Variable attenuator system and method

1. A variable attenuator comprising:

a first attenuator for attenuating a RF signal according to a fixed voltage;

a second attenuator connected in parallel to the first attenuator and attenuating the RF signal according to a control voltage for determining an attenuation mode; and

a first impedance matching unit for maintaining input/output impedance matching of the second attenuator,

wherein the second attenuator comprises:

a third capacitor connected in parallel to an input terminal of the first attenuator,

a first diode for attenuator the RF signal transmitted through the third capacitor, and

a second diode connected in parallel to an output terminal of the first attenuator.

2. The attenuator of claim 1 , further comprising:

a second impedance matching unit for maintaining input/output impedance matching of the first attenuator.

3. The attenuator of claim 1 , further comprising:

a first capacitor for removing serial current elements from an input RF signal and for providing the RF signal to the first attenuator; and

a second capacitor for removing serial current elements from an output signal of the first and second attenuators.

4. The attenuator of claim 1 , wherein the first attenuator comprises a diode.

5. The attenuator of claim 1 , wherein the fixed voltage is a power voltage divided by a certain level.

6. The attenuator of claim 1 , wherein the RF signal flows to the first attenuator in a low attenuation mode.

7. The attenuator of claim 1 , wherein the RF signal flows to the second attenuator in a high attenuation mode.

8. The attenuator of claim 1 , wherein the RF signal flows to the first and second attenuators in an intermediate attenuation mode.

9. The attenuator of claim 1 , wherein the second attenuator comprises a first and a second resistance means connected in serial between anodes of the first and second diodes.

10. The attenuator of claim 9 , wherein the second attenuator comprises a control voltage input terminal is provided between the first and second resistance means.

11. A variable attenuator comprising:

a first attenuator for attenuating a RF signal according to a first voltage;

a first impedance matching unit for maintaining impedance matching of the first attenuator in a low attenuation mode;

a second attenuator provided between input and output terminals of the first attenuator for attenuating the RF signal according to a control voltage for determining an attenuation mode,

wherein the second attenuator comprises:

a third capacitor connected in parallel to an input terminal of the first attenuator for cutting off a control voltage to the first attenuator;

a first diode for attenuating the RE signal transmitted through the third capacitor;

a second diode connected in parallel to an output terminal of the first attenuator; and

first and second resistance means corrected to anodes of the first and second diodes for applying the control voltage; and

a second impedance matching unit for maintaining input/output impedance matching of the second attenuator in a high attenuation mode,

wherein the second impedance matching unit comprises at least two resistors provided between the second attenuator and a ground connection.

12. The attenuator of claim 11 , wherein die first and second impedance matching units have the same resistance.

13. The attenuator of claim 11 , wherein the at least two resistors each have a resistance of 50Ω.

14. The attenuator of claim 11 , wherein the RF signal flows to the first attenuator in a low attenuation mode and flows to the second attenuator in a high attenuation mode.

15. The attenuator of claim 11 , wherein the RF signal flows to the first and second attenuators in an intermediate attenuation mode.

16. A variable attenuator comprising:

a first diode for attenuating a RF signal according to a first voltage;

a second diode, connected in parallel to an anode of the first diode for attenuating the RF signal, according to a control voltage;

a third diode connected in parallel to a cathode of the first diode for attenuating the RF signal, according to the control voltage;

a first resistor provided between a cathode of the second diode and a ground connection; and

a second resistor provided between a cathode of the third diode and the ground connection.

17. The attenuator of claim 16 , further comprising:

a capacitor connected to the anode of the first diode for cutting off a control voltage provided to the first diode.

18. The attenuator of claim 16 , further comprising:

third and fourth resistors for applying the control voltage to the anodes of the second and third diodes, respectively.

19. The attenuator of claim 16 , wherein the first and second resistors are approximately 50Ω.

20. The attenuator of claim 16 , wherein the RF signal flows to the first diode, in a low attenuation mode.

21. The attenuator of claim 16 , wherein the RF signal flows to the second and third diodes in a high attenuation mode.

22. The attenuator of claim 16 , wherein the RF signal flows to the first, second, and third diodes, in an intermediate attenuation mode.

23. A variable attenuator comprising:

a first attenuator for attenuating a RF signal according to a fixed voltage;

a second attenuator connected in parallel to the first attenuator and attenuating the RF signal according to a control voltage for determining an attenuation mode; and

a first impedance matching unit for maintaining input/output impedance matching of the second attenuator,

wherein the second attenuator comprises:

a first diode connected in parallel to an input terminal of the first attenuator; and

a second diode connected in parallel to an output terminal of the first attenuator

a third capacitor connected in parallel to an input terminal of the fist attenuator;

wherein the first diode attenuates the RF signal transmitted through the third capacitor.