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

Amplifiers
A.3.2
Inverting Op Amp with Inverting Negative Reference
The transfer equation takes the form of Y = –mX + b and is given in Equation A–2.
V OUT
V IN
R F
R G1
V REF
R F
R G2
A–2
The transfer function slope is negative, and the dc intercept is positive (Figure A–6). R G1
and R G2 are contained in the equation, thus it is easy to obtain the desired slope and dc
intercept by adjusting the value of both resistors. Because of the virtual ground at the inverting
input, R G2 is the terminating impedance for V REF . When the reference voltage is
0, the input voltage is constrained to negative voltages because positive input voltages
would cause the output voltage to saturate at ground.
+ 5 V
R G1
R F
V IN
R G2
V REF
+V CC
_
+
V OUT
V OUT — 1 V/Div
– 5 V
– 5 V
V IN — 1 V/Div
+ 5 V
V IN = 10 Vp-p
V REF = –1 V
V CC = 5 V R G1 = R G2 = R F = 10 k
Op Amp = TLV247x
Figure A–6. Inverting Op Amp with Inverting Negative Reference
A-6