ACS8946 Semtech Corporation, ACS8946 Datasheet - Page 11

• Manufacturer Part Number: ACS8946
• Description: Jitter Attenuating, Multiplying Phase Locked Loop, with Protection Switch, for Oc-12/stm-4 and GbE
• Manufacturer: Semtech Corporation

Characteristic is defined solely by the loop filter
bandwidth and is shown in Figure 5, which shows the
transfer characteristic using the recommended loop filter
bandwidth of 2 kHz with a damping factor of 1.2.
Figure 5 Jitter Transfer Characteristic, ACS8946
Stand-alone
In the combined solution, the ACS8525 device provides
additional low frequency jitter filtering. The Jitter Transfer
Characteristic of the combined ACS8946 and ACS8525 is
shown in Figure 6.
Figure 6 Jitter Transfer Characteristic, ACS8525 and
ACS8946 combined
Phase Noise Performance
The inherent jitter generation by the ACS8946 is shown in
the phase noise plot in Figure 7 measured on a
Revision 3/November 2006 © Semtech Corp.
ADVANCED COMMUNICATIONS
-12.0
-15.0
-18.0
-21.0
-24.0
-27.0
-3.0
-6.0
-9.0
3.0
0.0
100
ACS8946 RMS Jitter Transfer Curve
ACS8944 RMS Jitter Transfer Curve
1000
TBIL
Frequency (Hz)
10000
100000
FINAL
Page 11
155.52 MHz output clock using an input reference of
19.44 MHz.
Figure 7 Phase Noise Offset from Carrier of ACS8946
622.08 MHz output clock
In the combined line card solution, the inherent jitter
generated by the ACS8525 is attenuated by the ACS8946
as shown in the phase noise plot in Figure 8.
Figure 8 Phase Noise Offset from Carrier, ACS8525
155.52 MHz output clock, with and without ACS8946
Clock Cleaner
Lock Detector
A simple lock detector is incorporated which combines the
plus and minus phase errors from the phase detector,
ACS8525 + ACS8946
-100
-120
-140
-160
-20
-40
-60
-80
1.0E+02
-110
-130
-150
-170
0
-10
-30
-50
-70
-90
1.0E+02
Typical Phase Noise @ 155.52MHz
Typical Phase Noise Cleaning of ACS8525
1.0E+03
1.0E+03
1.0E+04
ACS8946 JAM PLL
1.0E+04
TBIL
TBIL
1.0E+05
1.0E+05
1.0E+06
DATASHEET
www.semtech.com
1.0E+06
1.0E+07
ACS8525 alone
Frequency (Hz)
Frequency (Hz)
1.0E+08
1.0E+07