Circuit and method for controlling termination impedance
A calibration circuit that can prevent a calibration operation from being delayed by a dummy capacitor when the calibration circuit starts to operate includes a switch unit configured to connect a calibration node to a precharge node in response to an enable signal. The calibration node is connected to an external resistor. The calibration circuit also includes a code generation unit configured to generate a calibration code in response to a voltage of the calibration node and a reference voltage, a calibration resistor unit configured to drive the calibration node in response to the calibration code and turn-off when the code generation unit is disabled, and a precharge unit configured to precharge the precharge node to a predetermined voltage level when the code generation unit is disabled.
1. A calibration circuit, comprising:
a switch unit configured to connect a calibration node to a precharge node in response to an enable signal;
a code generation unit configured to generate a calibration code in response to a voltage of the calibration node and a reference voltage;
a calibration resistor unit configured to drive the calibration node in response to the calibration code and to turn-off if the code generation unit is disabled; and
a precharge unit configured to precharge the precharge node to a predetermined voltage level if the code generation unit is disabled.
2. The calibration circuit as recited in claim 1 , wherein the code generation unit stops generating the calibration code if the enable signal is deactivated.
3. The calibration circuit as recited in claim 1 , wherein the code generation unit includes:
a comparison unit configured to compare a voltage of the precharge node with the reference voltage in response to the enable signal;
a counting unit configured to increase or decrease the calibration code according to a comparison result of the comparison unit; and
a transfer unit configured to transfer the calibration code to the calibration resistor unit if the enable signal is activated, and to disable the calibration code and transfer the disabled calibration code to the calibration resistor unit if the enable signal is deactivated.
4. The calibration circuit as recited in claim 3 , wherein, if the enable signal is deactivated, the counting unit stops increasing and decreasing the calibration code and stores the calibration code.
5. The calibration circuit as recited in claim 1 , wherein the predetermined voltage level is equal to the level of the reference voltage.
6. The calibration circuit as recited in claim 1 , wherein the precharge unit includes a transistor configured to supply the predetermined voltage to the precharge node in response to the enable signal.
7. The calibration circuit as recited in claim 1 , wherein the predetermined voltage is generated by division of a power supply voltage.
8. An impedance matching circuit, comprising:
a code generation unit configured to generate a calibration code according to a voltage of the calibration node and a reference voltage, in response to an enable signal;
a calibration resistor unit configured to drive the calibration node in response to the calibration code and turn-off if the code generation unit is disabled; and
a driving unit configured to drive the calibration node to a predetermined voltage level if the enable signal is activated.
9. The impedance matching circuit as recited in claim 8 , wherein the code generation unit stops generating the calibration code if the enable signal is deactivated.
10. The impedance matching circuit as recited in claim 8 , wherein the code generation unit includes:
a comparison unit configured to compare a voltage of the calibration node with the reference voltage in response to the enable signal;
a counting unit configured to increase or decrease the calibration code according to a comparison result of the comparison unit; and
a transfer unit configured to transfer the calibration code to the calibration resistor unit if the enable signal is activated, and to disable the calibration code and transfer the disabled calibration code to the calibration resistor unit if the enable signal is deactivated.
11. The impedance matching circuit as recited in claim 10 , wherein, if the enable signal is deactivated, the counting unit stops increasing and decreasing the calibration code and stores the calibration code.
12. The impedance matching circuit as recited in claim 8 , wherein the predetermined voltage level is equal to the level of the reference voltage.
13. The impedance matching circuit as recited in claim 8 , wherein the driving unit includes:
a pulse generator configured to generate a pulse signal that is activated for a short time if the enable signal is activated; and
a voltage supplier configured to supply the predetermined voltage to the calibration node in response to the pulse signal.