ADV8003 Hardware Manual
Rev. B, August 2013
346
8.6.
DAC CONFIGURATIONS
The ADV8003 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
.
The ADV8003 encoder has two R
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 ADV8003 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.
8.6.1.
Voltage Reference
The ADV8003 contains an on-chip voltage reference that can be used as a board level voltage reference via the V
REF
pin. Alternatively, the
ADV8003 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
is used with the ADV8003 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.
8.6.2.
Video Output Buffer and Optional Output Filter
A video buffer is necessary on the DAC outputs to match the 300Ω output impedance of the ADV8003 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 ADV8003 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
8.4.1 for more details on output oversampling.
For applications requiring an output buffer and reconstruction filter, the
buffers should be considered.
Table 89: 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
560
Ω
600
Ω
22pF
600
Ω
DAC
OUTPUT
75
Ω
BNC
OUTPUT
10µH
560
Ω
3
4
1
06398-
085
Figure 128: Example of Output Filter for SD, 16× Oversampling
Summary of Contents for ADV8003
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