AD8131
10
0
+5V
INPUT
+
10 F
–10
–20
0.1 F
–30
–40
–OUT
3
8
2
1
5
–50
–60
49.9Ω
AD8131
4
6
–70
+OUT
–80
–90
10 F
0.1 F
+
–100
–110
–120
–5V
Figure 43. Unity Gain, Single-Ended-to-Differential Amplifier
2.0
2.1
2.2
2.3
2.4
2.5 2.6
2.7
2.8
2.9
3.0
FREQUENCY (MHz)
As shown above, when −DIN is left floating, there is 100%
feedback of +OꢀT to −IN via the internal feedback resistor.
This contrasts with the typical gain of 2 operation where −DIN is
grounded and one third of the +OꢀT is fed back to −IN. The
result is a closed-loop differential gain of 1.
Figure 42. FFT Plot for AD8131/AD9203
UNITY-GAIN, SINGLE-ENDED-TO-DIFFERENTIAL
DRIVER
If it is not necessary to offset the output common-mode voltage
(via the VOCM pin), then the AD8131 can make a simple unity-
gain single-ended-to-differential amplifier that does not require
any external components. Figure 43 shows the schematic for
this circuit.
ꢀpon careful observation, it can be seen that only +DIN and VOCM
are referenced to ground. The ground voltage at VOCM is the
reference for this circuit. In this unity gain configuration, if a dc
voltage is applied to VOCM to shift the common-mode voltage, a
differential dc voltage will be created at the output, along with the
common-mode voltage change. Thus, this configuration cannot
be used when it is desired to offset the common-mode voltage of
the output with respect to the input at +DIN.
Rev. B | Page 19 of 20
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