Analysis of Two Filtering Techniques in Differential LC VCO Design using Asymmetric Tank Structure

This paper presents two InGaP/GaAs HBT (heterojunction bipolar transistor) differential cross-coupled voltage -controlled oscillators (VCO) designed with low phase noise for adaptive feedback-interference cancellation -systems (AF-ICS). The main idea is to use low pass and band pass filtering technique for noise frequency. With this, the -designed VCO, the first one achieved a phase noise of 130.40dBc/Hz at 1MHz offsets from the carrier frequency of 1.619GHz and the second one achieved 127.93dBc/Hz at 1MHz offsets from the carrier frequency of 1.604GHz. Each VCO dissipates an output power of 6.68dBm and 10dBm respectively by supplying 5V. Two pairs of base-collector (BC) junction diode are used as varactor to get a broad band tuning range for both VCOs.