Handbook for Sound Engineers

336 Chapter 12

• Low output impedance (<200:).


• Wide frequency response (>100 MHz).


• Low input noise.


• High symmetrical slew rate and/or high input
  dynamic range.


• Low inherent distortion.

By adding external feedback paths, gain, frequency
response, and stability can be controlled.

Op-amps are normally two-input differential
devices; one input inverting the signal and the second
input not inverting the signal, and hence called nonin-
verting. Several typical op-amp circuits are shown in
Fig. 12-32.

Because there are two inputs of opposite polarity, the
output voltage is the difference between the inputs
where

(12-36)

(12-37)

EO is calculated with the equation

(12-38)

Often one of the inputs is grounded, either through a

direct short or a capacitor. Therefore, the gain is either

(12-39)

or

(12-40)

To provide both a positive and negative output with

respect to ground, a positive and negative power supply

is required, as shown in Fig. 12-33. The supply should

be regulated and filtered. Often a + and  power supply

is not available, such as in an automobile, so the op-amp

must operate on a single supply, as shown in Fig. 12-34.

In this supply, the output dc voltage is set by adjusting

R 1 and R 2 so the voltage at the noninverting input is

about one-third the power supply voltage.

EO + =AVE 2

EO – =AVE 1

EO=AVu E 1 – E 2

EO=AVE 1

EO=AVE 2

Figure 12-32. Typical op-amp circuits.

+

+

(^) +

• 
  


• 
  


• 
  

  Rf
  Rf Rf
  Rf Rf
  R 1
  R 1
  R 1
  R 1
  R 1
  R 2
  R 2 R 2
  EO
  EO
  EO
  EO
  EO
  EO
  R 3
  D 2
  D 1
  R 4
  Rin Rin
  Ein
  E Ein
  0 =
  –Rf
  RinEin EO=

  
  


• Rf
  Rin
  Rin Ein
  E 0
  Ein
  Ein 1
  Ein Ein
  Ein
  EO
  EO =

1
RC
Rf ¾Ein dt
C
E 0 = RfCd
dtEin
Ein 2
Ein 3
EO =
Rf
R 1
(Ein1 + Ein2 + Ein3)
Ein

Vref
Vref
I. Rectifier.
A. dc amplifier (inverting). B. dc amplifier (noninverting). C. Analog-to-digital converter.
D. Differentiator. E. Integrator. F. Monostable multivibrator.
G. Averaging or summing amplifier. H. Sweep generator.