Offset-voltage calibration circuit

1. An offset-voltage calibration circuit comprising:

a comparator configured to receive at least two comparison voltages and output a result of a comparison between the comparison voltages;

an up/down counter (UDC) configured to output an up-counting or down-counting output signal in response to an output signal of the comparator; and

a current digital-to-analog converter (DAC) configured to control an amount of current supplied from a node to which each of the comparison voltages is applied, in response to an output signal of the UDC, and control a magnitude of each of the comparison voltages,

wherein the current DAC comprises first and second current DACs, and

wherein the first and second current DACs selectively operate in response to the output signal of the UDC.

2. The circuit of claim 1 , further comprising a DAC disposed at a front end of the comparator,

wherein the comparator receives an output signal of the DAC as an input signal.

3. The circuit of claim 2 , further comprising a switch configured to apply a common-mode voltage to input terminals of the comparator and those of the DAC to enable an offset-voltage calibration mode.

4. The circuit of claim 1 , wherein the comparator comprises a pre-amplifier and a latch, which are coupled in cascade, and

wherein an output voltage of the pre-amplifier is mirrored and applied to an input terminal of the latch.

5. The circuit of claim 4 , wherein the current DAC controls current applied to the latch by controlling the amount of current supplied from the node to which each of the comparison voltages is applied.

6. The circuit of claim 4 , wherein the input terminal of the latch corresponds to the node to which each of the comparison voltages is applied.

7. The circuit of claim 1 , wherein the current DAC controls the amount of current supplied from the node to which each of the comparison voltages is applied to equalize the at least two comparison voltages to each other.

8. The circuit of claim 1 , wherein each of the first and second current DACs comprises one or more switches, and the amount of current supplied from the node to which each of the comparison voltages is applied depends on the number of turned-on switches among the switches.

9. The circuit of claim 8 , wherein each of the first and second current DACs further comprises a variable current source configured to supply current to the switches.

10. The circuit of claim 1 , further comprising a thermometer logic (TL) disposed between the UDC and the current DAC and configured to allow a state of the current DAC to be sequentially changed in response to the output signal of the UDC.

11. The circuit of claim 1 , wherein the comparator is configured to receive first and second comparison voltages,

wherein the first current DAC is configured to control an amount of current supplied from a first node to which the first comparison voltage is applied, in response to the output signal of the UDC, thereby controlling a magnitude of the first comparison voltage, and

wherein the second current DAC is configured to control an amount of current supplied from a second node to which the second comparison voltage is applied, in response to the output signal of the UDC, thereby controlling a magnitude of the second comparison voltage.

12. The circuit of claim 1 , wherein the output signal of the UDC includes a plurality of bits,

wherein the first current DAC operates when an most significant bit (MSB) of the plurality of bits is a first value, and

wherein the second current DAC operates when the MSB of the plurality of bits is a second value.

13. An offset-voltage calibration circuit, comprising:

a comparator configured to receive at least two comparison voltages and output a result of a comparison between the comparison voltages;

an up/down counter (UDC) configured to output an up-counting or down-counting output signal in response to an output signal of the comparator;

a current digital-to-analog converter (DAC) configured to control an amount of current supplied from a node to which each of the comparison voltages is applied, in response to an output signal of the UDC, and control a magnitude of each of the comparison voltages; and

a thermometer logic (TL) disposed between the UDC and the current DAC and configured to allow a state of the current DAC to be sequentially changed in response to the output signal of the UDC.

14. The circuit of claim 13 , wherein the current DAC comprises two current DACs, and

wherein only one of the two current DACs operates in response to the output signal of the UDC.

15. The circuit of claim 13 , further comprising a DAC disposed at a front end of the comparator,

wherein the comparator receives an output signal of the DAC as an input signal.

16. The circuit of claim 15 , further comprising a switch configured to apply a common-mode voltage to input terminals of the comparator and those of the DAC to enable an offset-voltage calibration mode.

17. The circuit of claim 13 , wherein the comparator comprises a pre-amplifier and a latch, which are coupled in cascade, and

wherein an output voltage of the pre-amplifier is mirrored and applied to an input terminal of the latch.

18. The circuit of claim 17 , wherein the current DAC controls current applied to the latch by controlling the amount of current supplied from the node to which each of the comparison voltages is applied.

19. The circuit of claim 13 , wherein the current DAC controls the amount of current supplied from the node to which each of the comparison voltages is applied to equalize the at least two comparison voltages to each other.

20. The circuit of claim 13 , wherein each of the first and second current DACs comprises one or more switches, and the amount of current supplied from the node to which each of the comparison voltages is applied depends on the number of turned-on switches among the switches.