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Figure 4.14. Physical Circuit Test Results With Modified Supply Voltage
4.3 Interface Theory
Without a feedback mechanism, the op-amp acts as a comparator. The inverting input (V_ref) serves as a reference
voltage to compare the noninverting input to (V_in).
If V_in is above V_ref, then the output (V_out) saturates to the op-amp’s positive power supply (+5 V). Otherwise,
V_out saturates to the op-amp’s negative power supply (0 V).
This circuit is extremely simple, and the behavior near 2 V cannot be guaranteed. Most digital systems have
indeterminate ranges in which the correct interpretation of the digital state is not guaranteed. Different standards exist,
each with their own logic level ranges.
In your circuit, the voltage level detector circuit built in Section 4.2 simply reads in an analog signal and saturates to near
0 V or near 5 V, depending on whether the input is less than 2 V or higher than 2 V.
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