A Design of Predistortion Linearizer using 2nd Order Low Frequency Intermodulation Signal Injection

This paper presents a new predistortion methods which injects the 2nd order low frequency intermodulation signal of RF signal into the input bias line of the amplifier. We show this technique can suppress the 3rd IM and the 5th IM apparently by adjusting 2 factors, phase and amplitude, through mathematical analysis, and then confirm it with simulation. And we design digital cellular amplifier to show variation of the optimal performance without additional circuits or controls for the operating range. When the input signal CDMA IS-95 1FA was applied, measured ACPR improvements were 25dBc, 22.5dBc, and 6dBc at 0.855MHz, 1.25MHz, and 2.25MHz offset respectively. Also, when applying the CDMA IS-95 3FA, the measured ACPR improvement showed 16dBc at 0.885MHz offset.