bt829bkrf ETC-unknow, bt829bkrf Datasheet - Page 24

• Manufacturer Part Number: bt829bkrf
• Description: Video Streamii Decoders
• Manufacturer: ETC-unknow

14
1.0 Functional Description
1.4 UltraLock
1.4.1 The Challenge
1.4.2 Operation Principles of UltraLock
1.4 UltraLock
The line length (the interval between the midpoints of the falling edges of suc-
ceeding horizontal sync pulses) of analog video sources is not constant. For a sta-
ble source such as a studio grade video source or test signal generators, this
variation is very small: 2 ns. However, for an unstable source such as a VCR,
laser disk player, or TV tuner, line length variation is as much as a few microsec-
onds.
variations. The Bt829B employs a technique known as UltraLock to implement
locking to the horizontal sync and the subcarrier of the incoming analog video
signal and generating the required number of pixels per line.
UltraLock is based on sampling, using a fixed-frequency stable clock. Because
the video line length will vary, the number of samples generated using a fixed-fre-
quency sample clock will also vary from line-to-line. If the number of generated
samples-per-line is always greater than the number of samples-per-line required
by the particular video format, the number of acquired samples can be reduced to
fit the required number of pixels per line.
PAL) crystal or oscillator input signal source. The 8*Fsc clock signal, or CLKx2,
is divided down to CLKx1 internally (14.32 MHz for NTSC and 17.73 MHz for
PAL). Both CLKx2 and CLKx1 are made available to the system. UltraLock
operates at CLKx1 although the input waveform is sampled at CLKx2 then low-
pass filtered and decimated to CLKx1 sample rate.
els for PAL/SECAM within a nominal line time interval (63.5 s for NTSC and
64 s for PAL/SECAM). For square pixel NTSC and PAL/SECAM formats there
should only be 780 and 944 pixels-per-video line, respectively. This is because
the square pixel clock rates are slower than a 4*Fsc clock rate: for example,
12.27 MHz for NTSC and 14.75 MHz for PAL.
video by always acquiring more samples (at an effective 4*Fsc rate) than are
required by the particular video format. It then outputs the correct number of pix-
els per line. UltraLock then interpolates the required number of pixels so that it
maintains the stability of the original image, despite variation in the line length of
the incoming analog waveform.
pixel NTSC output. The first line is shorter than the nominal NTSC line time
interval of 63.5 s. On this first line, a line time of 63.2 s sampled at 4*Fsc
(14.32 MHz) generates only 905 pixels. The second line matches the nominal line
time of 63.5 s and provides the expected 910 pixels. Finally, the third line is too
long at 63.8
UltraLock outputs only 780 pixels.
Digital display systems require a fixed number of pixels per line, despite these
The Bt829B requires an 8*Fsc (28.64 MHz for NTSC and 35.47 MHz for
At a 4*Fsc (CLKx1) sample rate there are 910 pixels for NTSC and 1,135 pix-
UltraLock accommodates line length variations from nominal in the incoming
Figure 1-3 illustrates three successive lines of video being decoded for square
s within which 913 pixels are generated. In all three cases,
D829BDSA
VideoStream II Decoders
Bt829B/827B