GS4910B GENNUM [Gennum Corporation], GS4910B Datasheet - Page 60

• Manufacturer Part Number: GS4910B
• Description: HD/SD/Graphics Clock and Timing Generator with GENLOCK
• Manufacturer: GENNUM [Gennum Corporation]

3.6.4.2 Loop Bandwidth of the Audio PLL (GS4911B only)
3.6.5 Locking to Digital Timing from a Deserializer
The capacitive component of the filter controlling the audio loop bandwidth is
determined by the Audio_Cap_Genlock register and the resistive component is
determined by the Audio_Res_Genlock register. These two registers are located
at addresses 39h and 3Ah, respectively, of the host interface.
To determine the setting of Audio_Res_Genlock and Audio_Cap_Genlock, the
following equations must be solved:
where:
BW = the desired audio PLL loop bandwidth
JITTERIN = Jitter present on output PCLK, in seconds.
A_Feedback_Divide = the numerator of the audio PLL divide ratio
A_Feedback_Divide is calculated in the same way as demonstrated in
Section 3.6.2.2 on page 56.
NOTE: The bandwidth calculation represented by the above equation is only
approximate. As the programmed value of Audio_Res_Genlock becomes larger,
the approximation becomes more accurate.
NOTE2: The value programmed in the Audio_Res_Genlock register must be
between 32 and 42. The value programmed in the Audio_Cap_Genlock register
must be greater than 10. These limits define the exact range of loop bandwidth
adjustment available.
As described in
genlocked to either an analog reference, such as a Black & Burst signal, or to an
SDI input via the digital H, V, and F blanking signals normally produced by a
deserializer. When locking to an SDI input, the user should consider the possibility
of a switch of the SDI signal upstream from the system.
If the GS4911B/GS4910B is locked to the digital H, V, and F blanking signals
produced by a deserializer, and the SDI input to the deserializer is switched such
that the phase of the H input changes abruptly, the REF_LOST output will remain
LOW and the GS4911B/GS4910B will not crash lock to the new H phase. Instead,
the clock and timing outputs will very slowly drift towards the new phase. During
this period of drift, the LOCK_LOST output will be LOW, even though the device is
not genlocked.
The user should clear the Run_Window bits [2:0] of register adress 24h to force the
device to crash lock should such a switch occur. This will cause the
36655 - 2
Audio_Res_Genlock
Audio_Cap_Genlock
April 2006
Section 3.4.1 on page
=
≤
Audio_Res_Genlock 21
47
+
log
2
(
6 BW JITTERIN A _Feedback_Divide
×
×
–
43, the GS4911B/GS4910B may be
GS4911B/GS4910B Data Sheet
×
)
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