OPA211AI datasheet(17/37 Pages) TI1

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TOTAL HARMONIC DISTORTION

ELECTRICAL OVERSTRESS

OPA211

SignalGain=1+

DistortionGain=1+

OUT

Generator

Output

Analyzer

Input

AudioPrecision

SystemTwo

(1)

withPCController

Load

SIG.

GAIN

DIST.

GAIN

100W

1kW

10W

11W

101

R IIR

OPA211

OPA2211

www.ti.com...................................................................................................................................................... SBOS377G – OCTOBER 2006 – REVISED MAY 2009

Audio

Precision

System

Two

distortion/noise

MEASUREMENTS

analyzer, which greatly simplifies such repetitive

measurements. The measurement technique can,

OPA211 series op amps have excellent distortion

however,

performed

with

manual

distortion

characteristics. THD + Noise is below 0.0002% (G =

measurement instruments.

+1, VOUT = 3VRMS) throughout the audio frequency

range, 20Hz to 20kHz, with a 600

Ω load.

The distortion produced by OPA211 series op amps

Designers often ask questions about the capability of

is below the measurement limit of many commercially

operational

amplifier

withstand

electrical

available distortion analyzers. However, a special test

overstress. These questions tend to focus on the

circuit illustrated in Figure 48 can be used to extend

device inputs, but may involve the supply voltage pins

the measurement capabilities.

or even the output pin. Each of these different pin

Op amp distortion can be considered an internal error

functions have electrical stress limits determined by

source that can be referred to the input. Figure 48

the

voltage

breakdown

characteristics

the

shows a circuit that causes the op amp distortion to

particular semiconductor fabrication process and

be 101 times greater than that normally produced by

specific circuits connected to the pin. Additionally,

the op amp. The addition of R3 to the otherwise

internal electrostatic discharge (ESD) protection is

standard noninverting amplifier configuration alters

built

into

these

circuits

protect

them

from

the feedback factor or noise gain of the circuit. The

accidental ESD events both before and during

closed-loop gain is unchanged, but the feedback

product assembly.

available for error correction is reduced by a factor of

It is helpful to have a good understanding of this

101, thus extending the resolution by 101. Note that

basic ESD circuitry and its relevance to an electrical

the input signal and load applied to the op amp are

overstress event. See Figure 49 for an illustration of

the same as with conventional feedback without R3.

the ESD circuits contained in the OPA211 (indicated

The value of R3 should be kept small to minimize its

by the dashed line area). The ESD protection circuitry

effect on the distortion measurements.

involves several current-steering diodes connected

Validity

this

technique

can

verified

from the input and output pins and routed back to the

duplicating measurements at high gain and/or high

internal power-supply lines, where they meet at an

frequency

where

the

distortion

within

the

absorption device internal to the operational amplifier.

measurement

capability

the

test

equipment.

This protection circuitry is intended to remain inactive

Measurements for this data sheet were made with an

during normal circuit operation.

(1)

For measurement bandwidth, see Figure 3, Figure 4, and Figure 5.

Figure 48. Distortion Test Circuit

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