Frequency quadrupling transmitter architecture with digital predistortion for high-order modulation signal transmission

This paper demonstrates a novel transmitter architecture based on frequency quadrupling, in which modulated signals are generated at a frequency f₀, and subsequently up-converted to 4f₀ using a frequency quadrupler. This technique is a promising architecture for mm-wave communications, at frequencies where signal amplification, modulation and distribution at 4f₀ are challenging. To achieve acceptable output signal accuracy, predistortion of the input is mandatory. In this work, we validate the architecture using a low (microwave) demonstration frequency of f₀= 890MHz, with 4f₀=3.56GHz. High-order modulation signals are directly applied to a quadrupler, and “quadrupling digital predistortion” (Q-DPD) is used to restore the signal modulation format at the output. With a 5MHz bandwidth 256-QAM signal, before predistortion the output signal has an error vector magnitude (EVM) of 138%. After Q-DPD, the 256-QAM output signal has an EVM of 1.8% and adjacent channel power ratio (ACPR) of around -43dBc.