ANSI/CTA-2020:2007 pdf download.Other VBI Waveforms.
* Because this section covers sagnals recelved under all types of real world TV broadcast signal conditions, this wider range should be anticipated.
5.5.5 Spurious Signals
Spurious signals, overshoot and undershoot on the bits shall no( be more than * 10 IRE units.
5.6 System Considerations
5.6.1 Synchronization of AMOL and Video
A set of bits associated with a given frame/field of video shall remain associated with that frame/field, Delaying or advancing the AMOL data with respect to the active video infom’iation will cause erroneous reporting to occur.
5.6.2 Shifted AMOL signals
Although lines 20 and 22 of fields one and two are authorized by the FCC for AMOL use, the data can appear in other scan lines due to unintentional shifting caused by tape machines, time base correctors. compression equipment, editing equipment, and the like. For example, although it is specified to expect AMOL on line 20 and/or line 22, it is possible to find these signals shifted up or down one or two lines (or more) and/or shifted to the opposite field location.
Receiving equipment that is designed to pass the AMOL signal, such as compression encoder/decoders, TBCs (time base correctors), etc are not expected to compensate for shifted AMOL code. This forces the shifting problem to be solved rather than covered up.
6 TVG1x and TVG2x Waveforms
There are two waveforms defined in this section—TVG1x and TVG2x.
6.1 TVG1x Waveform
The signal characteristics of the TVG1 x format shall be identical to the format specified in CEA-608-C Section 5 with the differences descnbed in this section,
6.1.1 Signal Characteristics for Encoding
The encoded data amplitude level of a logic 1 data bit shall vary from CEA-608-C Section 5 as indicated In Table 3.
6.1.3 System Consldei’atlons – SynchronIzation at TVG1 x and Video
A set of bits associated with a given frame/field of video shall remain associated with that field but the respective frame could be delayed up to a maximum of 3 frame pipeline delay. Delaying the TVG1x data with respect to the active video information beyond this specification will result in errors.
6.2 TVG2x Waveform
This section cescnbes me signal format used to encooe data for transmission on NTSC video of the television picture in the VBI region. It contains important information related to both encoders and decoders. This information is provided to ensure compatibility between encoders and decoders.
6.2.1 Signal LocatIons
TVG2x shall be encoded with 51 bits per VBI line, corresponding to an apProximate 1Mbps waveform.
The 51 bits are defined by the dock run-in (8), Frame code (11), and 4 byte payload data (32).
6.2.2 TVG2x Waveform
The signal waveform shall be as defined in Figure 6. The Clock Run-In shall be a symmetrical sine wave with its maximum and minimum amplitudes being equal to the logic 1 and 0” levels respectively of the encoded data. The Clock Run-In shall also be in phase with all of the logic level transitions of the Start and Data bits. The 11 bit Frame Code bits shall follow the same specifications as the Data bits, but are always defined to be 10011101101 in binary. The signal spedfications shall be as defined in Table 5. which also contains a section related to encoders and another section related to decoders. The specifications for these two sections are different to allow for distortions introduced by the transmission channel. The encoder shall be designed to produce an output as close to the nominal specifications as possible. The decoder should be designed to accept as large a variance from the nominal specifications as possible The tolerances given for the decoder are suggested minimum tolerances.
