ADV8005 Hardware Reference Manual
UG-707
vbi_open
, Encoder Map,
Address 0xE483[4]
This bit is used to enable data on the Vertical Blanking Interval (VBI) to be accepted as valid data. This is valid for SD video data only.
Function
vbi_open
Description
1
Enabled
0
Disabled
vbi_data_en
, Encoder Map,
Address 0xE483[4]
This bit is used to enable data on the Vertical Blanking Interval (VBI) to be accepted as valid data. This is valid for SD video data only.
Function
vbi_data_en
Description
1
Enabled
0 (default)
Disabled
7.6.
DAC CONFIGURATIONS
The
encoder features six DACs which all operate in low-drive mode. Low-drive mode is defined as 4.33 mA full-scale current into a
300 Ω load, R
L
.
SET
pins which are used to control the full-scale DAC output current and, therefore, the DAC output voltage
levels; this is achieved through a resistor connected between the R
SET
pin and GND. For low-drive operation, both R
SET1
and R
SET2
must have a
value of 4.12 kΩ, and R
L
must have a value of 300 Ω.
The resistors connected to the R
SET1
and R
SET2
pins should have a 1% tolerance.
The
encoder uses two pins for compensating the DAC reference buffer, COMP1 and COMP2. A 2.2 nF capacitor should be connected
from each of these pins to AVDD2.
7.6.1.
Voltage Reference
contains an on-chip voltage reference that can be used as a board level voltage reference via the V
REF
pin. Alternatively, the
can be used with an external voltage reference by connecting the reference source to the V
REF
pin. For optimal performance, an
external voltage reference such as the
encoder reference voltage. If an external voltage reference is not used,
a 0.1 µF capacitor should be connected from the V
REF
pin to AVDD2.
7.6.2.
Video Output Buffer and Optional Output Filter
A video buffer is necessary on the DAC outputs to match the 300Ω output impedance of the
encoder output to the 75Ω input
impedance of the sink device. ADI produces a range of op amps suitable for this application, for example, the
. For more information
about line driver buffering circuits, refer to the relevant op amp datasheet.
An optional reconstruction (anti-imaging) low-pass filter (LPF) may be required on the
encoder processor DAC outputs if the part is
connected to a device that requires this filtering.
The filter specifications vary with the application. The use of 16× (SD), 8× (ED), or 4× (HD) oversampling can remove the requirement for a
reconstruction filter altogether. Refer to Section
for more details on output oversampling.
For applications requiring an output buffer and reconstruction filter, the
, and
buffers should be considered.
Table 83: Output Filter Requirements
Application
Oversampling
Cutoff Frequency (MHz)
Attenuation
–50 dB at
(MHz)
SD
2×
>6.5
20.5
SD
16×
>6.5
209.5
ED
1×
>12.5
14.5
ED
8×
>12.5
203.5
HD
1×
>30
44.25
HD
4×
>30
267
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