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The op-amp inverting amplifier is a typical circuit, with parallel negative feedback, based on the Miller theorem, where the op-amp differential input impedance is apparently decreased to zero Zeroed impedance uses an inverting (usually op-amp) amplifier with enormously high gain A v → ∞ {\displaystyle A_{v}\to \infty } .
Figure 1: Circuit of an ideal voltage inverting amplifier with an impedance connecting its output to its input. Consider a circuit of an ideal inverting voltage amplifier of gain − A v {\displaystyle -A_{v}} with an impedance Z {\displaystyle Z} connected between its input and output nodes.
The non-inverting input of the operational amplifier needs a path for DC to ground; if the signal source does not supply a DC path, or if that source requires a given load impedance, then the circuit will require another resistor from the non-inverting input to ground.
The input impedance of the simplified non-inverting amplifier is high: Z in = ( 1 + A OL B ) Z dif {\displaystyle Z_{\text{in}}=(1+A_{\text{OL}}B)Z_{\text{dif}}} 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 ...
Transimpedance amplifier with a reverse-biased photodiode. In the circuit shown in figure 1 the photodiode (shown as a current source) is connected between ground and the inverting input of the op-amp. The other input of the op-amp is also connected to ground. This provides a low-impedance load for the photodiode, which keeps the photodiode ...
Referring to the above diagram, if the op-amp is assumed to be ideal, then the voltage at the inverting (-) input is held equal to the voltage at the non-inverting (+) input as a virtual ground. The input voltage passes a current V in / R 1 {\displaystyle V_{\text{in}}/{R_{1}}} through the resistor producing a compensating current flow through ...