Resistive Sensor Interfacing

Abstract

Abstract. This chapter has the aim to give a complete overview on the first analog front-ends, describing some circuit and system solutions for the design of electronic interfaces suitable for resistive sensors showing different variation ranges: small, as in dedicated-application GMR sensors; wide, especially referred to GMR sensing devices whose baseline is unknown. After a description of the main interface parameters, the authors present several solutions, most of which do not require any calibration. These solutions are different according to the entity of resistive sensor variations, can utilize either AC or DC excitation voltages for the employed sensor and are developed in Voltage-Mode (VM, which considers the use of either the Operational Amplifier (OA) or the Operational Transconductance Amplifier (OTA) as main active block) as well as in Current-Mode (CM) approach (being in this case the Second Generation Current Conveyor (CCII) the active device). The described interfaces can be easily fabricated both as prototype boards, for a fast characterization, and as integrated circuits, also using modern microelectronics design techniques, in a standard CMOS technology with Low Voltage (LV) and Low Power (LP) characteristics, especially when designed for portable applications and instrumentation. Moreover, thanks to their reduced sizes in terms of chip area, the proposed solutions are suitable for being used for sensor arrays applications, where a number of sensors is employed, as in portable systems, to detect different environmental parameters.

Uncalibrated operational amplifier‐based sensor interface for capacitive/resistive sensor applications

“…Typical design techniques are referred to the voltage‐mode approach using operational amplifiers (OAs) and current‐mode approach by employing second generation current conveyors. Oscillating circuits are largely employed in many research and application fields, such as telecommunications, measurement systems and, also, as first analogue interfaces for sensor applications [1–23]. Typically, oscillators are based on an R − C integrating cell, providing a switching current source that charges and discharges a capacitor (e.g.…”

“…In fact, their output period is directly linked to the measurand value; moreover, thanks to their impedance‐to‐period ( Z–T ) conversion, their utilisation as first analogue front‐ends overcomes typical problems related to those interface circuits performing an impedance‐to‐voltage conversion (e.g. bridge‐based topologies) more suitable for reduced variations of the measurand, especially in low‐voltage low‐power solutions [1, 2, 35–55].…”

“…a capacitive sensor), followed by a voltage hysteresis comparator. In sensor interface, when the resistive or capacitive sensing device shows a wide variation baseline or range, oscillators result to be the best solution [1, 2, 24–34]. In fact, their output period is directly linked to the measurand value; moreover, thanks to their impedance‐to‐period ( Z–T ) conversion, their utilisation as first analogue front‐ends overcomes typical problems related to those interface circuits performing an impedance‐to‐voltage conversion (e.g.…”