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handbook of modern sensors

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5.6 Ratiometric Circuits 191<br />

(A)<br />

(B)<br />

Fig. 5.34. Ratiometric temperature detector (A) and analog divider <strong>of</strong> resistive values (B).<br />

(A)<br />

(B)<br />

Fig. 5.35. Schematics <strong>of</strong> a divider (A) and gain <strong>of</strong> a divider as a function <strong>of</strong> a denominator (B).<br />

voltage or current proportional to the ratio <strong>of</strong> two input voltages or currents:<br />

V 0 = k V N<br />

V D<br />

, (5.40)<br />

where the numerator is denoted as V N , the denominator is V D and k is equal to<br />

the output voltage, when V N = V D . The operating ranges <strong>of</strong> the variables (quadrants<br />

<strong>of</strong> operation) is defined by the polarity and magnitude ranges <strong>of</strong> the numerator and<br />

denominator inputs and <strong>of</strong> the output. For instance, if V N and V D are both either<br />

positive or negative, the divider is <strong>of</strong> a one-quadrant type. If the numerator is bipolar,<br />

the divider is a two-quadrant type. Generally, the denominator is restricted to a<br />

single polarity, because the transition from one polarity to another would require the<br />

denominator to pass through zero, which would call for an infinite output (unless

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