ADV7181BCP Analog Devices Inc, ADV7181BCP Datasheet - Page 97

• Manufacturer Part Number: ADV7181BCP
• Description: IC VIDEO DECODER NTSC 64-LFCSP
• Manufacturer: Analog Devices Inc
• Type: Video Decoderr

Specifications of ADV7181BCP

• Applications: Recorders, Set-Top Boxes
• Voltage - Supply, Analog: 3.15 V ~ 3.45 V
• Voltage - Supply, Digital: 1.65 V ~ 2 V
• Mounting Type: Surface Mount
• Package / Case: 64-LFCSP
• Adc/dac Resolution: 9b
• Screening Level: Industrial
• Package Type: LFCSP EP
• Pin Count: 64
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With: EVAL-ADV7181BEB - BOARD EVALUATION FOR ADV7181
• Lead Free Status / RoHS Status: Compliant, Contains lead / RoHS non-compliant

DIGITAL INPUTS
The digital inputs on the ADV7181 were designed to work with
3.3 V signals, and are not tolerant of 5 V signals. Extra compo-
nents are needed if 5 V logic signals are required to be applied
to the decoder.
Antialiasing Filters
For inputs from some video sources that are not bandwidth
limited, signals outside the video band can alias back into the
video band during A/D conversion and appear as noise on the
output video. The ADV7181 oversamples the analog inputs by
a factor of 4. This 54 MHz sampling frequency reduces the
requirement for an input filter; for optimal performance it is
recommended that an antialiasing filter be used. The
recommended low cost circuit for implementing this buffer and
filter circuit for all analog input signals is shown in Figure 41.
The buffer is a simple emitter-follower using a single npn
transistor. The antialiasing filter is implemented using passive
components. The passive filter is a third-order Butterworth
filter with a –3 dB point of 9 MHz. The frequency response of
the passive filter is shown in Figure 39. The flat pass band up to
6 MHz is essential. The attenuation of the signal at the output of
the filter due to the voltage divider of R24 and R63 is compen-
sated for in the ADV7181 part using the automatic gain control.
The ac coupling capacitor at the input to the buffer creates a
high-pass filter with the biasing resistors for the transistor. This
filter has a cutoff of
It is essential that the cutoff of this filter be less than 1 Hz to
ensure correct operation of the internal clamps within the part.
These clamps ensure that the video stays within the 5 V range
of the op amp used.
{2 × π × ( R39 || R89 ) × C93 }
–100
–120
–20
–40
–60
–80
100kHz
0
Figure 39. Third-Order Butterworth Filter Response
300kHz
1MHz
3MHz
FREQUENCY
10MHz
–1
= 0.62 Hz
30MHz
100MHz
300MHz
1GHz
Rev. B | Page 97 of 104
XTAL AND LOAD CAPACITOR VALUE SELECTION
Figure 40 shows an example reference clock circuit for the
ADV7181. Special care must be taken when using a crystal
circuit to generate the reference clock for the ADV7181. Small
variations in reference clock frequency can cause autodetection
issues and impair the ADV7181 performance.
Use the following guidelines to ensure correct operation:
•
•
•
value of Capacitors C1 and C2 must match C
specific crystal part number in the user’s system.
To find C
C1 = C2 = 2C
where C
Example
C
C1 = 33 pF
C2 = 33 pF
Know the C
Use the correct frequency crystal, which is 27 MHz.
Tolerance should be 50 ppm or better.
Use a parallel-resonant crystal.
load
= 20 pF
stray
load
is 3 pF to 8 pF, depending on board traces.
, use the following formula:
load
load
for the crystal part number selected. The
33pF
Figure 40. Crystal Circuit
– C
stray
27 MHz
XTAL
33pF
load
ADV7181
for the