Design Of The CMOS Terahertz Tunable Signal Source

There are numerous promising applications for the terahertz wave due to its features on penetration,propagation and absorption,such as biomedicine,security,imaging,spectroscopy and wide-band communi-cation.As an indispensable building block of THz communication,the THz tunable signal source is gaining increasing attention and has achieved many research progress.In recent years,with the ever-shrinking tran-sistor feature size,the transistor cut-off frequency is increasing.And,it is possible to realize THz circuit using CMOS process.Basically,CMOS process has the advantage of high integration and low cost,but the fact of the reduced transistor gain and passive component quality factor imposes a great challenge on the circuit design.Regarding the THz communication applications,the thesis studies the tunable signal source.To in-crease the output power and to reduce the phase noise,the transistor performance is exploited and impedance matching network is designed.To increase the tuning range,vairous frequency tuning methods are used.The thesis implements two CMOS THz tunable signal sources.Both of them extract the second harmonic component in order to realize the operating frequency that is above the maximum oscillation frequency,and adopt optimum condition and active condition of the transistor to increase the output power.The first tunable signal source is a transformer-based cross-coupled oscillator.To realize the tuning function,it changes the gate-source parasitic capacitance of the transistor by tuning the gate voltage.And to increase the tuning range,a varactor is in parallel with the gate impedance.The post-layout simulation results show that the transformer-based VCO consumes 32.9 mW,and achieves the operating frequency of 221.3 GHz,the tuning range of 8.8%,the output power of-5.9 dBm,and the phase noise of-82.8 dBc/Hz @1MHz.The second tunable signal source is a Colpitts-based ring oscillator.To increase the tuning range,several methods are developed.First,the equivalent source capacitance is changed by tuning the switching transistor.Second,the gate-source parasitic capacitance of the transistor is changed by tuning the bulk voltage.Third,the coupling between adjacent oscillators is controlled by injection locking.The post-layout simulation results show that the Colpitts-based VCO consumes 166 mW,and achieves the operating frequency of 220.6 GHz,the tuning range of 5.1%,the output power of 2.4 dBm,and the phase noise of-94.9dBc/Hz@1MHz.Through several techniques,the thesis implements the CMOS THz tunable signal source that reaches the output power level of milliwatt power.It lays an important foundation for the development of the terahertz wide-band communication system.