Datasheet

V
1
=
V
A
and
1
2
V
2
=
1
4
V
A
-
V
OUT
=
-R
F
V
1
R
1
V
2
R
2
+
R
S
=
R
L
N
2
-
R
2
R
2
-V
A
/2
V
T1
1:N
1/2R
L
1/2R
L
R
+
R
1
+
-
+
1/2R
S
1/2R
S
R
+
V
2
R
F
R
F
LMH6622
+
-
R
1
OUT
IN
LMH6672
-V
OUT
+V
OUT
V
S
+V
A
/2

V
1
DAC +
DAC -
ADC +
ADC -
-
V
TN
+
IN
OUT
LMH6622
www.ti.com SNOS986D –DECEMBER 2001–REVISED MARCH 2013
Figure 37. ADSL Receive Applications Circuit
The two R
S
resistors are used to provide impedance matching through the 1:N transformer.
(1)
Where R
L
is the impedance of the twisted pair line.
N is the turns ratio of the transformer.
The resistors R
2
and R
F
are used to set the receive gain of the pre-amp. The receive gain is selected to meet the
ADC full-scale requirement of a DSL chipset.
Resistor R
1
and R
2
along with R
F
are used to achieve cancellation of the output driver signal at the output of the
receiver.
Since the LMH6622 is configured as an inverting summing amplifier, V
OUT
is found to be,
(2)
The expression for V
1
and V
2
can be found by using superposition principle.
When V
S
= 0,
(3)
When V
A
= 0,
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