GS4915 Datasheet, PDF (16/27 Pages) Gennum Corporation – ClockCleaner™

Table 3-2: GS4915 Frequency Modes
FCTRL[1:0]
10
11
Frequency Mode
Fixed – 74.25MHz ± 0.4%
Fixed – 148.5MHz ± 0.4%
In both Auto and Fixed Frequency modes, the GS4915 will measure the selected input
clock frequency to determine if it is in any of the following ranges: 27MHz ± 0.4%,
74.25MHz ± 0.4%, or 148.5MHz ± 0.4% (these ranges include the 74.25MHz/1.001 and
148.5MHz/1.001 video clock frequencies).
Auto Frequency Mode
When FCTRL[1:0] = 00, the device will operate in Auto Frequency mode. In this mode,
the GS4915 will automatically clean the selected input clock if its frequency is found to
be contained in any of the ranges listed above.
The LOCK output pin will be HIGH whenever the device has successfully locked its
cleaning PLL to the selected input clock. In Auto Frequency mode, LOCK will be HIGH if
the input clock frequency is 27MHz ± 0.4%, 74.25MHz ± 0.4%, or 148.5MHz ± 0.4%.
If the input clock varies by more than ± 6.4%, the LOCK output pin will be LOW. Between
0.4% and 6.4%, the device may lock or bypass, as shown in Figure 3-1. Frequencies in
this range should not be applied to the device.
+6.4%
+0.4%
-0.4%
-6.4%
Locked
Undefined
Unlocked
Figure 3-1: Locked, Undefined and Unlocked regions
Fixed Frequency Mode
When FCTRL[1:0] ≠ 00, the device will operate in Fixed Frequency mode. In this mode,
the device will only clean the selected input clock if its frequency is found to be in the
range defined by the particular setting of the FCTRL[1:0] pins.
GS4915 ClockCleaner™
Data Sheet
39145 - 5
June 2009
16 of 27