High frequency amplifier configuration for improved feedback capacitance neutralization

1. A high frequency amplifier comprising:

an input terminal receiving a high frequency signal;

an output terminal;

a three-terminal active element having a first terminal connected with said input terminal and a second terminal connected with said output terminal, said three-terminal active element outputting an output signal from said output terminal in response to said high frequency signal;

a transmission line; and

a capacitive structure,

wherein said transmission line and said capacitive structure are connected in series between said first and output terminals, and operate together as a series resonance circuit, and

said transmission line functions as an open stub at a series resonance frequency of said series resonance circuit.

2. The high frequency amplifier according to claim 1 , wherein a length of said transmission line is equal to λ×(¼)×(2n−1), where λ is a propagation wavelength at said series resonance frequency, and n is a natural number.

3. The high frequency amplifier according to claim 1 , wherein said transmission line and said capacitive structure neutralize a feedback capacitance of said three-terminal active element at an operation frequency of said high frequency amplifier.

4. The high frequency amplifier according to claim 3 , wherein said length of said transmission line is equal to or longer than one fourth of a propagation wavelength at said operation frequency.

5. The high frequency amplifier according to claim 1 , wherein said transmission line reduces an absolute value of a reflection coefficient on said input terminal down to one or less at said series resonance frequency.

6. The high frequency amplifier according to claim 1 , wherein said transmission line has a first end connected with said input terminal and a second end connected with said output terminal through said capacitive structure.

7. The high frequency amplifier according to claim 6 , wherein said capacitive structure is formed as a coupling capacitance between said transmission line and a signal line connected between said second terminal and said output terminal.

8. The high frequency amplifier according to claim 1 , wherein said transmission line reduces an absolute value of a reflection coefficient on said output terminal down to one or less at said series resonance frequency.

9. The high frequency amplifier according to claim 1 , wherein said transmission line has a first end connected with said output terminal,

a portion of said transmission line operates as a coupled transmission line together with a signal line connected between said input terminal and said first terminal of said three-terminal active element.

10. The high frequency amplifier according to claim 1 , further comprising an additional transmission line having an end connected with said output terminal, wherein said transmission line has a first end connected with said input terminal and a second end connected with said output terminal through said capacitive structure, and

a portion of said additional transmission line operates as a coupled transmission line together with a signal line connected between said input terminal and said first terminal of said three-terminal active element.

11. The high frequency amplifier according to claim 1 , wherein said transmission line includes a micro strip line.

12. The high frequency amplifier according to claim 1 , wherein said transmission line includes a coplanar waveguide.

13. The high frequency amplifier according to claim 1 , wherein said three-terminal active element includes a field effect transistor having a gate connected with said input terminal and a drain connected with said output terminal.

14. The high frequency amplifier according to claim 1 , wherein said three-terminal active element includes a bipolar transistor having a base connected with said input terminal and a collector connected with said output terminal.