Inverting Operational Amplifier

Gain of Op-Amp

Build the following circuit in figure 1 with the power supply and a multimeter.

Fig. 1: Inverting Op-Amp

$U_{\rm DD}{\rm~=10~V},~U_{\rm SS}{\rm~=-10~V},~R_{\rm 1}{\rm~=10~k\Omega}$

Calculate the necessary value for $R_{\rm 2}$, so that the Output $U_{\rm OUT}$ is +5 V. Use the supply voltage of the operational amplifier for $U_{\rm IN}$.


$U_{\rm IN}{\rm~=}$
















$R_{\rm 2}{\rm~=}$

Analysis of inverting input currents

Fig. 2: Inverting Op-Amp: Analysis of currents of the inverting input

$U_{\rm DD}{\rm~=10~V},~U_{\rm SS}{\rm~=-10~V},~R_{\rm 1}{\rm~=10~k\Omega}$

Use the values from figure 1 for $U_{\rm IN},~U_{\rm OUT},~R_{\rm 2}$.

Complete the arrows in the scematic of the circuit.
Determine the the currents $I_{\rm 1}$ and $I_{\rm 2}$ indirectly by measuring the voltage across known resistors
and calculate the algebraic sum of the currents at node $N_{\rm {12}}$ using Kirchhoff’s Current Law (KCL).

$U_{\rm 1}{\rm~=}$


$U_{\rm 2}{\rm~=}$






















































$I_{\rm 1}{\rm~=}$


$I_{\rm 2}{\rm~=}$


$I_{\rm N12}{\rm~=}$

Analysis of inverting input voltages

Fig. 3: Inverting Op-Amp: Analysis of virtual GND of the inverting input

$U_{\rm DD}{\rm~=10~V},~U_{\rm SS}{\rm~=-10~V},~R_{\rm 1}{\rm~=10~k\Omega}$

Use the values from figure 1 for $U_{\rm IN},~U_{\rm OUT},~R_{\rm 2}$.


Complete the reference arrows in the scematic of the circuit.
Take the values for $U_{\rm 1},~U_{\rm 2},~U_{\rm OUT}$ from figure 2.
Calculate the voltage $U_{12}$ using Kirchhoff's Voltage Law (KVL) within the circuit loop.
Verify your calculated result by measuring $U_{12}$.


$U_{\rm 1}{\rm~=}$


$U_{\rm 2}{\rm~=}$


$U_{\rm OUT}{\rm~=}$


Calculated $U_{\rm 12}{\rm~=}$


Measured $U_{\rm 12}{\rm~=}$


Analyse the physical significance of the potential at $N_{12}$ relative to GND (defined as $U_{12}$) in the context of the operational amplifier's input configuration. What do you observe?


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What happens if you short-circuit $R_2$ (the feedback resistor)?
Experimentally verify this effect and explain the observed behavior regarding the output voltage.


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