Operational Transconductance Amplifier for Low Frequency Application Abhay Pratap Singh*, Sunil Kr. Pandey*, Manish Kumar* *(Dept. of Electronics and Communication Engineering Jaypee Institute of Information Technology, A-10, Sector-62, Noida-201307, India Email: [email protected], sunilpandeyiert@gmail.com , [email protected]) Abstract This paper presents the design of CMOS operational transconductance amplifiers (OTAs) with very small transconductance (of order of nano ampere per volt), which uses in very low frequency continuous time filters. This design uses current division technique to reduce the transconductance of OTA. This design is simulated in SPICE tool using 0.25μm technology model file. Keywords - Low Frequency, Low Transconductance, OTA, SPICE 1. Introduction Low frequency circuits have a very important role in systems for biomedical, telemetry, real time speech recognition and infield of neural networks [1]-[3]. Thus, there is a strong motivation for developing integrated solution for circuits that are capable of operating at very low frequency. The design of these circuits is not an easy task especially for integrated circuit (IC) implementation. We know that time constant of operational transconductance amplifiers-capacitor (OTA-C) filter is determine by the ratio of load capacitor to the OTA small signal transconductance. For an OTA-C filter implementation such low frequency implies large capacitance and very low transconductance [4]-[5]. Thus there are two different techniques to solve this problem. One is to design an OTA with very low transconductance and is to realization of very large capacitance on a chip. Due to silicon area limitation, practical capacitances are limited to be below 50pF. Hence for implementation of 10Hz pole, transconductance of 3nA/V are required. In this paper, current division technique is uses for implementation of very large time constant. Using this technique we design a low transconductance OTA which can be used in low frequency application. 2. Operational Transconductance Amplifier (OTA) OTA is a voltage controlled current source, its takes the difference of the two voltages as the input for the current conversion. There is an additional input for a current to control the amplifier's transconductance. Fig 1: Ideal model of OTA Fig 2: Equivalent circuit of OTA The output current I 0 of the ideal OTA can be expressed by equation ) ( 0 N P m V V g I where g m , the transconductance can be expressed in terms of bias current (I bias ), charge (q), Boltzmann constant (K) and temperature (T) in Kelvin, as follows: bias m qI KT g 2 Since the output of an OTA is derived as the current, the output impedance of the OTA is very high (ideally infinity). Since g m of the OTA is dependent on the I bias current, the output characteristics of the OTA may be controlled Abhay Pratap Singh et al ,Int.J.Computer Technology & Applications,Vol 3 (3), 1064-1066 IJCTA | MAY-JUNE 2012 Available [email protected]1064 ISSN:2229-6093
3
Embed
Operational Transconductance Amplifier for Low Frequency ... · PDF fileOperational Transconductance Amplifier for Low Frequency ... Due to silicon area limitation, ... Boltzmann constant
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Operational Transconductance Amplifier for Low Frequency
Application
Abhay Pratap Singh*, Sunil Kr. Pandey*, Manish Kumar*
*(Dept. of Electronics and Communication Engineering