Readout circuits sensors

A monolithic three-axis accelerometer with three independent capacitive readout circuits on a single chip is described elsewhere [7] (Fig. 6.1.14). The circuit is similar to Fig. 6.1.10 and achieves 0.085 aF/v/Hz resolution with 100 fF sense capacitors. The noise is actually dominated by Brownian noise in the sensor itself, as tests in vacuum demonstrate. The actual capacitance resolution is therefore somewhat better than stated. This circuit uses correlated double sampling (CDS) for biasing and to reject flicker noise. 

Fig. 7.18.3 shows the output of a prototype capacitive sensor fabricated by Bosch, showing a linear dc output voltage depending on the RME content in the fuel mixture. The sensor utilizes a coaxial capacitive probe and a dedicated readout circuit operating on a 5 V supply. 

Modulation-based readout circuits have gained popularity for interfacing with capacitive and inductive MEMS sensors to reduce the noise levels of l// noise and direct current (dc) offset in the circuit. Modulation-based circuits are based on sigma-delta (2A) converter [56,62,65], successive approximation register (SAR) analog-to-digital converter (ADC) [56,66], chopper modulation [54,55,58], pulse-width modulation (PWM) [57,61,63], and frequency modulation (FM) configurations [42,48,51,64,68],... 

M.S. Arefln, M.B. Coskun, T. Alan, J.-M. Redoute, A. Neild, M.R. Yuce, A microfabricated fringing field capacitive pH sensor with an integrated readout circuit. Applied Physics Letters, 104 (2014) 223503. 

The architecture of a wireless capsule system named the lab-in-a-pill (LIAP) is presented in Fig. 7.13 [113]. It consists of pH and temperature sensors and a custom-made application-specific integrated readout circuit. The pH sensor is a micro-fabricated ISFET with Ag/AgCl reference electrode. The temperature sensor is an n-channel silicon diode. The system consumes 15.5 mW. The circuit has a power saving feature to operate it for 42 h. 

N. Yazdi, H. Kulah, K. Najafi, Precision readout circuits for capacitive microaccelerometers, in Proceedings of the IEEE Sensors Conference, 2004, pp. 28-31. 

J.-L. Lu, M. Inerowicz, S. Joo, J.-K. Kwon, B. Jung, A low-power, wide-dynamic-range semi-digital universal sensor readout circuit using pulsewidth modulation, IEEE Sensors Journal 11 (2011) 1134-1144. 

The current-voltage (I-V) measurement system is composed of Keithley 236 Semiconductor Parameter Analyzer and a readout circuit of n-MOSFET. The sensitivity and linearity of flexible array sensor measured in the concentrations between pHl and pH 13 at room temperature (25 °C) were represented in Table 1. The ranges of sensitivity and linearity were from 49.77 mV/ pH to 56.74 mV/pH and from 0.994 to 0.998, respectively. At present, the pH array sensors have been fabricated successfully and applied to I-V measurement system. 

X-ray photons, produced by rotating anodes or by synchrotron radiation, are focused by means of bending mirrors and monochromated by means of a crystal oriented in such a way as to fulfill Bragg conditions. The monochromatic particles, after being scattered by the sample, are collected onto a two-dimensional detector. In the case of X-ray, the detector consists of a pixelated CMOS readout circuit connected to a semiconductor sensor. The photoelectric charge created by the absorption of an X-ray photon in the sensor is detected by... 

This chapter includes two different sensor system architectures for monolithic gas sensing systems. Section 5.1 describes a mixed-signal architecture. This is an improved version of the first analog implementation [81,91], which was used to develop a first sensor array (see Sect. 6.1). Based on the experience with these analog devices, a complete sensor system with advanced control, readout and interface circuit was devised. This system includes the circular microhotplate that has been described and characterized in Sect. 4.1. Additionally to the fabrication process, a prototype packaging concept was developed that will be presented in Sect. 5.1.6. A microhotplate with a Pt-temperature sensor requires a different system architecture as will be described in Sect. 5.2. A fully differential analog architecture will be presented, which enables operating temperatures up to 500 °C. 

Figure 3.24 — Typical system for piezoelectric crystal detector incorporating reference (C,) and test (CJ crystal sensors individually held in oscillating circuits (Or and 0 respectively) serviced by separate frequency counters (FC, and FCj, respectively) interfaced to a common microprocessor or other readout device. (Reproduced from [167] with permission of the American Chemical Society).

The output requirements are totally dependent on the user s needs. If a readout indicator is required, a wide selection is usually offered. An analog output suitable for recording, monitoring and control is commonly provided. In addition, most manufacturers offer a broad selection of output functions, including digital [binary coded decimal (BCD) coded] outputs, high, low, and proportional set points, signal peak or valley sensors, sample and hold circuits, and even closed-loop controls for specific applications. Many presently available instruments, even portable handheld units, include microprocessors that provide many of the above functions on standard models. 

The telemetry feature was based on LO resonant network, C being the sensor s capacity. By adding an inductor, the LC response wonld change in accordance to the capacity change, which is driven by the pressnre changes, hi order to fabricate the indnctor, a series of coils were printed on a flexible printed circnit, which serve as antenna to interrogate the sensor capacity. The readout system measures the oscillation frequency of the LC resonant circuit created by sensors and inductive coupling (Ohveira et al., 2015). 

Today s IR and visible sensors are used in two general configurations. One configuration - focal plane arrays, or FPAs - includes thousands or millions of elements, accessed through a readout- integrated circuit (ROIC). They, as well as the electronics for them, are discussed in Chapters 7 and 8. 

This chapter provides an overview of the readout integrated circuit (ROIC) used for infrared, visible, and other arrayed sensors. 

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