OPA211_08 Datasheet, PDF (15/17 Pages) Texas Instruments – 1.1nV/√Hz Noise, Low Power, Precision Operational Amplifier in Small DFN-8 Package

www.ti.com
Figure 41 illustrates both inverting and noninverting
op amp circuit configurations with gain. In circuit
configurations with gain, the feedback network
resistors also contribute noise. The current noise of
the op amp reacts with the feedback resistors to
create additional noise components. The feedback
resistor values can generally be chosen to make
these noise sources negligible. The equations for
total noise are shown for both configurations.
TOTAL HARMONIC DISTORTION
MEASUREMENTS
OPA211 series op amps have excellent distortion
characteristics. THD + Noise is below 0.0001% (G =
+1, V_O = 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 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
OPA211
OPA2211
SBOS377D – OCTOBER 2006 – REVISED FEBRUARY 2008
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.
Copyright © 2006–2008, Texas Instruments Incorporated
Submit Documentation Feedback
15
Product Folder Link(s): OPA211 OPA2211