High Precision Adaptive Calibration Feedback in RF Front-end for Digital Pre-distortion Application

This paper introduces an adaptive feedback calibration circuit designed for use in V2X (Vehicle-to-Everything) systems operating at 5.9 GHz within 5G NR systems. The adaptive loop comprises the observation receiver, functioning in the n47 frequency band (5855-5925 MHz), and the digital pre-distorter, both situated on the same die as the RF Power Amplifier. The TX signal, featuring a bandwidth of up to 40 MHz and a PAPR of 8 to 10 dB, undergoes digitization by a receiver with a notably high bandwidth, such as 120 MHz. Subsequently, the digitized signal is input into the digital pre-distortion circuit with a 10-bit high precision. Circuit characteristics obtained from post-layout simulations, as of the publication date, have been incorporated into a comprehensive model. Simulations assessing EVM and ACLR of the TX signal at the Front-end module output have been executed. The EVM value enhances from 5.2% RMS when the adaptive DPD is deactivated to 1.5% RMS when activated. Moreover, the ACLR decreases from -30 dBc to better than -40 dBc. The observation receiver of the calibration feedback system, designed using 130-nm SOI CMOS technology, possesses dimensions of 1750 µm × 3200 µm. The DPD circuit, situated on a separate die but utilizing the same process, features dimensions of 5980 µm × 6430 µm.