AD8146/AD8147/AD8148

Rev. 0 | Page 21 of 24

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.

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.

2kΩ

2kΩ

500Ω

500Ω

49.9Ω

49.9Ω

442Ω

82.5Ω

487Ω

39.2Ω

442Ω

487Ω

75Ω

100 FEET

100Ω

UTP

AD8148

+

–

VIDEO

SOURCE

18pF

30pF

18pF

30pF

Figure 38. Pre-Emphasis Network Using the AD8148 for 30 Meters of UTP Cable

12

6

FREQUENCY (MHz)

11

10

9

8

7

100

10

1

0.1

Figure 39. AD8148 Pre-Emphasis Network Frequency Response

9

–9

0.1

FREQUENCY (MHz)

6

3

0

–3

–6

1

10

100

PRE-EMPHASIS

NETWORK

WITH CABLE

CABLE ALONE

Figure 40. AD8148 Pre-Emphasis Network Cascaded With

30 Meters of UTP Cable vs. UTP Cable Alone