RF pre-amplifiers and power amplifiers
View Patent ↗An RF amplifier circuit includes a MOSFET connected to an RF output of the circuit via an impedance matching network including an inductor and a tuning capacitor connected in parallel with the inductor and the MOSFET. DC voltage is applied to the MOSFET via a series path through a radio frequency choke and the inductor of the impedance matching network.
1. An RF amplifier circuit comprising:
a transistor arranged to receive an RF input to be amplified, the RF input having an operating frequency;
an impedance matching network including a first inductor connected in series between the transistor and an RF output of the circuit and a tuning capacitor connected in parallel with the transistor and the first inductor;
a source of DC voltage supplied to the circuit between the first inductor and the RF output; and
a second inductor connected between the DC voltage source and the amplifier circuit between the first inductor and the tuning capacitor and functioning as an RF choke, wherein the capacitive value of the tuning capacitor is selected to be in resonance with the second inductor at the operating frequency of the RF input.
2. The RF amplifier circuit of claim 1 , further including a bypass capacitor connected on one side thereof between the DC voltage source and the second inductor.
3. The RF amplifier circuit of claim 2 , wherein the bypass capacitor is connected on the opposite side thereof to ground.
4. The RF amplifier circuit of claim 1 , further including a coupling capacitor connected between the first inductor and the RF output.
5. The RF amplifier circuit of claim 1 , wherein the RF input is at a predetermined frequency, the transistor has a predetermined output impedance and the amplifier output has a predetermined load impedance different from the transistor impedance, and wherein the capacitive value of the tuning capacitor is selected cooperative with the inductance value of the first inductor to match output impedance of the transistor to the amplifier load impedance and to resonate with the second inductor at about the predetermined frequency.
6. The RF Amplifier circuit of claim 5 , wherein the frequency is 81 MHz, the transistor output impedance is 12 Ohms, the load impedance is 50 Ohms, the inductance of the first inductor is 42.1 nHy, the inductance of the second inductor is 100 nHy, and the capacitance of the tuning capacitor is 108.5 pF.
7. An RF amplifier circuit comprising:
a transistor arranged to receive an RF input to be amplified, the RF input having an operating frequency;
an impedance matching network including a first inductor connected in series between the transistor and an RF output of the circuit and a tuning capacitor connected in parallel with the transistor and the first inductor;
a coupling capacitor connected in series with the first inductor between the first inductor and the RF output;
a second inductor, wherein the capacitive value of the tuning capacitor is selected to be in resonance with the second inductor at the operating frequency of the RF input;
a source of DC voltage supplied to the circuit via the second inductor between the first inductor and the coupling capacitor, the second inductor functioning as an RF choke; and
a bypass capacitor connected on one side thereof between the second inductor and the DC voltage source and on an opposite side thereof to ground.
8. The RF amplifier circuit of claim 7 , wherein the RF input is at a predetermined frequency, the transistor has a predetermined output impedance and the amplifier output has a predetermined load impedance different from the transistor impedance, and wherein the capacitive value of the tuning capacitor is selected cooperative with the inductance value of the first inductor to match the output impedance of the transistor to the amplifier load impedance and to resonate with the second inductor at about the predetermined frequency.
9. The RF Amplifier circuit of claim 8 , wherein the frequency is 81 MHz, the transistor output impedance is 12 Ohms, the load impedance is 50 Ohms, the inductance of the first inductor is 42.1 nHy, the inductance of the second inductor is 100 nHy, and the capacitance of the tuning capacitor is 108.5 pF.
10. An amplifier circuit for amplifying an RF input having an input frequency, comprising:
a MOSFET having a gate, and arranged to receive at the gate the RF input to be amplified, the MOSFET having an output impedance;
an impedance matching network for matching the output impedance of the MOSFET to a load impedance of the amplifier, the impedance matching network including a first inductor connected in series between the drain of the MOSFET and an RF output of the circuit and a tuning capacitor connected in parallel with the MOSFET and the first inductor;
a coupling capacitor connected in series with the first inductor between the first inductor and the RF output;
a second inductor;
a source of DC voltage supplied to the MOSFET via the second inductor and the first inductor, the second inductor functioning as an RF choke; and
wherein the capacitive value of the tuning capacitor is selected cooperative with the inductance value of the first inductor to maximize, at the input frequency, the transmission of RF output of the MOSFET to the RF output of the amplifier, and to resonate with the second inductor at about the input frequency.
11. The RF amplifier circuit of claim 10 , wherein the MOSFET is an n-channel MOSFET and the DC voltage is supplied to the drain of the MOSFET.