OP113/OP213/OP413
Rev. F | Page 13 of 24
APPLICATIONS
The OP113, OP213, and OP413 form a new family of high
performance amplifiers that feature precision performance in
standard dual-supply configurations and, more importantly,
maintain precision performance when a single power supply is
used. In addition to accurate dc specifications, it is the lowest
noise single-supply amplifier available with only 4.7 nV/√Hz
typical noise density.
Single-supply applications have special requirements due to the
generally reduced dynamic range of the output signal. Single-
supply applications are often operated at voltages of 5 V or 12 V,
compared to dual-supply applications with supplies of ±12 V or
±15 V. This results in reduced output swings. Where a dual-
supply application may often have 20 V of signal output swing,
single-supply applications are limited to, at most, the supply
range and, more commonly, several volts below the supply.
In order to attain the greatest swing, the single-supply output
stage must swing closer to the supply rails than in dual-supply
applications.
The OPx13 family has a new patented output stage that allows
the output to swing closer to ground, or the negative supply,
than previous bipolar output stages. Previous op amps had
outputs that could swing to within about 10 mV of the negative
supply in single-supply applications. However, the OPx13
family combines both a bipolar and a CMOS device in the output
stage, enabling it to swing to within a few hundred µV of ground.
When operating with reduced supply voltages, the input range
is also reduced. This reduction in signal range results in
reduced signal-to-noise ratio for any given amplifier. There are
only two ways to improve this: increase the signal range or
reduce the noise. The OPx13 family addresses both of these
parameters. Input signal range is from the negative supply to
within 1 V of the positive supply over the full supply range.
Competitive parts have input ranges that are 0.5 V to 5 V less
than this. Noise has also been optimized in the OPx13 family.
At 4.7 nV/√Hz, the noise is less than one fourth that of competitive
devices.
PHASE REVERSAL
The OPx13 family is protected against phase reversal as long as
both of the inputs are within the supply ranges. However, if
there is a possibility of either input going below the negative
supply (or ground in the single-supply case), the inputs should
be protected with a series resistor to limit input current to 2 mA.
OP113 OFFSET ADJUST
The OP113 has the facility for external offset adjustment, using
the industry standard arrangement. Pin 1 and Pin 5 are used in
conjunction with a potentiometer of 10 k total resistance,
connected with the wiper to V− (or ground in single-supply
applications). The total adjustment range is about ±2 mV using
this configuration.
Adjusting the offset to 0 has minimal effect on offset drift
(assuming the potentiometer has a tempco of less than
1000 ppm/°C). Adjustment away from 0, however, (as with all
bipolar amplifiers) results in a TCV
OS
of approximately
3.3 V/°C for every millivolt of induced offset.
It is, therefore, not generally recommended that this trim be
used to compensate for system errors originating outside of the
OP113. The initial offset of the OP113 is low enough that
external trimming is almost never required, but if necessary, the
2 mV trim range may be somewhat excessive. Reducing the
trimming potentiometer to a 2 k value results in a more
reasonable range of ±400 V.
