An operational amplifier (OPAMP) for portable devices with dual supply voltage is presented in this work. The design is realized with a 600mV supply for the core design and a 1.8V supply for the biasing circuit to improve input common mode range (ICMR), gain, and common mode rejection ratio (CMRR). The designed amplifier is implemented with dynamic threshold voltage MOSFET (DTMOS) transistors to decrease power consumption and increase the performance of the design. The power consumption of the core design is obtained as 2 mu W while the biasing circuitry consumes 7.38 mu W. The application of different supply voltages has greatly increased the gain of the circuit, where the circuit exhibits 100.2dB DC gain and 3.41MHz gain bandwidth product (GBW). CMRR of the designed circuit is 84.22dB. The simulations are performed in Cadence environment with 0.18 mu m CMOS technology.