Current-Mode Filters Advanced Synthesis Methods, Based on Intermediate Transfer Function Algorithm ELENA DOICARU 1 , MIRCEA BODEA 2 , CLAUDIUS DAN 2 1 Faculty of Automation, Computers and Electronics University of Craiova Bvd. Decebal 107, 200440 Craiova 2 Faculty of Faculty of Electronics, Telecommunication and Information Technologies POLITEHNICA University of Bucharest Bvd. Iuliu Maniu 1-3, 77209 Bucharest ROMANIA dmilena@electronics.ucv.ro, claus@mESsnet.pub.ro Abstract: - In this paper are presented two current mode techniques for low-voltage, continuous-time, analogue filter implementation. The first presented technique is adequate for very low power application and is based on a translinear approach. The second presented technique is adequate for high frequency application. In the paper, firstly, the state-space description and the used synthesis techniques of current-mode filters are presented. Then the two different current-mode integrators are presented and analyzed. Finally, as a test vehicle for the proposed techniques, two low voltage, third order, continuous-time filters, for low power applications structure implementation are described and analyzed. Key-Words: - Analogue signal processing circuits, CMOS analogue filters, low power and voltage circuits. 1 Introduction The existing CMOS technologies provide ample opportunities to integrate entire system on a single chip. To date, the ability to integrate large digital systems has far out weighted the ability to integrate the analogue systems. The greatest impediment to analogue CMOS VLSI design has been the difficulty to get consistent circuit performance over the broad range of requirements for signal gain, frequency and/or phase response, delay, power consumption and signal integrity. In the same time the analogue design in mixed signal environments becomes more difficult and challenging as the IC’s power supply voltage scales down, to the values slightly higher than the MOS threshold voltage. The analogue signal processing at low values of supply voltages can best be performed in the current-operation domain, because the very low voltage swings are avoided. In translinear circuits the MOS transistors usually operate in weak inversion (or sub-threshold) region, [1], where the current-voltage characteristic is exponential. So these circuits can be used in very low power application. The main problems associated to the sub-threshold region operation are the relatively low speed capability and inferior matching. But these problems are relatively solved in sub-micron tech- nology. Yet, significantly better performances in frequency response are obtained when the MOS transistors operate in strong inversion. Therefore we conceived two integrator cells. In the first one the MOS transistors operate in weak inversion and in the other MOS transistors operate in strong inversion. Also we developed synthesis techniques, based on intermediate transfer functions method, for both integrator cells. This paper first presents the synthesis techniques for continuous time current-mode filters operating at low supply voltage. Then the used current-mode integrators are presented and analyzed. The basic current-mode integrators are based: - the first, on the translinear technique and - the second, on an adapted form of pseudodifferential transconductor presented in [2], but ours have a folded cascod structure and presents good performances for the low-cost standard CMOS technology. Finally the structure of a two different third order low-pass current-mode filters in 1μm CMOS technology are presented. In this technology the SPICE simulations show: - For the first filter a 1 kHz cut-off frequency, a dynamic range greater than 45dB for 1V supply voltage and power consumption smaller than 0,5 mW. WSEAS TRANSACTIONS on ELECTRONICS Elena Doicaru, Mircea Bodea and Claudius Dan ISSN: 1109-9445 111 Issue 4, Volume 5, April 2008