Investigation of a New Technique for Adaptive Cancellation of Noise in MOSFET Op. Amps.

The paper presents a new technique for adaptive cancella- tion of noise in MOSFET IC operational amplifiers. It employs two operational amplifiers, one is passive with its inverting and noninvert- ing inputs short circuited. This operational amplifier is only responsi- ble to amplify its equivalent input noise and to give a proportional output voltage. The second operational amplifier is active and is used to amplify the signal to be processed together with its equivalent input noise and gives, thus, a proportional output voltage. The two opera- tional amplifiers are coupled to each other through a common floating gate so that the noise of the passive amplifier is subtracted from the input of the second one and makes it, therefore, noise-free (~lnV/√  Hz or 0.1 µV rms within 2.5 kHz bandwidth) over a wide variety dynamic range of input voltage (~120 dB) and ambient temperature. A feed- back loop is added to improve the amplifier linearity (better than 2%). The standard 2 µm CMOS technology is used for the realization of the proposed noise-free operational amplifier.