Digital Predistortion of Frequency Multiplier-Based Vector Signal Sources With Constrained Transmitter and Observation Receiver Bandwidth

This article proposes a novel digital predistortion (DPD) scheme to linearize frequency multiplier (FX)-based vector signal sources that are subject to constrained transmitter and observation receiver bandwidth. Specifically, the proposed technique aims to reduce the digital-to-analog converter (DAC) sampling speed and the bandwidth of the transmitter RF front-end required by conventional DPD schemes for FX-based signal generation while maintaining excellent linearized output signal quality. This article starts by formulating an additive error model for an FX driven by a <tex-math notation="LaTeX">D</tex-math> th root function subject to bandwidth constraint. This model is then utilized to derive the expression of the proposed DPD model and underlying DPD training algorithm while allowing for the reduction of the required transmitter observation receiver (TOR) bandwidth. The extent of the TOR bandwidth relaxation is determined based on the bandwidth of the <tex-math notation="LaTeX">D</tex-math> th root function output. Using the proposed DPD scheme, extensive simulations and measurements carried out on two different FXs revealed a 22–25-dB improvement in adjacent channel power ratio (ACPR), when the transmitter and receiver bandwidths are limited to 4 <tex-math notation="LaTeX">×</tex-math> and 3 <tex-math notation="LaTeX">×</tex-math> the signal bandwidth, respectively. Moreover, the error vector magnitude (EVM) after DPD is reduced from 13.6%–21.1% to 1%–1.6% when the transmitter and receiver bandwidths are reduced down to 2 <tex-math notation="LaTeX">×</tex-math> and 1 <tex-math notation="LaTeX">×</tex-math> the signal bandwidth, respectively.