Transmitter RF power control
View Patent ↗An electronic system for accurately controlling the RF output power from a power amplifier ( 21 ) is implemented using a multiplier ( 28 ) which multiplies the output power by itself to provide a DC component which is fed to a variable gain amplifier ( 29 ) which provides a controlling signal via a comparator ( 24 ) and an integrator ( 25 ) to the power amplifier. The transfer function between controlling signal and output power is substantially linear, even during dynamic variation of the controlling signal. The system is capable of a large dynamic range, and exhibits constant control loop bandwidth over this range. This is of particular use to TDMA applications with a large dynamic range of levelled output powers because a fixed filter function can be used to shape the transmitted burst.
1. An RF transmitter power control system having
an oscillator;
a power amplifier receiving the output of the oscillator as a first input, having a control input, and generating an output signal for passing to an antenna;
a sampling device for deriving a signal representative of the output signal;
a multiplier for multiplying the representative signal by itself to provide an output component which is linearly related to the representative signal;
a variable gain amplifier receiving the linear output component of the multiplier as a first input and having a variable control input as a control reference and an output;
a comparator for comparing the output of the variable gain amplifier with a reference and producing a difference signal; and
an integrator for integrating the difference signal and providing it as a control input to the power amplifier.
2. A system according to claim 1 , wherein the oscillator is a voltage controlled oscillator.
3. A system according to claim 1 , wherein the multiplier comprises an analogue multiplier.
4. A system according to claim 1 , wherein the multiplier comprises a Gilbert cell.
5. A system according to claim 1 , wherein the multiplier has a limiting amplifier input.
6. A system according to claim 1 , wherein the RF oscillator provides a local oscillator for the multiplier.
7. A system according to claim 1 , wherein the variable gain amplifier comprises a four quadrant multiplier.
8. An RF transmitter having a power control system according to claim 1 .
9. A cellular telephone handset having an RF transmitter according to claim 8 .