9. Technologies
DVIDL-OPT series – User's Manual
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9.2.
Pixel Accurate Reclocking
Signal reclocking is an essential important procedure in digital signal
transmission. After passing the reclocking circuit, the signal becomes
stable, jitter-free, and can be transmitted over more equipment like
processors, or event controllers. Without reclocking, sparkles, noise,
and jaggies appear on the image.
Lightware’s sophisticated Pixel Accurate Reclocking technology
fixes more problems than general TMDS reclocking. It removes not
only intra-pair skew but inter-pair skew as well. The Pixel Accurate
Reclocking circuit eliminates the following errors:
Intra-pair skew
Skew between the + and - wires within a differential wire pair (e.g.
Data2- and Data2+). It’s caused by different wire lengths or slightly
different wire construction (impedance mismatch) in DVI cable. It
results in jitter.
Intra-pair skew
+
-
Inter-pair skew
Skew between two differential wire pairs in a cable. It is caused by
different wire pair lengths or different number of twists in the DVI
cable. Too much inter-pair skew results color shift in the picture or
sync loss.
+
-
Inter-pair skew
+
-
Jitter
Signal instability in the time domain. The time difference between two
signal transitions should be a fixed value, but noise and other effects
cause variations.
Jitter
+
-
Noise
Electromagnetic interference between other electronic devices such
as mobile phones, motors, etc. and the DVI cable are coupled onto the
signal. Too much noise results in increased jitter.
Noise
+
-
9.3.
Dual-Link DVI signal
The Dual-Link DVI interface can operate in either Single-Link or Dual-
Link mode. The chosen mode depends on the pixel clock frequency of
the signal and it is selected by the hardware automatically. For pixel
clock frequencies lower than 165 MHz, Single-Link mode is selected.
For higher pixel clock frequencies (up to 330 MHz), Dual-Link mode is
selected. It is important to know that pixel clock frequency is not the
same as TMDS clock frequency when it comes to Dual-Link DVI.
The pixel clock frequency in Single-Link transmission is a 10th part of
the data rate. The maximum data rate of the Single-Link transmission is
1.65 Gbps per TMDS channel and the maximum pixel clock frequency
is 165 MHz. In this case the pixel clock frequency equals the TMDS
clock frequency. The pixel clock frequency in Dual-Link transmission
(when in Dual-Link mode) is a 5th part of the data rate. The maximum
data rate of Dual-Link transmission is still 1.65 Gbps per TMDS channel
but the maximum pixel clock frequency is 330 MHz. In this case the
pixel clock frequency is two times the TMDS clock frequency.
The DVI standard maximizes the data rate of the TMDS channels in
1.65 Gbps. Dual-Link DVI interface enables a higher resolution
compared to the Single-Link transmission by doubling the number of
wire pairs to transmit the video signal. In Single-Link cables 3 wire
pairs carry the color information (red, green and blue) and one wire
pair carries the clock signal (TMDS clock).
Video lines of the Single-Link interface
TMDS clock
Red
Green
PC or Mac
Display
Blue
