Research And Design Of Current Mode Filters

Current-mode filters are typically built by cascading a positive current conveyor with some resistances and capacitances.Current conveyor as a standard component is used in current-mode circuits frequently. At present, the study of current conveyor technique, lots of designers works on the second generation current conveyor and the improved circuit instructure of CCII inside and outside of the country, besides, the design of the improved circuit instructure of CCⅢcurrent-mode filter based on CCIII and the current feedback operational amplifier (CFOA) is very little.Everyone know that, CCII only has one singe output port,if design current-mode filter based on CCII, there are two shortages:one is current direct and feedback can't exist at the same time, because carry out current feedback will make output resistance lower.another is the circuit instructure is rather complex,it need lots of negative and active parts of apparatus to fulfill the request.Compare to CCII,the third generation current conveyor has some character: such as frequency response is wider, plus error is lower, output impedance is higher and linear character is better.So the current-mode continuous-time filter based on CCIII circuit instructure becomes one of the new research directions in the world. So this paper studies the design of the third generation current conveyor circuit instructure, CFOA and the current-mode continuous-time filter. It is based on the design idea of some existing CCIII circuits, falling to designing the filter which is based on the third generation current conveyor and CFOA.In this paper, with a±1.5 V power supply,in the structure of the conventional CCIII, we design another proposed CCIII which is based on the proposed cascade current mirrors. Because the proposed cascade current mirrors which provided high output impendence, so the proposed CCIII provides high output impedance at port Z. Based on third-generation current conveyor, through the use of compensation capacitor isolation between the output and the amplification, the way is to eliminate the low frequency zero, we designed a new current feedback operational amplifiers with low-voltage and low power consumption. This CFOA can be as a voltage-current conveyor which output as the input of the current-mode continuous-time filter based on the proposed CCIII.When give simulation to all designed circuits, using HSPICE software, based on TSMC 0.35μm technology, simulation results show that:a of the CCIII model improve from 0.921 to 0.972 and improve theβof the CCIII model from 0.924 to 0.987,and also the output resistance increased significantly, from the original grade KΩincrease to the grade MΩ. DC gain of the CFOA is 96.3dB, unity gain bandwidth of 765M,static power consumption 0.82mW, the state closed loop bandwidth is fixed under the 64.3MHz. The filters which have been designed can carry out low pass, high pass and band pass three kinds of filtering, The three filtering have low passive and low active sensitivity, besides, bandwidth is rather wide. Simulation results show that the proposed circuit is feasible.