GS1515-CQM Gennum Corporation, GS1515-CQM Datasheet - Page 12

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

into the summing node of the integrator achieves the
sweep. The sweep is disabled once phase lock is asserted.
The direction of the sweep is also changed once LFS
saturates at either end.
MUTE
The logic controls the mute block whenever the PLL_LOCK
signal has a LOW logic state. Whenever the mute signal is
asserted, previous state of the output is latched.
BYPASS
The BYPASS block bypasses the re-clocked/mute path of
the data whenever a logic low input is applied to the
BYPASS input. In the bypass mode, the mute does not
have any effect on the outputs. Also, in the bypass mode,
the internal PLL still locks to a valid HDTV signal and would
show PLL_LOCK.
CABLE DRIVER
The output of the GS1515 is a dual/complimentary current
mode cable driver stage. The output swing and impedance
can be varied. The following table may be used to select
the R
interpolation can be used to determine the specific value of
the resistor for a given output swing at the load impedance.
For linear interpolation, either Figure 20 or the information in
Table 2 should be used. The admittance should be found
and then, by inverting the admittance, a resistor value for
the R
0.8V 75Ω cable drivers. It can also be used as a differential
transmission line driver. In this case, the pull-up resistor
should match the impedance of the transmission line
because the pull-up resistor acts as the source impedance.
When it is used in this case, a higher value of R
could be used in order to reduce the swing and to save
power. Other HD-LINX™ products can handle such low
input swings. It should be noted that the minimum R
resistor cannot be less than 50Ω for reliability reasons
because of higher current density.
522 - 23 - 03
SET
SET
Fig. 20 Signal Swing for Various R
1.0
0.8
0.6
0.4
0.2
0.0
can be found. The output can be used as dual
resistor for the desired line impedance. Linear
0.00
75Ω
0.01
1/RSET (Ω)
50Ω
SET
0.02
Admittances
SET
resistor
0.03
SET
12 of 17
When the outputs are used to differentially drive some other
device such as the GS1508, it is recommended to use 50Ω
transmission lines with the smallest possible signal swing
while allowing 10% variation at the output swing to select
the right choice of the R
the recommended R
compensate for the return-loss in this situation. The
uncompensated waveform at the output is shown in Figure
21.
NOTE: Figures 21 and 22 show the waveforms on an
oscilloscope using a 75Ω to 50Ω pad.
Fig. 21 Uncompensated Output Eye Waveform
Fig. 22 Compensated Output Eye Waveform
SET
resistor is 150Ω. There is no need to
SET
resistor. To drive the GS1508,