Study On Fully-integrated Current-mode Continuous-time Filters Based On Current Mirrors

Current-mode circuits have more advantages such as wide bandwidth, high speed,high precision, large dynamic range, simple structure, so it has attracted much attentionfrom many researchers. Continuous-time filter doesn’t need A/D switch, D/A switch,data processing and other links to achieve the purpose of changing the filterperformance like the digital filter, and it has low power consumption. Current-modecontinuous-time filter combines the advantages of the current-mode circuit andcontinuous-time filter, it is suitable for fully integration. In the current-modecontinuous-time filter basic unit, the current mirror is one of the most basic and flexibleparts, using it can easily design the basic unit of the filter, in order to further thecomposition of filter. Current-mode continuous-time filter based on current mirrors,which uses CMOS current mirror circuits as the basic unit of the filter and then applythe basic unit circuits to design current-mode continuous-time filters. In this paper, theprinciple of current mirror circuits and relevant theory and technologies for designingand implementing fully integrated current-mode continuous-time filters are studiedsystematically, fully integrated current-mode continuous-time filter circuits usingcurrent mirrors are proposed. PSPICE simulations are completed reference to practicalcircuits, where parameter of CMOS technology is TSMC0.18μm, the simulationresults verify that the proposed circuits are correct and valid. To sum up, the mainachievements and conclusions in this paper are as follows:(1) A current-mode continuous-time general nth-order filter configuration usingcurrent mirrors is proposed. The filter uses n basic current mirrors and n unlossintegrators, and can realize low pass, high pass, band pass, band reject and all passfiltering responses by changing input signal forms. As a design example, a fourth-orderfilter related CMOS circuit is presented. PSPICE simulation is carried out and thesimulation results show that the proposed circuit is valid. The circuit has severaladvantages, such as low voltage, low power dissipation, wide frequency band and verylow filter sensitivities, which will has a broad prospect in application.(2) A current-mode high-order filter using current mirrors via linear transformationis proposed. Linear transformation theory is studied deeply, a simple and systematicdesign table is given to realize current-mode filters using current mirrors. Using theproposed design table, high-order elliptic filters can be designed easily. As an example,a third-order elliptic lowpass filter is realized. PSPICE simulations reference to therealized circuit have been carried out and the simulation results are agree with the theoretical analysis. The circuit has several advantages, such as low voltage, simplecircuit, low filter sensitivities, adjustable cutoff frequency, which is suitable for fullyintegration.The study of fully integrated current-mode continuous-time filter in recent yearshas made considerable progress, but related theory and methods for studying fullyintegrated current-mode continuous-time filter based on current mirrors are constantlybeing improved because of its short history. This paper has studied the fully integratedcurrent-mode continuous-time filters deeply, and made several achievements in thedesign and realization of fully integrated current-mode continuous-time filter based oncurrent mirrors. These achievements will enrich fully integrated current-modecontinuous-time filter design ideas and provide certain guiding significance to its theorydevelopment.