OPA211AI datasheet(15/17 Pages) TI

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TOTAL HARMONIC DISTORTION

OPA211

OPA2211

SBOS377D – OCTOBER 2006 – REVISED FEBRUARY 2008

Figure 41 illustrates both inverting and noninverting

feedback factor or noise gain of the circuit. The

op amp circuit configurations with gain. In circuit

closed-loop gain is unchanged, but the feedback

configurations

with

gain,

the

feedback

network

available for error correction is reduced by a factor of

resistors also contribute noise. The current noise of

101, thus extending the resolution by 101. Note that

the op amp reacts with the feedback resistors to

the input signal and load applied to the op amp are

create additional noise components. The feedback

the same as with conventional feedback without R3.

resistor values can generally be chosen to make

The value of R3 should be kept small to minimize its

these noise sources negligible. The equations for

effect on the distortion measurements.

total noise are shown for both configurations.

Validity

this

technique

can

verified

duplicating measurements at high gain and/or high

frequency

where

the

distortion

within

the

MEASUREMENTS

measurement

capability

the

test

equipment.

Measurements for this data sheet were made with an

OPA211 series op amps have excellent distortion

Audio

Precision

System

Two

distortion/noise

characteristics. THD + Noise is below 0.0001% (G =

analyzer, which greatly simplifies such repetitive

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

measurements. The measurement technique can,

range, 20Hz to 20kHz, with a 600

Ω load.

however,

performed

with

manual

distortion

The distortion produced by OPA211 series op amps

measurement instruments.

is below the measurement limit of many commercially

available equipment. However, a special test circuit

illustrated in Figure 42 can be used to extend the

measurement capabilities.

Op amp distortion can be considered an internal error

source that can be referred to the input. Figure 42

shows a circuit that causes the op amp distortion to

be 101 times greater than normally produced by the

op amp. The addition of R3 to the otherwise standard

noninverting

amplifier

configuration

alters

the

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