Impedance matching circuit and related method thereof

1. An impedance matching circuit, comprising:

an input terminal, for receiving an input signal;

a variable impedance unit, coupled to the input terminal, having an equivalent impedance for providing an input impedance at the input terminal;

a signal quality evaluating unit, coupled to the input terminal, for evaluating a signal quality of the input signal; and

a control unit coupled to the variable impedance unit and the signal quality evaluating unit, for outputting a control signal according to an evaluating result of the signal quality evaluating unit to adjust the equivalent impedance of the variable impedance unit, wherein the control unit comprises:

a variable impedance device, having a first terminal and a second terminal, the first terminal coupled to a first predetermined potential;

a control device, coupled to the signal quality evaluating unit and the variable impedance device, for selling an impedance value of the variable impedance device according to the evaluating result;

a detecting unit, coupled to the second terminal, for providing the second terminal with a second predetermined potential to detect a current passing through the variable impedance device, and generating a plurality of reference voltages according to the current; and

a comparing unit, coupled to the detecting unit, for comparing the reference voltages to generate a comparing result, and outputting the control signal according to the comparing result to set the equivalent impedance of the variable impedance unit.

2. The impedance matching circuit of claim 1 , wherein the signal quality evaluating unit comprises:

a bit error rate detecting unit, for detecting a bit error rate of the input signal to evaluate the signal quality of the input signal.

3. The impedance matching circuit of claim 1 , wherein the signal quality evaluating unit comprises:

a cyclic redundancy check (CRC) detecting unit, for executing a CRC detection upon the input signal to evaluate the signal quality of the input signal.

4. The impedance matching circuit of claim 1 , wherein the signal quality evaluating unit comprises:

a voltage level detecting unit, for detecting a voltage level of the input signal to evaluate the signal quality of the input signal.

5. The impedance matching circuit of claim 1 , wherein the signal quality evaluating unit evaluates the signal quality of the input signal according to variations of a horizontal synchronization (Hsync) signal, a vertical synchronization (Vsync) signal, and a data enable signal.

6. The impedance matching circuit of claim 1 , wherein the control unit adjusts the equivalent impedance of the variable impedance unit by comparing the evaluating result with a threshold.

7. The impedance matching circuit of claim 1 , wherein the control unit adjusts the equivalent impedance of the variable impedance unit by outputting a plurality of candidate control signals, so as to generate a plurality of candidate impedance values, the signal quality evaluating unit evaluates a plurality of signal qualities corresponding to the candidate impedance values respectively to generate a plurality of signal quality results, and the control unit further selects a signal quality result which is larger than a threshold from the signal quality results to determine the control signal.

8. The impedance matching circuit of claim 1 , wherein the control device sets the variable impedance device corresponding to a plurality of candidate impedance values respectively, the signal quality evaluating unit evaluates a plurality of signal qualities corresponding to the candidate impedance values respectively to determine a plurality of signal quality results, and the control unit further selects a signal quality result which is larger than a threshold from the signal quality results to determine the control signal.

9. The impedance matching circuit of claim 1 , wherein the input terminal, the variable impedance unit, the signal quality evaluating unit, and the control unit are all positioned in a single chip.

10. An impedance matching method, comprising:

utilizing a variable impedance unit to provide an input impedance at an input terminal;

evaluating a signal quality of an input signal received by the input terminal; and

generating a control signal according to an evaluating result of the signal quality evaluation to adjust an equivalent impedance of the variable impedance unit comprising:

providing a variable impedance device, the variable impedance device having a first terminal and a second terminal, the first terminal coupled to a first predetermined potential;

setting an impedance value of the variable impedance device according to the evaluating result;

detecting a current passing through the variable impedance device, and generating a plurality of reference voltages according to the current;

comparing the reference voltages to generate a comparing result; and

outputting the control signal according to the comparing result to adjust the equivalent impedance of the variable impedance unit.

11. The impedance matching method of claim 10 , wherein the step of evaluating the signal quality comprises:

evaluating a bit error rate of the input signal to evaluate the signal quality of the input signal.

12. The impedance matching method of claim 10 , wherein the step of evaluating the signal quality comprises:

executing a cyclic redundancy check (CRC) detection upon the input signal to evaluate the signal quality of the input signal.

13. The impedance matching method of claim 10 , wherein the step of evaluating the signal quality comprises:

evaluating the signal quality of the input signal according to variations of an Hsync signal, a Vsync signal, and a data enable signal.

14. The impedance matching method of claim 10 , wherein the step of evaluating the signal quality comprises:

evaluating a voltage level of the input signal to evaluate the signal quality of the input signal.

15. The impedance matching method of claim 10 , further comprising:

comparing the evaluating result with a threshold to generate a comparing result; and

adjusting the equivalent impedance of the variable impedance unit according to the comparing result.

16. The impedance matching method of claim 10 , further comprising:

generating a plurality of candidate control signals to adjust the equivalent impedance of the variable impedance unit so as to generate a plurality of candidate impedance values;

evaluating a plurality of signal qualities corresponding to the candidate impedance values respectively to generate a plurality of signal quality results; and

selecting a signal quality result which is larger than a threshold from the signal quality results to determine the control signal.

17. The impedance matching method of claim 10 , wherein the step of generating the control signal comprises:

setting the variable impedance device to generate a plurality of candidate impedance values;

evaluating a plurality of signal qualities of the candidate impedance values respectively to determine a plurality of signal quality results; and

selecting a signal quality result which is larger than a threshold from the signal quality results to determine the control signal.

18. The impedance matching method of claim 10 , being applied in a display controller.