8.0DUAL-SLOPE CONVERSION
At the beginning of a conversion, the voltage across Cint is zero. The signal is then applied to the integrator and the voltage across Cint rises by the formula:
T1
ECint = Esig RintCint
At the end of a fixed period of 10000 counts, T1, the counters are reset to 00000. The signal input is turned off and a stable reference voltage of the opposite polarity is now applied to the input. Since the reference voltage is constant, the slope, in volts/sec, during this second period, T2, is constant and independent of input signal levels. The time required to discharge the capacitor back to zero volts is then proportional to the signal voltage. The relationship between the signal integration time, T1, and the reference integration time, T2, can be expressed by the formula:
Eref T2 = Esig T1
After the clock is stopped by the capacitor voltage reaching zero, a third period, T3, allows the circuit to
Figure 8.1
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