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An op amp without negative feedback (a comparator) The amplifier's differential inputs consist of a non-inverting input (+) with voltage V + and an inverting input (−) with voltage V −; ideally the op amp amplifies only the difference in voltage between the two, which is called the differential input voltage.
Schmitt triggers are commonly implemented using an operational amplifier or a dedicated comparator. [nb 2] An open-loop op-amp and comparator may be considered as an analog-digital device having analog inputs and a digital output that extracts the sign of the voltage difference between its two inputs.
A comparator is designed to produce well-limited output voltages that easily interface with digital logic. Compatibility with digital logic must be verified while using an op-amp as a comparator. Some multiple-section op-amps may exhibit extreme channel-channel interaction when used as comparators.
where Z dif is the op-amp's input impedance to differential signals, and A OL is the open-loop voltage gain of the op-amp (which varies with frequency), and B is the feedback factor (the fraction of the output signal that returns to the input). [3] [4] In the case of the ideal op-amp, with A OL infinite and Z dif infinite, the input impedance ...
Comparators are closely related to operational amplifiers, but a comparator is designed to operate with positive feedback and with its output saturated at one power rail or the other. If necessary, an op-amp can be pressed into service as a poorly performing comparator, but its slew rate will be impaired.
For amplifiers with both positive and negative power supplies (with respect to earth, as op-amps often have), the PSRR for each supply voltage may be separately specified (sometimes written: PSRR+ and PSRR−), but normally the PSRR is tested with opposite polarity signals applied to both supply rails at the same time (otherwise the common-mode ...