A CMOS folded-cascode operational amplifier having low flicker noise

摘要

The flicker noise (1/f noise) contribution of the mirror and bias transistors MNM1, MNM2, MPB1, MPB2 in a folded-cascode amplifier is reduced by using thin oxide layers in these devices. The cascode transistors MN1, MN2, MPC1, MPC2 and input transistors MP1, MP2 possess a thicker oxide layer so they can withstand greater voltages. The mirror and bias transistors may have an oxide thickness of 70 nm and operate at 3.3 volts. The cascode and input devices may have an oxide thickness of 350 nm and operate at 18 volts. The clamp transistor MPX protects MNM2. The input devices may have thin oxides (figure 4). The amplifier may be part of an IC comprising both analogue and digital circuits. The IC may be used in portable equipment.