A Chopper Instrumentation Amplifier with Offset Reduction Loop

This chapter discusses the design and implementation of a chopper current-feedback instrumentation amplifier (CFIA). This amplifier can be used in stand-alone sensor read-out systems that need to drive an external analog-to-digital converter (ADC). Firstly, the requirements on the amplifier are described. It is targeted for thermistor read-out applications in wafer steppers (see Chap. 1). The design of the CFIA is then discussed. Both the input and intermediate stages of the CFIA are chopped to achieve a low 1/f noise corner. To reduce chopper ripple, a continuous-time (CT) offset reduction loop (ORL) is proposed. Due to its CT nature, it does not cause noise folding, thus offering improved power efficiency over auto-zeroed amplifiers. It will be shown that this ORL can be applied to both general-purpose instrumentation amplifiers and operational amplifiers.