Datasheet

R
2
OPA1641
R
1
SignalGain=1+
DistortionGain=1+
R
3 V =3V
O RMS
Generator
Output
Analyzer
Input
AudioPrecision
SystemTwo
(1)
withPCController
SIGNAL
GAIN
DISTORTION
GAIN
R
1
R
2
R
3
¥
100W
1kW
1kW
10W
11W
1
11
101
101
R
2
R
1
R
2
R IIR
1 3
Load
OPA1641
OPA1642
OPA1644
SBOS484B –DECEMBER 2009–REVISED AUGUST 2010 www.ti.com
TOTAL HARMONIC DISTORTION configuration alters the feedback factor or noise gain
MEASUREMENTS of the circuit. The closed-loop gain is unchanged, but
the feedback available for error correction is reduced
The OPA164x series op amps have excellent
by a factor of 101, thus extending the resolution by
distortion characteristics. THD + Noise is below
101. Note that the input signal and load applied to the
0.00005% (G = +1, V
O
= 3V
RMS
, BW = 80kHz)
op amp are the same as with conventional feedback
throughout the audio frequency range, 20Hz to
without R
3
. The value of R
3
should be kept small to
20kHz, with a 2kΩ load (see Figure 7 for
minimize its effect on the distortion measurements.
characteristic performance).
Validity of this technique can be verified by
The distortion produced by the OPA164x series op
duplicating measurements at high gain and/or high
amps is below the measurement limit of many
frequency where the distortion is within the
commercially available distortion analyzers. However,
measurement capability of the test equipment.
a special test circuit (such as Figure 33 shows) can
Measurements for this data sheet were made with an
be used to extend the measurement capabilities.
Audio Precision System Two distortion/noise
analyzer, which greatly simplifies such repetitive
Op amp distortion can be considered an internal error
measurements. The measurement technique can,
source that can be referred to the input. Figure 33
however, be performed with manual distortion
shows a circuit that causes the op amp distortion to
measurement instruments.
be 101 times (or approximately 40dB) greater than
that normally produced by the op amp. The addition
space
of R
3
to the otherwise standard noninverting amplifier
(1) For measurement bandwidth, see Figure 7 through Figure 12.
Figure 33. Distortion Test Circuit
12 Copyright © 2009–2010, Texas Instruments Incorporated
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