Download Report

ADV7401/03 & ADV7188/84/80
VBI Extraction Sensitivity for System 2
1.Setup Description
TG2000 Signal Generator CVBS
CVBS
RCA
RF
Modulator
RF CH3
RF Signal = 57dB
ADv7403
Decoder Eval Board
Digital
Video
Serialiser
KAY 847 Attenuator
SDI
RF Signal
27dB to 57dB
VCR
VHF IN
CVBS OUT
VM700
GS1532
Figure 1. Hardware Setup for Evalutaion
Tektronix SDP200 software was used to generate NTSC CVBS video with sample Closed
Captioning on Line 21 Figure 2.
Figure 2 Line 21 of Signal Generated by TG2000
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 1 of
12
Run in clock
7 cycles @ 0.5035MHz
Period = 1.986 us
Start
Parity
Parity
10.5 us
(to 50% amp)
0 1 2 3 4 5 6 7 01 2 3 45 6 7
Colour Burst
9 cycles @ 3.58MHz
1.986 us
10.003 us
Data
27.382 us
33.764 us
61.146 us
L 21...
L 22...
Figure 3 Sample Closed Caption Waveform with Timing Information
This is signal was fed to the RCA modulator to produce an RF signal which was then passed thro
a programable attenuator, the Kay 847 Attenuator. The RF signal was then demodulated to
CVBS video via a VCR, the Masushita PV-4624S.
The resulting signal is a applied to the CVBS input of the ADV7403 Evaluation Board with a video
serialiser as backend. The serialised video was fed to the Tektronix VM700 to observe the digital
data the ADV7403 produced
2.System 2 Sensitivity Testing
2.1 Closed Captioned Data Recovery using VBI System 2.
VBI Extraction System 2 is the default ANC System on the ADV7403. This system is used to
decode Gemstar 1x, V-Chip and also Closed Caption. This extracted VBI data is available as
ancillary data in the 656 output
In System 2 data extraction is enabled on a per line basis. GDECEL[15:0](Registers 0x48, 0x49)
allows the user to enable and disable the data recovery on selected video lines on even fields
and GDECOL[15:0](Registers 0x4A, 0x4B) for odd fields. So we must program the decoder to
extract VBI data from Line 21.
Enabling CC Data Recovery via System 2 on the ADV7403
0x4A bit 3 to 1
This data can then be read from the ancillary data stream on Line 20.
ANC data is output 1 Line in advance of where it might be expected due to the fact that data is
sliced prior to the comb filters which introduce latency due to standard video processing. The data
was interpreted and verified. Section 5 gives a detailed description of how the sample closed
caption data from line 21 of the applied signal can be extracted from the ancillary data. It also
describes how the encapsulating data may be interpreted.
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 2 of
12
igure 5 CC Captioning Data on line
Figure 4 Ancillary Data displayed by VM700.
2.2 Testing the Sensitivity of Closed Caption as passed in Ancillary Data.
The modulated video signal was measured as 57dB using a Leader LFC-944C Meter.
The signal was attenuated to various levels and accuracy of the extracted data was noted.
Results With Default Threshold
Strength of Signal From Demodulator
Weakest signal before erroneous results
Acceptable signal with Error Correction
Correct Data with numerous Errors
Cannot Extract Correct Data
dB (mV)
57(0.71mV)
34(0.05mV)
32(0.04mV)
30(0.03mV)
27(0.02mV)
Comment
Data valid and constant
Data valid and constant
Data valid and constant
Data Toggles to invalid data Frequently.
Data Toggles Continuously & Looses Detection
2.3 Use of Threshold Adjustment
In debug mode one may adjust the slicing threshold. This may be used to provide more reliable
data-extraction in low level signals with a high noise content.
System 2 Threshold Adjustment on the ADV7403
0x40 bit 7 to 1 Hidden space (Enable Debug mode in the )
0x45 bits 7,6 Hidden space (2 bit control of Slicing threshold level)
If using a 28Mhz crystal the timing parameters in debug mode must be reprogrammed
This can be done by setting the Gemstar registers as below
0x40
0x41
0x42
0x43
0x44
0x45
ACh
76h
8Fh
DEh
F7h
B2h
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 3 of
12
Threshold Setting
00
01
10(Default)
11
Threshold Setting
00
01
10(Default)
11
Threshold Setting
00
01
10(Default)
11
57dB
Data valid & Constant
Data valid & Constant
Data valid & Constant
Data valid & Constant
Effect on Data Extraction in Debug Mode
34dB
Data valid & Constant
Data valid & Constant
Data valid & Toggles infrequently
Data Toggles to invalid data very frequently
Effect on Data Extraction in Debug Mode
32dB
30dB
Data valid & Constant
Data valid & Constant
Data valid & Constant
Data Toggles to invalid data infrequently
Data Toggles to invalid data frequently
Data Toggles to invalid data very frequently
Data Toggles Continuously & Looses
Data Toggles Continuously & Looses
Detection
Detection
Effect on Data Extraction
27dB
Data Toggles to invalid data very frequently also
looses detection
Data Toggles Continuously & Looses Detection
Data Toggles Continuously & Looses Detection
Looses Detection
Effect of using Manual Luma Gain.
The default mode on the ADV7403 is to use the AGC feature. However there is also the option of
using a Fixed Luma Gain. To investigate the operation of CC extraction via System 2 in this
situation, three Luma Gains were applied manually and the above tests were repeated.
A Luma Gain of 0.77, this value was read back from the AGC as a signal direct from the
generator was applied to the decoder. Gain values of 1 and 0.3 were applied.
It was noted that with lower fixed gain values there were more errors in the data reproduced.
Again the extraction could be improved with the lowering of the slice threshold.
Conclusion
From this evaluation we find that without adjusting the slice level threshold reliable VBI Slicing
can be performed on signals
≈36db and above
by reducing the slice level threshold we can achieve valid slicing on signals
≈33db and above.
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 4 of
12
2.3 Testing the Sensitivity of Closed Caption as passed out Via I2C in Evaluation Mode.
In evaluation mode one may read back via i2c the sliced CC data from each field. The sensitivity
of these readback registers along with the closed caption detection status bit was tested with
signals of various noise levels.
Enabling Evaluation Mode for System 2 on the ADV7403
0x4C bit 1 to 1 GDE_EVAL_EN enables Evaluation Mode.
Data Can be read via I2c from the Following Registers
0x96 1st Gemstar/Closed Captioning Byte on line
0x97 2nd Gemstar/Closed Captioning Byte on line
CCAP Dectection Status Bit
0x13 bit 1 Value of 1 flags CCAP detection.
dB
57
50
42
32
31
27
24
Readback Register 0x96 & 0x97
Data Correctly Sliced
Data Correctly Sliced
Data Correctly Sliced
Data Correctly Sliced
Data toggles to incorrect data
Invalid Data Read
Invalid Data Read
CCAP Detection Status Bit
Steady Toggle from 1 to 0
Steady Toggle from 1 to 0
Steady Toggle from 1 to 0
Steady Toggle from 1 to 0
Steady Toggle from 1 to 0
Steady Toggle from 1 to 0
Detection Failed. Steady value of 1
Oberservations
• If VBI_EN is enabled, 0x03 bit 7, this greatly reduces system 2 capability to detect CCAP
and flag the status bit. Test showed a failure to detect CCAP at 37dB.
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 5 of
12
3 Interpreting the Ancillary data Packets.
3.1 System 2 with Gemstar Format Module half Byte Mode.
Byte D[9]
D[8]
D[7]
D[6]
D[5]
D[2]
D[1]
D[0]
0
1
2
3
4
5
6
7
8
9
10
0
1
1
1
EP
EP
EP
EP
EP
EP
0
1
1
0
EF
0
0
0
0
0
0
1
1
1
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
0
0
0
line[3:0]
0
0
0
Gemstar word1[7:4]
Gemstar word1[3:0]
Gemstar word2[7:4]
Gemstar word2[3:0]
0
1
1
0
0
1
1
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
0
0
CS[8]
CS[7]
CS[6]
CS[5]
CS[2]
CS[1]
CS[0]
0
1
1
0
EP
EP
EP
EP
EP
EP
CS[8]
D[4]
CS[4]
D[3]
CS[3]
1
Description
Fixed
Preamble
DID
SDID
Data Count
User Data
Words
Checksum
Table 1. Gemstar Format Module half Byte Mode.
To for this format set the following bits.
0x4C bit 0 to 0 ( Selects half Byte)
0x4C bit 3 to 1 ( Selects System 2 Gemstar Format over the default Ancillary Data format)
Ancillary Data return from VM700.
000
3ff
3ff
140
200
120
108
228
1c0
12c
104
3.1.1 Extracting Closed Captioned Data Bytes and Supplementary information
Preamble Byte 0 to Byte 2:
This is a fixed sequence of 0x00, 0xFF and 0xFF.
Byte 0[9:2]: 00h
Byte 1[9:2]: FFh
Byte 2[9:2]: FFh
Data Identification Word (DID) Byte 3:
This should have a value of 0x140 for Gemstar or CC
Byte 3[9:0]:140h
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 6 of
12
Secondary Data Identification Word(SDID) Byte 4:
This Byte contains information about the video line from which the data was retrieved, Gemstar
was of 1x or 2x format, closed captioning has identical format to Gemstar 1x and whether the
information was retrieved from odd or even field.
12Ch
0100101100b
0 odd
0
gemstar 1x/CC
1011
11d +10d= 21
Line 21.
Byte 4:12Ch or 0100101100b
bit 7: 0 odd field bit 6: 0 gemstar 1x
bits 5 to 3:1011b or 11d*
*For System 2 with Gemstar Format Module the SDID provides a code which is unique for each
of the 16 possible lines from which gemstar data can be sliced. It can be interpreted as the line
number from which the data was extracted less 10d.
Data Count (DC) Byte 5:
This value represents the number of User Data Words in the packet divided by 4. This number
will always be an integral number of 4 and padding will be included if necessary.
Byte 5:104h or 0100000100b
Byte5[3:2]: 01 this tells us that there are 4 Userdata words in this packet.
User Data words(UDW) Bytes 6 to9 or 6 to 13
These are the data byte contained in the applied signal. A maximum of four bytes of data can be
contained in a data packet. Closed captioning & Gemstar 1x contain 2 bytes and gemstar 2x can
contain 4. The position of the bits in the bytes are in reverse order to transmission. The is
depicted in the figure below.
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 7 of
12
Finding CCAP Word 1:
Byte 7:
Byte 6:
0010 0000 0000
120
0001 0010 0000
Finding CCAP Word 2:
Byte 9:
Byte 8:
0001 0000 1000
228
0010 0010 1000
0000 1000
Reverse Order
0010 1010
Reverse Order
0001 0000
0101 0100
Checksum (CS) Final Byte 10 or 14:
This word is used to determine the integrity of the ancillary data packet. The 10 bit value conisists
of a 9 bit value and the 10th bit is the inverse of the 9th bit. The nine bit value equates to the sum
of the 9 LSB of the DID, SDID, DC and the UDW
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 8 of
12
3.2 System 2 with Ancillary Format Module-Nibble output Mode (ITU BT 1364).
To for this format, depicted in Table 2 set the following bits.
0x4C bit 0 to 0 ( Selects half Byte)
0x4C bit 3 to 0 ( Selects System 2 Gemstar Format over the default Ancillary Data format)
Ancillary Data return from VM700.
000
3ff
3ff
154
214
200
158
108
2c8
1a8
200
108
120
108
228
5.2.1 Extracting Closed Captioned and Supplementary information
Finding VBI Word 1
Byte 11:
Byte 10
0010 0000 0000
Finding VBI Word 2
120
Byte 13:
Byte 12:
0001 0010 0000
0001 0000 1000
228
0010 0010 1000
0000 1000
Reverse Order
0010 1010
Reverse Order
0001 0000
0101 0100
Preamble Byte 0 to Byte 2:
This is a fixed sequence of 0x00, 0xFF and 0xFF.
Byte 0[9:2]: 00h
Byte 1[9:2]: FFh
Byte 2[9:2]: FFh
Data Identification Word (DID) Byte 3:
In System 2 this will have the defaulted value of 10101b
Byte 3[9:0]:154h or 0101010100
Byte 3[6:2]: 10101
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 9 of
12
Secondary Data Identification Word(SDID) Byte 4:
In System 2 this will have the defaulted value of 101010b
Byte 4:1a8h or 0110101000b
Byte 4[7:2]: 101010
Data Count (DC) Byte 5:
This value represents the number of User Data Words in the packet divided by 4. This number
will always be an integral number of 4 and padding will be included if necessary. This count
includes the identification users words ( IDO,to ID3 )which are described as below.
Byte 5:108h or 0100001000b
Byte5[6:2] 00010b
Byte5[6:2]: 2d this tells us that there are 8 Userdata words to follow. The first 4 are always ID
Userdata words and the remainder contain the CC datawords
ID0 User Data Byte6:
When using System 2 NTSC this will have a value of 0101 for gemstar 1x
Byte6[5:2]: 214or 1000010100 Byte6[5:2]: 0101b
ID1 and ID2 User Data Bytes 7 & 8:
These bytes provide information about the line number that data was extracted from.This is the
line number as the numbering system in ITU-R BT 470
Line number[9:5]
->
Byte7[6:2]
Line_number[4:0]
->
Byte8[6:2]
Byte8[7] provides information about the field.
Byte7:200h or 1000000000b
Line_number[9:5]:00000b
Byte8:158h or 0101011000b
Line_number[4:0]:10110b or 22d Note 1 line offset!!!
Byte8[7]:0 indicating an odd field.
ID3 User Data Word, Byte9:
For System 2 VBI extraction VDP_TTXT_TYPE[1:0] will have a value of 01b for PAL and a value
of 10b for NTSC.
Byte9: 108h 0100001000b
VDP_TTXT_TYPE[1:0]:10
NTSC.
User Data words(UDW) Bytes 10 to13 or 10 to 17
These are the data byte contained in the applied signal. A maximum of four bytes of data can be
contained in a data packet. Closed captioning & Gemstar 1x contain 2 bytes and gemstar 2x can
contain 4. The extraction of this information is described in the above figure.
Checksum (CS) Final Byte 14 or 18:
This word is used to determine the integrity of the ancillary data packet. The 10 bit value conisists
of a 9 bit value and the 10th bit is the inverse of the 9th bit. The nine bit value equates to the sum
of the 9 LSB of the DID, SDID, DC and the UDW
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 10 of
12
Table 2. Ancillary Data in Nibble Output Format.
Byte
B9
B8
B7
B6
B5
B4
B3
B2
B1
B0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
3
EP
EP
0
0
I2c_did6_2[4:0]
Description
Ancillary Data
Preamble
DID- Data
identification
word
4
EP
EP
I2c_sdid7_2[5:0]
0
0
5
EP
EP
0
0
0
SDIDSecondary
data
identification
word
Data Count
6
EP
EP
padding[1:0]
0
0
ID0 – user data
word 1
7
EP
EP
0
Line_number[9:5]
0
0
ID1 – user data
word 2
Line_number[4:0]
0
0
ID2 – user data
word 3
0
0
0
0
DC[4:0]
VBI_DATA_STD[3:0]
8
EP
EP
Even _
Field
9
EP
EP
0
0
10
EP
EP
0
0
VDP_TTXT
_TYPE[1:0]
Vbi_word_1[7:4]
11
EP
EP
0
0
Vbi_word_1[3:0]
0
0
12
EP
EP
0
0
Vbi_word_2[7:4]1
0
0
13
EP
EP
0
0
Vbi_word_2[3:0]
0
0
14
EP
EP
0
0
Vbi_word_3[7:4]
0
0
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
n-3
1
0
0
0
0
0
0
0
0
0
n-2
n-1
1
B8
0
0
Checksum
0
0
0
0
0
0
0
0
0
0
0
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
ID3 – user data
word 4
User data word
5
User data word
6
User data word
7
User data word
8
User data word
9
[Pad 200h,
These padding
words may or
may not be
present
depending on
ancilliary data
type ] User
data word
Video Group Limerick
Page 11 of
12
4.Summary of Findings and Observations
Sensitivity and Usability of System 2 and VDP
•
•
•
•
System 2 can slice data reliably and place in ancillary data from RF signals ≈30db and
above. This can be improved upon to ≈27db and above by adjusting the slice level
threshold.
System 2 I2C readback capability is reliable with RF signals 32db.At lower level the data
begins to be corrupted. However the status bit indicating closed caption detection did not
failed until 27db!
The status bit will fail at a much higher level ~37db if the VBI region is not filtered. This
occurs when VBI_EN is enabled.
These results were recorded from an ideal lab setup. Customers in the field are
achieving reliable VBI slicing from RF signals as low as 41dB with threshold
adjustment.
Observations about operation of System 2
• System 2 closed captioning data on line 20 of Ancillary data.
• Bits in the bytes of ancillary data are in reverse order to the CC data transmitted.
• System 2 ancillary packets line information is based on LineCount so there is a -10 lines
offset in the decoded value.
• System 2 ITU BT 1364 compatible version of ancillary data does not give information
about the framing sequence in the user words.
VBI Extraction Sensitivity using System 2 VBI Slicer
nnicheallaigh
Analog Devices B.V.
Video Group Limerick
Page 12 of
12