TRANSMITTER AND RECEIVER

摘要

When a load of an antenna changes instantaneously, a cellular phone detects the load change in real time and compensates for it. The characteristic curv es of power efficiency and gain of a power amplifier are drawn together on a Smith chart beforehead. The range of the operating points of the amplifier i s estimated on the Smith chart from the results of measurements of the current and gain of the amplifier. The direction and level of the change in the inpu t impedance of the amplifier is determined using impedance information contain ed in the Smith chart. The change is compensated for by controlling a variable- load circuit.