Amplifier circuit
An amplifier circuit includes: plural transistors; plural first transmission lines respectively connected between input terminals of the plural transistors; plural second transmission lines respectively connected between output terminals of the plural transistors; an input node connected to the input terminal of a first stage transistor among the plural transistors; an output node connected to the output terminal of a final stage transistor among the plural transistors; and a capacitance connected to the output terminal of the first stage transistor via a third transmission line.
1. An amplifier circuit comprising:
plural transistors;
plural first transmission lines respectively configured to be connected between input terminals of the plural transistors;
plural second transmission lines respectively configured to be connected between output terminals of the plural transistors;
an input node configured to be connected to the input terminal of a first stage transistor among the plural transistors;
an output node configured to be connected to the output terminal of a final stage transistor among the plural transistors; and
a capacitance configured to be connected to the output terminal of the first stage transistor via a third transmission line not passed through a terminating resistor,
wherein the third transmission line has a line length such that output signals of the plural transistors and a reflected wave become same phase.
2. The amplifier circuit according to claim 1 ,
wherein a line length of the third transmission line is 0.11 times or more and 0.18 times or less of a wavelength at a center frequency of a signal input to the input node.
3. The amplifier circuit according to claim 1 ,
wherein a reference terminal of each of the plural transistors is connected to a reference potential node, and
the capacitance is connected between the third transmission line and the reference potential node.
4. The amplifier circuit according to claim 1 ,
wherein the transistor is an n-channel field-effect transistor,
the input terminal of the transistor is a gate terminal of the n-channel field-effect transistor, and
the output terminal of the transistor is a drain terminal of the n-channel field-effect transistor.
5. The amplifier circuit according to claim 1 ,
wherein the transistor is a pnp bipolar transistor,
the input terminal of the transistor is a base terminal of the pnp bipolar transistor, and
the output terminal of the transistor is an emitter terminal of the pnp bipolar transistor.
6. The amplifier circuit according to claim 1 ,
wherein the capacitance is a variable capacitance.
7. The amplifier circuit according to claim 1 , further comprising:
a terminating resistor configured to be connected to the input terminal of the final stage transistor.
8. The amplifier circuit according to claim 1 , further comprising:
a bias power supply configured to be connected to the output terminal of the first stage transistor via the third transmission line.
9. The amplifier circuit according to claim 1 ,
wherein line widths of the plural second transmission lines become wider as they are near the output node.