Op Amps for Everyone - The Repeater Builder's Technical ...

Amplifiers
A.3.16 T Network in the Feedback Loop
Sometimes it is desirable to have a low-resistance path to ground in the feedback loop.
Standard inverting op amps cannot do this when the driving circuit sets the input resistor
value and the gain specification sets the feedback resistor value. Inserting a T network
in the feedback loop yields a degree of freedom that enables both specifications to be met
with a low dc resistance path to ground in the feedback loop.
V OUT
V IN
R 2
R 3
R 2 R 3
R 4
R 1
V REF R
1 2
R 3
R 2 R 3
R 4
R 1
A–23
+ 5 V
R 1 R 2 R 3
R
+V 4
CC
V IN _
+
V REF
V OUT
V OUT — 0.5 V/Div
0 V
– 2.5 V
V IN — 0.5 V/Div
+ 2.5 V
V IN = 250 mVp-p V REF = 114 mV
V CC = 5 V
R 2 = 100 k
R 1 = R 3 = R 4 = 10 k
Op Amp = TLV247x
Figure A–20. T Network in the Feedback Loop
A-20