Integrated circuit comparators having improved input resolution and methods of operating same
View Patent ↗An integrated circuit comparator includes a pair of differential input transistors having gate terminals configured to receive a pair of differential input signals and a comparator output circuit electrically coupled to the pair of differential input transistors. A pair of differential offset compensation transistors are also provided. This pair of differential offset compensation transistors, which is electrically coupled to the pair of differential input transistors, has gate terminals that are configured to receive a pair of unequal dc offset voltages. The source and drain terminals of a first one of the pair of differential input transistors are electrically connected to corresponding source and drain terminals of a first one of the pair of differential offset compensation transistors and the source and drain terminals of a second one of the pair of differential input transistors are electrically connected to corresponding source and drain terminals of a second one of the pair of differential offset compensation transistors.
1. An integrated circuit comparator, comprising:
a pair of differential input transistors having gate terminals configured to receive a pair of differential input signals;
a comparator output circuit electrically coupled to said pair of differential input transistors; and
a pair of differential offset compensation transistors electrically coupled to said pair of differential input transistors, said pair of differential offset compensations transistors having gate terminals configured to receive a pair of unequal dc offset voltages;
wherein source and drain terminals of a first one of said pair of differential input transistors are directly connected to corresponding source and drain terminals of a first one of said pair of differential offset compensation transistors; and
wherein source and drain terminals of a second one of said pair of differential input transistors are directly connected to corresponding source and drain terminals of a second one of said pair of differential offset compensation transistors.
2. The comparator of claim 1 , further comprising a control circuit configured to generate the pair of unequal dc offset voltages.
3. The comparator of claim 2 , wherein the control circuit is configured so that a dc common voltage associated with the pair of unequal dc offset voltages is equivalent to a dc common voltage associated with the pair of differential input signals.
4. The comparator of claim 2 , wherein said control circuit is configured to short the gate terminals of said pair of differential input transistors together during a comparator calibration operation.
5. The comparator of claim 4 , wherein said control circuit is further configured to adjust at least one of the pair of unequal dc offset voltages at least once during the comparator calibration operation.
6. The comparator of claim 5 , wherein said control circuit is further configured to measure a differential output of said comparator output circuit during the comparator calibration operation.
7. The comparator of claim 6 , wherein said control circuit is further configured to repeatedly adjust the at least one of the pair of unequal dc offset voltages until a dither is detected at the differential output of said comparator output circuit, during the comparator calibration operation.
8. The comparator of claim 1 , wherein said pair of differential input transistors are equivalently sized; wherein said pair of differential offset compensation transistors are equivalently sized; and wherein said pair of differential offset compensation transistors are smaller than said pair of differential input transistors.
9. An integrated circuit comparator, comprising:
a pair of differential input transistors having gate terminals configured to receive a pair of differential input signals;
a comparator output circuit electrically coupled to said pair of differential input transistors;
a pair of differential offset compensation transistors electrically coupled to said pair of differential input transistors, said pair of differential offset compensations transistors having gate terminals configured to receive a pair of unequal dc offset voltages; and
a control circuit comprising a finite state machine, said control circuit configured to:
generate the pair of unequal dc offset voltages;
short the gate terminals of said pair of differential input transistors together during a comparator calibration operation;
adjust at least one of the pair of unequal dc offset voltages at least once during the comparator calibration operation;
measure a differential output of said comparator output circuit during the comparator calibration operation; and
repeatedly adjust the at least one of the pair of unequal dc offset voltages until a dither is detected at the differential output of said comparator output circuit, during the comparator calibration operation.
10. The comparator of claim 9 ,
wherein source and drain terminals of a first one of said pair of differential input transistors are electrically connected to corresponding source and drain terminals of a first one of said pair of differential offset compensation transistors; and
wherein source and drain terminals of a second one of said pair of differential input transistors are electrically connected to corresponding source and drain terminals of a second one of said pair of differential offset compensation transistors.
11. An integrated circuit comparator, comprising:
a pair of differential input transistors having gate terminals configured to receive a pair of differential input signals;
a comparator output circuit electrically coupled to said pair of differential input transistors;
a pair of differential offset compensation transistors electrically coupled in parallel with said pair of differential input transistors so that source and drain terminals of a first one of said pair of differential input transistors are electrically connected to source and drain terminals of a first one of said pair of differential offset compensation transistors and source and drain terminals of a second one of said pair of differential input transistors are electrically connected to source and drain terminals of a second one of said pair of differential offset compensation transistors, said pair of differential offset compensations transistors having gate terminals configured to receive a pair of dc offset voltages; and
a control circuit configured to generate the pair of dc offset voltages at levels set during a comparator calibration operation that comprises measuring a differential voltage signal at an output of said comparator output circuit while the gate terminals of said pair of differential input transistors are receiving an equivalent signal.
12. The comparator of claim 11 , wherein said control circuit is configured to short the gate terminals of said pair of differential input transistors together during the comparator calibration operation.
13. The comparator of claim 11 , wherein said control circuit comprises a dc offset voltage generator having a resistor ladder therein.
14. The comparator of claim 11 , wherein said pair of differential input transistors are equivalently sized; wherein said pair of differential offset compensation transistors are equivalently sized; and wherein said pair of differential offset compensation transistors are smaller than said pair of differential input transistors.