Research And Design Of CDCTA-based Current-mode Multiple-loop Feedback Filter

Compared with voltage-mode circuits,the current-mode circuits have obvious advantage in analog and digital signal processors because of its high speed,increased bandwidth,low voltage source and wide dynamic range and other excellent features.Current-mode continuous-time filter is a front subject for domestic and foreign researchers now,it has good prospects and development in communication,electronic measurement,instruments,automatic control,etc.Current differencing cascaded transconductance amplifier(CDCTA)is the most new current-mode active device and has good potentially broad application in the field of current-mode circuits,especially in current-mode continuous-time filter.Multiple loop feedback filter is a current-mode continuous-time filter,it has simple circuit structure,low sensitivity and suitable for modular,etc.So,the research of multiple loop feedback filter which possesses high perfoamance has a important significance.This paper describes in detail the research status of CDCTA and multiple loop feedback filter,also studies CDCTA's baisic principle,circuit implementation and its current mode multiple loop feedback filter's design theory,design method and implementation.The main work and innovative achievement of thesis are as follows:(1)A systematic design of current-mode multiple-loop feedback filters based on a single CDCTA is presented.The proposed CDCTA circuit consists of a current differencing unit and n cascaded highly linear voltage-controlled transconductance amplifiers,and it possesses wide bandwidth and linear-tunable feature.Based on this CDCTA,a systematic design of current-mode all-pole multiple-loop feedback filter is proposed.By altering the parameters of the design matrix,multiple nth-order CM all-pole low pass filters structures can be synthesized without changing internal circuit.The nth-order filters have low complexity and meet the requirement of no active and passive element matching conditions as adopting only a single CDCTA and n grounded capacitors.Meanwhile,the frequency of the nth-order filters can be linearly tuned by the bias voltage.A fourth-order Butterworth filter is designed as an example,and its Cadence simulation results have good agreement with the theoretical analysis.(2)A structural design of current-mode multiple-loop feedback filters with arbitrary transmission zeros and poles is presented by introducing a modified current differencing cascaded transconductance amplifier(MCDCTA).the MCDCTA is built by adding parallel operationaltransconductance amplifiers in CDCTA,which extends the number of the output x port vastly.The proposed circuit employs only one MCDCTA,one grounded resistor and n grounded capacitors,which is suitable for IC fabrication.In addition,multiple nth-order current-mode filter structures with arbitrary transmission zeros and poles can be generated by means of multi-loop feedback method.The structural design of current-mode multiple-loop feedback filters is verified with two third-order current-mode Butterworth filter structures,Cadence software using GlobalFoundries'0.18 ?m CMOS process is used to simulate the proposed circuit,simulation results confirms that each of two structures can realize five filter functions:low-pass,high-pass,band-pass,band-stop and all-pass.