Abstract
The constraints on the design of CMOS operational amplifiers with rail-to-rail input and output range for extremely low supply voltage operation，are addressed. Two design approaches for amplifiers based on complementary input differential pairs are presented. The first，fabricated in a standard 0.35um CMOS process，realizes a feedforward action to accommodate the common-mode (CM) component of the input signals to the amplifiers input range. Then we choose the class-AB output stage to ensure the output swing is rail-to-rail. This Op-amp yields an unit-gain frequency of 1.9MHz，slew rate of 0.8V/us，chip area 0.089 mm2，and bandwidth-power ratio of 23.31 MHz/mW. Some specifications are even better than the of the proposed 1V rail to rail Op-amp. Another Op-amp，fabricated in a standard 0.25um CMOS process， lets several critical transistors in weak inversion region. The feedback class-AB is used to allow further lowering of operating voltage. This Op-amp had an unit-gain frequency of 1.8MHz，and DC gain of 81dB with bandwidth-power ratio of 32.73 MHz/mW. Experimental results are provided and the corresponding performance are discussed and compared.