MCP6271R Microchip Technology Inc., MCP6271R Datasheet - Page 18

• Manufacturer Part Number: MCP6271R
• Description: 170 ?a, 2 Mhz Rail-to-rail Op Amp
• Manufacturer: Microchip Technology Inc.

The Difference Amplifier
Figure 7 illustrates an implementation of the difference-amplifier
function. The DC transfer function of this circuit is equal to:
If R
equals:
In this circuit, the maximum allowable voltage of the amplifier’s
inputs limit the input common-mode range. It is possible to
have input voltages at V
voltages. The gain oonboth input signals is equal. This resistor
configuration also subtracts the common-mode voltage of the two
input signals. In addition, by setting the two resistor ratios to be
greater than one, you can easily implement a gain larger than one.
In a single-supply environment, a voltage reference (V
center the output signal between ground and the power supply.
Otherwise, it is possible to drive the output beyond the ground or
V
shift the output signal into the linear region of the amplifier.
16
Figure 5: In a single-supply circuit, you need a voltage to make
this system work correctly. By connecting V
the output will attempt to go below ground with a positive input.
This circuit will work well with a V
voltage is negative. But, you have to ask yourself, “where will that
negative voltage come from in a single-supply circuit?”
Figure 6: Using this type of voltage reference circuit to drive the
V
gain will level shift the output of the circuit amplifier into its linear
region. Try to set the V
range of the circuit.
Analog and Interface Guide – Volume 2
SHIFT
DD
MCP1525-2.5
V
SHIFT
1
Reference)
rail. The purpose and effects of this reference voltage is to
/R
Operational Amplifiers
V
V
V
(Precision
OUT
OUT
SHIFT
(Figure 5) input of an amplifier configured in an inverting
Voltage
2
is equal to R
V
= V
= (V
IN
R
3
V
1
1
(R
OUT
R
– V
4
1
(R
+R
= V
2
1
)(R
2
+R
)/((R
3
SHIFT
SHIFT
R
2
R
/R
2
/R
1
1
1
) /((R
4
and V
3
1
, the closed-loop output of this circuit
voltage around the center of the input
+R
) + V
(1 + R
V
V
2
DD
3
4
= 2.5V ±1.0%
+R
)R
2
SHIFT
SHIFT
1
that exceed the power-supply
4
)
2
)R
/R
–
+
1
1
ground connect if the input
) – V
) – V
R
+
–
2
MCP606
SHIFT
2
(R
IN
2
(R
/R
pin to ground,
2
1
/R
) +
1
)
SHIFT
) can
V
V
OUT
SHIFT
Figure 7: The difference amplifier operates best in a dual-supply
environment. In a dual-supply environment, connect VDual- and
single- supply can power the two amp-instrumentation amplifier.
Single-supply circuits require a center-supply reference, V
ground. In the single-supply environment, where there is no “mid-
supply” connect, connecting the V
Figure 8 illustrates two possible circuits for the voltage, V
The precision, voltage-reference device in Figure 8A is a suitable
high-precision solution for your single-supply circuits. This voltage
reference will give you accurate, DC results at room and over
temperature. Figure 8B illustrates an alternative solution. In
this circuit, splitting the resistor, R
ground provides a voltage for V
governing equations for the voltage of V
difference amplifier. The accuracy of this circuit depends on the
resistor matching and stability of V
Figure 8: A precision voltage reference (A) or a resistor divider
(B) between V
V
instrumentation amplifiers and the two-amp instrumentation
amplifiers use these circuits.
SHIFT
V
V
in Figure 7. Single-supply difference amplifiers, three-amp
IN-
IN+
V
(A)
DD
DD
V
V
and ground is used to generate the voltage at
SHIFT
OUT
(if R
R
R
= (V
3
1
1
OR
1
= R
– V
2
R
2
V
and R
SHIFT
)(R
4
V
V
SHIFT
+
SHIFT
V
IN-
IN+
–
DD
V
2
4
V
DD
/R
OUT
. Figure 8 summarizes the
SHIFT
(Figure 7) between V
R
3
.
1
(if R
pin to ½ V
3
R
= R
) + V
= (V
R
4A
R
= V
SHIFT
3
1
1
R
1
4
= R
4
)
DD X
– V
SHIFT
– R
2
R
V
(B)
and gain of the
2
and R
R
SHIFT
4B
4A
)(R
MCP601
+
–
4B
|| R
DD
2
/ (R
/R
R
3
3
4B
1
is appropriate.
) + V
= R
4A
| R
4
V
)
SHIFT
4B
SHIFT
OUT
DD
)
V
SHIFT
OUT
and
to
.