A switched differential op-amp with low offset and reduced 1/f noise

Fully differential techniques are becoming a popular method to alleviate the problem of low dynamic range in an analog VLSI environment. Low-frequency noise contributions and input offset voltage remain, however, as two inherent difficulties in MOS analog designs. In this paper, a dynamic technique for implementing low-noise low-offset differential op-amps by time-sharing conventional single-ended output op-amps is introduced. A differential op-amp (DOA) implemented using this technique requires relatively little redesign effort, provides both positive and negative differential inputs, and demonstrates significant reduction in noise and input offset voltage over its single-ended counterpart. The op-amp is applicable in many sampled-data networks, such as in the design of SC filters, and can be easily interfaced with existing single-ended or differential networks.