Variable gain power amplifier
View Patent ↗A variable gain power amplifier includes a power amplifying unit and a signal generating unit. The power amplifying unit includes a control terminal, and a gain of the power amplifying unit is variable by a control signal provided through the control terminal. The signal generating unit generates the control signal to be provided to the control terminal. The signal generating unit includes a switching circuit to be turned on and off by a binary signal, a constant current source that generates a constant current, and a variable current source that generates a variable current. Also, the signal generating unit generates, when the switching circuit is on, a control signal of a magnitude that turns on the power amplifying unit and depends on a magnitude of a sum of the constant current and the variable current. When the switching circuit is off, the signal generating unit generates a control signal of a magnitude that turns off the power amplifying unit.
1. A variable gain power amplifier, comprising:
a power amplifying unit including a control terminal through which a control signal that varies a gain of said power amplifying unit is provided; and
a signal generating unit that generates said control signal to be provided to said control terminal,
wherein said signal generating unit comprises: a current mirror circuit, a constant current source that generates a constant current, and a variable current source that generates a variable current;
said variable current source comprises a variable resistance element;
said signal generating unit generates said control signal of a magnitude that turns on said power amplifying unit;
said control signal is a mirror current generated by said current mirror circuit based on a reference current of said current mirror circuit; and
said reference current of said mirror circuit is the sum of a positive current generated by said constant current source and a positive current generated by said variable current source; and
a magnitude of said positive current generated by said variable current source is controlled by said variable resistance element.
2. The variable gain power amplifier according to claim 1 , further comprising a switching circuit to be turned on and off by a binary signal,
wherein said switching circuit includes two transistors that constitute a differential pair with each other.
3. The variable gain power amplifier according to claim 1 ,
wherein said signal generating unit includes a bias circuit connected to a first end of a first resistance element, a second end of which is connected to said control terminal of said power amplifying unit; and
said bias circuit includes a diode connected to a ground via a second resistance element.
4. The variable gain power amplifier according to claim 3 , further comprising a switching circuit to be turned on and off by a binary signal,
said switching circuit is connected to said first end of said first resistance element via said current mirror circuit.
5. The variable gain power amplifier according to claim 1 ,
wherein said power amplifying unit includes a bipolar transistor; and
a base terminal of said bipolar transistor corresponds to said control terminal.
6. The variable gain power amplifier according to claim 2 ,
wherein said transistors are PNP-type transistors.