Calibration circuit
View Patent ↗To include a first replica buffer that has substantially the same circuit configuration as a pull-up circuit which constitutes an output buffer and a second replica buffer that has substantially the same circuit configuration as a pull-down circuit which constitutes the output buffer. When a first calibration command ZQCS is issued, both a control signal ACT 1 and ACT 2 is activated, and a calibration operation is performed for both the first replica buffer and the second replica buffer in parallel.
1. A calibration circuit for adjusting impedance of an output buffer having a pull-up circuit and a pull-down circuit, the calibration circuit comprising:
a first replica buffer that has substantially the same circuit configuration as one of the pull-up circuit and the pull-down circuit; and
a second replica buffer that has substantially the same circuit configuration as the other of the pull-up circuit and the pull-down circuit,
wherein a calibration operation for the first replica buffer and a calibration operation for the second replica buffer are performed in parallel, in response to a first calibration command.
2. The calibration circuit as claimed in claim 1 , wherein the calibration operation for the second replica buffer is performed based on adjacent impedance of the first replica buffer.
3. The calibration circuit as claimed in claim 1 , wherein in response to a second calibration command the calibration operation for the first replica buffer is performed and then the calibration operation for the second replica buffer is performed.
4. The calibration circuit as claimed in claim 3 , wherein a calibration period specified by the first calibration command is shorter than a calibration period specified by the second calibration command.
5. The calibration circuit as claimed in claim 1 , further comprising a counter for adjusting impedance of each of the first and the second replica buffers, wherein the counter performs operations in synchronization with an internal clock whose frequency is lower than that of an external clock.
6. The calibration circuit as claimed in claim 1 , further comprising a third replica buffer that has substantially the same circuit configuration as the first replica buffer and is set to have substantially the same impedance as the first replica buffer, and
wherein the calibration operation for the first replica buffer is performed based on a potential between the first replica buffer and an external resistor, and the calibration operation for the second replica buffer is performed based on a potential between the second replica buffer and the third replica buffer.
7. A data processing system comprising a semiconductor device including an output buffer having a pull-up circuit and a pull-down circuit and a calibration circuit for adjusting impedance of the output buffer, and I/O device being connected to the semiconductor device via a data bus, wherein the calibration circuit includes:
a first replica buffer that has substantially the same circuit configuration as one of the pull-up circuit and the pull-down circuit; and
a second replica buffer that has substantially the same circuit configuration as the other of the pull-up circuit and the pull-down circuit,
wherein a calibration operation for the first replica buffer and a calibration operation for the second replica buffer are performed in parallel, in response to a first calibration command.
8. The data processing system as claimed in claim 7 , wherein the calibration operation for the second replica buffer is performed based on adjacent impedance of the first replica buffer.
9. The data processing system as claimed in claim 7 , wherein in response to a second calibration command the calibration operation for the first replica buffer is performed and then the calibration operation for the second replica buffer is performed.
10. The data processing system as claimed in claim 7 , wherein a calibration period specified by the first calibration command is shorter than a calibration period specified by the second calibration command.
11. The data processing system as claimed in claim 7 , further comprising a counter for adjusting impedance of each of the first and the second replica buffers, wherein the counter performs operations in synchronization with an internal clock whose frequency is lower than that of an external clock.
12. The data processing system as claimed in claim 7 , further comprising a third replica buffer that has substantially the same circuit configuration as the first replica buffer and is set to have substantially the same impedance as the first replica buffer, and
wherein the calibration operation for the first replica buffer is performed based on a potential between the first replica buffer and an external resistor, and the calibration operation for the second replica buffer is performed based on a potential between the second replica buffer and the third replica buffer.
13. A semiconductor device comprising a calibration circuit, wherein the calibration circuit includes:
an output buffer that has a plurality of P-channel transistors connected in parallel and a plurality of N-channel MOS transistors connected in parallel;
a first replica buffer that has a plurality of P-channel transistors connected in parallel:
a second replica buffer that has a plurality of N-channel transistors connected in parallel:
a first counter in which a count value thereof is updated in synchronization with a first control signal, an impedance of the first replica buffer being controlled based on the count value of the first counter by selecting one or more P-channel transistors to be turned on among the P-channel transistors included in the first replica buffer:
a second counter in which a count value thereof is updated in synchronization with a second control signal, an impedance of the second replica buffer being controlled based on the count value of the second counter by selecting one or more N-channel transistors to be turned on among the N-channel transistors included in the second replica buffer:
a pre-stage circuit that sets an impedance of the output buffer based on the count values of the first counter and the second counter: and
a control signal generating circuit that activates the first and second control signals simultaneously in response to a first calibration command so that a calibration operation for the first replica buffer and a calibration operation for the second replica buffer is performed simultaneously.
14. The semiconductor device as claimed in claim 13 , wherein the calibration operation for the second replica buffer is performed based on a relationship between latest impedance of the first replica buffer and the impedance the second replica buffer.
15. The semiconductor device as claimed in claim 13 , wherein the control signal generating circuit activates the first control signal in response to a second calibration command so that the calibration operation for the first replica buffer using the first counter is performed and then activates the second control signal so that the calibration operation for the second replica buffer using the second counter is performed.
16. The semiconductor device as claimed in claim 15 , wherein a calibration period specified by the first calibration command is shorter than a calibration period specified by the second calibration command.
17. The semiconductor device as claimed in claim 13 , wherein frequency of the first and second control signals are lower than that of an external clock.
18. The semiconductor device as claimed in claim 13 , wherein the calibration circuit further includes a third replica buffer that has substantially the same circuit configuration as the first replica buffer and is set to have substantially the same impedance as the first replica buffer, and
the calibration operation for the first replica buffer is performed based on a potential between the first replica buffer and an external resistor, and the calibration operation for the second replica buffer is performed based on a potential between the second replica buffer and the third replica buffer.