Study and investigation of a new technique for adaptive cancellation of MOSFET op amp noise

Abstract

The need for noise-free operational amplifiers for use in many precision applications has greatly increased recently. This paper presents a new technique for adaptive cancellation of noise in MOSFET IC operational amplifiers. It employs a new circuit configuration comprising two operational amplifiers having common current source, one is passive with its inverting and non inverting inputs short circuited. This operational amplifier is only responsible for amplifying its equivalent input noise and to give a proportional output voltage. The second operational amplifier is active and used to amplify the signal to be processed together with the operational amplifier equivalent input noise and gives a proportional output voltage. The two operational amplifiers are cross coupled to each other so that the noise of the passive amplifier is amplified and subtracted from the output of the second one and makes it, therefore noise free (/spl sim/0.22 nV//spl radic/(HZ) or 20 m Vrms within 2.5 kHz bandwidth over frequencies extending from very low frequency up to GHz), over a very wide dynamic range of input voltage (/spl sim/120 dB) and ambient temperature (/spl sim/0 to 50/spl deg/C). A feedback loop is added to improve the amplifier linearity (better than 2%). The standard submicron MOSFET technology (/spl sim/0.2 /spl mu/m to 2 /spl mu/m) is used for the realization of the proposed noise free op amp.