9

LT1797

Distortion

There are two main contributors to distortion in op amps:

output crossover distortion as the output transitions from

sourcing to sinking current and distortion caused by

nonlinear common mode rejection. If the op amp is

operating in the inverting mode, there is no common mode

induced distortion. If the op amp is operating in the PNP

APPLICATIO S I FOR ATIO

very good, typically 95dB. When the LT1797 switches

between input stages there is significant nonlinearity in the

CMRR. Lower load resistance increases the output cross-

over distortion, but has no effect on the input stage

transition distortion. For lowest distortion the LT1797

should be operated single supply, with the output always

sourcing current and with the input voltage swing between

Characteristic curves.

Figure 1. Simplified Schematic

1797 F01

Q18

Q1

Q3 Q4

QB1

Q7

Q11

Q13

Q9

Q6

Q2

Q12

Q8

Q14

Q10

Q5

Q17

Q15

Q19

Q20

Q16

R1

R3

R4

R7

R8

R5

R6

R2

D1

D2

–IN

+IN

BIAS

I1

OUT

+1

+1

CM

C1

C2

I3

I2

I4

I5

I6

I7

1/2 SUPPLY