Sigma-delta modulator with residue converter for low-offset measurement system

1. A signal processing system comprising:

a sensor readout channel configured to convert an electronic signal into a digital quantity, the sensor readout channel comprising:

a first-order sigma-delta modulator having a modulator input and a modulator output;

first outside chopping switches located at the modulator input;

second outside chopping switches located at the modulator output;

an auxiliary path comprising an analog-to-digital converter (ADC) having an auxiliary path input and an auxiliary path output, the auxiliary path input configured to receive as its input signal a signal output by a memory element of the first-order sigma-delta modulator; and

a signal combiner configured to combine a modulator output signal generated by the first-order sigma-delta modulator with an auxiliary path output signal generated by the auxiliary path to generate a combined output signal.

2. The signal processing system of claim 1 , wherein the memory element comprises an integrator.

3. The signal processing system of claim 1 , further comprising an impedance for converting a sensed physical quantity into the electronic signal.

4. The signal processing system of claim 3 , wherein:

the electronic signal is a voltage; and

the impedance is a resistor configured to convert an electrical current into the voltage.

5. The signal processing system of claim 4 , wherein the sensor readout channel further comprises a digital accumulator configured to digitally integrate the combined output signal to generate the digital quantity representing a net amount of charge that has flowed through the impedance.

6. The signal processing system of claim 4 , wherein the digital quantity represents a net amount of charge that has been delivered from a battery coupled to the impedance.

7. The signal processing system of claim 1 , wherein the sensor readout channel further comprises a digital accumulator configured to digitally integrate the combined output signal to generate an accumulated combined output signal.

8. The signal processing system of claim 1 , wherein the sensor readout channel further comprises a digital accumulator configured to digitally integrate the modulator output signal to generate an accumulated modulator output signal, and the combiner is configured to combine the accumulated modulator output signal with the auxiliary path output signal to generate the combined output signal.

9. The signal processing system of claim 1 , further comprising an anti-aliasing filter coupled between an input for receiving the electronic signal and the modulator input.

10. The signal processing system of claim 9 , wherein the anti-aliasing filter is located in a path of the sensor readout channel between the first outside chopping switches and the second outside chopping switches.

11. The signal processing system of claim 9 , wherein the first outside chopping switches are located in a path of the sensor readout channel between the input for receiving the electronic signal and the anti-aliasing filter.

12. The signal processing system of claim 1 , further comprising an adaptive gain element applied to the auxiliary path output in order to minimize signal-to-noise degradation due to non-idealities of analog components of the signal processing system.

13. The signal processing system of claim 1 , wherein the sigma-delta modulator comprises a 3-level quantizer.

14. The signal processing system of claim 13 , wherein the 3-level quantizer is configured to, during production test of the signal processing system, detect the combined output signal in response to a pilot signal injected into an input of the signal processing system to determine a threshold mismatch of the 3-level quantizer.

15. The signal processing system of claim 1 , wherein the auxiliary signal path is configured such that it is only enabled upon a readout request for the combined output signal.

16. A method comprising, in a signal processing system comprising a sensor readout channel configured to convert an electronic signal into a digital quantity, the sensor readout channel comprising a first-order sigma-delta modulator having a modulator input and a modulator output:

switching first outside chopping switches located at the modulator input and second outside chopping switches located at the modulator output in synchronization;

receiving, by an auxiliary path comprising an analog-to-digital converter (ADC) having an auxiliary path input and an auxiliary path output, as its input signal a signal output by a memory element of the first-order sigma-delta modulator; and

combining a modulator output signal generated by the first-order sigma-delta modulator with an auxiliary path output signal generated by the auxiliary path to generate a combined output signal.

17. The method of claim 16 , wherein the memory element comprises an integrator.

18. The method of claim 16 , further comprising converting a sensed physical quantity into the electronic signal with an impedance.

19. The method of claim 18 , wherein:

the electronic signal is a voltage; and

the impedance is a resistor configured to convert an electrical current into the voltage.

20. The method of claim 19 , further comprising digitally integrating, with a digital accumulator integral to the sensor readout channel, the combined output signal to generate the digital quantity representing a net amount of charge that has flowed through the impedance.

21. The method of claim 19 , wherein the digital quantity represents a net amount of charge that has been delivered from a battery coupled to the impedance.

22. The method of claim 16 , further comprising digitally integrating, with a digital accumulator integral to the sensor readout channel, the combined output signal to generate an accumulated combined output signal.

23. The method of claim 16 , further comprising:

digitally integrating, with a digital accumulator integral to the sensor readout channel, the modulator output signal to generate an accumulated modulator output signal; and

combining the accumulated modulator output signal with the auxiliary path output signal to generate the combined output signal.

24. The method of claim 16 , further comprising an anti-aliasing filter coupled between an input for receiving the electronic signal and the modulator input.

25. The method of claim 24 , wherein the anti-aliasing filter is located in a path of the sensor readout channel between the first outside chopping switches and the second outside chopping switches.

26. The method of claim 24 , wherein the first outside chopping switches are located in a path of the sensor readout channel between the input for receiving the electronic signal and the anti-aliasing filter.

27. The method of claim 16 , further comprising applying an adaptive gain element to the auxiliary path output in order to minimize signal-to-noise degradation due to non-idealities of analog components of the signal processing system.

28. The method of claim 16 , wherein the sigma-delta modulator comprises a 3-level quantizer.

29. The method of claim 28 , further comprising, during production test of the signal processing system, detecting the combined output signal in response to a pilot signal injected into an input of the signal processing system to determine a threshold mismatch of the 3-level quantizer.

30. The method of claim 16 , enabling the auxiliary signal path only upon a readout request for the combined output signal.