17
LT1204
U
SA
O
PP
L
IC
AT
ITY
P
I
CA
L
by 1, 0.5, 0.25 and 0.125 to form an amplifier with a gain
of 16, 8, 4, 2, when LT1204 #1 is selected. LT1204 #2
is connected to the same attenuator. When enabled
(LT1204 #1 disabled), it results in gain of 1, 0.5, 0.25 and
0.125. The wide input common mode range of the
LT1204 is needed to accept inputs of 8V
P-P
.
4-Input Differential Receiver
LT1204s can be connected inverting and noninverting as
shown to make a 4-input differential receiver. The receiver
can be used to convert differential signals sent over a low
cost twisted pair to a single-ended output or used in video
loop-thru connections. The logic inputs A0 and A1 are tied
together because the same channels are selected on each
LT1204. By using the Disable feature, the number of
differential inputs can be increased by adding pairs of
LT1204s and tying the outputs of the noninverting LT1204s
(#1) together. Switching transients are reduced in this
receiver because the transient from LT1204 #2 subtracted
from the transient of LT1204 #1.
Programable Gain Amplifier (PGA)
Two LT1204s and seven resistors make a Programable
Gain Amplifier with a 128-to-1 gain range. The gain is
proportional to 2
N
where N is the 3-bit binary value of the
select logic. An input attenuator alters the input signal
4-Input Differential Receiver
1
3
5
7
13
–
+
1
3
5
7
13
–
+
+
+
+
LT1204
#1
1.5k
100Ω
LT1204
#2
1.5k
124Ω
124Ω
249Ω
499Ω
V
IN
= 62.5mV
P-P
TO 8V
P-P
+
+
+
V
OUT
= 1V
P-P
1204 TA03
Programable Gain Amplifier Accepts Inputs
from 62.5mV
P-P
to 8V
P-P
IN 1
IN 2
IN 3
IN 4
–IN 1
–IN 2
–IN 3
–IN 4
1k
1k
1k
1k
75Ω
ENSHDNA1A0
68Ω
68Ω
1k*
1k*
TWISTED PAIR
CABLE
1k*
1k*
1204 TA04
*OPTIONAL
75Ω
V
OUT
–
+
+
+
LT1204
#2
A0
A1
EN
SHDN
+
–
+
+
+
LT1204
#1
A0
A1
EN
SHDN
+
