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Digital predistortion linearization of frequency multipliers

This paper presents a novel technique to linearize frequency multipliers for use with modulated signals. Using amplitude and phase mapping functions, a modulated signal may be translated to an integer multiple of the carrier frequency with minimal distortion. To validate this technique, a Schottky-diode frequency tripler was built to transmit digital signals at 2.46 GHz with an 820 MHz input carrier frequency. Measured results show that with an IS-95B input signal, the digital predistorter achieved 26 dB of improvement in the Adjacent Channel Power Ratio (ACPR) at 2.46 GHz. Its output Error Vector Magnitude (EVM) was 13% with predistortion, whereas it was near 100% without predistortion. Additionally, an adaptive digital predistorter was designed, and simulation showed a 40 dB improvement in IMD with 4-tone signal input.