frequency. During this state, the offsets of the buffer, integrator and comparator
are stored on the auto-zero capacitor.
(6) Integrate input
During this state, the input signal is applied to the A-D converter. Since the
offsets are stored on the auto-zero capacitor, the integrator's slope is determined
solely by the input voltage. To display Decrees C, the input signal is integrated for
83.3 ms. Thus, the integrator output reaches a value proportional to the input
signal and the fixed integrate time. To display degrees F, the input signal is
integrated for 150 ms. Since the output of the integrator is proportional to both the
input signal and the integrate time, this effectively multiplies the input by 1.8
(150/83.3).
(7) Integrate reference
At the end of the integrate input state, the comparator output depends on the
polarity of the input signal. The polarity flip-flop is latched at the beginning of the
integrate reference state and the reference voltage of the opposite polarity
integrated. This causes the integrator to ramp towards its quiescent (auto-zero)
point at a slope dependent on the reference voltage. When the quiescent level is
reached (zero-crossing), the display is updated and the A-D converter
automatically reverts to the auto-zero mode until the end of the conversion cycle.
The time required to reach zero-crossing is proportional to the input signal.
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