BT848 ETC, BT848 Datasheet - Page 90

• Manufacturer Part Number: BT848
• Description: Single-Chip Video Capture for PCI
• Manufacturer: ETC

PC B
Power Planes
80
OARD
Supply Decoupling
L
AYOUT
Analog Signal
Power Planes
Digital Signal
Interconnect
Interconnect
C
ONSIDERATIONS
The power plane area should encompass all Bt848 power pins, voltage reference
circuitry, power supply bypass circuitry for the Bt848, the analog input traces, any
input amplifiers, and all the digital signal traces leading to the Bt848.
layout for the power plane should be such that the two planes are at the same elec-
trical potential, but they should be isolated from each other in the areas surround-
ing the chip. Also, the source path for current should be through the digital plane.
This is the same layout as shown for the ground plane (Figure 38). When using a
regulator, circuitry must be included to ensure proper power sequencing. The cir-
cuitry shown in Figure 39 should help in this regard.
The bypass capacitors should be installed with the shortest leads possible, consis-
tent with reliable operation, to reduce the lead inductance. These capacitors should
also be placed as close as possible to the device.
itor to ground, located as close as possible to the device.
and ground planes, as well as between the digital power and ground planes. These
capacitors are at the same electrical potential, but are physically separate, and pro-
vide additional decoupling by being physically close to the Bt848 power and
ground planes. See Figure 40 for additional information about power supply de-
coupling.
The digital signals of the Bt848 should be isolated as much as possible from the an-
alog signals and other analog circuitry. Also, the digital signals should not overlay
the analog power plane.
ital PCB power and ground planes.
Long lengths of closely-spaced parallel video signals should be avoided to mini-
mize crosstalk. Ideally, there should be a ground line between the video signal trac-
es driving the YIN and CIN inputs.
minimize noise coupling.
The Bt848 has digital power (VDD) and analog power (VAA and VPOS). The
Each group of VAA and VDD pins should have a 0.1 F ceramic bypass capac-
Additionally, 10 F capacitors should be connected between the analog power
Any termination resistors for the digital signals should be connected to the dig-
Also, high-speed TTL signals should not be routed close to the analog signals to
L848A_A
Single-Chip Video Capture for PCI
Bt848/848A/849A
Brooktree
®