Star Tech Journal

STAR*TECH JOURNAL/JANUARY 1983
16
tMNUFACTs.
SUMMARY OF MAJOR OP-AMP CIRCUITS (PART 1)
By Frank Becker, Atari, Inc., Somerset, NJ
This 3-part series is written as a quick reference guide on
OP-AMP circuits for technicians and will not get into
detailed mathematical analysis. Such detailed analysis
can be obtained from any good electronics text book.
-------
As the name implies, the inverting OP-AMP configuration
inverts the input and provides gain that is determined by
the values of resistor RF (for feedback resistor) and RI
(for input resistor).
Voltage gain for the Inverting OP-AMP:
OP-AMPS
The term OP-AMP stands for Operational Amplifier. Its
most important characteristics are summarized below:
AV=Vo=-RF
Vin
RI
I. Very high open-loop gain:
The ideal OP-AMP has infinite open-loop gain. This is
voltage gain without any feedback resistors.
(Minus sign means inversion.)
2. Very high input resistance.
AV= -RF= -IOOK = -10
RI
IOK
3. Very low output resistance.
Example 1: If RF= IO0K and RI - I0K, what is the
voltage gain AV?
BASIC OP-AMP SYMBOL
v+
1v
power>
IN
0
-1v
output
Non-inverting _ _ _,
input
+
10v
V- power>
*Power lines are sometimes not drawn for simplicity but
are always there.
OUT 0
-10v
DEFINITION OF TERMS
Inverting input - Output signal and input signal are
inverted. (See Inverting Amplifier.)
Non-inverting input -
phase.
Output and input signals are in
AV - Voltage Gain - Defined as Av= V out
Vin
-AV - Same as above but output signal is inverted from
input ( 180° out of phase).
Example 2: "Gravitar" audio output
R1
V10-
10K
3.9K
-- -N\J'N-
1
V2
INVERTING AMPLIFIER
>-~-AUD2
RF
Al performs two functions: Sums VI and V2 and inverts
the inputs.
RI
Vin
Vout
Voltage gain for signal VI:
For VI, AV= -RFI = -3.9K = -.40
RI
I0K
For V2, Av = -RFI = -3.9K = -I
R3
3.9K