Hybrid ADC circuit and method
There is described a hybrid ADC device for converting an analog input signal (Vin) into a digital output signal (Vout), the device comprising a first ADC circuit configured to receive the analog input signal (Vin) and convert it into a first digital signal (Y 0 ); a DAC circuit configured to receive the first digital signal and convert it into a first analog signal; a delay circuit configured to delay the analog input signal; a first combiner configured to generate an analog residual signal by subtracting the first analog signal from the delayed analog input signal; a second ADC circuit configured to receive the residual analog signal and convert it into a second digital signal (Y 1 ); a filter circuit configured to receive the first digital signal and output a filtered first digital signal (Y 0 ′), the filter circuit having a transfer function corresponding to a combined transfer function of the DAC circuit and the second ADC circuit; and a second combiner configured to generate the digital output signal (Vout) by adding the second digital signal and the filtered first digital signal, wherein the first ADC circuit comprises an anti-aliasing filter. Furthermore, a corresponding method and an automobile radar system are described.
1. A hybrid ADC device for converting an analog input signal into a digital output signal, the device comprising:
a first ADC circuit configured to receive the analog input signal and convert it into a first digital signal, the first ADC circuit comprising:
an SAR-based quantizer having an output for outputting the first digital signal,
an anti-aliasing filter having an output coupled to an input of the SAR-based quantizer, and
a feedback loop combiner having a first input coupled to receive the analog input signal, a second input coupled to the output of the SAR-based quantizer, and an output coupled to an input of the anti-aliasing filter;
a DAC circuit configured to receive the first digital signal and convert it into a first analog signal;
a delay circuit configured to delay the analog input signal;
a first combiner configured to generate an analog residual signal by subtracting the first analog signal from the delayed analog input signal;
a second ADC circuit configured to receive the residual analog signal and convert it into a second digital signal;
a filter circuit configured to receive the first digital signal and output a filtered first digital signal, the filter circuit having a transfer function corresponding to a combined transfer function of the DAC circuit and the second ADC circuit; and
a second combiner configured to generate the digital output signal by adding the second digital signal and the filtered first digital signal.
2. The device according to claim 1 , wherein the anti-aliasing filter comprises a passive low-pass filter arranged to filter the analog input signal prior to converting the analog input signal into the first digital signal.
3. The device according to claim 1 , wherein the first ADC circuit comprises a CT Sigma-Delta ADC with passive loop filter.
4. The device according to claim 3 , wherein the passive loop filter comprises an RC filter circuit.
5. The device according to claim 1 , wherein the delay circuit comprises an all-pass filter.
6. The device according to claim 1 , wherein the second ADC circuit comprises a low-pass filter, an amplifier, and a CT Delta-Sigma ADC circuit.
7. A method of converting an analog input signal into a digital output signal, the method comprising:
receiving the analog input signal at a first ADC circuit and converting it into a first digital signal, the first ADC circuit comprising:
an SAR-based quantizer having an output for outputting the first digital signal,
an anti-aliasing filter having an output coupled to an input of the SAR-based quantizer, and
a feedback loop combiner having a first input coupled to receive the analog input signal,
a second input coupled to the output of the SAR-based quantizer, and an output coupled to an input of the anti-aliasing filter;
receiving the first digital signal at a DAC circuit and converting it into a first analog signal;
delaying the analog input signal utilizing a delay circuit;
generating an analog residual signal by subtracting the first analog signal from the delayed analog input signal in a first combiner;
receiving the residual analog signal at a second ADC circuit and converting it into a second digital signal;
receiving the first digital signal at a filter circuit and outputting a filtered first digital signal, the filter circuit having a transfer function corresponding to a combined transfer function of the DAC circuit and the second ADC circuit; and
generating the digital output signal by adding the second digital signal and the filtered first digital signal in a second combiner.
8. The method according to claim 7 , wherein the anti-aliasing filter comprises a passive low-pass filter arranged to filter the analog input signal prior to converting the analog input signal into the first digital signal.
9. The method according to claim 7 , wherein the first ADC circuit comprises a CT Sigma-Delta ADC with passive loop filter.
10. The method according to claim 9 , wherein the passive loop filter comprises an RC filter circuit.
11. The method according to claim 7 , wherein the delay circuit comprises an all-pass filter.
12. The method according to claim 7 , wherein the second ADC circuit comprises a low-pass filter, an amplifier, and a CT Delta-Sigma ADC circuit.
13. An automobile radar system comprising a hybrid ADC device for converting an analog input signal into a digital output signal, the device comprising:
a first ADC circuit configured to receive the analog input signal and convert it into a first digital signal, the first ADC circuit comprising:
an SAR-based quantizer having an output for outputting the first digital signal,
an anti-aliasing filter having an output coupled to an input of the SAR-based quantizer, and
a feedback loop combiner having a first input coupled to receive the analog input signal, a second input coupled to the output of the SAR-based quantizer, and an output coupled to an input of the anti-aliasing filter;
a DAC circuit configured to receive the first digital signal and convert it into a first analog signal;
a delay circuit configured to delay the analog input signal;
a first combiner configured to generate an analog residual signal by subtracting the first analog signal from the delayed analog input signal;
a second ADC circuit configured to receive the residual analog signal and convert it into a second digital signal;
a filter circuit configured to receive the first digital signal and output a filtered first digital signal, the filter circuit having a transfer function corresponding to a combined transfer function of the DAC circuit and the second ADC circuit; and
a second combiner configured to generate the digital output signal by adding the second digital signal and the filtered first digital signal.
14. The device according to claim 13 , wherein the anti-aliasing filter comprises a passive low-pass filter arranged to filter the analog input signal prior to converting the analog input signal into the first digital signal.
15. The device according to claim 13 , wherein the first ADC circuit comprises a CT Sigma-Delta ADC with passive loop filter.
16. The device according to claim 15 , wherein the passive loop filter comprises an RC filter circuit.
17. The device according to claim 13 , wherein the delay circuit comprises an all-pass filter.
18. The device according to claim 13 , wherein the second ADC circuit comprises a low-pass filter, an amplifier, and a CT Delta-Sigma ADC circuit.
19. The device according to claim 13 , wherein the DAC circuit and the first ADC circuit are configured for sampling at a same frequency.
20. The device according to claim 13 , wherein the first ADC circuit and the second ADC circuit are configured for sampling at a same frequency.