Design of two stage high gain opamp computer science essay

In designing an opamp, numerous electrical characteristics, e. g. , gain-bandwidth, slew rate, common-mode range, output swing, offset, all have to be taken into consideration. Furthermore, since opamps are designed to be operated with negative-feedback connection, frequency compensation is necessary for closed-loop stability.

Transistors M1, M2, M3, and M4 form the first stage of the op amp the differential amplifier with differential to single ended transformation. Transistors M1 and M2 are standard N channel MOSFET (NMOS) transistors which form the basic input stage of the amplifier. The gate of M1 is the inverting input and the gate of M2 is the non-inverting input.

Fig 1 & Fig 2 shows the Gain and Phase plot for basic two stage opamp. After simulation we have analyzed that the gain of the opamp is 94.34db and have a phase margin of 109.7 degree at 40 MHz frequency. This analysis can be made possible using different sizing of the MOS transistor at different stages.

A High Swing Ultra-Low-Power Two Stage CMOS OP-AMP in 0.18 um Technology with 1.2v supply, is presented. Cascode technique has been used to increase the dc gain. The unity-gain bandwidth is also enhanced using a gain-stage in the Miller capacitor feedback path. The proposed opamp provides 236MHz unity-gain bandwidth, 109.7 degree phase margin.