Enhanced WirelessTransmitters using an inter-stage notch filter

This paper proposes a new technique in suppressing nonlinear distortion in nonlinear wireless transmitters. Several interfering signals with high power levels can cause unwanted nonlinear distortion of the poweramplifiers. A simple cascade system of a notch filter and the power amplifier is presented which potentially suppresses the interfering signals and also minimises third order intermodulation products. The proposed method is simulated in Agilent ADS using a commercial nonlinear class-ABbasestationpower amplifier model. A two tone test was carried out at 761 MHz and 763 MHz. The simulated results show an suppression of distortion by about 8 dB. The proposed technique is experimentally verified for a QPSK signal in the presence of a single interfering tone, where distortion suppression of around 10 dB have been measured.