Auto-zero algorithm for reducing measurement noise in analog-to-digital systems over a wide range of sampling rates

1. A data acquisition (DAQ) system comprising:

an input terminal configured to receive a signal;

a first circuit configured to sample the signal according to a specified sampling rate that defines a sampling time interval, wherein during each sampling time interval:

the signal is a reference signal during a first time period of the sampling time interval for obtaining first samples representative of the reference signal; and

the signal is an input signal during a second time period of the sampling time interval for obtaining second samples representative of the input signal;

wherein a ratio of the second time period to the first time period is determined based on the sampling rate; and

a second circuit configured to:

process the first samples to obtain an offset value;

process the second samples to obtain an input signal value; and

adjust the input signal value based on the offset value.

2. The DAQ system of claim 1 , wherein the second circuit comprises:

a first digital signal processing path for processing the first samples; and

a second digital signal processing path distinct from the first digital signal processing path for processing the second samples.

3. The DAQ system of claim 2 , wherein at least one of the first digital signal processing path and the second digital signal processing path comprises:

a low-pass filter configured to receive and filter samples;

an average decimation filter configured to average the filtered samples to produce an average sample value; and

a binary shifter configured to adjust the average sample value.

4. The DAQ system of claim 3 , wherein the binary shifter is configured to adjust the average sample value according to the ratio of the second time period to the first time period.

5. The DAQ system of claim 1 , wherein the ratio of the second time period to the first time period is one of:

one, when the sampling frequency is equal to or lower than a specified frequency associated with at least a portion of the first circuit; or

a power-of-two greater than one, when the sampling frequency is greater than the specified frequency associated with the at least a portion of the first circuit.

6. The DAQ system of claim 5 , wherein the at least a portion of the first circuit is a signal conditioning path for the signal.

7. The DAQ system of claim 6 , wherein the specified frequency is a flicker noise frequency of the signal conditioning path.

8. The DAQ system of claim 1 , wherein the first circuit comprises a successive approximation register digital-to-analog converter configured to generate the first samples and the second samples based on the signal.

9. The DAQ system of claim 1 , wherein the reference signal is a zero signal.

10. A method for sampling a signal according to a sampling rate that defines a sampling time interval, the method comprising:

during a first time period of each sampling time interval:

receiving, at an input terminal of a data acquisition device, a reference signal; and

sampling, by the data acquisition device, the reference signal according to the sampling rate to obtain first samples representative of the reference signal;

during a second time period of each sampling time interval:

receiving, at the input terminal of the data acquisition device, an input signal; and

sampling, by the data acquisition device, the input signal according to the sampling rate to obtain second samples representative of the input signal;

processing, by the data acquisition device, the first samples to obtain an offset value;

processing, by the data acquisition device, the second samples to obtain an input signal value; and

adjusting, by the data acquisition device, the input signal value based on the offset value;

wherein a ratio of the second time period to the first time period is determined based on the sampling rate.

11. The method of claim 10 ;

wherein said processing the first samples comprises processing the first samples via a first digital signal processing path of the data acquisition device; and

wherein said processing the second samples comprises processing the second samples via a second digital signal processing path of the data acquisition device distinct from the first digital signal processing path.

12. The method of claim 11 , wherein said processing the first samples and said processing the second samples comprises:

low-pass filtering the first samples and the second samples;

averaging the low-pass filtered first samples to obtain a first average sample value and averaging the low-pass filtered second samples to obtain a second average sample value; and

adjusting the first average sample value and the second average sample value.

13. The method of claim 12 , wherein said adjusting the first average sample value and the second average sample value comprises adjusting the first average sample value and the second average sample value according to the ratio of the second time period to the first time period.

14. The method of claim 11 , further comprising:

conditioning the reference signal and the input signal via a signal conditioning path;

wherein the ratio of the second time period to the first time period is one of:

one, when the sampling frequency is equal to or lower than a specified frequency characteristic of the signal conditioning path; or

a power-of-two greater than one, when the sampling frequency is greater than the specified frequency characteristic of the signal conditioning path.

15. A system comprising:

a sampling circuit configured to:

obtain first samples representative of a reference signal by sampling the reference signal according to a sampling rate during a first time period of each sampling time interval defined by the sampling rate:

obtain second samples representative of an input signal by sampling the input signal according to the sampling rate during a second time period of each sampling time interval defined by the sampling rate, wherein a ratio of the second time period to the first time period is determined based on the sampling rate; and

a digital signal processing circuit configured to:

process the first samples to obtain an offset value;

process the second samples to obtain an input signal value; and

adjust the input signal value based on the offset value.

16. The system of claim 15 , wherein the digital signal processing circuit comprises:

a first digital signal processing path for processing the first samples; and

a second digital signal processing path distinct from the first digital signal processing path for processing the second samples.

17. The system of claim 16 , wherein the first digital signal processing path and the second digital signal processing path each comprise:

a low pass filter configured to receive and filter samples;

an average decimation filter configured to average the filtered samples to produce an average sample value; and

a binary shifter configured to adjust the average sample value according to the ratio of the second time period to the first time period.

18. The system of claim 15 , further comprising:

a signal conditioning path configured to condition the reference signal and the input signal prior to the reference signal and the input signal being sampled;

wherein the ratio of the second time period to the first time period is one of:

one, when the sampling frequency is equal to or lower than a specified frequency characteristic of the signal conditioning path; or

a power-of-two greater than one, when the sampling frequency is greater than the specified frequency characteristic of the signal conditioning path.

19. The system of claim 18 , wherein the specified frequency is a flicker noise frequency of the signal conditioning path.

20. The system of claim 15 , wherein the reference signal is a zero signal.