Research On Independently Tunable Concurrent Dual-band VCO

The concurrent multi-band and multi-mode transceiver is a trend in modern wireless communication systems,and the independently controllable capabilitites make the various communication standards have no effects on each other.Accordingly,radio frequency(RF)and microwave components are required to achieve multi bands with flexible tuning characteristics,which results in a huge advantage for the multi-band circuits and makes them more in line with the requirements of the wireless communications.Oscillators and Voltage-controlled oscillators(VCOs),the vital RF and microwave devices of wireless transceivers to provide carrier frequencies and clock signals for the communication systems,have been investigated in response to this need.To solve the problem of asynchronicity caused by switchable dual-band resonators,the thesis proposed novel research methods to develop the concurrent dual-band oscillator and VCO.The primary purpose of the thesis is to verify the independent tuning characteristics for dual-resonant frequencies by odd-and even-mode analysis method,which makes the two oscillation frequencies have flexible dual-band operations with frequency reconfigurability.Based on the principle of the flexible tuning characteristics,analytical equations are obtained to introduce a method for circuit size reduction and tuning range extension,and the relations between size and tuning range are interdependence and interacting.In addition,the unique design approache brings about the filtering characteristic to increase band-to-band isolation of the dual-band resonators,and the sufficient spurious suppressions can effectively suppress nonlinear mixing components to achieve a pure dual-band spectrum output.Moreover,the use of stepped-impedance(SI)structure can control the frequency spacing of two oscillation frequencies by adjusting impedance rate,and the rate also adds a way to determine dual-oscillation frequencies.Therefore,due to special properties of concurrence,miniaturization,easy operation and independent tuning capabilities,the developed concurrent dual-band oscillator and VCO are expected to be widely utilized in the design of microwave and millimeter integrated circuits.Firstly,in order to replace the switching devices and support concurrent dual-band outputs,the thesis presented a new design of concurrent dual-band oscillator.The core of the proposed dual-band oscillator is a active SI dual-mode resonator,which is compensated by two transistors operating at two different frequencies as negative resistance devices.Once the lossy resonator is changed into a lossless one,it means that the active resonator exhibits potentially unstable for startup of oscillation,and the matching networks are used to fulfill steady oscillation condition for negative oscillator.Furthermore,the two oscillation frequencies can be controlled by the impedance ratio.Secondly,based on the concurrence,the study of the independent tuning characteristics is carried out and employed in the application for concurrent dual-band VCO design.By embedding two sets of varactor in particular positions,the odd-and even-mode analysis method is utilized to prove and deduce the independent tuning capabilities,and the derived results prove the validation of the collaboration among multiple parameters.Then,the mathematical deductions are analyzed to optimize the tuning ranges of the dual-oscillation frequencies and the circuit sizes,and a restrictive relation between them is obtained.As a result,it should take a trade-off between the tuning range and circuit size for satisfied performances.However,because of the complete structure of the developed dual-band bandpass filter(BPF),it is difficult to freely design the frequency response of the higher passband,resulting in a poor frequency selectivity and a bad phase noise.Thirdly,with the continuation of independent tuning characteristics,by adopting the shared dual-mode resonator topology to design concurrent dual-band VCO is presented.The design method has two advantages.One advantage is that the filtering characteristic is introduced to improve band-to-band isolation of the dual-band BPF,and it is benefit to largely suppress the unwanted harmonic-mixing signals.The other advantage is that the degree of freedom for two frequency responses design is enhanced,which optimizes the frequency selectivity of the higher passband with a low phase noise.Moreover,the SI structure combined with independent tuning characteristics can enrich the methods of determining dual-oscillation frequencies.Thus,the shared design technique for independently tunable concurrent dual-band VCO possesses three merits:boost the passband suppressions,improve the performance of phase noise and increase the way to change gap of two oscillation frequencies.