Datasheet

TOTAL HARMONIC DISTORTION
ELECTRICAL OVERSTRESS
R
2
OPA211
R
1
SignalGain=1+
DistortionGain=1+
R
3 V
OUT
Generator
Output
Analyzer
Input
AudioPrecision
SystemTwo
(1)
withPCController
Load
SIG.
GAIN
DIST.
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
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, be performed with manual distortion
characteristics. THD + Noise is below 0.0002% (G =
measurement instruments.
+1, V
OUT
= 3V
RMS
) 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
an operational amplifier to 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 of 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 R
3
to the otherwise internal electrostatic discharge (ESD) protection is
standard noninverting amplifier configuration alters built into these circuits to 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 R
3
.
the ESD circuits contained in the OPA211 (indicated
The value of R
3
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 of this technique can be verified by 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 is within the absorption device internal to the operational amplifier.
measurement capability of 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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