11
LT1101
1101fa
Single Supply: Minimum Output
Voltage vs Common Mode
Voltage
Single Supply: Minimum
Common Mode Voltage vs
Output Voltage
Minimum Supply Voltage vs
Temperature
TYPICAL PERFOR A CE CHARACTERISTICS
UW
APPLICATIO S I FOR ATIO
WUUU
Single Supply Applications
The LT1101 is the first instrumentation amplifier which is
fully specified for single supply operation, (i.e. when the
negative supply is 0V). Both the input common mode
range and the output swing are within a few millivolts of
ground.
Probably the most common application for instrumenta-
tion amplifiers is amplifying a differential signal from a
transducer or sensor resistance bridge. All competitive
instrumentation amplifiers have a minimum required
common mode voltage which is 3V to 5V above the
negative supply. This means that the voltage across the
bridge has to be 6V to 10V or dual supplies have to be used
(i.e., micropower) single battery usage is not attainable on
competitive devices.
The minimum output voltage obtainable on the LT1101 is
a function of the input common mode voltage. When the
common mode voltage is high and the output is low,
current will flow from the output of amplifier A into the
output of amplifier B. See the Minimum Output Voltage vs
Common Mode Voltage plot.
Similarly, the Single Supply Minimum Common Mode
Voltage vs Output Voltage plot specifies the expected
common mode range.
When the output is high and input common mode is low,
the output of amplifier A has to sink current coming from
the output of amplifier B. Since amplifier A is effectively in
unity gain, its input is limited by its output.
Common Mode Rejection vs Frequency
The common mode rejection ratio (CMRR) of the LT1101
starts to roll off at a relatively low frequency. However, as
shown on the Common Mode Rejection Ratio vs Fre-
quency plot, CMRR can be enhanced significantly by
connecting an 82pF capacitor between pins 1 and 2. This
improvement is only available in the gain 100 configura-
tion, and it is in excess of 30dB at 60Hz.
Offset Nulling
The LT1101 is not equipped with dedicated offset null
terminals. In many bridge transducer or sensor applica-
tions, calibrating the bridge simultaneously eliminates the
instrumentation amplifier’s offset as a source of error. For
example, in the Micropower Remote Temperature Sensor
Application shown, one adjustment removes the offset
errors due to the temperature sensor, voltage reference
and the LT1101.
OUTPUT VOLTAGE (V)
0
0
MINIMUM COMMON MODE VOLTAGE (V)
20
40
60
80
120
2
468
10 12
100
LT1101 • TPC21
G = 10
G = 100
V
+
= 1.8V TO 15V
V
–
= OV
–55°C
–55°C
125°C
125°C
25°C
25°C
LT1101 • TPC22
MINIMUM OUTPUT VOLTAGE (mV)
0
COMMON MODE VOLTAGE (V)
6
8
10
9
7
5
3
80
4
2
1
0
2010
4030
60 70 90
50
100
G = 10
G = 100
125°C
125°C
25°C
–55°C
–55°C
V
+
= 1.8V TO 15V
V
–
= OV
NO LOAD
25°C
TEMPERATURE (°C)
–50
0
MINIMUM SUPPLY, OUTPUT SWING,
COMMON MODE RANGE (V)
1.0
2.5
0
50
75
LT1101 • TPC23
0.5
2.0
1.5
–25 25
100
125
COMMON-MODE RANGE
AT MINIMUM SUPPLY
MINIMUM
SUPPLY VOLTAGE
V
–
= 0V
OUTPUT SWING
AT MINIMUM SUPPLY
