| With the development of high-frequency electronic technology and broadband technology,it has been found that current mode circuits can perfectly replace voltage mode circuits in many aspects.Compared with voltage mode circuits,current mode circuits have better performance and lower energy consumption.Especially in circuit applications in the high frequency field,the current mode circuit has the advantages of low impedance,large dynamic range,and good high frequency performance,which can help people better solve the problems encountered in practical applications.The mixed-mode filter based on general-purpose active devices,with the excellent characteristics of the mixed-mode circuit,can realize the filtering functions of various modes such as voltage,current,transconductance and transimpedance.Current Feedback Operational Amplifier(CFOA)is one of the most important active devices in the design of mixed-mode general-purpose second-order filter circuits.It has good dynamic characteristics,including higher slew rate;lower sensitivity;wide dynamic range;the ability to construct filter circuits that can achieve multiple functions with fewer components.The circuit principle of the current feedback operational amplifier,CMOS circuit diagram,and the fractional-order general second-order filter circuit designed were analyzed in this thesis systematically.A general second-order filter circuit based on a transimpedance operational amplifier is also designed.Based on the above designed circuit,the AD844 model was being used to complete the filter circuit simulation.The simulation results prove the effectiveness and correctness of the circuit.The main work and conclusions of this paper are as follows:(1)A fractional-order general second-order filter based on the current feedback operational amplifier is designed.The filter circuit consists of 3 current feedback operational amplifier modules,2 fractional-order capacitors and 5 resistors,which can realize input,output voltage mode and current mode filters at the same time without changing the circuit structure Low-pass,High-pass and Band-pass function.The AD844 spice model is used to simulate the circuit,and the results show that the designed filter circuit can realize the high-pass,band-pass and low-pass filter functions of voltage or current modes without changing the circuit structure.The filter has the advantages of low sensitivity,flexible function and independent adjustment of natural frequency?and quality factor Q in the meantime.In addition,the asymmetric attenuation phenomenon in the simulation results is analyzed,and its reference value is explained.(2)A general second-order filter circuit based on transimpedance operational amplifier is designed,and the detailed design process and circuit diagram are given.Compared to implementing this filter circuit with a current-feedback op-amp,the DC offset current can be greatly reduced and a higher gain-bandwidth product is provided.By changing the position and type of the AC power supply without changing the circuit structure,high-pass,band-pass and low-pass filtering functions can realize simultaneously in two modes of voltage or current.Meanwhile,the filter circuit also has the advantages of low sensitivity,natural frequency ? and quality factor Q can be adjusted independently.This thesis had studied the theory of mixed-mode universal second-order filter deeply,and also analyzed the fractional-order universal second-order filter circuit based on current feedback operational amplifier and the universal second-order filter circuit based on transimpedance operational amplifier on the premise of referring to a large number of domestic and foreign references.Some research achievements have been made in the design of the first-order filter circuit.These research results enrich the design ideas of mixed-mode universal second-order filters and have certain guiding significance for the development of mixed-mode universal second-order filter theory. |
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