REV. B
ADV7172/ADV7173
–51–
If an output filter is required for the CVBS, Y, UV, Chroma
and RGB outputs of the ADV7172/ADV7173, the filter shown
below can be used. The plot of the filter characteristics is
shown in Figure 93. An Output Filter is not required if the
outputs of the ADV7172/ADV7173 are connected to most
analog monitors or analog TVs; however, if the output signals
are applied to a system where sampling is used (e.g., Digital
TVs), then a filter is required to prevent aliasing.
1.8H
22pF
270pF
330pF
FILTER I/P FILTER O/P
75
Figure 92. Output Filter Used with Output Buffer
APPENDIX 7
OPTIONAL OUTPUT FILTER
FREQUENCY – Hz
0
–40
–80
100M10M100k
MAGNUTUDE – dB
–10
–20
–30
–50
–60
–70
1M
Figure 93. Output Filter Plot
APPENDIX 8
OPTIONAL DAC BUFFERING
When external buffering is needed of the ADV7172/ADV7173
DAC outputs, the configuration in Figure 94 is recommended.
This configuration shows the DAC outputs, A, B, C, running at
half (18 mA) their full current (36 mA) capability. This will
allow the ADV7172/ADV7173 to dissipate less power; the analog
current is reduced by 50% with a R
SET1
= 300 Ω and R
SET2
=
600 Ω and an R
LOAD
of 75 Ω. This mode is recommended for
3.3 V operation as optimum performance is obtained from the
ADV7172/ADV7173
V
REF
PIXEL
PORT
V
AA
OUTPUT
BUFFER
DAC A CVBS
CHROMA
G
LUMA
B
R
300
R
SET1
OUTPUT
BUFFER
DAC B
OUTPUT
BUFFER
DAC C
OUTPUT
BUFFER
DAC D
OUTPUT
BUFFER
DAC E
OUTPUT
BUFFER
DAC F
DIGITAL
CORE
600
R
SET2
Figure 94. Output DAC Buffering Configuration
DAC outputs at 18 mA with a V
AA
of 3.3 V. This buffer also adds
extra isolation on the video outputs (see buffer circuit in Figure
95). Note that DACs D, E, and F will always require buffering
as the full-scale output current from these DACs is limited to
8.66 mA. With DACs A, B, and C, buffering is optional, based
on the user requirements for performance and power consumption.
When calculating absolute output full-scale current and voltage,
use the following equations:
V
OUT
= I
OUT
× R
LOAD
I
OUT
=
V
REF
× K
()
R
SET
K = 4.2146 constant , V
REF
= 1.235 V
AD8051
V
CC
+
V
CC
–
1
5
4
3
2
OUTPUT TO
TV MONITOR
INPUT/
OPTIONAL
FILTER O/P
Figure 95. Recommended Output DAC Buffer
