Enhance the Op-Amp Performance by Improving Gain and CMRR Ratio

Abstract

In this paper the Op amp circuit is implemented at low voltage, high gain, high CMRR ratio and low frequency for a biomedical application. This work evince that the composite cascade differential stage op amp operating in the weak inversion region of MOSFET, can operate at a supply voltage of 2v and provide a gain of 114db, Unity gain frequency of 6KHz and gain bandwidth of 686.98KHz ( pf) and CMRR ratio is of 153dB (1HZ) .The schematic of op-amp is designed using 0.25µm CMOS technology. This technique result satisfies the requirements of a biomedical application. Keywords-operational amplifiers, gain, CMRR, unity gain frequency I. INTRODUCTONP-amp is much known by its best performance, and the overall system performance is strongly impacted by the op-amp performance. Now days the schematic is designed by CMOS process. Complementary metal-oxide semiconductor (CMOS) technology is back bone for mixedsignal. Presently the CMOS technology is a leading semiconductor technology for processors, memories and specific integrated circuits (ASICs).The main motive of CMOS, it provides power saving. A CMOS circuit has approximately no static power dissipation. Power is merely dissipated when the circuit actually switches. Many more CMOS gates are integrated on a single chip IC, resulting in much better performance then bipolar technology. In case of CMOS technology the design of analog circuits becomes increasingly more difficult as the device modelling faces new challenges in deep sub micrometer processes and emerging circuit applications. In recent years, biomedical instrumentation amplifiers more strongly grow [1]. The requirements for a biomedical application are low power, low frequency and high gain [1] [2], amplifiers that occupy least amount of area of the chip. BSIM3 has been the most-used mainstream MOSFET model since the end of the 90s [5]. There are three version of it, but basically only the third version has been used, in other words BSIM3 [4] is said to be a third generation model. The integrated circuit field is expanding rapidly [2]. The continuous scaling of CMOS processes continually challenged to design operational amplifiers. Scaling down of CMOS feature sizes enable yet faster speeds, the supply voltage is scaled down to enhance device reliability and improve power consumption. The relation of short channel MOSFET transition frequency ( ) and open-loop gain ( . ) are given as [3]1.1 . 1.2As can be seen from Equations 1.1 and 1.2 if the is higher than the size is scaling down according to , and therefore faster operating transistors. Thus, amplifiers designed in smaller feature size processes exhibit moderate bandwidth but higher open loop gain. As move to lower feature size processes they require list supply voltage. Battery operated products is the best example of low power microelectronic. The motivation for the low power electronics has developed from Portable battery operated equipment, having a long in operating life and small in size and weight to satisfy customer. The proposed design offers an op ...