LT6604-2.5 Linear Technology, LT6604-2.5 Datasheet - Page 9

• Manufacturer Part Number: LT6604-2.5
• Description: Dual Very Low Noise Differential Amplifier and 2.5MHz Lowpass Filter
• Manufacturer: Linear Technology

APPLICATIONS INFORMATION
Interfacing to the LT6604-2.5
Note: The LT6604-2.5 contains two identical lowpass
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
fi lters can be used simultaneously by replicating the ex-
ample circuits. The referenced pin numbers correspond
to the A channel fi lter.
Each LT6604-2.5 channel requires two equal external re-
sistors, R
inputs to the fi lter are the voltages V
to these external components, Figure 1. The difference
between V
average of V
Similarly, the voltages V
27 and 29 of the LT6604-2.5 are the fi lter outputs. The dif-
ference between V
voltage. The average of V
mode output voltage. Figure 1 illustrates the LT6604-2.5
IN
IN
, to set the differential gain to 1580Ω/R
IN
+
and V
+
and V
OUT
IN
IN
–
+
–
is the differential input voltage. The
–1
and V
is the common mode input voltage.
2
1
0
OUT
3
2
1
0
3
2
1
0
OUT
V
V
V
500mV
+
OUT
and V
+
and V
P-P
–
(DIFF)
V
is the differential output
V
IN
V
OUT
IN
V
IN
IN
+
V
+
IN
IN
–
+
OUT
–
+
and V
–
appearing at pins
–
t
t
t
is the common
V
V
IN
V
V
V
IN
IN
IN
IN
IN
–
+
–
–
+
+
–
presented
0.1μF
0.1μF
1580Ω
. The two
1580Ω
402Ω
402Ω
IN
1580Ω
1580Ω
0.01μF
0.01μF
. The
0.01μF
Figure 1
Figure 2
+
–
Figure 3
34
4
6
2
34
4
6
2
2V
1/2
LT6604-2.5
+
–
25
1/2
LT6604-2.5
+
–
7
34
3.3V
25
4
6
2
7
5V
1/2
LT6604-2.5
+
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
differential output voltage is 2V
2.5MHz. The common mode output voltage is determined
by the voltage at V
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
Figure 2 shows how to AC couple signals into the LT6604-
2.5. In this instance, the input is a single-ended signal.
AC-coupling allows the processing of single-ended or
differential signals with arbitrary common mode levels.
The 0.1μF coupling capacitor and the 1580Ω gain setting
resistor form a high pass fi lter, attenuating signals below
1kHz. Larger values of coupling capacitors will proportion-
ally reduce this highpass 3dB frequency.
In Figure 3 the LT6604-2.5 channel is providing 12dB of
gain. The common mode output voltage is set to 2V.
–
–
+
0.1μF
25
+
–
0.1μF
7
3.3V
27
29
27
29
P-P
+
–
0.1μF
27
29
. The common mode output voltage is 1.65V, and the
V
V
OUT
OUT
V
V
OUT
OUT
+
–
V
V
+
–
OUT
OUT
+
–
3
2
1
0
3
2
1
0
V
3
2
1
0
V
V
OCM
. Since V
V
V
V
V
OUT
OUT
OUT
OUT
V
V
+
–
OUT
OUT
+
–
660425 F01
660425 F03
+
–
660425 F02
MID
t
t
P-P
OCM
t
www.DataSheet4U.com
.
for frequencies below
LT6604-2.5
is shorted to V
660425f
MID
9
,