Study On Fully-integrated Continuous-time Filters Based On Current Feedback Operational Amplifier

With the development of Very Large Scale Integrated Circuit(VLSI), the study of MOS transistor-only( MOS-only) active components and filter circuits attract widespread attentions. Multifunction filter circuits have many possible applications such as three-way high-fidelity loudspeakers in crossover networks, touchtone telephone systems, phase-locked loop FM stereo demodulators, analog sections of high-speed data communication systems, signal processing in cable modems, and so on.The current feedback operational amplifier(CFOA) is one of the most important active building blocks in fully integrated continuous circuits. The CFOA has many essential advantages such as wider and nearly constant bandwidth independent of closed-loop gain, higher slew rate, lower sensitivity, larger dynamic range, lower power consumption and ease of realizing various functions with lesser number of passive components. Numerous analog circuits have been implemented based on CFOA and these circuits can be classified from three aspects: 1. The order : low order and high order filter circuits; 2. Input-output: single input single output(SISO), single input multiple output(SIMO), multiple input single output(MISO) and multiple input multiple output(MIMO) circuits; 3. The mode: voltage-mode, current-mode and mix-mode circuits. More and more kinds of circuits are integrated in a single chip and there are serious interference among them. The normal single-ended circuits are difficult to reduce the circuit disturbance meanwhile the fully differential circuit configuration are widely concerned. Recently differential circuits have been widely used in high frequency analog signal processing such as switched capacitor filter, multistandard wireless receivers and so on.Up to now, the active filters used by CFOA are innumerable, but the filters employing FDCFOA are few. Compared with single-ended component, FDCFOA has many advantages: larger output dynamic range, higher flexibility to design many kinds of circuits, reduced harmonic distortion, higher ability to reduce influence of clock-feed-through, higher ability to charge injection errors and power-supply noises and so on.The circuit theory, CMOS schema of Current Feedback Operational Amplifier(CFOA) and applications in fully integrated continuous-time filter are studied systemically in this article. The fully-differential Current Feedback Operational Amplifier and its application in mixed mode biquadratic filter are introduced. Based on designed circuits, Taiwan Semiconductor Manufacturing Company(TSMC) 0.18μm andBerkeley short-channel IGFET model(BSIM) 90 nm CMOS technology are used to complete the simulations of filter circuits. The simulation results verify the availability and ability of the presented circuit. In summary, the main work and conclusion of the article are:(1)A mixed-mode universal biquadratic filter based on Current Feedback Operational Amplifiers(CFOAs) is presented. The circuit can realize the current mode(CM) and voltage mode(VM) universal biquad functions simultaneously(low-pass(LP),high-pass(HP), band-pass(BP) filters) by the same circuit configuration. PSPICE simulations using TSMC 0.18μm COMS technology are completed. Moreover, the independent adjustment of quality factor without affecting of natural frequency is allowed and sensitivities are very low.(2)A Nth order voltage mode universal filter based on CFOA is proposed. The circuit using 2n CFOAs, n capacitors and 3n-1 resistors can realize the voltage mode universal filter functions. Taking third-order and fourth-order Butterworth filters for examples, PSPICE simulations using TSMC 0.18μm COMS technology are completed.(3)A 5th-order voltage-mode low pass filter based on CFOA are realized using leapfrog-type. The article make a detail description to the process of designing filter using leapfrog-type and complete the PSPICE simulation to designed circuit. The filter circuit has a narrow transition band and a good cut-off characteristics.(4)A fully differential mixed mode biquadratic filter is presented based on fully differential current feedback operational amplifier. The FDCFOA filter can realize fully differential input and output voltage mode(VM) and current mode(CM) functions.Compared with available CFOA circuits, the proposed filter circuit can reduce harmonic distortion greatly. PSPICE simulations using BSIM 90 nm COMS technology are completed. The natural frequency can be adjusted independently without affecting quality factor, and the sensitivities are low.This paper has a study on fully-integrated continuous-time filter in depth by refereeing a mount of references and makes some breakthroughs. These achievements enrich the design method of fully-integrated continuous-time filter and have a certain theoretical significance and practical value.