Measuring system and method

1. A measuring system, comprising

a pulse generator for providing pulse signals with different voltage levels;

an under test device coupled to the pulse generator to receive the pulse signals;

a variable resistor coupled to the under test device and adjusted its resistance value according to a control signal;

a detecting control system detecting voltage ringing ranges of a first terminal of the under test device at different resistance value and generating the control signal to adjust the resistance value of the variable resistor according to the voltage ringing ranges.

2. The measuring system as claimed in claim 1 , wherein the voltage ringing range is a voltage difference between a first sub-peak and a second sub-peak at the first terminal.

3. The measuring system as claimed in claim 1 , wherein the detecting control system adjusts its resistance value so that a ratio of a first voltage ringing range to a second voltage ringing range is smaller than a specific value.

4. The measuring system as claimed in claim 3 , wherein when the ratio is smaller than the specific value, the detecting control system detects whether leakage currents occur at a second terminal of the under test device.

5. The measuring system as claimed in claim 4 , wherein when the detecting control system detects no leakage current at the under test device, the pulse generator increases voltage levels of the pulse signal until the detecting control system detects the leakage current flowed from the under test device.

6. The measuring system as claimed in claim 1 , wherein the pulse generator comprises:

a power supply for providing a dc voltage;

a first transmission line with a characteristic impedance;

a diode coupled between the first transmission line and a resistor;

a second transmission line with the characteristic impedance; and

a switch device comprising a first terminal coupled to the first transmission line and a second terminal and coupling the second terminal to the second transmission line or the power supply according to a switch signal.

7. The measuring system as claimed in claim 1 , wherein the variable resistor is a voltage variable resistor.

8. The measuring system as claimed in claim 1 , wherein the variable resistor and the under test device are coupled in parallel.

9. The measuring system as claimed in claim 1 , wherein the measuring system is applied for a liquid crystal display.

10. A measuring method, comprising:

generating a pulse signal to an under test device and a variable resistor, wherein the variable resistor adjusted its resistance value according to a control signal;

detecting voltage ringing ranges of a first terminal of the under test device at the different resistance values;

generating the control signal to adjust the resistance values of the variable resistor according to the voltage ringing ranges so that a ratio of a first voltage ringing range to a second voltage ringing range is smaller than a specific value.

11. The measuring method as claimed in claim 10 , wherein the voltage ringing range is a voltage difference between a first sub-peak and a second sub-peak at the first terminal.

12. The measuring method as claimed in claim 10 , wherein when the ratio is smaller than the specific value, a detecting control system detects whether leakage currents occur at a second terminal of the under test device.

13. The measuring method as claimed in claim 12 , wherein when the detecting control system detects no leakage current at the under test device, the pulse generator increases voltage levels of the pulse signal until the detecting control system detects the leakage current flowed from the under test device.

14. The measuring method as claimed in claim 10 , wherein the variable resistor is a voltage variable resistor.

15. The measuring method as claimed in claim 10 , wherein the variable resistor and the under test device are coupled in parallel.

16. The measuring method as claimed in claim 10 , wherein the measuring method is applied for a liquid crystal display.