A Ka-Band 1024-QAM CMOS I/Q Modulator Using a 15th-Order Cascaded Subharmonically Injection-Locked Frequency Multiplier Chain With FTL

This article presents the design and analysis of a Ka-band advanced in-phase and quadrature (I/Q) modulator using a 90-nm CMOS process. To achieve a subharmonic number of up to 15 while maintaining good quadrature accuracy, a cascaded subharmonically injection-locked frequency multiplier (SILFM) chain, incorporating a frequency-tracking loop (FTL) and differential injection, is employed in the local oscillation (LO) generation for the proposed I/Q modulator. Accurate modulation quality is ensured by performing vector modulation through four reflection-type modulators. The design methodology of the cascaded SILFM, along with theoretical results, is presented, focusing on locking range, quadrature accuracy with injection, phase noise, and jitter. The SILFM consumes a total dc power of 74 mW and features a measured locking range from 27 to 28.7 GHz, a minimum phase noise of −122.8 dBc/Hz at a 1-MHz offset, and an rms jitter of 27.5 fs integrated from 1 kHz to 40 MHz. In addition, the proposed I/Q modulator demonstrates superior performance up to 1024 quadrature amplitude modulation (1024-QAM) due to the LO chain’s low jitter and high quadrature accuracy. The measured rms error vector magnitudes (EVMs) are within 1.46% and −26.4 dB for QAM and orthogonal frequency-division multiplexing (OFDM) schemes.