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 curves 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 is 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 input impedance of the amplifier is determined using impedance information contained in the Smith chart. The change is compensated for by controlling a variable-load circuit.