220–325-GHz 25-dB-Gain Differential Amplifier With High Common-Mode-Rejection Circuit in 60-nm InP-HEMT Technology

This letter presents a broadband and high-gain differential amplifier (DA) with a common-mode rejection circuit (CMRC) using 60-nm InP-HEMT technology. The differential pair in the DA is designed with common-source FET amplifiers. The CMRC implemented by short and open stubs with resistor degenerates the common-mode gain of the DA. Rat-race couplers (RRCs) are used as baluns for DA input and output. The fabricated DA chip exhibits superior gain and output power of 25 ± 3.5 dB and >3.5 dBm over the full WR3.4-band (220-325 GHz). Furthermore, the common-mode rejection is experimentally investigated using the common-mode test circuit of the DA. It is suggested that the fabricated DA chip has high common-mode rejection.