Texas Instruments | Level Shifting Signals With Differential Amplifiers (Rev. A) | Application notes | Texas Instruments Level Shifting Signals With Differential Amplifiers (Rev. A) Application notes

Texas Instruments Level Shifting Signals With Differential Amplifiers (Rev. A) Application notes
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Level Shifting Signals With Differential Amplifiers
The INA105 is a unity gain differential amplifier
consisting of a premium grade operational amplifier
and an on-chip precision resistor network. The selfcontained INA105 makes it ideal for many
applications. One such application is precision level
shifting.
Figure 1 shows a general case of a unity gain
differential amplifier that performs a signal level shift
proportional to the voltage VSHIFT appearing on pin 3 of
the OPA27. An operational amplifier is used to drive
the INA105’s “Ref” pin (pin 1) with a low impedance
source to preserve true differential operational of the
INA105.
A basic understanding of the circuit operation can be
gained by considering the INA105 as a three input
summing amplifier. The voltage transfer function is
then EOUT = E2 – E1 + VREF. As this relation shows, the
output will respond to a difference signal and
algebraically add the voltage at the “Ref” input.
Therefore, VREF may take on any arbitrary value that
will not saturate the INA105 amplifier’s output. In the
case of the circuit in Figure 1, VREF = VSHIFT, yielding an
output of EO = E2 – E1 + VSHIFT.
Precision fixed level shifting can be easily
accomplished by using a voltage reference source like
the REF5010. A REF5010 used with an additional
INA105 can be used to provide an accurate, low-drift,
+5-V reference to drive the “Ref” pin of the
differentially connected INA105 as shown in Figure 2.
If, for example, the input signal is a bipolar ±5-V
signal, the output will be level shifted to a unipolar 0 to
10-V signal. The same reference circuit also has –5 V
available and may thus be used for the opposite
conversion from unipolar 0 to 10-V to bipolar ±5-V
signals. Due to this circuit cutting the effective voltage
reference in half relative to ground, this type circuit
configuration allows the creation of non-standard bias
voltages such as 1.5 V or 1.65 V, which are half of 3 V
and 3.3 V, respectively. Precision level shifting is often
used due to the improved accuracy, low noise, and low
temperature coefficient compared to a resistor divider.
The benefits of a precision voltage reference in level
shifting allow for an accurate voltage over temperature
and time.
E1
2
5
SPACER
6
E1
2
E2
5
3
EO
+VCC
2
6
E2
3
EO
2
6 1
REF5010
5
2
VSHIFT
3
OPA27
INA105
4
-5V
6 1
INA105
6
Figure 1. Level Shifting Circuit Using the INA105’s
VREF Pin
INA105
SPACER
1
3
SPACER
SPACER
Figure 2. Precision Level Shift Circuit From a Fixed
Voltage Reference
SPACER
SPACER
SPACER
SBOA038A – January 1994 – Revised April 2018
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Level Shifting Signals With Differential Amplifiers
Copyright © 1994–2018, Texas Instruments Incorporated
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The INA105 in conjunction with a precision voltage
reference also has the flexibly to create bipolar outputs
such as in Figure 3. Figure 3 is an alternative to
design to Figure 2 that allows for a the –5-V output.
This example uses a REF3450 precision voltage
reference that offers a fixed 5-V output but the
flexibility is also extended to other precision voltage
references.
VREF
4
6
INA213 1
4
E1
2
VOUT
5
2
+VCC
VREF
3
6
E2
3
1
VBIAS
EO
+VCC
5
VREF
REF2030
2
+5V Out
6
2
1
INA105
REF3450
2
6
4
Figure 4. Precision Level Shift Circuit With
REF2030
5
3
-5V Out
1
INA105
Figure 3. Precision Level Shift Circuit With Bipolar
Options
Table 1. Device Information
DEVICE
OPTIMIZED PARAMETERS
INA105
Precision Unity Gain Differential Amplifier
REF5010
10-V, Low-Noise, Very Low Drift, Precision
Voltage Reference
REF3450
5-V, Low-Drift, Low-Power, Small-Footprint
Series Voltage Reference
OPA27
Ultra-Low Noise Precision Operational
Amplifiers
INA213
26-V, Bidirectional, Zero-Drift, High
Accuracy, Low-/High-Side, Voltage Out
Current Shunt Monitor
REF2030
3-V and 1.5-V, Low-Drift, Low-Power, DualOutput Vref and Vref/2 Voltage Reference
SPACER
For precision level shifting in low voltage applications,
the INA213 is an alternative to the INA105. The
INA213 operates from a single 2.7-V to 26-V power
supply that makes it suitable for lower voltage systems
with single supplies. This type of application the
REF2030 a suitable precision voltage reference
companion device to the INA213 for level shifting as
the REF2030 is a dual output precision voltage
reference that can both source VCC and the VBIAS (½
VCC) level shifting voltage for a signal chain and level
shifting applications.
Table 2. Alternate Device Information
DEVICE
OPTIMIZED PARAMETERS
REF3425
2.5-V, Low-Drift, Low-Power, SmallFootprint Series Voltage Reference
REF5050
5-V, Low-Noise, Very Low Drift, Precision
Voltage Reference
ATL431
2.5-V, Low-Iq Adjustable Precision Shunt
Regulator
SPACER
SPACER
SPACER
2
Level Shifting Signals With Differential Amplifiers
SBOA038A – January 1994 – Revised April 2018
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Copyright © 1994–2018, Texas Instruments Incorporated
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