ADA4856-3 Analog Devices, ADA4856-3 Datasheet - Page 15

• Manufacturer Part Number: ADA4856-3
• Description: Single-Supply, High Speed, Fixed G = +2, Rail-to-Rail Output Video Amplifier
• Manufacturer: Analog Devices

Specifications of ADA4856-3

• -3db Bandwidth: 225MHz
• Slew Rate: 800V/µs
• Vos: 1.3mV
• Ib: 3.8µA
• # Opamps Per Pkg: 3
• Input Noise (nv/rthz): 14nV/rtHz
• Vcc-vee: 3V to 5.5V
• Isy Per Amplifier: 7.8mA
• Packages: CSP

20 MHz ACTIVE LOW-PASS FILTER
The ADA4856-3 triple amplifier lends itself to higher order
active filters. Figure 42 shows a 20 MHz, 6-pole, Sallen-Key
low-pass filter.
The filter has a gain of approximately 18 dB, which is set by
three fixed gain of 2 stages, and a flat frequency response out to
14 MHz. This type of filter is commonly used at the output of a
video DAC as a reconstruction filter. The frequency response of
the filter is shown in Figure 43.
V
IN
93.1Ω
–10
–20
–30
–40
–50
–60
R1
20
10
0
Figure 43. 20 MHz, Low-Pass Filter Frequency Response
1
TWO POLES
C1
33pF
113Ω
604Ω
R3
Figure 42. 20 MHz, 6-Pole Low-Pass Filter
R2
FOUR POLES
121Ω
C3
33pF
C2
22pF
732Ω
R5
R4
–
+
OP AMP
FREQUENCY (MHz)
C5
47pF
SIX POLES
475Ω
U1
C4
15pF
R6
10
–
OP AMP
+
C6
15pF
U2
OUT1
–
OP AMP
+
U3
OUT2
OUT3
100
200
V
OUT
Rev. A | Page 15 of 20
VIDEO LINE DRIVER
The ADA4856-3 was designed to excel in video driver applications.
Figure 44 shows a typical schematic for a video driver operating
on bipolar supplies.
In applications that require multiple video loads be driven
simultaneously, the ADA4856-3 can deliver. Figure 45 shows
the ADA4856-3 configured with triple video loads. Figure 46
shows the triple video load performance.
V
IN
V
IN
V
(G)
V
IN
IN
CABLE
Figure 46. Large Signal Frequency Response for Various Loads
(R)
(B)
75Ω
75Ω
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
Figure 45. Video Driver Schematic for Triple Video Loads
75Ω
75Ω
1
PD
V
V
75Ω
4
1
2
3
S
OUT
= 5V
Figure 44. Video Driver Schematic
ADA4856-3
ADA4856-3
= 1V p-p
+
–
16
5
+V
–V
15
6
R
R
R
S
S
FREQUENCY (MHz)
L
L
L
= 150Ω
= 75Ω
= 50Ω
14
7
10µF
0.1µF
0.1µF
10µF
10
75Ω
75Ω
–V
–V
13
8
S
S
0.1µF
V
V
OUT
OUT
12
11
10
0.1µF
9
0.1µF
0.1µF
(B)
75Ω
75Ω
75Ω
(R)
CABLE
CABLE
CABLE
+V
+V
ADA4856-3
0.1µF
75Ω
75Ω
75Ω
S
0.1µF
S
0.1µF
75Ω
100
+
75Ω
75Ω
75Ω
+
10µF
V
10µF
OUT
200
V
V
V
OUT
OUT
OUT
(G)
1
2
3