Analog-to-digital converter with input voltage biasing DC level of resonant oscillator
View Patent ↗An analog-to-digital converter is disclosed comprising a resonant oscillator comprising an input operable to receive an analog input signal and an output operable to output an oscillating signal. A DC offset detector detects a DC offset in the oscillating signal caused by the analog input signal, wherein the DC offset is converted into a digital output signal representing the analog input signal.
1. An analog-to-digital converter comprising:
a resonant oscillator comprising an input operable to receive an analog input signal and an output operable to output an oscillating signal; and
a DC offset detector operable to detect a DC offset in the oscillating signal caused by the analog input signal, wherein the DC offset is converted into a digital output signal representing the analog input signal.
2. The analog-to-digital converter as recited in claim 1 , wherein the resonant oscillator comprises a ceramic resonator.
3. The analog-to-digital converter as recited in claim 1 , wherein the resonant oscillator comprises a crystal.
4. The analog-to-digital converter as recited in claim 1 , wherein the resonant oscillator comprises a silicon oscillator.
5. The analog-to-digital converter as recited in claim 1 , wherein the DC offset detector is operable to:
measure a first time the oscillating signal is above a threshold;
measure a second time the oscillating signal is below the threshold; and
detect the DC offset based on a time delta between the first time and the second time.
6. The analog-to-digital converter as recited in claim 5 , wherein the DC offset detector is further operable to:
accumulate a number of the time deltas over a number of cycles of the oscillating signal; and
detect the DC offset based on the accumulated time deltas.
7. The analog-to-digital converter as recited in claim 6 , wherein:
the DC offset detector is further operable to generate a bias signal in response to the accumulated time deltas; and
the bias signal is operable to drive the DC offset in the oscillating signal toward zero.
8. The analog-to-digital converter as recited in claim 7 , wherein the bias signal has substantially no effect on an input impedance of the resonant oscillator.
9. The analog-to-digital converter as recited in claim 8 , wherein the DC offset detector comprises a current source and a current sink operable to generate the bias signal.
10. The analog-to-digital converter as recited in claim 5 , wherein the DC offset detector is further operable to Vernier a clock signal used to generate the first and second times in order to increase a resolution of the analog-to-digital conversion.
11. The analog-to-digital converter as recited in claim 5 , wherein the DC offset detector is further operable to dither the threshold in order to increase a resolution of the analog-to-digital conversion.
12. A method of converting an analog signal into a digital signal, the method comprising:
biasing a resonant oscillator with the analog input signal to generate an oscillating signal;
detecting a DC offset in the oscillating signal caused by the analog input signal, wherein the DC offset; and
converting the DC offset into the digital signal representing the analog signal.
13. The method as recited in claim 12 , wherein the resonant oscillator comprises a ceramic resonator.
14. The method as recited in claim 12 , wherein the resonant oscillator comprises a crystal.
15. The method as recited in claim 12 , wherein the resonant oscillator comprises a silicon oscillator.
16. The method as recited in claim 12 , wherein detecting the DC offset comprises:
measuring a first time the oscillating signal is above a threshold;
measuring a second time the oscillating signal is below the threshold; and
detecting the DC offset based on a time delta between the first time and the second time.
17. The method as recited in claim 16 , wherein detecting the DC offset further comprises:
accumulating a number of the time deltas over a number of cycles of the oscillating signal; and
detecting the DC offset based on the accumulated time deltas.
18. The method as recited in claim 17 , wherein:
generating a bias signal in response to the accumulated time deltas; and
drive the DC offset in the oscillating signal toward zero in response to the bias signal.
19. The method as recited in claim 18 , wherein the bias signal has substantially no effect on an input impedance of the resonant oscillator.
20. The method as recited in claim 19 , further comprising generating the bias signal using a current source and a current sink.
21. The method as recited in claim 16 , wherein detecting the DC offset further comprises Verniering a clock signal used to generate the first and second times in order to increase a resolution of the analog-to-digital conversion.
22. The method as recited in claim 16 , wherein detecting the DC offset further comprises dithering the threshold in order to increase a resolution of the analog-to-digital conversion.