ADA4424 AD [Analog Devices], ADA4424 Datasheet - Page 11

• Manufacturer Part Number: ADA4424
• Description: 6-Channel SD/ED/HD Video Filter with Charge Pump
• Manufacturer: AD [Analog Devices]

APPLICATIONS INFORMATION
CVBS OUTPUT
The composite video signal (CVBS_OUT) is produced by
passively summing the Y and C channels (see Figure 1), after
amplification by their respective gain stages. Each signal
experiences a 6.2 dB loss from the passive summation and is
subsequently amplified by 6.2 dB in the fixed stage following
the summer. The net signal gain through the composite video
path is, therefore, 0 dB, and the resulting composite signal
present at the ADA4424-6 output is the sum of Y and C with
unity gain.
CORNER FREQUENCY SELECTION
The component channels of the ADA4424-6 allow for a 1 dB
filter corner frequency of either 25 MHz or 39 MHz/34 MHz.
The FC_SEL pin operates as described in Table 5.
Table 5. ED/HD Bandwidth Selection
FC_SEL (Pin 12)
Low (0)
High (1)
INPUT DC OFFSET CANCELLATION
The luma channels (Y_IN, HY_IN) of the ADA4424-6 are capable
of detecting and cancelling dc input offsets of up to 1.1 V. Four
distinct modes of detection/cancellation are available. These are
selected via the MODE1 and MODE0 pins. The chroma (C_IN)
and color difference (HPb_IN, HPr_IN) inputs do not support
offset cancellation. It is recommended that these inputs be ac-
coupled.
Automatic Detection/Cancellation Mode
There are two modes of automatic operation. The primary mode
samples the input signal between the rising edge of the horizon-
tal sync pulse and the start of active video (back porch), averages
the value over the sampling interval, and subtracts it from the
output signal. This is the more accurate method and is able to
reduce the input-referred offsets to less than 25 mV.
An alternate method is available for copy-protected signals, where
sampling the back porch may not provide a reliable dc average.
This method detects the input negative sync tip, and clamps it
to a fixed value (−214 mV for SD, and −300 mV for ED/HD).
Sample intervals for SD and ED are shown in Figure 16, and
the HD sample intervals are shown in Figure 17.
HD/ED
ED
HD
−1 dB Corner Frequency (Typ)
25 MHz
39 MHz (HY); 34 MHz (Pb, Pr)
Rev. C | Page 11 of 16
Figure 16. Back Porch and Sync Tip Sample Intervals (SD/ED)
Figure 17. Back Porch and Sync Tip Sample Intervals (HD)
SYNC TIP SAMPLE INTERVAL
SYNC TIP SAMPLE INTERVAL
BACK PORCH SAMPLE INTERVAL
BACK PORCH SAMPLE INTERVAL
BLACK LEVEL
BLACK LEVEL
ADA4424-6