Study On Fully-integrated Continuous-time Filters Based On Active Devices

With the popularization of the fourth generation mobile communication technology(4G)and the development of the fifth generation mobile communication technology(5G),the requirements of the mobile communication system are becoming higher and higher.As an important module in mobile communication system,filter is using to extract valid band and eliminate all kinds of signal noise and interference.The performance requirements of the filter are also rising.Meanwhile,with the continuous advancement of the information age and the development of Very Large Scale Integrated Circuit(VLSI),the study of MOS transistor-only(MOS-only)active components,basic modules and filter circuits attract widespread attentions.So,filters are required to have the characteristics of wider bandwidth,higher integration,faster processing speed,less sensitivity,lower power consumption,more simple circuit structure and so on.The universal active device has good characteristics such as high integration,wide bandwidth,high speed,low voltage swing,low impedance performance.Therefore,using of universal active devices can meet the high performance of the filter,and the filter can be better applied to modern communication systems.The fully-integrated continuous-time filter can process analog signals directly,eliminating A/D,D/A conversion,holding,sampling,anti-aliasing filters and avoiding the effect of clock feedthrough.Operational Transconductance Amplifler(OTA)and Current Conveyor(CCI)are important universal active devices.Numerous fully-integrated continuous-time filters have been implemented based on OTA and CCII and these circuits can be classified from four aspects: according to the mode,it can be divided into voltage-mode,current-mode and mix-mode;according to the order,it can be divided into low order and high order;according to the way of realization,it can be divided into direct design method and indirect design method;according to the number of the input-output ports,it can be divided into single input single output(SISO),single input multiple output(SIMO),multiple input single output(MISO)and multiple input multiple output(MIMO).The circuit theory,CMOS circuit diagram of OTA and CCI,and the design method of the fully-integrated continuous-time filters and analog multipliers are studied systemically in this article.Firstly,according to the characteristics of multi-output Differential Differential Current Conveyor(MDDCC),a four-quadrant analog multiplier based on MDDCC is proposed.The circuit consists of four MDDCCs,eight NMOS transistors and a passive grounded resistor.The 0.18μm CMOS technology of TaiwanSemiconductor Manufacturing Company(TSMC)is used to complete the simulations of circuit.The simulation results show that the analog multiplier can realize the functions of multiplication,signal modulation and signal frequency multiplication.At the same time,the circuit has good linear characteristics,high cut-off frequency and small voltage output noise.Secondly,the mixed-mode universal biquadratic filter based on OTAs is presented.Changing the type of power supply or the location of the power input,the circuit can achieve the voltage mode(VM)and current mode(CM)universal biquad functions,the two modes of the filter can achieve low-pass(LP),high-pass(HP)and band-pass(BP)filters.Berkeley short-channel IGFET model(BSIM)90nm CMOS technology is used to complete the simulations of circuit.The circuit has low passive sensitivity and active sensitivity and the circuit performance is more stable.Finally,two methods(the cascaded connection method and the active simulation method)are introduced to design the high-order filter based on OTA.The design theory and simulation process of the two methods are studied systemically.The design example and the PSPICE simulation of the circuit are carried out.Various modes filters based on CCI and OTA play an important role in the signal processing.The filters have a wide range of applications in the field of microelectronics,automatic control,instrumentation and electronic measurement.