Datasheet

LT6604-10
9
660410fb
APPLICATIONS INFORMATION
Interfacing to the LT6604-10
Note: The LT6604-10 contains two identical fi lters. The
following applications information only refers to one fi lter.
The two fi lters are independent except that they share
the same negative supply voltage V
–
. The two fi lters
can be used simultaneously by replicating the example
circuits. The referenced pin numbers correspond to the
channel A fi lter.
The LT6604-10 channel requires two equal external resis-
tors, R
IN
, to set the differential gain to 402/R
IN
. The inputs
to the fi lter are the voltages V
IN
+
and V
IN
–
presented to these
external components, Figure 1. The difference between V
IN
+
and V
IN
–
is the differential input voltage. The average of
V
IN
+
and V
IN
–
is the common mode input voltage. Simi-
larly, the voltages V
OUT
+
and V
OUT
–
appearing at Pins 27
and 29 of the LT6604-10 are the fi lter outputs. The differ-
ence between V
OUT
+
and V
OUT
–
is the differential output
voltage. The average of V
OUT
+
and V
OUT
–
is the common
mode output voltage. Figure 1 illustrates the LT6604-10
operating with a single 3.3V supply and unity passband
gain; the input signal is DC coupled. The common mode
input voltage is 0.5V, and the differential input voltage is
2V
P-P
. The common mode output voltage is 1.65V, and the
differential output voltage is 2V
P-P
for frequencies below
10MHz. The common mode output voltage is determined
by the voltage at V
OCM
. Since V
OCM
is shorted to V
MID
,
the output common mode is the mid-supply voltage. In
addition, the common mode input voltage can be equal
to the mid-supply voltage of V
MID
.
Figure 2 shows how to AC couple signals into the LT6604-10.
In this instance, the input is a single-ended signal. AC
coupling allows the processing of single-ended or dif-
ferential signals with arbitrary common mode levels. The
0.1µF coupling capacitor and the 402 gain setting resistor
form a high pass fi lter, attenuating signals below 4kHz.
Larger values of coupling capacitors will proportionally
reduce this highpass 3dB frequency.
–
+
402
402
0.01µF
0.1µF
3.3V
–
+
V
IN
–
V
IN
+
25
27
4
34
6
2
29
7
660410 F01
V
OUT
+
V
OUT
–
V
t
3
2
1
V
IN
+
V
IN
–
V
t
3
2
1
V
OUT
+
V
OUT
–
0 0
1/2
LT6604-10
–
+
402
402
0.01µF
0.1µF
0.1µF
0.1µF
3.3V
–
+V
IN
+
25
27
4
34
6
2
29
7
660410 F02
V
OUT
+
V
OUT
–
V
3
2
2
1
V
t
1
0
0
–1
V
IN
+
V
OUT
+
V
OUT
–
1/2
LT6604-10
Figure 1
Figure 2