PCB layout recommendation

AN2526

6/10

2

PCB layout recommendation

For the purpose of maintaining 75

Ω track for all the analog lines, a 4-layer structure is

recommended. All the analog tracks are routed on the top layer of the board. The middle two

layers are used for both analog and digital ground.

The middle two layers are identical and separated into two sections, analog and digital

grounds. They are separated by a slot area and are only connected at the top layer through

ferrite bead. This ensures that the digital switching noise does not get coupled to the analog

portion.

All the analog tracks are routed on top of the analog ground and all the digital tracks are

routed on top of digital ground. There is one signal, the SEL line, which needs to cross from

analog to the digital portion. The crossing is done at the bottom layer exactly below where

the ferrite bead is used to bridge the analog and digital ground. Since the SEL digital line is

mostly static during operation, it does not cause any disruption to the analog portion.

stability of the analog supply lines is of significant importance since the bias level of

STMAV340 is referenced to it. Any instability on the analog supply affects the switch

characteristics.

Each set of video signals, RGB1, RGB2, and RGB_OUT are routed with the same track

length. This guarantees minimum channel-to-channel delay. To guarantee the impedance

match on the analog lines, no via is used for routing these signals.

12

Jumper

JP1, JP2, JP3, JP4, JP5, JP6,

JP7, JP8, JP9, JP10.

HDR 2X1

13

10k Resistor

R1, R2

0603

Table 4.

Bill of materials (BOM) (continued)

No

Component

Designator

Package

Manufacturer