"Chapter 1 - The Op Amp's Place in the World" - HTL Wien 10

Inverting Op Amps
6-6
comparison also shows that the open loop gain, A, is equal to the op amp open loop gain,
a, for the noninverting circuit.
A aZ G
Z G Z F
(6–13)
Equation 6–13 is also derived with the aid of Figure 6–4, which shows the open loop noninverting
op amp.
VTEST
Figure 6–4. Open Loop Noninverting Op Amp
+
_ a
VRETURN
ZF
ZG
aVTEST
The test voltage, V TEST, is multiplied by the op amp open loop gain to obtain the op amp
output voltage, aV TEST. The voltage divider rule is used to calculate Equation 6–15, which
is identical to Equation 6–14 after some algebraic manipulation.
6.4 Inverting Op Amps
V RETURN aV TEST Z G
Z F Z G
V RETURN
V TEST
A aZ G
Z F Z G
(6–14)
(6–15)
The inverting op amp circuit is shown in Figure 6–5. The dummy variable (V A) is inserted
to make the calculations easier, and a is the op amp open loop gain.
Figure 6–5. Inverting Op Amp
VIN
ZG
VA
+
_ a
IB
ZF
VOUT