Circuits and Systems, 2013, 4, 11-15 http://dx.doi.org/10.4236/cs.2013.41003 Published Online January 2013 (http://www.scirp.org/journal/cs) A New Design Technique of CMOS Current Feed Back Operational Amplifier (CFOA) Hassan Jassim Department of Electrical Engineering, College of Engineering, Babylon University, Babylon, Iraq Email: hssn_jasim@yahoo.com Received September 14, 2012; revised October 29, 2012; accepted November 6, 2012 ABSTRACT A new design technique employing CMOS Current Feedback Operational Amplifier (CFOA) is presented. This design approach applies CFA OTA as input stage cascaded with class AB cross-coupled buffer stage. The performance pa- rameters of CMOS CFOA such as bandwidth, slew rate, settling time are extensively improved compared with conven- tional CFOA. These parameters are very important in high frequency applications that use CMOS CFOA as an active building block such as A/D converters, and active filters. Also the DC input offset voltage and harmonic distortion (HD) are very low values compared with the conventional CMOS CFOA are obtained. P-Spice simulation results using 0.35 µm MI-ETEC CMOS process parameters shows considerable improvement over existing CMOS CFOA simulated model. Some of the performance parameters for example are DC gain of 67.2 dB, open-loop gain bandwidth product of 104 MHz, slew rate (SR+) of +91.3 V/µS, THD of −67 dB and DC input offset voltage of −0.2 mV. Keywords: Synthesis CFA OTA and CMOS CFOA; Cross Coupled Buffer Stage; High Performance CFOA; Low Input Offset Voltage CFOA; Low Distortion CFOA 1. Introduction The role of analog integrated circuits in modem elec- tronic systems remains important, even though digital circuits dominate the market for VLSI solutions. Analog systems have always played an essential role in interface- ing digital electronics to the real world in applications such as analog signal processing and conditioning, in- dustrial process, motion control and biomedical meas- urements [1]. However, the conventional CMOS CFOA design is still facing certain problems, first, the offset voltage on the current feedback can not be made zero. CFOA usually adopts an analog buffer as the input stage. As a result, the non-inverting input has very high im- pedance, while the inverting input has very low imped- ance. Hence, the CFOAs offset is higher than folded cascade voltage amplifier (VFA) Design. Second, the constant bandwidth feature of the CFOA is only ap- proximate if the inverting input impedance is not small enough [2,3]. The low-input offset voltage is considered as an important aspect of the performance of an amplifier especially when signals are in the range of few hundred micro volts [4]. Several CMOS realizations for the CFOA have been reported in the literature [5-12]. The design still suffers from many drawbacks such as high distortion, high noise, high consumption of power and complex circuitry. The CFOA has been always seen as an extension of the CCII, therefore, the design approach was cascade with CCII+ with a voltage follower to real- ize a complete circuit. The obtained bandwidth was al- ways the degraded version of CCII+. The current feedback operational amplifier (CFOA), a two-port (four-terminal) network. The CFOA could be realized by using second generation current conveyor CCII+ cascaded with a voltage follower [13]. This paper describes an alternative approach to CMOS CFOA design which provides symmetrical high imped- ances (infinite for DC) inputs together with high per- formance parameters in high frequency operation. This design approach applies CFA OTA as input stage cas- caded with class AB cross-coupled buffer as output stage. The symmetrical input stage of CFA OTA will reduce the DC offset voltage of CMOS CFOA with improve- ment of high frequency parameters. Moreover, class AB cross coupled buffer stage provide high current drive capability. P-Spice simulation results confirm the theo- retical calculations. 2. Theoretical Background of CFB OTA The two output terminals are not seen as one port each, but as four independent terminals that can have different impedance levels. As a consequence, hybrid stages ap- pear, namely a H input stage and a H output stage. The H input stage, which has become well known through the CFB opamp, can also be understood as an extended input Copyright © 2013 SciRes. CS