Low-voltage rail-to-rail CMOS differential difference amplifier

This paper introduces a low-voltage rail-to-rail wide range CMOS Differential Difference Amplifier (DDA). The input stage of this DDA comprises two rail-to-rail VI converters with large signal handling capability. In each V-I converter, an N-type converter cell is connected in parallel with its P-type counterpart cell in order to cover all the operating range of the common-mode input voltage. Its constant transconductance is achieved through the use of two maximum-current selecting circuits and an output substraction stage. Simulation results of the DDA with 3 V supply show that the DDA has a rail-to-rail constant input transconductance, a rail-to-rail output swing, 66 dB open-loop gain, and a 2.2 MHz bandwidth with C_L=30 pF and R_L=250 Ω. Low-voltage DDA-based circuits, such as an adder/substractor and an integrator, are given in this paper. They constitute basic blocks of modern low-voltage analog signal and information processing systems