High frequency power amplifier
View Patent ↗Provided is a compact high frequency power amplifier having a high degree of freedom of design with respect to a gain fluctuation immediately after start-up of an amplifier. The high frequency power amplifier includes a speed-up circuit that transiently increases a reference voltage during rise of a control voltage to increase an amount of bias supplied to an amplification transistor from a bias circuit. The speed-up circuit includes a capacitor and an overshoot control circuit. The overshoot control circuit determines an increasing amount of the reference voltage when the reference voltage is transiently increased according to a charge amount charged in the capacitor, and the overshoot control circuit also determines a time constant in charging and discharging the capacitor.
1. A high frequency power amplifier comprising:
a first transistor that performs power amplification of a high frequency signal;
a bias circuit that supplies a bias to the first transistor according to a reference voltage;
a power-supply circuit that applies the reference voltage to the bias circuit, the reference voltage controlling an amount of bias supplied to the first transistor from the bias circuit;
a control voltage terminal to which a control signal is applied, the control signal controlling start-up and stopping of the bias circuit; and
a speed-up circuit that increases the amount of bias supplied to the first transistor from the bias circuit by transiently increasing the reference voltage output from the power-supply circuit during rise of the control voltage,
wherein the speed-up circuit includes:
a capacitor in which one end is connected to the control voltage terminal;
a time-constant control circuit that is connected to the other end of the capacitor;
a discharge circuit that is connected in parallel with the capacitor; and
an overshoot control circuit that is connected to the time-constant control circuit and the power-supply circuit,
the overshoot control circuit determines an increasing amount of the reference voltage output from the power-supply circuit when the reference voltage is transiently increased according to a charge amount charged in the capacitor, and
the time-constant control circuit determines a time constant in charging and discharging the capacitor through the time-constant control circuit and the overshoot control circuit.
2. The high frequency power amplifier according to claim 1 , wherein
the bias circuit includes a second transistor that supplies a bias to the first transistor,
the overshoot control circuit includes a first resistor in which one end is grounded,
the time-constant control circuit includes;
a third transistor in which an emitter is grounded through the first resistor;
a second resistor in which one end is connected to a base of the third transistor; and
a fourth transistor in which an emitter is connected to the base of the third transistor through the second resistor while a collector is connected to a collector of the third transistor and a collector of the second transistor,
one end of the capacitor is connected to a base of the fourth transistor, and the other end is connected to the control voltage terminal,
the discharge circuit includes an FET, a gate of the FET is grounded, a source of the FET is connected to the base of the fourth transistor, and a drain of the FET is connected to the control voltage terminal,
the power-supply circuit includes a third resistor, one end of the third resistor is connected to the control voltage terminal, and the other end is connected to the base of the second transistor,
an emitter of the second transistor of the bias circuit is connected to a base of the first transistor, and
a base of the second transistor is grounded through the first resistor.
3. The high frequency power amplifier according to claim 1 , wherein
the bias circuit includes a first FET that supplies a bias to the first transistor,
the overshoot control circuit includes a first resistor in which one end is grounded,
the time-constant control circuit includes:
a third transistor in which an emitter is grounded through the first resistor;
a second resistor in which one end is connected to a base of the third transistor; and
a fourth transistor in which an emitter is connected to the base of the third transistor through the second resistor while a collector is connected to a collector of the third transistor and a drain of the first FET,
one end of the capacitor is connected to a base of the fourth transistor, and the other end is connected to the control voltage terminal,
the discharge circuit includes a second FET, a gate of the second FET is grounded, a source of the second FET is connected to the base of the fourth transistor, and a drain of the second FET is connected to the control voltage terminal,
the power-supply circuit includes a third resistor, one end of the third resistor is connected to the control voltage terminal, and the other end is connected to the first FET,
a source of the first FET of the bias circuit is connected to a base of the first transistor, and
a gate of the first FET is grounded through the first resistor.
4. The high frequency power amplifier according to claim 2 , wherein
the power-supply circuit includes:
a fifth transistor in which a collector is connected to the base of the second transistor while an emitter is grounded through the first resistor;
a fourth resistor in which one end is connected to a base of the fifth transistor while the other end is grounded; and
a sixth transistor, in which a collector is connected to a collector of the second transistor, a base is connected to the base of the second transistor, and an emitter is grounded through the fourth resistor.
5. The high frequency power amplifier according to claim 2 , wherein
the power-supply circuit further includes:
a fifth transistor in which a collector is connected to the base of the second transistor while a base is connected to the collector; and
a sixth transistor, in which a collector is connected to an emitter of the fifth transistor, a base is connected to the collector, and an emitter is connected to the other end of the first resistor, and
the third resistor, the fifth transistor, and the sixth transistor constitute a temperature compensation circuit that performs temperature compensation of the reference voltage.