OPA211AIDRGR Datasheet, PDF (17/37 Pages) Texas Instruments – 1.1nV/√Hz Noise, Low Power, Precision Operational Amplifier in Small DFN-8 Package

OPA211
OPA2211
www.ti.com...................................................................................................................................................... SBOS377G – OCTOBER 2006 – REVISED MAY 2009
TOTAL HARMONIC DISTORTION
MEASUREMENTS
OPA211 series op amps have excellent distortion
characteristics. THD + Noise is below 0.0002% (G =
+1, V_OUT = 3V_RMS) throughout the audio frequency
range, 20Hz to 20kHz, with a 600Ω load.
The distortion produced by OPA211 series op amps
is below the measurement limit of many commercially
available distortion analyzers. However, a special test
circuit illustrated in Figure 48 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 48
shows a circuit that causes the op amp distortion to
be 101 times greater than that normally produced by
the op amp. The addition of R₃ to the otherwise
standard noninverting amplifier configuration alters
the feedback factor or noise gain of the circuit. The
closed-loop gain is unchanged, but the feedback
available for error correction is reduced by a factor of
101, thus extending the resolution by 101. Note that
the input signal and load applied to the op amp are
the same as with conventional feedback without R₃.
The value of R₃ should be kept small to minimize its
effect on the distortion measurements.
Validity of this technique can be verified by
duplicating measurements at high gain and/or high
frequency where the distortion is within the
measurement capability of the test equipment.
Measurements for this data sheet were made with an
Audio Precision System Two distortion/noise
analyzer, which greatly simplifies such repetitive
measurements. The measurement technique can,
however, be performed with manual distortion
measurement instruments.
ELECTRICAL OVERSTRESS
Designers often ask questions about the capability of
an operational amplifier to withstand electrical
overstress. These questions tend to focus on the
device inputs, but may involve the supply voltage pins
or even the output pin. Each of these different pin
functions have electrical stress limits determined by
the voltage breakdown characteristics of the
particular semiconductor fabrication process and
specific circuits connected to the pin. Additionally,
internal electrostatic discharge (ESD) protection is
built into these circuits to protect them from
accidental ESD events both before and during
product assembly.
It is helpful to have a good understanding of this
basic ESD circuitry and its relevance to an electrical
overstress event. See Figure 49 for an illustration of
the ESD circuits contained in the OPA211 (indicated
by the dashed line area). The ESD protection circuitry
involves several current-steering diodes connected
from the input and output pins and routed back to the
internal power-supply lines, where they meet at an
absorption device internal to the operational amplifier.
This protection circuitry is intended to remain inactive
during normal circuit operation.
R₁
R₂
Signal Gain = 1+ ^R2
R₁
Distortion Gain = 1+ ^R2
R₁ II R₃
R₃
OPA211
V_OUT
Generator
Output
Analyzer
Input
Audio Precision
System Two⁽¹⁾
with PC Controller
Load
SIG. DIST.
GAIN GAIN R1 ^R2 ^R3
1 101 ¥ 1kW 10W
11 101 100W 1kW 11W
(1) For measurement bandwidth, see Figure 3, Figure 4, and Figure 5.
Figure 48. Distortion Test Circuit
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Product Folder Link(s): OPA211 OPA2211