A low conversion loss passive frequency doubler

We propose a distributed passive frequency doubler using a bandgap nonlinear transmission line (NLTL) that can achieve low conversion loss even for small input power levels. We also develop a theoretical model of second harmonic generation for a homogeneous NLTL and show adverse effects of dispersion. To resolve dispersion, a bandgap NLTL is introduced which can reach the theoretical limit of second harmonic generation for a given input amplitude. To boost the input voltage amplitude and enhance the performance of the frequency doubler, a standing wave resonator using a bandgap NLTL is proposed. Using this technique, a 20GHz doubler is designed and implemented in a 65nm CMOS process. The doubler is tested from 14GHz to 25GHz and achieves conversion loss of 3.5dB with input power of 2.7dBm around the center frequency.