On design of a 55 GHz Si/SiGe HBT frequency doubler operating close to fmax

In this paper we present for the first time experimental results on a frequency doubler using a Si/SiGe HBT as the non-linear element. Despite the high output operating frequency being close to f,sub>max, 67 GHz, for the Si/SiGe HBT, the conversion efficiency in a not completely optimised circuit was founid to be better than -12 dB. The 3 dB bandwidth for the doubler was about 7.4%. These results are found to be comparable to an HFET doubler operating equally close to its fmax. The results agree well with the prediction for the multiplier from a developed physics-based large-signal HBT model. Prediction by the model using harmonic balance simulation at 55 GHz shows that a conversion efficiency for the Si/SiGe HBT of about 5dB can be expected from future optimised circuits.