Analog to digital conversion circuit with very narrow bandpass digital filtering
An analog to digital conversion circuit includes an analog to digital converter (ADC) circuit operable to convert an analog signal having an oscillation frequency into a first digital signal having a first data rate frequency, where the analog signal includes a set of pure tone components. The analog to digital conversion circuit further includes a digital decimation filtering circuit operable to convert the first digital signal into a second digital signal having a second data rate frequency. The analog to digital conversion circuit further includes a digital bandpass filter (BPF) circuit operable to convert the second digital signal into an outbound digital signal having a third data rate frequency, where the digital bandpass filter circuit is set to produce a bandpass region approximately centered at the oscillation frequency of the analog signal and having a bandwidth tuned for filtering a pure tone.
1. An analog to digital conversion circuit comprises:
an analog to digital converter (ADC) circuit operable to convert an analog signal having an oscillation frequency into a first digital signal having a first data rate frequency, wherein the analog signal includes a set of pure tone components;
a digital decimation filtering circuit operable to convert the first digital signal into a second digital signal having a second data rate frequency; and
a digital bandpass filter (BPF) circuit including a plurality of taps having a plurality of coefficients, wherein the digital BPF circuit is operable to convert the second digital signal into an outbound digital signal having a third data rate frequency, wherein the plurality of coefficients for the plurality of taps is set to produce a bandpass region approximately centered at the oscillation frequency of the analog signal and having a bandwidth tuned for filtering a pure tone, wherein the first data rate frequency is a first integer multiple of the third data rate frequency, wherein the second data rate frequency is a second integer multiple of the third data rate frequency, and wherein the first data rate frequency is greater than the second data rate frequency.
2. The analog to digital conversion circuit of claim 1 further comprises:
the first data rate frequency is a third integer multiple of the second data rate frequency.
3. The analog to digital conversion circuit of claim 1 , wherein the ADC circuit includes an oversampling modulator and the digital decimation filtering circuit, wherein the oversampling modulator includes:
a 1-bit sigma-delta modulator operable to convert the analog signal into the first digital signal having a 1-bit digital data stream at the first data rate frequency.
4. The analog to digital conversion circuit of claim 1 , wherein the digital decimation filtering circuit comprises:
an anti-aliasing filter; and
a decimator.
5. The analog to digital conversion circuit of claim 1 , wherein the digital BPF circuit further comprises:
a first BPF circuit for a first signal component of the analog signal; and
a second BPF circuit for a second signal component of the analog signal.
6. The analog to digital conversion circuit of claim 1 further comprises:
the first data rate frequency is 2 17 times the third data rate frequency; and
the second data rate frequency is 2 12 times the third data rate frequency.
7. The analog to digital conversion circuit of claim 1 further comprises:
the first data rate frequency includes a first bit rate per interval;
the second data rate frequency includes a second bit rate per interval; and
the third data rate frequency includes a third bit rate per interval.
8. The analog to digital conversion circuit of claim 1 further comprises:
a processing module operable to determine an impedance value from the outbound digital signal, wherein the outbound digital signal is a vector having real and imaginary components.
9. The analog to digital conversion circuit of claim 1 , wherein the bandwidth tuned for filtering the pure tone is less than 0.05 of channel spacing, and wherein the channel spacing is the bandwidth between two pure tones of the set of pure tone components.
10. A drive sense system comprises:
a comparator operable to produce a comparison signal by comparing a sensed drive signal with a reference signal;
a drive circuit operable to:
generating a drive supply signal based on a feedback signal; and
supply the drive signal to a sensor, wherein an electrical characteristic change of the sensor causes a change to the drive signal producing the sensed drive signal;
an analog to digital converter (ADC) circuit operable to convert the comparison signal into a first digital signal having a first data rate frequency;
a digital to analog converter operable to convert the first digital signal into the feedback signal;
a digital decimation filtering circuit operable to convert the first digital signal into a second digital signal having a second data rate frequency; and
a digital bandpass filter (BPF) circuit including a plurality of taps having a plurality of coefficients, wherein the digital BPF circuit is operable to convert the second digital signal into an outbound digital signal having a third data rate frequency, wherein the plurality of coefficients for the plurality of taps is set to produce a bandpass region approximately centered at the oscillation frequency of the analog signal and having a bandwidth tuned for filtering a pure, wherein the first data rate frequency is a first integer multiple of the third data rate frequency, wherein the second data rate frequency is a second integer multiple of the third data rate frequency, and wherein the first data rate frequency is greater than the second data rate frequency.
11. The analog to digital conversion circuit of claim 10 further comprises:
the first data rate frequency is a third integer multiple of the second data rate frequency.
12. The analog to digital conversion circuit of claim 10 , wherein the ADC circuit includes an oversampling modulator and the digital decimation filtering circuit, wherein the oversampling modulator includes:
a 1-bit sigma-delta modulator operable to convert the analog signal into the first digital signal having a 1-bit digital data stream at the first data rate frequency.
13. The analog to digital conversion circuit of claim 10 , wherein the digital decimation filtering circuit comprises:
an anti-aliasing filter; and
a decimator.
14. The analog to digital conversion circuit of claim 10 , wherein the digital bandpass filter circuit further comprises:
a first digital BPF circuit for a first signal component of the analog signal; and
a second digital BPF circuit for a second signal component of the analog signal.
15. The analog to digital conversion circuit of claim 10 further comprises:
the first data rate frequency is 2 17 times the third data rate frequency; and
the second data rate frequency is 2 12 times the third data rate frequency.
16. The analog to digital conversion circuit of claim 10 further comprises:
the first data rate frequency includes a first bit rate per interval;
the second data rate frequency includes a second bit rate per interval; and
the third data rate frequency includes a third bit rate per interval.
17. The analog to digital conversion circuit of claim 10 further comprises:
a processing module operable to determine an impedance value from the outbound digital signal, wherein the outbound digital signal is a vector having real and imaginary components.
18. The analog to digital conversion circuit of claim 10 , wherein the bandwidth tuned for filtering the pure tone is less than 0.05 of channel spacing, wherein the channel spacing is the bandwidth between two pure tones of the set of pure tone components.