GS1515-CQM Gennum Corporation, GS1515-CQM Datasheet - Page 13

• Manufacturer Part Number: GS1515-CQM
• Description: Hd-linx(tm) HDTV Serial Digital Reclocker
• Manufacturer: Gennum Corporation

TABLE 2: R
JITTER DEMODULATION (DM)
The differential jitter demodulation (DM) signal is available
at the DM and DM pins. This signal is the phase correction
signal of the PLL loop, which is amplified and buffered. If
the input jitter is modulated, the PLL tracks the jitter if it is
within loop bandwidth. To track the input jitter, the VCO has
to be adjusted by the phase detector via the charge pump.
Thus, the signal which controls the VCO contains the
information of the input jitter modulation. The jitter
demodulation signal is only valid if the input jitter is less
than 0.5UIp-p.
impedance, which could be low pass filtered with
appropriate capacitors to eliminate high frequency noise.
DFT_V
signals.
The DM signals can be used as diagnostic tools. Assume
there is an HDTV SDI source, which contains excessive
noise during the horizontal blanking because of the
transient current flowing in the power supply. In order to
discover the source of the noise, one could probe around
the source board with a low frequency oscilloscope
(Bandwidth < 20MHz) that is triggered with an appropriately
filtered DM/DM signal. The true cause of the modulation will
be synchronous and will appear as a stationary signal with
respect to the DM/DM signal.
Figure 23 shows an example of such a situation. An HDTV
SDI signal is modulated with a modulation signal causing
about 0.2UI jitter in Figure 23 (Channel 1). The GS1515
receives this signal and locks to it. Figure 23 (Channel 2)
shows the DM signal. Notice the wave shape of the DM
signal, which is synchronous to the modulating signal. The
DM/DM signal could also be used to compare the output
jitter of the HDTV signal source.
R
EE
SET
500.0 Ω
150.0 Ω
should be connected to GND to activate DM/DM
RESISTOR
75.0 Ω
53.6 Ω
52.3 Ω
49.9 Ω
SET
Values for Various Output Load Conditions
The DM/DM signals have 10kΩ output
THE R
(= 1/R
ADMITTANCE (g) OF
SET
SET
0.0020
0.0067
0.0133
0.0187
0.0192
0.0200
RESISTOR)
RESISTOR
OUTPUT CURRENT
13 of 17
15.161mA
20.702mA
21.216mA
22.032mA
2.506mA
7.896mA
POWER SUPPLY NOISE REDUCITON
See Application Note 522-61.
TRANSMISSION LINE,
TERMINATED AT THE
RESISTOR AT THE
Fig. 23 Jitter Demodulation Signal
SOURCE = 75Ω)
END. (PULL-UP
0.094V
0.296V
0.569V
0.776V
0.796V
0.826V
TRANSMISSION LINE,
TERMINATED AT THE
RESISTOR AT THE
SOURCE = 50Ω)
END. (PULL-UP
0.063V
0.197V
0.379V
0.517V
0.530V
522 - 23 - 03