Handbook for Sound Engineers

Tubes, Discrete Solid State Devices, and Integrated Circuits 337

The diodes and zener diodes in Fig. 12-35 are used
to protect the op-amp from damage caused by tran-
sients, reverse voltage, and overdriving. D 6 and D 7 clip
the inputs before overdriving, D 1 and D 2 protect against
reverse polarity, D 4 and D 5 regulate the supply, and D 3
limits the total voltage across the op-amp.

The dc error factors result in an output offset voltage
EOo, which exists between the output and ground when
it should be zero. The dc offset error is most easily
corrected by supplying a voltage differential between
the inverting and noninverting inputs, which can be

accomplished by one of several methods, Fig. 12-36.

Connecting the feedback resistor Rf usually causes an

offset and can be found with the equation

(12-41)

To obtain minimum offset, make the compensating

resistor shown in Fig. 12-36A equal to

(12-42)

If this method is not satisfactory, the methods of Figs.

12-36B or C might be required.

Many op-amps are internally compensated. Often it

is advantageous to compensate a device externally to

optimize bandwidth and slew rate, lowering distortion.

Internally compensated op-amp ICs come in standard

Figure 12-33. Positive- and negative-type power supply.

Figure 12-34. Simple circuit for operating on a single-
ended power supply.

Figure 12-35. Diode protection circuits for op-amps.

VCC

VEE

VCC

VEE

Ground

+

+ +

VCC

VEE

R 2

R 1

Input

Output

R 1

R 2

D 6 D 7

D 5 D 3

D 1

D 4

D 2

VCC

VEE

+



Input 1

Output

Input 2

Figure 12-36. Various methods of correcting dc error.

EOo=IbiasRf

Rf

ECC EEE

Rcomp

Rf

R 1

R 3

R 2

Rin

R 1 R 2 R 3

Rin

R 4

VEE

+

+

+

Rcomp = Rf Rin

Rf + Rin

R 3 = R^1 R^2

R 1 + R 2

A.

B.

C.

Input

Input

Input

Output

Output

Output

Rcomp

Rf Rin

Rf+Rin

-------------------=