THz CMOS VCOs with wide tuning range and ASK transmitter using Q-switching VCO are proposed. The VCOs have been designed at G-band (163 GHz) and J-band (239 GHz), respectively. The ASK transmitter has been implemented using the later VCO.
First, the G-band VCO adopts a push-push standing-wave structure. By properly distributing negative gm cells in a transmission-line (TL) resonator, wide frequency tuning range with low phase noise can be obtained. The electrical length of the TL resonator is determined to have a high 2nd harmonic output power. Second, the J-band push-push transformer-based VCO is proposed. It has been also analyzed to achieve high efficiency and a wide tuning range at THz frequencies. Analyses show that the coupling factor of the transformer to obtain high output power has to be carefully chosen by consideration of gate-to-drain voltage gain as well as matching impedances seen from the drain and to the gate of a VCO transistor at the 2nd harmonic frequency. Analysis also shows that the transformer-based resonator allows a wide tuning range. The Q factor of the resonator is enhanced by the introduction of a parallel inductor to a varactor, which leads to high $P_{OUT}$ and low phase noise. Finally, the 254 GHz ASK transmitter using Q-switching characteristic of the J-band VCO is proposed. Design method for high data rate and high on/off ratio has been analyzed.