High EMI immunity CMOS opamp: design and measurements

In this paper, a new approach to design a CMOS operational amplifier is presented which provides a good trade-off between high gain and strong immunity to electromagnetic interferences. The proposed amplifier is based on two main blocks: the first is a fully differential folded cascode amplifier with modified differential input pair and the second is a source cross coupled AB class buffer. Thanks to the folded cascade stage and to the symmetrical output buffer, the amplifier exhibits both intrinsic robustness to interferences and good amplifier performances. The circuit was fabricated in a 0.8/spl mu/m n-well CMOS technology (AMS CYE process). Experimental results, in terms of EMI immunity, are presented and successfully compared to commercial amplifiers. Measurements carried out on the chip and the amplifier overall performances are provided along with the corresponding simulation results.