M2060/61/62, M2065/66/67
Integrated
Circuit
Systems, Inc.
VCSO FEC PLL FOR SONET/OTN
P r e l i m i n a r y I n f o r m a t i o n
External Loop Filter
To provide stable PLL operation, the M2060/61/62 or
M2065/66/67 requires use of an external loop filter. This
is provided via the provided filter pins (see Figure 5).
The loop filter is implemented as a differential circuit
to minimize system noise interference.
RLOOP CLOOP
RPOST
CPOST
CPOST
RLOOP CLOOP
nOP_IN OP_OUT
RPOST
OP_IN
nOP_OUT
nVC
VC
4
9
8
5
6
7
Figure 5: External Loop Filter
PLL bandwidth is affected by loop filter component
values, “Mfec” and “Mfin” values, and the “PLL Loop
Constants” listed in AC Characteristics on pg. 11.
The FEC_SEL setting can be used to actively change PLL
loop bandwidth in a given application. See “Mfec and
Rfec Divider Look-Up Tables (LUTs)” on pg. 3.
See Table 10, Example Values for Loop Filter External
Components, on pg. 8.
PLL Simulator Tool Available
A free PC software utility is available on the ICS website
(www.icst.com). The M2000 Timing Modules PLL
Simulator is a downloadable application that simulates
PLL jitter and wander transfer characteristics. This
enables the user to set appropriate external loop
component values in a given application.
1
Example Values for Loop Filter External Components
for Particular M206x Series Devices
VCSO Parameters: K
= 800kHz/V, R = 100k
Ω
(pin NBW = 0), VCSO Bandwidth = 700kHz.
VCO
IN
Device
Device Configuration
Example External Component Values
Nominal Performance With These Values
FIN_SEL MRSEL
1:0
FRef
FVCSO
R loop
C loop
R post
C post
PLL Loop Damping Passband
1:0
Bandwidth Factor Peaking(dB)
(MHz)
(MHz)
M2060, M2060 622.08 622.08
1 1
0 1
6.5
5.9
6.5
6.5
0.05
0.06
0.05
0.05
5.6kΩ
243.0kΩ
8.2kΩ
10µF
0.1µF
10µF
10µF
68kΩ
34kΩ
100kΩ
100kΩ
470pF
470pF
470pF
470pF
530Hz
1kHz
M2060, M2065 155.52 669.3266 1 0
1 0 0
0 1
M2061, M2066 77.76 622.08
M2061
0 1
0 0
360Hz
19.44 622.08
1 1
8.2kΩ
360Hz
Table 10: Example Values for Loop Filter External Components
Note 1: KVCO , VCSO Bandwidth, M Divider Value, and External Loop Filter Component Values determine Loop Bandwidth, Damping Factor, and
Passband Peaking. For PLL Simulator software, go to www.icst.com.
Refer to the M206x Series product web page at
www.icst.com/products/summary/m2060-2067.htm
for additional product information.
M2060/61/62 M2065/66/67 Datasheet Rev 0.4
8 of 12
Revised 30Jul2004
Integrated Circuit Systems, Inc. ● Networking & Communications ● www.icst.com ● tel (508) 852-5400