8 - Sensor interface, analogue processing and digital conversion

Abstract

This chapter focuses on sensor interface circuits, peak detector circuits, sample-and-hold circuits, and both analog-to-digital converter (ADC) and digital-to-analog converters (DAC). Interface circuits are required to convert the sensor's output signal into a convenient form. A high impedance and low-level sensor signal may have to be buffered and amplified before being processed by subsequent circuits. The peak detector circuits and the sample-and-hold circuits often process sensor signals. It may be that the largest signal within a certain period is required or the value of a signal at a particular instance is needed. The first stage in any measurement system is often a sensor or a transducer. This is a device for converting the quantity under investigation, such as the mechanical movement, temperature, pressure, and force, into an electrical signal. Some transducers have high output impedance that is essentially capacitive, such as piezoelectric accelerometers, pressure transducers, and capacitive (condenser) microphones. Transducers of this kind operate by producing a charge that is proportional to the measurement variable. The charge can be converted into a voltage by using an op-amp connected as a current integrator.analog