248-GHz Subharmonic Mixer Last Transmitter With I/Q Imbalance and LO Feedthrough Calibration

This letter presents a 248 GHz compact direct-conversion transmitter with IQ and LO feedthrough (LOFT) calibration capability, which can achieve a data rate of 20-Gb/s with 16-QAM. The transmitter design incorporates a subharmonic double-balanced mixer configuration, simplifying the complexity of the local oscillator (LO) chain. Furthermore, a Wilkinson power divider and a transmission line terminated by variable capacitors are used to generate LO signals with a 45° phase difference. This configuration, combined with variable gain amplifiers, allows for the precise balancing of IQ amplitude and phase. The measured image rejection ratio and LOFT suppression ratio are better than 25 and 28 dB, respectively, in the range of 242–252 GHz. The DC power consumption of the transmitter is 96.3 mW.