Attenuator

1. An attenuator comprising:

a first diode having an anode and a cathode that are connected to an input terminal and an output terminal, respectively;

a first control voltage terminal connected to said anode of said first diode;

a first capacitance;

a second diode having an anode and a cathode, said anode being connected to said cathode of said first diode, said cathode of said second diode being connected to said anode of said first diode through said first capacitance;

a first resistance connected at a first end to said cathode of said second diode;

a second capacitance;

a second resistance connected at a first end to said cathode of said first diode through said second capacitance;

a third capacitance;

a third diode having an anode and a cathode, said anode being connected to second ends of said first and second resistances through said third capacitance;

a fourth capacitance;

a fourth diode having an anode and a cathode, said cathode being connected to said second ends of said first and second resistances through said fourth capacitance;

a fifth capacitance connected at a first end to said cathode of said third diode and to said anode of said fourth diode, a second end of said fifth capacitance being grounded;

a second control voltage terminal connected to said cathode of said second diode;

a third control voltage terminal connected to said anode of said third diode;

a fourth control voltage terminal connected to said cathode of said fourth diode; and

a linearizer provided between said input terminal and said anode of said first diode, wherein said linearizer linearizes a signal input to said input terminal only when low level voltages are applied to said first and fourth control voltage terminals at the same time that high level voltages are applied to said second and third control voltage terminals.

2. The attenuator as claimed in claim 1 , wherein said linearizer includes:

a fifth control voltage terminal;

a fifth diode having an anode and a cathode, said anode being grounded, said cathode being connected to a connection point between said input terminal and said anode of said first diode; and

a third resistance connected between said fifth control voltage terminal and said connection point between said input terminal and said anode of said first diode, wherein a low level voltage is applied to said fifth control voltage terminal only when low level voltages are applied to said first and fourth control voltage terminals at the same time that high level voltages are applied to said second and third control voltage terminals.

3. The attenuator as claimed in claim 2 , wherein said linearizer further includes a fourth resistance connected between said fifth diode and said connection point between said input terminal and said anode of said first diode.

4. The attenuator as claimed in claim 3 , wherein said linearizer further includes a sixth diode having an anode and a cathode, said anode being grounded, said cathode being connected to said anode of said fifth diode.

5. The attenuator as claimed in claim 1 , further comprising a sixth capacitance connected between said anode of said first diode and a connection point between said first capacitance and said input terminal.

6. The attenuator as claimed in claim 1 , wherein said first capacitance is a variable capacitance.

7. The attenuator as claimed in claim 1 , further comprising an inductor connected in series to said first capacitances, between said cathode of said second diode and said anode of said first diode, said inductor series-resonating with said first capacitance.

8. The attenuator as claimed in claim 1 , further comprising an inductor connected in parallel with said first and second diodes, said inductor parallel-resonating with junction capacitances of said first and second diodes and said first capacitance.

9. The attenuator as claimed in claim 1 , including a seventh capacitances, wherein said first end of said first resistance is connected to said cathode of said second diode through said seventh capacitance.