adv7322 Analog Devices, Inc., adv7322 Datasheet - Page 63

• Manufacturer Part Number: adv7322
• Description: Multiformat 11-bit Hdtv Video Encoder
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
PCB BOARD LAYOUT
The ADV7322 is optimally designed for lowest noise
performance, both radiated and conducted noise. To
complement the excellent noise performance of the ADV7322,
it is imperative that great care be given to the PC board layout.
The layout should be optimized for lowest noise on the
ADV7322 power and ground lines. This can be achieved by
shielding the digital inputs and providing good decoupling. The
lead length between groups of V
and V
possible to minimized inductive ringing.
It is recommended that a 4-layer printed circuit board is used,
with power and ground planes separating the layer of the signal
carrying traces of the components and solder side layer.
Component placement should be carefully considered in order
to separate noisy circuits, such as crystal clocks, high speed logic
circuitry, and analog circuitry.
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
0
Figure 89. Filter Plot for Output Filter for HDTV, 2× Oversampling
0
1M
1M
DD_IO
Figure 88. Filter Plot for Output Filter for PS, 8× Oversampling
PHASE (Deg)
GROUP DELAY (sec)
GROUP DELAY (Sec)
and GND_IO pins should be kept as short as
CIRCUIT FREQUENCY RESPONSE
CIRCUIT FREQUENCY RESPONSE
10M
10M
FREQUENCY (Hz)
FREQUENCY (Hz)
AA
and AGND, V
100M
MAGNITUDE (dB)
100M
MAGNITUDE (dB)
PHASE (Deg)
DD
and DGND,
1G
1G
480
400
320
240
160
80
0
–80
–160
–240
480
360
240
120
0
–120
–240
18n
16n
14n
12n
10n
8n
6n
4n
2n
0
18n
15n
12n
9n
6n
3n
0
Rev. PrA | Page 63 of 88
There should be a separate analog ground plane and a separate
digital ground plane.
Power planes should encompass a digital power plane and an
analog power plane. The analog power plane should contain the
DACs and all associated circuitry, V
power plane should contain all logic circuitry.
The analog and digital power planes should be individually
connected to the common power plane at a single point
through a suitable filtering device, such as a ferrite bead.
DAC output traces on a PCB should be treated as transmission
lines. It is recommended that the DACs be placed as close as
possible to the output connector, with the analog output traces
being as short as possible (less than 3 inches). The DAC
termination resistors should be placed as close as possible to the
DAC outputs and should overlay the PCB’s ground plane. As
well as minimizing reflections, short analog output traces will
reduce noise pickup due to neighboring digital circuitry.
To avoid crosstalk between the DAC outputs, it is recommended
that as much space as possible be left between the tracks of the
individual DAC output pins. The addition of ground tracks
between outputs is also recommended.
Supply Decoupling
Noise on the analog power plane can be further reduced by the
use of decoupling capacitors.
Optimum performance is achieved by the use of 10 nF and
0.1 µF ceramic capacitors. Each group of V
pins should be individually decoupled to ground. This should
be done by placing the capacitors as close as possible to the
device with the capacitor leads as short as possible, thus
minimizing lead inductance.
A 1 µF tantalum capacitor is recommended across the V
supply in addition to 10 nF ceramic. See the circuit layout in
Figure 90.
Digital Signal Interconnect
The digital signal lines should be isolated as much as possible
from the analog outputs and other analog circuitry. Digital
signal lines should not overlay the analog power plane.
Due to the high clock rates used, avoid long clock lines to the
ADV7322 to minimize noise pickup.
Any active pull-up termination resistors for the digital inputs
should be connected to the digital power plane and not the
analog power plane.
Analog Signal Interconnect
Locate the ADV7322 as close as possible to the output
connectors to minimize noise pickup and reflections due to
impedance mismatch.
REF
circuitry. The digital
AA
, V
DD
, or V
ADV7322
DD_IO
AA