The Study Of Continuous-time Current-mode Filters Based On Current Conveyors

The technique of continuous-time filter design is one of the advanced subjects in microelectronics, circuits and system. It is widely used in communication, electronic measurement, instrument & appearance and cybernation. Especially it has an important application in mixed signal circuits of digit and analog, communication IC. Current-mode filters have been paid attention due to their high speed, low power and simple structures and compatibility with CMOS technology.The dissertation studies the realization method of modified current conveyors and the structures, realizations and design methods of second-order and high-order current-mode filters based on modified current conveyors. This work is sponsored by the Young Teacher Foundation of JiLin University.In the dissertation, the international and internal current states of continuous-time filters and the developments and trends of the universal active elements are reviewed. The design methods of current-mode current conveyors filters are examined. The modified circuits of modified differential different current conveyor (MDDCC), fully balanced second-generation current conveyor (FBCCII) and fully balanced four-terminal floating nullor (FBFTFN) are proposed. The current-mode second-order and high-order filters based on them are synthesized.The PSPICE simulation to the proposed circuits at the MOS transistor lever is carried out. The characteristics of filters are discussed and analyzed. At last, the summary of the dissertation the tendency direction of the continuous-time current-mode current conveyors filter for the future researches is prospected. The main achievements consist of following several aspects:1. The modified circuits of modified differential different current conveyor (MDDCC), fully balanced second-generation current conveyor (FBCCII) and fully balanced four-terminal floating nullor (FBFTFN) are proposed. On the basis of theory of CCII, because differential difference amplifier (DDA) has high input impedance and strong capacity of arithmetic operation, we create a new active element, which is called as modified differential different current conveyor (MDDCC) by the principle of cross-coupled current mirror. The MDDCC circuit combines the advantages of DDA and CCII, and takes place of the CCII circuit. As to its fully differential structure, it is superior to the CCII circuit.On the basis of the documents, the modified circuits of FBCCII and FBFTFN are proposed. Its input and output terminals are symmetry strictly. This is because fully balanced operation improves the performance of analog system in terms of noise rejection, dynamic range and harmonic distortion and reduces the effect of coupling between various blocks.The principle of the three modified current conveyors are analyzed, the frequency characteristics, the circuit implements, and the application to analog signal processing are proposed.2. The current-mode second-order filters based on MDDCCs and FBCCIIs are proposed. The universal current-mode biquadratic filter is composed of three MDDCCs and seven RC elements. And the low-pass, band-pass, high-pass, band-stop and all-pass filters can be realized simultaneously. The circuit has several advantages, such as very low passive sensitivities, multiple output and performance stability, all resistances and capacities of the circuit are grounded and suitability for fully integration.The current-mode biquad with minimum number of passive elements based onMDDCCs is proposed. The biquadratic filters enable simultaneous realization of LP and BP or BP and HP by two different sets of selection of passive elements. The filter ideally exhibits zero input and very high output resistance. The frequency character, passive sensitivities and the non-idealities of the filters are discussed. Contrasting with the curves of simulation, the errors between the actual value and the standard value of the electronic components results in the deviation of the output current tracking curves, which is independent of the characteristics angular frequency and quality factor, the error affects the output amplitude. Thus, the filter has an advantage of low passive sensitivities.The principles, structures and characteristics of all kinds of block buildings based on FBCCII are systematically investigated, and a balanced band-pass biquad filter is designed. The fully balanced band-pass biquad filter based on FBCCII is advantageous over the one based on the single-end CCII in many aspects, such as dynamic range, harmonic distortion, distortion and noise rejection.According to the rule of Mason, the systematic structure of voltagentnode biquadratic filter is obtained. The universal biquadratic filter based on FBCCIIs is realized in accordance with the theory of inter-reciprocities and the adjoint networks. The versatile current-mode filter can realize low pass, high pass, band pass filtering responses simultaneously.The passive sensitivities of all biquadratic filters are no more than 1.3. The current-mode high-order filters based on modified current conveyors are designed using the method of inductor simulation, frog-leap structure and cascade connection. A systematic design method and theory of inductor simulation are introduced. With the theory and method of the grounded inductor and floating inductor, the high-order low-pass, band-pass, high-pass filters based on CCIIs and modified current conveyors can be realized. The effect on the floating simulating inductors results of the deviation of the voltage and current is analyzed. Simulation inductor based on MDDCC is presented in order to remove passive inductor in the fully integrated circuits. Continuous-time high-pass filters with simulation inductor on the basis of MDDCC and DDCC are implemented. The performances of thesimulation inductor and analyzed through PSPICE software, and the simulation results show that amplitude frequency character of the proposed circuits is superior to the one of DDCC in high-pass filter.The advantage of designing active filters by simulating the inductors of a passive LCR realization of the filter include low component sensitivities and the ability to utilize the extensive knowledge of LCR filter design. The frog-leap structure and the cascade current-mode filter based on FBCCII and FBFTFN. With the law of Mason, the fully balanced second-order high-pass filter based on FBCCII is realized at first, the two second-order high-pass filters are connected in cascade to obtain the fully balanced four-order high-pass filter. The two structures are very simple, effective, easy to implement and suitable for the mixed analog and digital circuits. All of the resistances and capacities are grounded and suitable for fully integration.In summary, all the related theories and the analytical and synthesized method, the performance analysis and the comparison of filters proposed in the research about the continuous-time current-mode current conveyor filters will provide a guide to the design of the practical filters, enrich the filter theories, promote the continuous-time current-mode signal processing as well as the neural network studying.