A Laser-Trimmed Rail-to-Rail Precision CMOS Operational Amplifier

This brief presents a rail-to-rail input-output precision operational amplifier with integrated laser-trimmable polysilicon resistors for reducing the input offset voltage. The amplifier is fabricated in a standard Taiwan Semiconductor Manufacturing Company 0.18-μm complementary-metal-oxide-semiconductor process technology. The resistors' trimming sequence allows for minimizing the offset voltage over the complete input common mode voltage range (ICMR) extending from the ground to the supply. Experimental results are presented to demonstrate the steps involved in offset-voltage trimming. The prototype amplifier drives a 400-pF capacitive load and operates from a 3.3-V supply. The amplifier is unity-gain stable with a phase margin of 58° and has an open-loop direct-current gain greater than 130 dB with a unity-gain bandwidth of 0.5 MHz. Experimental results show that an untrimmed input offset voltage ranging from +0.1 to +0.5 mV over the ICMR was reduced to -30 to + 30 μV.