Datasheet

R
2
OPA827
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
R
600W
L
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
NOTE:(1)MeasurementBW=80kHz.
OPA827
SBOS376H –NOVEMBER 2006–REVISED MAY 2012 www.ti.com
TOTAL HARMONIC DISTORTION of the circuit. The closed-loop gain is unchanged, but
MEASUREMENTS the feedback available for error correction is reduced
by a factor of 101, thus extending the resolution by
The OPA827 series op amps have excellent distortion
101. Note that the input signal and load applied to the
characteristics. THD + Noise is below 0.0001%
op amp are the same as with conventional feedback
(G = +1, V
O
= 3V
RMS
) throughout the audio frequency
without R
3
. The value of R
3
should be kept small to
range, 20Hz to 20kHz, with a 600Ω load (see
minimize its effect on the distortion measurements.
Figure 3).
The validity of this technique can be verified by
The distortion produced by the OPA827 series is
duplicating measurements at high gain and/or high
below the measurement limit of many commercially
frequency where the distortion is within the
available testers. However, a special test circuit
measurement capability of the test equipment.
(illustrated in Figure 43) can be used to extend the
Measurements for this data sheet were made with an
measurement capabilities.
Audio Precision System Two distortion/noise
analyzer, which greatly simplifies such repetitive
Op amp distortion can be considered an internal error
measurements. This measurement technique,
source that can be referred to the input. Figure 43
however, can be performed with manual distortion
shows a circuit that causes the op amp distortion to
measurement instruments.
be 101 times greater than that distortion normally
produced by the op amp. The addition of R
3
to the
otherwise standard noninverting amplifier
configuration alters the feedback factor or noise gain
Figure 43. Distortion Test Circuit
14 Copyright © 2006–2012, Texas Instruments Incorporated