A 110 to 122-GHz Four-Channel Oversampling Digital-to-Phase Transmitter for Scalable, Energy-Efficient Arrays

An oversampling digital-to-phase (ODP) transmitter (TX) is proposed based on scaling independent channels consisting of a multiplier chain ($\mathbf{X} N$), two-bit quadrature phase shifter (PS), and a power amplifier (PA). Each channel operates under constant envelope conditions for maximum power efficiency. Direct digital modulation is applied to the RF carrier of each channel. The prototype array, fabricated in a 22-nm FD-SOI CMOS technology, consists of four channels operating over a 3-dB bandwidth from 110 to 122 GHz. The CMOS chip is flip-chip mounted onto a Low-Temperature Co-fired Ceramic (LTCC) interposer with integrated Vivaldi antennas and wire-bonded to a PCB. The 4-element array exhibits a measured peak effective isotropic radiated power (EIRP) of 26.6 dBm with ± 25° scanning range. With just two bits of phase control per channel, the proposed array is able to achieve 8-PSK modulation at 1.5 Gbps, 1 dB power back off, and 12.3% EVM. Despite no explicit amplitude modulation, 8-APSK modulation is achieved at 150 Mbps, 3-dB power back off, and 12.8% EVM. The proposed direct modulation scheme is a scalable millimeter-wave (mm-wave) TX architecture for digital modulation and beamsteering.