The Study Of Fully Integrated Current-mode Continuous-time Filters

In recent years, fully integrated current-mode continuous-time filters have become one of the several research fields where analog VLSI technologies have obtained significant achievements. The study on related circuits and design methods and its applications are hotspot research subjects in the world now. Current-mode continuous-time filters have drawn great attentions for their important features of wide bandwidth, high speed, low power consumption, low operating voltage and simple topologies. It also has a broad application prospect in telecommunication, video signal processing, computer store system, electronic measure, autocontrol, etc.Research works in this paper is started after a fully investigation on the research results given by both abroad and domestic researchers. Theory and technologies for designing and implementing current-mode continuous-time filters and improved circuits of second generation current conveyor are studied systematically. Two improved circuits and their CMOS circuits for second generation current conveyor are proposed. Several typical current-mode continuous-time filters are realized by using proposed current conveyor and current mirrors. Computer simulations of all mentioned circuits above are completed reference to practical circuits, where parameter of CMOS technologies process is 1.2μm PSPICE simulation results verify the correctness and effectiveness of proposed circuits. All researches in this paper are funded by Jilin University, related project is 'Current-mode Continuous-time Filter Based on Current Mirror' (Jilin university innovation fund).Main achievements and conclusions in this paper are as follows:1. A high output impedance multi-function current-mode biquad filter based on Multi-output Differential Difference Current Conveyor (MDDCC) is proposed firsttime.An MDDCC-based universal current-mode filter configuration with high output impedance is proposed. With three MDDCCs, five or four grounded resistors and two grounded capacitors, the circuit realizes simultaneously the response features of band-pass plus low-pass or band-pass plus high-pass. At the output terminal of the filter, non-inverting output response, inverting output response or differential output property are all realized. The MDDCC output terminal is used as filter output terminal, so, the filter has high output impedance. Theoretical analysis and computer simulation results both indicate that, the two filter parameters of w0 and Q can be adjusted independently. The proposed circuit has all of the current-mode circuit advantages, and it has simple structure, strong universalism, very low filter sensitivities and suitability for fully integration.2. A Fully Balanced second-generation Current Conveyor (FBCCII) is proposed. According to the principle of FBDD A implementation, an FDCCII CMOS circuiton the basis of CCII and DDCC current conveyor is proposed, which duplicates the output current of FBDDA to the current output terminal. FBCCII is composed by adding two common-mode signal feedback circuits to FDCCII circuit. Computer simulation results show that, current-following ratio of FBCCII is superior to that of CCII;X terminal input resistance of CCII and FBCCII are both in the level of 1000 Q, but X terminal input impedance of FBCCII basically holds at about 1 .Ik Q, and it is stable when frequency is lower than 10MHz;Y terminal input impedance of FBCCII is remarkably higher than that of CCII, and is more approached to the theoretical value;When/^40MHz, Z terminal output resistance of FBCCII can be still as high as 100k^, which is remarkably better than CCII, so, FBCCII has higher effective operating bandwidth. FBCCII not only contains all functions of CCII but also presents superior features. It is the fully balanced structure of FBCCII that introduces better common-mode signal restrain ability and wider dynamic output range.3. A Multi-output Differential Difference Current Conveyor (MDDCC) based on current mirror is proposed.According to the principle of cross coupling current mirror, the MDDCC circuitmodel is composed by combining DDCC+ with DDCC-, and the CMOS implementation circuits is given. Simulation results show that, the voltage-following property of MDDCC is remarkably superior to that of CCII;MDDCC has wider current-following operating bandwidth than CCII, the input impedance of X terminal of MDDCC is lower than that of CCII by the scale of 10~2;the input impedance of Y terminal remarkably higher than that of CCII;the output impedance of Z terminal is twice of that of CCII. In a word, MDDCC, which has a simple structure and is suitable for fully integration, not only contains all functions of CCII but also presents superior features;it is the differential structure of MDDCC that introduces better output distortion property.4. Several current-mode filters are proposed, which are based on MDDCC, FBCCII and current mirror integrator and differentiator.(1) A MDDCC-based fully differential unloss and loss integrator as well as differentiator are proposed, which enriches the designing system of current-mode filter. Leapfrog-type Cauer low-pass current-mode filter, differential leapfrog-type current-mode low-pass filter as well as high-pass filter are all implemented by using the signal flow graph method. Maintaining the modularization feature of cascade structure, the leapfrog-type filter can offer low sensitivity feature relative to cascade structure.(2) A simulated inductance based on MDDCC is proposed, Butterworth high-pass filter, Butterworth band-pass filter as well as a Cauer low-pass filter are all built up by using the inductance simulating method. Compared with the current-mode filter which is composed by DDCC simulated inductances, MDDCC simulated inductance is more suitable for the simulated current-mode high-pass filter.(3) A differential current-mode double-integrator filter employing the differential integrator based on MDDCC is built up. Adopting current feedback, this filter has advantages of current-mode circuits. Using differential structure, it can cancel even-order harmonics. It has simple structure and is suitable for fully integration.(4) A multi-function current-mode biquad filter configuration with three inputs and one output using current mirrors is proposed. The filter uses two basic currentmirrors and two unloss integrators, and can realize low-pass, high-pass, band-pass, band-reject and all-pass filtering responses by changing input signal forms. The operating bandwidth of the filter can reach more than 10MHz. The filter circuit is low sensitivity, versatility and suitable for fully integration.(5) An improved leapfrog-type filter which cascades current mirror integrator with differentiator is proposed. The limitation that filter can only be implemented by using current mirror integrator is broken, signal flow graph and circuit structure of elliptic filter are simplified by this improved design method.(6) Computer simulations for all mentioned circuits above are completed in accordance with practical circuits, where, CMOS technologies process parameters of 1.2ju,m are chosen. PSPICE simulation results verify the correctness and effectiveness of proposed circuits.The study of fully integrated current-mode continuous-time filters has acquired quite great progress, but due to their short history, related theory and methods are still under developing. On the basis of the productions acquired by the predecessors, this paper has studied the fully integration current-mode continuous-time filters deeply, and obtained several achievements on improved circuit of current conveyor, current mirror circuit, and on design and implement current-mode continuous-time filters. This paper will promote the evolution of fully integrated current-mode continuous-time filters in some degree.