Design of terahertz CMOS oscillator circuit in different technologies for 6G applications

Today's technology has pioneered the creation of circuit components and systems that can work at high frequencies in various domains where a steady signal source is required, including communication, spectroscopy, servo motor control, and so on. It is observed, particularly in the sector of communication, that the operating frequencies of transceiver ICs for high data rates also reach the terahertz range. Research have led to the requirement for studies to create the sub-parts that make up the transmitter and receiver architectures individually and adapt to terahertz frequencies as frequency has increased. Furthermore, communication technology beyond 5G requires reliable circuits that operate at sub-THz frequencies. In this thesis, sub-THz range is targeted to enhance the performance of integrated signal sources in terms of conversion efficiency (DC to RF) by utilizing unorthodox methods. A fundamental differential oscillator circuit topology is investigated in two particular technology of 22 nm FDSOI and 65 nm CMOS. The same oscillator topology is used to seek stable oscillation at sub-THz frequencies in both technologies. Theoretical foundations are investigated in order to enhance transistor small signal models and oscillator circuit models. With these enhanced circuit models, the fundamental differential oscillator circuit is employed, and the theoretical background of the oscillator is created utilizing Z(Y)-parameters. 22-nm FDSOI is a noticeable technology for designing efficient signal source with low leakage and fast operation advantages. Two oscillator circuits of 300 GHz and 350 GHz operations are designed using Process Design Kit (PDK) models. Capabilities and high frequency performance of 22 nm FDSOI is examined. 600 mV and 200 mV peak-to-peak signals are acquired from 300 GHz and 350 GHz oscillators respectively in 22 nm FDSOI. In the same manner with the objective of this thesis, a tape-out ready 190 GHz fundamental differential oscillator is developed in 65 nm CMOS. It is resulted with 1.915% DC-to-RF efficiency. That oscillator circuit constructed in 65 nm CMOS is used to investigate the effect of transistor body connection on DC-to-RF efficiency at sub-THz frequencies. There are three types of body connections available: conventional grounded body, body connected to the source terminal, and floating body. The best performance is obtained with floating body transistors that achieves 1.57 V peak-to-peak (Vp-p) differential drain voltage at 209.3 GHz according to the accurate simulations. The results with grounded body and body-source connected transistors are 1.26 Vp-p and 1.23 Vp-p at 210.6 GHz and 210 GHz respectively. Additionally, a differential to single-ended transformer is used to connect 50-ohm load for future measurement studies and power calculation. With the transformer, all three oscillator circuits with distinct body connections oscillate at around 191 GHz. For grounded body, body connected to the source, and floating body configurations, the output power is -7.49 dBm, -8 dBm, and -6.35 dBm, respectively.