c
2
1
1
2
R
C
=
´ p ´
´
f
(
)
6
2
out
IN
IN
ref
1
5
6
R
R
V
V
V
V
R
R
R
+
-
æ
ö
=
-
+ ç
÷
+
è
ø
3
6
4
2
1
2
out
3
4
1
3
4
5
6
2
1
R
R
R
R
R
R
V
1
(IN )
1
Vref
(IN )
R
R
R
R
R
R
R
R
R
æ
ö
æ
öæ
ö
æ
ö
æ
ö
=
+
+ +
+
-
-
ç
÷
ç
֍
÷
ç
÷
ç
÷
+
+
+
è
ø
è
ø
è
ø
è
øè
ø
+
±
OUT
V+
C2
C3
V-
R3
R1
C1
+
±
V-
V+
IN-
IN+
VREF
C4
R4
C6
C7
R7
R2
R5
C5
R6
Schematic and PCB Layout
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SBOU193 – July 2017
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DUAL-DIYAMP-EVM
3.4
Difference Amplifier With Reference Buffer
Figure 13
shows the schematic for the difference amplifier with reference buffer circuit configuration.
Figure 13. Difference Amplifier with Reference Buffer Schematic
The difference amplifier utilizes both inverting and non-inverting inputs and produces an output that is
dependent on the difference between the inputs. The gain of the difference amplifier is dependent on the
ratio of R2 to R1 (and subsequently R4 to R3). The reference buffer in the circuit buffers the reference
voltage to maintain the common mode rejection of the difference amplifier.
Equation 10
displays the transfer function of the difference amplifier with reference buffer circuit
configuration.
(10)
If R
1
= R
3
and R
2
= R
4
,
Equation 10
simplifies to
Equation 11
:
(11)
Capacitors C1 and C4 provide the option to filter the output of the amplifier.
Equation 12
calculates the
cut-off frequency of the filter.
where
•
R
1
= R
3
•
R
2
= R
4
•
C
1
= C
4
(12)
