Offset compensation scheme using a DAC
An offset compensation scheme using a digital-to-analog converter (DAC) is disclosed. In some embodiments, a DAC is coupled to a circuit having an undesired current or voltage offset and is configured to at least in part compensate for the undesired current or voltage offset. For example, in some embodiments, the DAC injects current or voltage into the circuit that shifts a current or voltage of the circuit by an amount equal or similar in magnitude but opposite in polarity to a shift in the current or voltage of the circuit caused by the undesired current or voltage offset.
1. A system for offset compensation, comprising:
a circuit having an undesired current or voltage offset; and
a digital-to-analog converter (DAC) coupled to the circuit and configured to at least in part compensate for the undesired current or voltage offset;
wherein:
the DAC is configured to at least in part compensate for the undesired current or voltage offset including by injecting current or voltage into the circuit;
the injected current or voltage shifts a current or voltage of the circuit; and
a shift in the current or voltage of the circuit due to the injected current or voltage is similar in magnitude but opposite in polarity to a shift in the current or voltage of the circuit caused by the undesired current or voltage offset.
2. A system as recited in claim 1 , wherein the injecting current or voltage into the circuit comprises drawing current or voltage from the circuit.
3. A system as recited in claim 1 , wherein the DAC has a variable gain.
4. A system as recited in claim 1 , wherein the DAC has an associated reference current or voltage that depends on a transconductance of a differential pair of the circuit.
5. A system as recited in claim 1 , wherein the DAC has an associated offset cancellation range and wherein when a reference current or voltage associated with the DAC is scaled, the offset cancellation range of the DAC is changed.
6. A system as recited in claim 1 , wherein the DAC has an associated reference current or voltage comprising a scaled version of a bandgap current or voltage.
7. A system as recited in claim 1 , further comprising a DAC bias circuit.
8. A system as recited in claim 7 , wherein the DAC bias circuit comprises a transconductance replica circuit.
9. A system as recited in claim 7 , wherein the DAC is a first DAC and further comprising a second DAC in the DAC bias circuit for scaling a reference current or voltage associated with the first DAC.
10. A system as recited in claim 1 , wherein the DAC is configured to be calibrated by a binary search algorithm.
11. A system as recited in claim 1 , wherein the DAC is configured to be calibrated by a sequential search algorithm.
12. A system as recited in claim 1 , wherein the DAC has an associated reference current or voltage that is scaled based on a calibration value of the DAC.
13. A system as recited in claim 1 , wherein calibration of the DAC is performed using an operating clock frequency of the circuit.
14. A system as recited in claim 1 , wherein the DAC is implemented in NMOS (n-type metal-oxide-semiconductor field effect transistors).
15. A system as recited in claim 14 , wherein the DAC is controlled by low voltage logic.
16. A system as recited in claim 1 , wherein the circuit comprises an amplifier.
17. A system as recited in claim 1 , wherein the circuit comprises a slice of an analog-to-digital converter (ADC).
18. A system as recited in claim 1 , wherein the circuit comprises one slice of a plurality of slices included in an analog-to-digital converter (ADC) and wherein the DAC comprises one DAC of a DAC array associated with the ADC.
19. A system as recited in claim 18 , wherein the plurality of DACs included in the DAC array of the ADC are calibrated sequentially, in parallel, or in groups.
20. A method for offset compensation, comprising:
receiving an indication of an undesired current or voltage offset in a circuit; and
compensating at least in part for the undesired current or voltage offset using a digital-to-analog converter (DAC), wherein the DAC is coupled to the circuit;
wherein:
compensating at least in part for the undesired current or voltage offset includes injecting current or voltage into the circuit;
the injected current or voltage shifts a current or voltage of the circuit; and
a shift in the current or voltage of the circuit due to the injected current or voltage is similar in magnitude but opposite in polarity to a shift in the current or voltage of the circuit caused by the undesired current or voltage offset.
21. A method as recited in claim 20 , wherein the DAC has an associated offset cancellation range and wherein when a reference current or voltage associated with the DAC is scaled, the offset cancellation range of the DAC is changed.
22. A method as recited in claim 20 , wherein the injecting current or voltage into the circuit comprises drawing current or voltage from the circuit.
23. A method as recited in claim 20 , wherein the DAC has a variable gain.
24. A method as recited in claim 20 , wherein the DAC has an associated reference current or voltage that depends on a transconductance of a differential pair of the circuit.
25. A method as recited in claim 20 , wherein the DAC has an associated reference current or voltage comprising a scaled version of a bandgap current or voltage.