Nevion FRS-3G-DUAL - Manual (Page 20)

FRS-3G-DUAL Rev. B
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More about the frame synchronizer
The frame synchronizer consists of a few important parts that deserve further explanation:
4.1 De-glitcher
The de-glitcher corrects timing errors within a single video line. The de-glitcher has a 2048
samples buffer. When the first signal is present, we call it the “initial phase signal”, data is
taken from the centre of this buffer. If the timing reference of the video signal changes,
when for instance a new source being switched into the signal path, the timing errors
occurring by this change will be corrected if the new timing reference is within +/-1024
samples of the “initial phase signal”. This also goes for all consecutive timing references.
If a signal is more than +/-
1024 samples off relative to the “initial phase signal”, the output
will repeat the last frame, refill the 2048 samples buffer and take out data from the centre of
the buffer. This new signal is now considered the “initial phase signal”. Audio will fade out
when a frame repeat is being done, and fade in at the new frame.
Hence, it produces an error free video output without frame wrapping when the video input
comes from a router with synchronous input video signals that all lies within +/-1024
samples of each other.
The de-glitcher output is always seamless. When a signal is repeated the audio
is faded out. It fades in at the new frame.
4.2 Frame synchronizer
The frame synchronizer consists of a frame store buffer and some control logic. The frame
store buffer can store up to 8 full 3GHD frames. Data is fetched from this buffer according
to the user specified delays. The control logic sets the frame synchronizer into different
modes dependent on the presence of a sync input.
4.2.1 Frame sync mode
If a sync input (BlackBurst or Tri-level) is present, the frame synchronizer will have an
output signal that has a delay relative to the sync reference. As covered in chapter 3.2.7,
two parameters can be used to control this delay: Phase delay and Additional frame delay.
Let us first focus on the phase delay, also called output phase delay. This parameter can be
positive or negative, and determines the relationship between the video output and the sync
input signal. This parameter really adds a delay on an internal sync signal, isync
1 . The
output is always synchronous and in phase with isync, see Figure 11.
Figure 11: Positive phase delay
1 Note that isync is not a physical entity, but a term used in this context to explain the delay process and the use of the
configurable parameters related to this process.