High speed SAR ADC using comparator output triggered binary-search timing scheme and bit-dependent DAC settling
A method of increasing SAR ADC conversion rate and reducing power consumption by employing a new timing scheme and minimizing timing delay for each bit-test during binary-search process. The high frequency clock input requirement is eliminated and higher speed rate can be achieved in SAR ADC.
1. A finite-state machine for binary-search process to eliminate a high frequency clock input for a SAR (Successive Approximation Register) data converter, comprising:
a comparison state with a comparator-enable signal enables a comparator to compare an input voltage difference (EN_COMP) and a comparison-complete signal representing completion of a comparison (COMP_UPDATE);
a data settling state until COMP_UPDATE clears EN_COMP, and then COMP_UPDATE is de-asserted; and
a data conversion complete state.
2. A finite-state machine of claim 1 , wherein the signals EN_COMP and COMP_UPDATE represent different states and define state transition.
3. A comparator triggered binary-search timing circuit, comprising:
a flip-flop;
a sample trigger circuit coupled to the flip-flop;
a bit-test trigger circuit coupled to the flip-flop;
a clear logic coupled to the flip-flop; and
a comparator forming a closed loop with the flip-flop to enable conversion.
4. The comparator triggered binary-search timing circuit of claim 3 , wherein flip-flop is asserted either by the sample pulse through sample trigger path or by the comparator output through bit-test trigger path Sample trigger and bit-test trigger consist of timing delay elements.
5. The comparator triggered binary-search timing circuit of claim 3 , wherein the comparator output signal is connected to Clear logic to clears flip-flop, and flip-flop output is connected back to comparator to enable the start of the comparison Clear logic consists of timing delay element.
6. The comparator triggered binary-search timing circuit of claim 3 , wherein bit-test trigger timing delay is bit-dependent with respect to the corresponding DAC bit capacitor values to minimize the conversion time during binary-search process.
7. The comparator triggered binary-search timing circuit of claim 6 , comprising a multiplexer to select different timing delay for different bit-test during a binary-search to reduce conversion time.
8. The comparator triggered binary-search timing circuit of claim 6 , comprising a counter to select individual optimized delay for each bit to reduce timing delay during a SAR binary-search for fast conversion.
9. The comparator triggered binary-search timing circuit of claim 6 , comprising a delay element with programmed timing based on Process, Voltage and Temperature (PVT) to optimize data converter performance over PVT corners.
10. A method of eliminating high frequency clock input in a SAR (Successive Approximation Register) data converter, comprising:
triggering a flip-flop with a delayed sample pulse from a comparator;
triggering the flip-flop with a delayed bit-test pulse from the comparator;
clearing the flip-flop with a delayed pulse from a comparator output;
starting comparison with the flip-flop; and
forming a closed loop configuration with delay elements in the loop.
11. The method of claim 10 , wherein the sample trigger, bit-test trigger and clear logic includes delay elements to control timing delay.
12. The method of claim 10 , wherein the flip-flop is asserted either by the sample pulse through sample trigger path or by the comparator output through bit-test trigger path, and wherein the flip-flop is cleared through Clear logic path.
13. The method of claim 10 , wherein the bit-test trigger timing delay is bit-dependent with respect to a corresponding data converter bit capacitor values to minimize conversion time during a binary-search.
14. The method of claim 13 , comprising selecting different timing delay with a multiplexer for different bit-test during binary-search to reduce conversion time.
15. The method of claim 13 , comprising selecting individual optimized delay with respect to each bit with a counter to reduce timing delay during SAR binary-search process.
16. The method of claim 13 , comprising programming the timing delay of a delay element based on Process, Voltage and Temperature (PVT) to optimize data converter performance over PVT corners.