Typical Applications
3 OPAMP INSTRUMENTATION AMP WITH RAIL-TO-
RAIL INPUT AND OUTPUT
Using the LM6134, a 3 opamp instrumentation amplifier with
rail-to-rail inputs and rail to rail output can be made. These
features make these instrumentation amplifiers ideal for sin-
gle supply systems.
Some manufacturers use a precision voltage divider array of
5 resistors to divide the common-mode voltage to get an
input range of rail-to-rail or greater. The problem with this
method is that it also divides the signal, so to even get unity
gain, the amplifier must be run at high closed loop gains.
This raises the noise and drift by the internal gain factor and
lowers the input impedance. Any mismatch in these preci-
sion resistors reduces the CMR as well. Using the LM6134,
all of these problems are eliminated.
In this example, amplifiers A and B act as buffers to the
differential stage
(Figure 7).
These buffers assure that the
input impedance is over 100 MXand they eliminate the
requirement for precision matched resistors in the input
stage. They also assure that the difference amp is driven
from a voltage source. This is necessary to maintain the
CMR set by the matching of R1– R2 with R3– R4.
TL/H/12349–44
FIGURE 7
FLAT PANEL DISPLAY BUFFERING
Three features of the LM6132/34 make it a superb choice
for TFT LCD applications. First, its low current draw (360 mA
per amplifier @5V) makes it an ideal choice for battery pow-
ered applications such as in laptop computers. Second,
since the device operates down to 2.7V, it is a natural
choice for next generation 3V TFT panels. Last, but not
least, the large capacitive drive capability of the LM6132
comes in very handy in driving highly capacitive loads that
are characteristic of LCD display drivers.
The large capacitive drive capability of the LM6132/34 al-
lows it to be used as buffers for the gamma correction refer-
ence voltage inputs of resistor-DAC type column (Source)
drivers in TFT LCD panels. This amplifier is also useful for
buffering only the center reference voltage input of Capaci-
tor-DAC type column (Source) drivers such as the LMC750X
series.
Since for VGA and SVGA displays, the buffered voltages
must settle within approximately 4 ms, the well known tech-
nique of using a small isolation resistor in series with the
amplifier’s output very effectively dampens the ringing at the
output.
With its wide supply voltage range of 2.7V to 24V), the
LM6132/34 can be used for a diverse range of applications.
The system designer is thus able to choose a single device
type that serves many sub-circuits in the system, eliminating
the need to specify multiple devices in the bill of materials.
Along with its sister parts, the LM6142 and LM6152 that
have the same wide supply voltage capability, choice of the
LM6132 in a design eliminates the need to search for multi-
ple sources for new designs.
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