Datasheet
ADV7320/ADV7321
Rev. A | Page 62 of 88
BOARD DESIGN AND LAYOUT
DAC TERMINATION AND LAYOUT
CONSIDERATIONS
The ADV7320/ADV7321 contain an on-board voltage
reference. The ADV7320/ADV7321 can be used with an
external V
REF
(AD1580).
The R
SET
resistors are connected between the R
SET
pins and AGND
and are used to control the full-scale output current and, therefore,
the DAC voltage output levels. For full-scale output, R
SET
must
have a value of 3040 Ω. The R
SET
values should not be changed.
R
LOAD
has a value of 300 Ω for full-scale output.
VIDEO OUTPUT BUFFER AND OPTIONAL
OUTPUT FILTER
Output buffering on all six DACs is necessary to drive output
devices, such as SD or HD monitors. Analog Devices produces
a range of suitable op amps for this application, for example, the
AD8061. More information on line-driver buffering circuits is
given in the relevant op amps’ data sheets.
An optional analog reconstruction low-pass filter (LPF) may be
required as an anti-imaging filter if the ADV7320/ADV7321 are
connected to a device that requires this filtering.
The filter specifications vary with the application.
Table 38. External Filter Requirements
Application Oversampling
Cutoff
Frequency
(MHz)
Attenuation
–50 dB @
(MHz)
SD 2× >6.5 20.5
SD 16× >6.5 209.5
PS 1× >12.5 14.5
PS 8× >12.5 203.5
HDTV 1× >30 44.25
HDTV 2× >30 118.5
560
Ω
600
Ω
3
4
1
22pF600
Ω
DAC
OUTPUT
75
Ω
BNC
OUTPUT
10
μ
H
560
Ω
05067-085
Figure 85. Example of Output Filter for SD, 16× Oversampling
0
–80
–70
–60
–50
–40
–30
–20
–10
0
–30
–60
–90
–120
–150
–180
–210
–240
1M 10M 100M
FREQUENCY (Hz)
CIRCUIT FREQUENCY RESPONSE
1G
GROUP DELAY (Seconds)
PHASE (Degrees)
MAGNITUDE (dB)
21n
18n
15n
12n
9n
6n
3n
0
24n
GAIN (dB)
05067-086
Figure 86. Filter Plot for Output Filter for SD, 16× Oversampling
560
Ω
3
4
1
6.8pF600
Ω
6.8pF 600
Ω
DAC
OUTPUT
75
Ω
BNC
OUTPUT
4.7
μ
H
560
Ω
05067-087
Figure 87. Example of Output Filter for PS, 8× Oversampling
82pF33pF
75Ω
DAC
OUTPUT
220nH470nH
500Ω
3
4
1
BNC
OUTPUT
500Ω
300Ω
3
4
1
75Ω
05067-088
Figure 88. Example of Output Filter for HDTV, 2× Oversampling
Table 39. Possible Output Rates from the ADV7320/ADV7321
Input Mode Address
0x01, Bits 6 to 4
PLL Address
0x00, Bit 1
Output Rate
(MHz)
SD Only Off 27 (2×)
On 216 (16×)
PS Only Off 27 (1×)
On 216 (8×)
HDTV Only Off 74.25 (1×)
On 148.5 (2×)