AN2526 Datasheet, PDF (6/10 Pages) STMicroelectronics – STMAV340 has 4 channels and a 2 to 1 video switch

PCB layout recommendation
Table 4.
No
12
13
Bill of materials (BOM) (continued)
Component
Designator
Jumper
10k Resistor
JP1, JP2, JP3, JP4, JP5, JP6,
JP7, JP8, JP9, JP10.
R1, R2
Package
HDR 2X1
0603
AN2526
Manufacturer
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.
STMAV340 supply is connected to V_CC5V analog and GND analog. To further guarantee
the stability of STMAV340 supply, a 100 nF capacitor is used to decouple the V_CC pin. The
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.
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