Amplifiers with Improved IMD Performance for Multi-Channel Wireless Systems

A linearization technique for reducing spectral regrowth caused by the third-order non-linearity, that uses the injection of the fundamental signal second harmonic together with the fundamental signal at the amplifier input has been applied in this paper. The second harmonic is led from the output to the amplifier input trough the feedback loop. Designed amplifier with additional components at feedback loop (phase shifter, attenuator, bandpass filter, power divider and combiner) has been tested for OQPSK modulation at 2.5 GHz carrier frequency. Optimising phase shift and attenuation of the feedback loop signals 16 dB improvement in the adjacent channel power ratio (ACPR) for ±900 KHz offset from carrier frequency over 30 KHz bandwidth was obtained in simulation by program ADS. The measured results for the amplifier with second harmonics feedback referring to output powers for seven fundamental signal frequencies at the amplifier input and the higher order IMD signals are shown as well.