In this paper, we present a new structure of a CMOS Op Amp offering high performances differential frequency response with high CMRR, high slew rate and input/output rail-to-rail mode. These performances are due both to a new efficient gain stage with a compact layout and to a simple way to obtain a high CMRR. Simulation experiments have been performed with three different (0.8 /spl mu/m, 1.2 /spl mu/m, 2.4 /spl mu/m) CMOS technologies. In particular for the 0.8 /spl mu/m one, the main performances-under single 5 V power supply are a unity gain bandwidth of 40 MHz, a phase margin of 63 degrees, a slew rate of 60 V//spl mu/s, all performed on heavy load such as 2.5 k/spl Omega//spl par/20 pF. Simulated results have been experimentally confirmed for the 2.4 /spl mu/m CMOS technology for which we have measured a low frequency CMRR of 100 dB.