THz power generation beyond transistor f_max

This chapter describes the implementation of sub-terahertz oscillators using a multiple-push technique in digital CMOS technology. The application of sub-terahertz, especially in spectroscopy, is introduced along with emerging high-performance CMOS technology for sub-terahertz circuits. Basic operation principles and design considerations are discussed for the implementation of a push-push and quadruple-push oscillator. A 410-GHz push-push oscillator is demonstrated using in a 45-nm logic CMOS process. The second harmonic in the cross-coupled oscillator is combined at the push-push node, while the differential fundamental signals are canceled. A quasi-optical technique with high sensitivity and wide bandwidth is devised using an on-chip antenna and FTIR system to evaluate the performance of the oscillator. A 410-GHz push-push signal with the power level of -49 dBm (12.6 nW) is observed. A 553-GHz quadruple-push oscillator is also demonstrated in the same technology. A passive network constructively combines the fourth harmonic currents in the coupling transistors of the quadrature oscillator while other lower harmonics are canceled. Quasi-optical measurements showed that the circuit generates four harmonic signals at 553 GHz with a power level of 220 nW, while suppressing unwanted harmonic signals. The circuit consumes 64 mW from a 1.4-V supply. Those circuits would be readily integrated with various analog and digital circuits to implement practical and affordable sub-THz systems for security, healthcare, industrial, defense, and communication applications.