Active Filter Design using Bulk Driven Operational Transconductance Amplifier Topology

Abstract

In this paper, an Active filter design using OTA has been done. Operational transconductance amplifier is taking input as a voltage and produces output as a current at the output terminal. Active filter design using operational transconductance amplifier such as Low pass filter (LPF), High pass filter (HPF), Band pass filter (BPF), Band rejection filter (BRF),(or) notch filter are implemented. The total number of components used in these circuits is small, and design equation and voltagecontrol characteristics are attractive. Active filter designs using the transconductance amplifier are discussed. It is shown that these structures offer improvements in design simplicity and compared to op amp based structures as well as reduced component count. Simulation results of the design have been obtained and cutoff frequencies for low pass filter at 1.5 kHz, where as high pass filter 20 kHz and Bandwidth 700 kHz. At Transconductance of 10nA/v. This work has been carried out using Pspice Simulation software and the results obtained are in accordance with theoretical facts. OTA is an amplifier whose differential input voltage produces an output current at the output terminal. it also called as voltage controlled current source . There is usually an additional input for a current to control the amplifier's trans conductance. The OTA is similar to a standard operational amplifier in that it has a high impedance differential input stage and that it may be used with negative feedback. Many of the basic OTA based structures use capacitors are attractive for integration Component count of these structures is often very low when compared to VCVS designs. Convenient internal or external voltage or current control of filter characteristics is attainable with these designs. They are attractive for frequency referenced applications. Several groups have recently utilized OTAs in continuous-time monolithic filter structures. [1]. From a practical viewpoint, the high-frequency performance of discrete bipolar OTAs, such as the CA3080, is quite good. The first commercially available integrated circuits units were produced by RCA (Radio Corporation of America) in 1969 in the form of the CA3080 and they have been improved since that time. Although most units are constructed with bipolar transistors, field effect transistor units are also produced. The OTA is not as useful by itself in the vast majority of standard op-amp functions as the ordinary op-amp because its output is current.OTA application such as variable frequency oscillator and filter and variable gain amplifier stages which are more difficult to implement with standard op-amps.its output of a current contrasts to that of standard operational amplifier whose output is voltage. It is usually used open-loop without negative feedback in linear application. This is possible because the magnitude of the resistance attached to its output controls its output voltage. Therefore a resistance can be chosen that keeps the output from going into saturation, even with high differential input voltage. The transconductance gain (gm) can be varied over several decades by adjusting an external dc bias current, IABC. The major limitation of existing OTAs is restricted differential input voltage swing required to maintain linearity [3]. For the CA 3080, it is limited to about 30 mV p-p to maintain a reasonable degree of linearity. Although feedback structures in which the sensitivity of the filter parameters is reduced be discussed, major emphasis will be placed upon those structures in which the standard filter parameters of interest are directly proportional to gm of the OTA.