OPA2211-HT_15 Datasheet, PDF (16/22 Pages) Texas Instruments – 1.1 nV/√Hz Noise, Low Power, Precision Operational Amplifier

OPA2211-HT
SBOS684A – AUGUST 2013 – REVISED AUGUST 2013
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
OPA2211 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 OPA2211 series op amps
is below the measurement limit of many commercially
available distortion analyzers. However, a special test
circuit illustrated in can be used to extend the
measurement capabilities.
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. Figure 43 illustrates the ESD
circuits contained in the OPA2211 (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.
www.ti.com
Op amp distortion can be considered an internal error
source that can be referred to the input. 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.
An ESD event produces a short duration, high-
voltage pulse that is transformed into a short
duration, high-current pulse as it discharges through
a semiconductor device. The ESD protection circuits
are designed to provide a current path around the
operational amplifier core to prevent it from being
damaged. The energy absorbed by the protection
circuitry is then dissipated as heat.
When an ESD voltage develops across two or more
of the amplifier device pins, current flows through one
or more of the steering diodes. Depending on the
path that the current takes, the absorption device
may activate. The absorption device has a trigger, or
threshold voltage, that is above the normal operating
voltage of the OPA2211 but below the device
breakdown voltage level. Once this threshold is
exceeded, the absorption device quickly activates
and clamps the voltage across the supply rails to a
safe level.
When the operational amplifier connects into a circuit
such as that illustrated in Figure 43, the ESD
protection components are intended to remain
inactive and not become involved in the application
circuit operation. However, circumstances may arise
where an applied voltage exceeds the operating
voltage range of a given pin. Should this condition
occur, there is a risk that some of the internal ESD
protection circuits may be biased on, and conduct
current. Any such current flow occurs through
steering diode paths and rarely involves the
absorption device.
16
Submit Documentation Feedback
Product Folder Links: OPA2211-HT
Copyright © 2013, Texas Instruments Incorporated