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handbook of modern sensors

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490 16 Temperature Sensors<br />

Fig. 16.21. An error curve for a silicon transistor (PN100) as a temperature sensor.<br />

(A)<br />

(B)<br />

Fig. 16.22. Simplified circuit for a semiconductor temperature sensor (A) and current-to-voltage<br />

curves (B).<br />

cromachined membrane <strong>of</strong> a silicon pressure sensor to compensate for temperature<br />

dependence <strong>of</strong> piezoresistive elements.<br />

An inexpensive yet precision semiconductor temperature sensor may be fabricated<br />

by using fundamental properties <strong>of</strong> transistors to produce voltage which is proportional<br />

to absolute temperature (in Kelvin). That voltage can be used directly or it can<br />

be converted into current [12]. The relationship between base–emitter voltage (V be )<br />

and collector current <strong>of</strong> a bipolar transistor is the key property to produce a linear<br />

semiconductor temperature sensor. Figure 16.22A shows a simplified circuit where<br />

Q 3 and Q A form the so-called current mirror. It forces two equal currents I C1 = I and<br />

I C2 = I into transistors Q 1 and Q 2 . The collector currents are determined by resistor

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