OPA1678 Datasheet, PDF (14/41 Pages) Texas Instruments – Low-Distortion Audio Operational Amplifiers

OPA1678, OPA1679
SBOS855 – FEBRUARY 2017
7 Detailed Description
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7.1 Overview
The OPA167x devices are unity-gain stable, dual– and quad-channel op amps with low noise and distortion. The
Functional Block Diagram shows a simplified schematic of the OPA167x (one channel shown). The device
consists of a low noise input stage with a folded cascode and a rail-to-rail output stage. This topology exhibits
superior noise and distortion performance across a wide range of supply voltages that are not delivered by
legacy commodity audio operational amplifiers.
7.2 Functional Block Diagram
V+
V_IN+
V_IN-
Tail
Current
V_BIAS1
Class AB
Control
V_O
Circuitry
V_BIAS2
V-
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7.3 Feature Description
7.3.1 Phase Reversal Protection
The OPA167x family has internal phase-reversal protection. Many op amps exhibit phase reversal when the
input is driven beyond the linear common-mode range. This condition is most often encountered in noninverting
circuits when the input is driven beyond the specified common-mode voltage range, causing the output to
reverse into the opposite rail. The input of the OPA167x prevents phase reversal with excessive common-mode
voltage. Instead, the appropriate rail limits the output voltage. This performance is shown in Figure 31.
20
15
10
5
0
-5
-10
-15
VIN
-20
VOUT
Time (125 s/div)
C004
Figure 31. Output Waveform Devoid of Phase Reversal During an Input Overdrive Condition
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