Research Of Time-continuous Analog Filter Based On CDTA

In recent years the integrated circuit technology has a significant development.As one of the important application of integrated circuit, the integratedtime-continuous analog filter is also tend to be a hot topic about microelectronicsand circuit&system both in domestic and overseas. The filter based onCDTA(Current Differencing Transconductance Amplifier) has the characteristics oflow work-voltage, extensive range of dynamic, good linearity, high speed, lowconsumption, simple construction. As all of the above advantages, this filter has themaximum potential in filter design.This dissertation mainly focuses on the study of the CDTA, and the study ofbiquad filter based on CDTA. Firstly it introduced the concept, type anddevelopment of filter and the development situation of CDTA. Refer to the researchof current mode circuit, CDTA and filters, a new realization of CDTA is represented.Moreover the paper also came up with some time-continuous biquad filters which arebased on CDTA and the method of signal flow graph. The main innovations andworks about this dissertation are as follows:(1)An all NMOS transistors based current differencing transconductanceamplifier is designed. The proposed circuit has the advantages of low impedance,low source voltage, low consumption, little imbalance and drifting, bettercharacteristics in high frequency, low noises. To testify the correction of theproposed construction, a theory analysis of port char acteristics and input impedance&output impedance is made. And PSpice is used to simulate these parameters. Allthe simulation is show that the proposed circuit and its performance are correct.(2)Single CDTA implement a three-input single-output mult ifunction biquadfilter is presented. The circuit consists of single CDTA, two capacitances and tworesistors. And compared with other single CDTA based biquad filters, the proposedcircuit possesses the simple constructions, the minimum using of passive compo nent,and it can realized all biquad filter function(Low Pass, Band Pass, High Pass, BandElimination, All Pass) by altering the input current terminals properly.(3)Signal flow graph synthetically implement the multifunction filter based onCDTA is presented. The method is that, as with the principle of CDTA, second low pass filter signal flow is transferred to biquad filter signal flow. Then used the basiccircuit module based on CDTA to simulate signal flow sub-graph. That is realizedthe transformation from signal flow graph to biquad filter. By this method, amulti-input multi-output biquad filter is proposed. All the above presented filter hasthe advantages that the nature frequency ω0and quality factor Q can beelectronically tuned, and the sensitivity of the filter is very low. PSpice has used tosimulate these circuits, and simulation results confirmed the theory.