Analysis and Compensation of Nonidealities in Frequency Multiplier-Based High-Frequency Vector Signal Generators

This paper expounds on the application of frequency multipliers for the frequency upconversion of amplitude- and vector-modulated signals to high frequencies. First, a complex baseband equivalent Volterra series behavioral model is derived for representing the envelope transformation of frequency multipliers. Based on this model, a low-complexity baseband digital predistortion (DPD) scheme is developed to mitigate unwanted distortions exhibited by the frequency multipliers. The proposed DPD scheme consists of three modules: (1) a polynomial predistorter (PD) is first employed to mitigate the memoryless (ML) distortions associated with the frequency conversion; (2) a Dth order root module is included to correct for the phase modulation (PM)-PM distortions exhibited by the frequency multiplier with a frequency multiplication factor of D; and (3) a pruned Volterra-based PD is added to correct for residual distortions attributed to the output stage. As a proof of concept using a low-complexity experimental setup, the proposed DPD scheme is used to linearize several frequency multipliers, namely, a frequency doubler with an output at 12.5 GHz, a frequency quadrupler to produce an output at 25 GHz, and a frequency tripler with an output at 63 GHz. The proposed DPD scheme showed excellent capacity to linearize these frequency multipliers when driven by orthogonal frequency division multiplexing signals with modulation bandwidths up to 400 MHz with less than 56 coefficients.