AD8147 Analog Devices, AD8147 Datasheet - Page 21

• Manufacturer Part Number: AD8147
• Description: Triple Differential Driver for Wideband Video
• Manufacturer: Analog Devices

Figure 39 illustrates the frequency response of the pre-emphasis
network.
Figure 40 illustrates the frequency response of the pre-emphasis
circuit cascaded with the cable compared with that of the cable
alone. It can be seen that the overall response is flat to within
±0.4 dB. The ±0.4 dB ripple in the response is due to the fact
that the pre-emphasis network is linear, comprised of two real-
axis pole/zero pairs, and the cable response is nonlinear.
Figure 39. AD8148 Pre-Emphasis Network Frequency Response
12
11
10
9
8
7
6
0.1
V
S
= ±5V
SOURCE
VIDEO
1
75Ω
FREQUENCY (MHz)
Figure 38. Pre-Emphasis Network Using the AD8148 for 30 Meters of UTP Cable
10
82.5Ω
39.2Ω
487Ω
487Ω
442Ω
100
442Ω
18pF
18pF
30pF
30pF
Rev. 0 | Page 21 of 24
500Ω
500Ω
EXPOSED PADDLE (EP)
The 24-lead LFCSP has an exposed paddle on the underside of
its body. To achieve the specified thermal resistance, it must
have a good thermal connection to one of the PCB planes. The
exposed paddle must therefore be soldered to a pad on the top
of the board that is connected to an inner plane with several
thermal vias. The AD8147/AD8148 use the paddle as a ground
reference; therefore, for these parts, the PCB plane used must be
the ground plane.
+
–
AD8148
2kΩ
2kΩ
–3
–6
–9
Figure 40. AD8148 Pre-Emphasis Network Cascaded With
9
6
3
0
0.1
V
S
30 Meters of UTP Cable vs. UTP Cable Alone
= ±5V
49.9Ω
49.9Ω
1
AD8146/AD8147/AD8148
FREQUENCY (MHz)
PRE-EMPHASIS
CABLE ALONE
WITH CABLE
100 FEET
100Ω
UTP
NETWORK
10
100