High Gain 130-GHz Frequency Doubler With Colpitts Output Buffer Delivering Pout up to 8 dBm with 6% PAE in 55-nm SiGe BiCMOS

A mm-Wave frequency doubler in an SiGe BiCMOS technology is presented. The core of the circuit comprises a push-push pair, for second-harmonic generation, and a stacked common-collector Colpitts oscillator which works as a common-base injection-locked amplifier to boost the conversion gain and output power. The class-C operation of the transistor in the Colpitts buffer leads to a pulsed current shape with enhanced second-harmonic content. As a result, the power conversion gain of the frequency doubler is increased by up to 10 dB, compared to the push-push pair alone. Moreover, the common-collector configuration keeps separate the oscillator tank from the load, allowing independent optimization of the harmonic conversion efficiency and the load impedance for maximum power delivery. Realized in an SiGe BiCMOS technology with 330-GHz f_max, the proposed frequency doubler delivers Pout up to 8 dBm at 130 GHz with 13-dB conversion gain and 6.3% power added efficiency. A Figure-of-Merit is proposed to benchmark frequency doublers and the presented chip shows up to 3 times improvement compared to the previously reported designs in the same frequency range.