Patent ID: 8823388

Claim:
A calibration circuit, comprising: a delay circuit, delaying an input signal to output an output signal, wherein a delay time between the input signal and the output signal is related to an equivalent capacitance and an equivalent resistance of the delay circuit; a phase detector, coupled to the delay circuit, comparing phases of the input signal and the output signal to obtain a comparison result; and a controller, coupled to the delay circuit and the phase detector, generating a control signal according to the comparison result of the phase detector to adjust the equivalent resistance of the delay circuit, wherein the delay circuit has a delay unit, and the delay unit comprises: a first variable resistor, coupled to a first system voltage, wherein a resistance of the first variable resistor is controlled by the control signal; a second variable resistor, coupled to the first system voltage, wherein a resistance of the second variable resistor is controlled by the control signal; a first capacitor, having a first end coupled to the first variable resistor for outputting a signal complementary to the input signal, and having a second end coupled to a second system voltage; a second capacitor, having a first end coupled to the second variable resistor for outputting the output signal, and having a second end coupled to the second system voltage; a first switch, having a first terminal coupled to the first variable resistor and the first end of the first capacitor, and having a control terminal for receiving the input signal; a second switch, having a first terminal coupled to the second variable resistor and the first end of the second capacitor, and having a control terminal for receiving the signal complementary to the input signal; and a current source, having a first terminal coupled to a second terminal of the first switch and a second terminal of the second switch, and having a second terminal coupled to the second system voltage.