A fully-differential operational amplifier using a new chopping technique and low-voltage input devices

摘要

A fully differential CMOS operational amplifier is presented. It uses a new chopping technique that works without the use of switching transistors in the high gain path, resulting in high noise performance and low offset. It is designed in a low-cost 180nm process with a 5V supply voltage. In critical places, such as the differential pair, 1.8V-devices are used, as they provide much better matching and noise performance, and at the same time have lower parasitics. They are protected from breakdown conditions by several circuit techniques. Some of them are described below. The operational amplifier is used in a differential programmable gain amplifier for processing signals of up to 50 kHz bandwith with a SINAD > 100 dB, making it suitable as a preamplifier for 18-Bit ADCs.