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Signal transducers of capacitive microelectronic sensors

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Microelectronic sensors state of the art is characterized by wide using of special designs of signal transformation which would improve measurement accuracy including transformation function linearization, temperature compensation, noise reduction etc. [1]. In contrast to digital technique, devices of preliminary analog signal transformation require much more attention with relation to measuring transformation as well as to elemental base. Taking into consideration the fact that outward things show up mainly in analog form, the sensor input signal has an analog form too. Consequently, preliminary analog signal transducers normalizing the signal for its following digitization essentially influence the device parameters in whole [2]. For the last years scientific publications have been focused on actuality of analog signal transducers further development and their compatibility with digital microcontrollers [3-6]. Strong interest in making measurement process more intelligent shows up, particularly in connection with analog sensor nodes [7,8]. Analog signal transducers are particularly actual for microelectronic capacitive transducers (position transducers, chemical analysis sensors, humidity sensors). This actuality can be attributed to the serious difficulty with small capacitance values measurements (a typical value of a microelectronic capacitive sensing device capacitance amounts to several picofarads at all) [9-14]. When analyzing capacitive sensors signal transformation problem one probably would note at least three main methods of measurement. The first method is based on capacitance impedance measurement at certain fixed frequency or several fixed frequencies. The second method assumes capacitance charging time measurement at some fixed charging current. In the simplest case it can be time-domain measurement of RTCX circuit, where CX is transducer measuring capacitance, RT is a resistor, defining the current. The thi[...]

Field characteristic of magnetic sensors on the split hall structures

  Galvanomagnetic sensors are widely used for magnetic field measurement due to their capability to work in a wide range of magnetic flux density (from 10-6 T to several tens of Tesla) and temperature (from 1 K to 400 K), their small sizes (several millimeters) and low cost (in large-scale production) [1, 2]. Hall sensors are a kind of galvanomagnetic sensors. A typical Hall sensor is a rectangular semiconductor slab with two pairs of electrodes: one pair is used for energizing the slab whilst the other is intended for Hall voltage measurement (these two electrodes are referenced to as potential electrodes, they are placed symmetrically along the current-flow line) [3, 4]. One can distinguish two typical variants of probes of Hall sensors - with normal (transverse) and with axial position of a sensor in a probe. Such probes are intended for measuring the only magnetic-field vector’s projection which is normal to the probe’s work surface. This fact causes two problems. The first problem is restricted spatial resolution; the second one is impossibility of simultaneous measurement of three magnetic-field vector’s projections (BX, BY, BZ) in a certain point of space. As shown in Fig. 1a, there no difficulties concerned to measurement of the magnetic-field vector’s projection normal to a certain surface. In order to measure this projection sensor is to be placed immediately on this surface. The distance d between the surface being measured and the effective layer (active region) can be rather short and depends on the width of the effective layer’s substrate. Thinning the substrate appropriately, one can achieve the distance d nearly equal to 0.2…0.3 mm. However if the magnetic-field vector’s projections parallel to the surface are to be measured then the sensor’s structure is to be set vertically (Fig. 1b). This causes the minimal possible distance d between the sensor’s active reg[...]

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