Datasheet
LT1809/LT1810
20
180910fa
TYPICAL APPLICATIONS
Figure 6. Single Supply A/D Driver
Figure 7. 4096 Point FFT Response
–
+
LT1809
LTC1420
PGA GAIN = 2
REF = 4.096V
5V
3
2
4
1
6
7
5V
12 BITS
10Msps
•
•
•
1k
1k
V
IN
1V
P-P
ON 2.5V DC
470pF
1µF
0.15µF
3
2
1
–A
IN
V
CM
1809 F06
+A
IN
49.9Ω
FREQUENCY (MHz)
0
–120
AMPLITUDE (dB)
–100
–80
–60
–40
–20
0
1234
1809 F07
5
V
S
= 5V
A
V
= +2
f
SAMPLE
= 10Msps
f
IN
= 1.394MHz
SFDR = 80dB
Single Supply Video Line Driver
The LT1809 is a wideband rail-to-rail op amp with a large
output current that allows it to drive video signals in low
supply applications. Figure 8 depicts a single supply
video line driver with AC coupling to minimize the qui-
escent power dissipation. Resistors R1 and R2 are used
to level-shift the input and output to provide the largest
signal swing. A gain of 2 is set up with R3 and R4 to re-
store the signal at V
OUT
, which is attenuated by 6dB due
to the matching of the 75 line with the back-terminated
resistor, R5. The back termination will eliminate any re-
fl ection of the signal that comes from the load. The input
termination resistor, R
T
, is optional—it is used only if
matching of the incoming line is necessary. The values of
C1, C2 and C3 are selected to minimize the droop of the
luminance signal. In some less stringent requirements, the
value of capacitors could be reduced. The – 3dB bandwidth
of the driver is about 95MHz on 5V supply and the amount
of peaking will vary upon the value of capacitor C4.
Figure 8. 5V Single Supply Video Line Driver
Figure 9. Video Line Driver Frequency Response
–
+
LT1809
V
IN
1809 F08
C1
33µF
C2
150µF
R
T
75Ω
R
LOAD
75Ω
V
OUT
R2
5k
R3
1k
R4
1k
C4
3pF
R1
5k
5V
2
3
6
7
4
R5
75Ω
75Ω
COAX CABLE
C3
1000µF
+
+
+
FREQUENCY (MHz)
–2
VOLTAGE GAIN (dB)
4
5
–3
–4
3
0
2
1
–1
0.2 10 100
1809 F09
–5
1
V
S
= 5V