ACS8944 Semtech Corporation, ACS8944 Datasheet - Page 7

• Manufacturer Part Number: ACS8944
• Description: Jitter Attenuating, Multiplying Phase Locked Loop for Oc-12/stm-4
• Manufacturer: Semtech Corporation

Figure 4 Jitter Transfer Characteristic, ACS8944
Stand-alone
In the combined solution, the ACS8525 device provides
additional low frequency jitter filtering. The jitter transfer
characteristic of the combined ACS8944 and ACS8525 is
shown in Figure 5.
Figure 5 Jitter Transfer Characteristic, ACS8525 and
ACS8944 combined
Phase Noise Performance
The inherent jitter generation by the ACS8944 is shown in
the phase noise plot in Figure 6 for a PLL bandwidth of
2 kHz, output frequency of 155.52 MHz and input of
19.44 MHz.
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
ACS8944 RMS Jitter Transfer Curve
1000
Frequency (Hz)
10000
100000
FINAL
Page 7
Figure 6 Phase Offset from Carrier, ACS8944
In the combined line card solution, the inherent jitter
generated by the ACS8525 is attenuated by the ACS8944
as shown in the phase noise plot in Figure 7, which uses
a PLL bandwidth of 2 kHz.
Figure 7 Phase Offset from Carrier, ACS8525
with/without ACS8944
Loop Filter Components
The loop filter comprises two identical sets of passive RC
components that connect to the differential charge pump
outputs and internal VCO control inputs. Pins VCN and
ACS8525 + ACS8944
-100
-120
-140
-160
-20
-40
-60
-80
-110
-130
-150
-170
1.0E+02
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
ACS8944 JAM PLL
1.0E+04
TBIL
1.0E+05
1.0E+05
1.0E+06
DATASHEET
1.0E+06
www.semtech.com
1.0E+07
ACS8525 alone
Frequency (Hz)
Frequency (Hz)
1.0E+08
1.0E+07