Semiconductor device and circuit protecting method

1. A semiconductor device, comprising:

a first transistor, arranged to generate an output signal according to a control signal; and

a clamping circuit including a second transistor and a resistive element, wherein the clamping circuit is arranged to generate the control signal according to an input signal, and to clamp the control signal to a predetermined signal level when the input signal exceeds the predetermined signal level, and wherein the resistive element is coupled between a gate terminal of the second transistor and a source terminal of the first transistor.

2. The semiconductor device of claim 1 , wherein the control signal is a voltage drop between a gate terminal of the first transistor and a source terminal of the first transistor, and the clamping circuit is arranged to clamp the control signal to the predetermined signal level when the input signal is higher than the predetermined signal level.

3. The semiconductor device of claim 1 , wherein the clamping circuit is arranged to clamp a gate current on a gate terminal of the first transistor to a predetermined current when the input signal is higher than the predetermined signal level.

4. The semiconductor device of claim 1 , wherein the first transistor has a first threshold voltage, and the second transistor has a second threshold voltage different from the first threshold voltage.

5. The semiconductor device of claim 4 , wherein the first threshold voltage and the second threshold voltage have different polarities.

6. The semiconductor device of claim 1 , wherein the first transistor is an enhancement-mode high-electron-mobility transistor (E-HEMT) and the second transistor is a depletion-mode high-electron-mobility transistor (D-HEMT).

7. The semiconductor device of claim 1 , wherein when the input signal exceeds the predetermined signal level, a first voltage drop between a gate terminal of the first transistor and a source terminal of the first transistor is higher than the first threshold voltage, and a second voltage drop between a gate terminal of the second transistor and a source terminal of the second transistor is smaller than the second threshold voltage.

8. The semiconductor device of claim 1 , wherein

a first connecting terminal of the second transistor is arranged to receive the input signal;

a second connecting terminal of the second transistor is arranged to couple to a gate terminal of the first transistor to output the control signal;

a first connecting terminal of the first transistor is arranged to output the output signal; and

a second connecting terminal of the first transistor is arranged to couple to a gate terminal of the second transistor.

9. The semiconductor device of claim 1 , wherein the resistive element is arranged to adjust the predetermined signal level.

10. The semiconductor device of claim 9 , wherein the resistive element is arranged to reduce the predetermined signal level.

11. The semiconductor device of claim 1 , wherein the first transistor and the clamping circuit are integrated onto a single chip.

12. The semiconductor device of claim 1 , wherein the resistive element is an adjustable resistor.

13. The semiconductor device of claim 1 , wherein the resistive element is a passive device.

14. A semiconductor device, comprising:

a first transistor, arranged to generate an output signal according to a control signal; and

a second transistor, arranged to clamp the control signal to a predetermined signal level;

wherein the predetermined signal level is based on a threshold voltage of the second transistor; and

wherein a first connecting terminal of the second transistor is arranged to receive an input signal;

a second connecting terminal of the second transistor is arranged to couple to a gate terminal of the first transistor to output the control signal;

a first connecting terminal of the first transistor is arranged to output the output signal; and

a second connecting terminal of the first transistor is arranged to couple to a gate terminal of the second transistor.

15. The semiconductor device of claim 14 , wherein when the second transistor clamps the control signal to the predetermined signal level, a voltage drop between the gate terminal of the second transistor and a source terminal of the second transistor is smaller than the threshold voltage.

16. The semiconductor device of claim 14 , further comprising:

a resistive element, arranged to adjust the predetermined signal level.

17. The semiconductor device of claim 16 , wherein the resistive element is coupled between the gate terminal of the second transistor and a source terminal of the first transistor.

18. The semiconductor device of claim 16 , wherein the resistive element is arranged to reduce the predetermined signal level.

19. A circuit protecting method, comprising:

providing a first transistor to generate an output signal according to a control signal;

providing a second transistor to generate the control signal according to an input signal;

providing a resistive element coupled between a gate terminal of the second transistor and a source terminal of the first transistor for adjusting the predetermined signal level; and

using the second transistor to clamp the control signal to a predetermined signal level when the input signal exceeds the predetermined signal level.

20. The circuit protecting method of claim 19 , wherein using the second transistor to clamp the control signal to the predetermined signal level when the input signal exceeds the predetermined signal level comprises:

controlling a voltage drop between the gate terminal of the second transistor and a source terminal of the second transistor to be smaller than the second threshold voltage when the input signal exceeds the predetermined signal level.