Reduction of mobile phone transmitter amplifier distortion due to output mismatch

摘要

The gate voltage bias of a transmitter output amplifier 1 is selected in dependence on the magnitude of the signal reflected from the antenna 2, thereby to reduce distortion. The reflected signal is sensed by a directional coupler 3, detected by a diode detector 6, and fed to a comparator 11 which selects the gate voltage bias via switch 14. This adaptive gate bias scheme allows an antenna isolator to be eliminated. Switches 5 and 9 allow the directional coupler 3 and detector diode 6 to be used also to sense the forward signal for input to an automatic power control circuit APC. The comparator 11 and selector 14 may be replaced by an ADC and DAC circuit (figure 4).