110 - 170 GHz 25% Duty-cycle Gilbert-cell Frequency Doubler with 6.5 dBm Peak Output Power in BiCMOS 55 nm Technology

Frequency multipliers are key components for signal generation above 100GHz. Push-push doublers are popular but suffer from low conversion gain (CG) and limited fundamental rejection. Mixers with quadrature inputs offer higher gain and fundamental suppression but need a bandwidth-limiting 90° phase shifter. This work leverages Gilbert-cells mixers driven by in-phase signals but operated at a reduced duty-cycle (δ), allowing to retain the superior CG and fundamental suppression without the 90° phase shifter. A low-frequency loop controls δ and gives maximum CG by suppressing the output DC component. The signal driving the mixer switching-quad is generated by a transmission-line network which compensates for the undesirable phase shift introduced by transistors parasitics. Realized in SiGe BiCMOS, the circuit proves Pout=6.5dBm at 148GHz with 7.4% efficiency and 8dB CG. With -3dB bandwidth of 125-170GHz, Pout>0dBm from 110 to 170GHz and a fundamental rejection above 40dB, the frequency doubler compares favorably against previous works.