Existing electronic upper frequency is being constantly challenged to cater for new and state-of-the-art wireless applications. The conventional voltage controlled oscillator (VCO) designs are not sufficient to meet the trend. This calls for innovative and novel architectures. Utilizing the concept of distributed-loaded phase shifters we delve on the idea of implementing a tunable wideband VCO in W and V band.
By periodically loading a coplanar waveguide transmission line with varactors, we can vary the phase velocity of the signal travelling through the line and thus creating a true time delay element. Through proper feedback, this system becomes analogous to a ring oscillator which is tunable by an analog control voltage.
Based on these concepts, a distributed-loaded phase shifter was designed in 90nm CMOS technology with center frequency of 100 GHz (W-band) and 60 GHz (V-band). A bandwidth of ~27% and ~30% were achieved respectively. The worst case insertion loss and worst case return loss were kept less than 10dB for both the bands. The performance is limited by the limited tuning range of CMOS varactors and deteriorating quality factor with increasing frequency.