are coupled to an input capacitor.