Johan Hendrik Huijsing

Dynamic offset-cancellation techniques

This chapter describes the theory and design of the different kinds of dynamic offset-cancellation techniques. These techniques can reduce the offset of an amplifier by a factor of 100 to 1000 and do not need trimming. Knowledge of these techniques is necessary to improve the accuracy of CMOS smart temperature sensors. Also in this chapter, a new technique is proposed that can even further reduce the offset. This technique is called the “nested chopper technique”. An implementation of this new technique is shown and measurement results are discussed.

Dynamic Offset Cancellation Techniques for Operational Amplifiers

At low frequencies, offset, 1/f noise and drift are the dominant error sources of operational amplifiers. This is especially true in CMOS technology. This chapter reviews precision techniques that can be used to achieve low 1/f noise and low offset in operational amplifiers.

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.

A Chopper Instrumentation Amplifier with Gain Error Reduction Loop

This chapter describes a stand-alone chopper current-feedback instrumentation amplifier (CFIA) that has improved performance compared to the one described in Chap. 4. It maintains the latter’s low noise and low offset, and also obtains high gain accuracy and low gain drift without trimming. This is achieved by applying dynamic element matching (DEM) to the input and feedback transconductors so as to average out their mismatch. To eliminate the resulting DEM ripple, a gain error reduction loop (GERL) is employed to continuously null the Gm mismatch. The concept and analysis of DEM and the GERL is presented in Sects. 5.2 and 5.3. Then the similarities and differences between the offset reduction loop (ORL) and the GERL are discussed, together with their effects on the input and feedback Gm transfer functions.

Current-Feedback Instrumentation Amplifiers and Gain Accuracy Improvement Techniques

As discussed in Chap. 1, compared to other instrumentation amplifier topologies, the current-feedback instrumentation amplifier (CFIA) is more suitable for bridge read-out because of its high CMRR [1, 2], rail-sensing capability [1], high input impedance and power efficiency [3, 4].