GS4915_09 Datasheet, PDF (17/27 Pages) Gennum Corporation – ClockCleaner

For example, if FCTRL[1:0] = 01, the GS4915 will only clean the input clock if its
frequency is 27MHz ± 0.4%; if FCTRL[1:0] = 10, the GS4915 will only clean the input
clock if its frequency is 74.25MHz ± 0.4%; and if FCTRL[1:0] = 11, the GS4915 will only
clean the input clock if its frequency is 148.5MHz ± 0.4%.
In Fixed Frequency mode, the LOCK output pin will be set HIGH after the device has
locked its cleaning PLL to the selected input clock, and only if the input clock frequency
matches the frequency selected by the setting of the FCTRL[1:0] pins. Otherwise, LOCK
will be LOW.
3.4.2 Bypass Modes
The bypass mode of the device is determined by the setting of the external
AUTOBYPASS and BYPASS pins.
Table 3-3: GS4915 Bypass Modes
AUTOBYPASS
BYPASS
0
X
1
0
1
1
NOTE: 'X' indicates a "don't care" condition.
Bypass Mode
Autobypass Mode
Forced Output Mode
Manual Bypass Mode
Autobypass Mode
When AUTOBYPASS is LOW, the device will operate in Autobypass mode. In this mode,
the GS4915 will bypass its cleaning stage and pass the selected input clock signal
directly to the output whenever LOCK is LOW.
Manual Bypass Mode
When AUTOBYPASS and BYPASS are both HIGH, the GS4915 will operate in Manual
Bypass Mode. In this mode, the GS4915 will bypass its cleaning stage and pass the
selected input clock signal directly to the output.
NOTE: If operating in Manual Bypass mode, the LOCK output pin should be ignored.
Depending on the set frequency mode of the device and the detected frequency of the
selected input clock, the cleaning PLL of the device may achieve lock and so may set the
LOCK pin HIGH; however, the output clock will always be a copy of the input clock, and
NOT the cleaned clock.
Forced Output Mode
If AUTOBYPASS is HIGH and BYPASS is set LOW, the device will operate in Forced
Output mode. In this mode, the cleaning stage of the device is never bypassed, and so the
output clock will always be the clock output by the device's PLL, even in an unlocked
condition.
GS4915 ClockCleaner™
Data Sheet
39145 - 5
June 2009
17 of 27