Bio/CMOS Interfaces for Amperometric Sensing in Constant Bias

This is instead the first chapter dealing with design in Complementary Metal-Oxide Semiconductor (CMOS). This chapter addresses CMOS methods that exploit a constant bias to drive the Bio/CMOS interface. Initially, the chapter introduces the basic configurations for driving amperometric biosensors. Then, the chapter moves to a couple of equivalent circuits for the electrochemical interface by extending the simplest circuit introduced in Chap. 2 : the Randles model. These two extended models are discussed in terms of their limits of applications. Then, one of these two equivalent circuits is used to demonstrate the risk of saturation that may occur in the case of one of the basic configurations previously proposed. The text enlarges to variants of the basic configurations by proposing alternative CMOS architectures, which use current mirrors or blocks for noise and mismatch cancellation. An extremely useful and clever CMOS method for reading the interface current is also deeply discussed. This method proposes an approach that converts the current from the sensors to an output signal, which encodes the measured concentration in the frequency. The chapter moves by discussing the need for calibration with respect to the temperature of the interface and by describing a couple of CMOS interfaces with the aim of measuring such a temperature. Of course, the chapter closes by showing ways to multiplex the several sensors we may have at the Bio/CMOS interface.