Integrated
Circuit
Systems, Inc.
Preliminary Information
M908-02
VCSO B
ASED
C
LOCK
G
ENERATOR
P
IN
A
SSIGNMENT
(9 x 9 mm SMT)
XTAL_1 / REF_IN
GND
nFOUT5
FOUT5
nFOUT4
FOUT4
nFOUT3
FOUT3
VCC
XTAL_2
FOUT6
nFOUT6
FOUT7
nFOUT7
VCC
DNC
DNC
DNC
27
26
25
24
23
22
21
20
19
G
ENERAL
D
ESCRIPTION
The M908-02 is a PLL (Phase Locked Loop) based
clock generator that uses an
internal VCSO (Voltage Controlled
SAW Oscillator) to produce a very
low jitter output clock. From the
M908-02-155.5200
, an output clock
frequency of
155.52
MHz is provided
from eight LVPECL clock output
pairs. (Other frequencies are available; consult factory.)
The accuracy of the output frequency is assured by the
internal PLL that phase-locks the internal VCSO to the
reference input frequency (
19.44
MHz for the
M908-02-155.5200
). The input reference can either be an
external crystal, utilizing the internal crystal oscillator,
or a stable external clock source such as a packaged
crystal oscillator.
28
29
30
31
32
33
34
35
36
M908-02
(Top View)
18
17
16
15
14
13
12
11
10
nFOUT2
FOUT2
nFOUT1
FOUT1
GND
nFOUT0
FOUT0
VCC
GND
F
EATURES
◆
Output clock frequency range 75MHz to 175MHz
(Consult factory for frequency availability)
◆
Eight identical LVPECL output pairs
◆
Jitter 0.7ps rms (at 155.52MHz, over 12kHz-20MHz), typ.
◆
Ideal for OC-48/STM-16 clock reference
◆
Output-to-output skew < 100ps
◆
External XTAL or LVCMOS reference input
◆
Integrated SAW (surface acoustic wave) delay line
◆
Single 3.3V power supply
◆
Small 9 x 9 mm SMT (surface mount) package
Figure 1: Pin Assignment
Example Output Frequency Configurations
(
M908-02-155.5200
)
VCSO and
Ref Clock
PLL
Output
Frequency Multiplication
Frequency
(MHz)
Ratio
(MHz)
19.44
8
155.52
Application
GND
GND
GND
OP_IN
nOP_OUT
nVC
VC
OP_OUT
nOP_IN
1
2
3
4
5
6
7
8
9
OC-48/STM-16
Table 1: Example Output Frequency Configurations
S
IMPLIFIED
B
LOCK
D
IAGRAM
M908-02-155.52 (Other Frequencies Available)
VSCO
External
Crystal
or
Reference
Clock Input
(19.44MHz)
XTAL
OSC
Frequency
Multiplying
PLL
LVPECL
Output
Clock Pairs
(155.52MHz)
External Loop Filter
Figure 2: Simplified Block Diagram
M908-02 Datasheet Rev 0.4
M908-02 VCSO Based Clock Generator
Revised 30Jul2004
●
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Networking & Communications
●
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M908-02
VCSO B
ASED
C
LOCK
G
ENERATOR
Preliminary Information
D
ETAILED
B
LOCK
D
IAGRAM
R
LOOP
C
LOOP
R
POST
C
POST
C
POST
R
LOOP
C
LOOP
R
POST
External
Loop Filter
Components
M908-02
Phase
Detector
OP_IN
nOP_IN
OP_OUT
nOP_OUT
nVC
VC
XTAL_1 / REF_IN
XTAL_2
R
IN
SAW Delay Line
XTAL
OSC
R
IN
Loop Filter
Amplifier
Phase
Shifter
FOUT7
nFOUT7
FOUT6
nFOUT6
VCSO
M Divider
M=8
FOUT5
nFOUT5
FOUT4
nFOUT4
FOUT3
nFOUT3
FOUT2
nFOUT2
FOUT1
nFOUT1
FOUT0
nFOUT0
Phase Locked Loop (PLL)
Figure 3: Detailed Block Diagram
P
IN
D
ESCRIPTIONS
Number
1, 2, 3, 10, 14, 26
4
9
5
8
6
7
11, 19, 33
12, 13
15, 16
17, 18
20, 21
22, 23
24, 25
29, 30
31, 32
27
28
34, 35, 36
Name
GND
OP_IN
nOP_IN
nOP_OUT
OP_OUT
nVC
VC
VCC
FOUT0, nFOUT0
FOUT1, nFOUT1
FOUT2, nFOUT2
FOUT3, nFOUT3
FOUT4, nFOUT4
FOUT5, nFOUT5
FOUT6, nFOUT6
FOUT7, nFOUT7
XTAL_1 / REF_IN
XTAL_2
DNC
I/O
Configuration
Description
Ground
Input
Output
Input
Power
Power supply ground connections.
External loop filter connections. See Figure 5.
Power supply connection, connect to +
3.3
V.
Output
No internal terminator
Clock output pairs, differential LVPECL output
(
155.52
MHz for the
M908-02-155.5200
)
Input
Input
Do Not Connect.
External crystal connection. Also accepts
LVCMOS/LVTTL compatible clock source.
External crystal connection. Leave unconnected
when driving pin
27
with external clock reference.
Internal nodes. Connection to these pins can
cause erratic device operation.
Table 2: Pin Descriptions
M908-02 Datasheet Rev 0.4
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Circuit
Systems, Inc.
M908-02
VCSO B
ASED
C
LOCK
G
ENERATOR
Preliminary Information
F
UNCTIONAL
D
ESCRIPTION
The M908-02 is a PLL (Phase Locked Loop) based
clock generator that generates output clocks
synchronized to an input reference clock.
The M908-02 combines the flexibility of a VCSO
(Voltage Controlled SAW Oscillator) with the stability of
a crystal oscillator.
Input Reference
The
19.44
MHz input reference can either be an external,
discrete crystal device or a stable external clock source
such as a packaged crystal oscillator:
A
PPLICATION
I
NFORMATION
This section includes information on the optional
external crystal and on the external loop filter.
The subsections on the loop filter provide example
component values and also briefly describe the SAW
PLL simulator tool and additional application
information available at www.icst.com.
External Crystal Specifications
If an external crystal is used with the on-chip crystal
oscillator circuit (XTAL OSC), the external crystal
should have the following general specifications:
Crystal Specifications
Parameter
Min Typ Max Unit
AT-cut quartz
Fundamental
16
40
50
•
If an external crystal is used with the on-chip crystal
oscillator circuit (XTAL OSC), the external crystal
should be a parallel-resonant, fundamental mode
crystal. Apply it to the
XTAL_1 / REF_IN
and
XTAL_2
input
pins. External crystal load capacitors are also
required.
•
If an external LVCMOS/LVTTL clock source is used,
apply it to the
XTAL_1 / REF_IN
input pin.
In either case, the reference clock is supplied directly to
the phase detector of the PLL.
The PLL
The PLL (Phase Locked Loop) includes the phase
detector, the VCSO, and a feedback divider (labeled
“M Divider”).
The feedback divider is a digital circuit that divides the
VCSO output frequency by a numerical value “M” in
order to match the input reference frequency.
By controlling the frequency and phase of the VCSO,
the phase detector precisely locks the frequency and
phase of the feedback divider output to that of the input
reference. This creates an output frequency that is a
multiple of the reference frequency (which is output
from the VCSO).
The relationship between the VCSO output frequency,
the M Divider, and the input reference frequency is
defined as follows:
Fvcso = M
×
Fxtal
For the
M908-02-155.5200
(see “Ordering Information” on pg. 6):
•
VCSO output frequency =
155.52
MHz
•
M=
8
•
Input reference frequency =
19.44
MHz
Therefore, for the
M908-02-155.5200
:
155.52
MHz =
8
×
19.44
MHz
f
0
ESR
Crystal Type
Mode of Oscillation
Frequency Range
MHz
Equivalent Series Resistance
Spurious Response (non-harmonic)
Load Capacitance,
parallel load resonant
Drive Level
16
0.1
Ω
-
40
dBc
pF
mW
C
L
P
0
32
1.0
Table 3: Crystal Specifications
The external crystal will be applied to the
XTAL_1 / REF_IN
and
XTAL_2
input pins. External crystal load capacitors
are also required.
Recommended External Crystal Configuration
M908-02
M9xx-0x
XTAL_1 / REF_IN
C1
XTAL
XTAL_2
C2
XTAL OSC
Figure 4: Recommended External Crystal Configuration
XTAL Load Capacitance Specification = 18 pF
C1 = 27 pF
C2 = 33 pF
External load capacitors C1 and C2 present a load of 15 pf
to the crystal (they are seen in series by the crystal through
the common ground connection). With the additional of PCB
trace capacitance and M908-02 input capacitance, the total
load to the crystal is about 18 pf.
The VCSO center output frequency of
155.52
MHz
enables the product of
M
×
input crystal frequency
to fall within the lock range of the VCSO.
M908-02 Datasheet Rev 0.4
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External Loop Filter
To provide stable PLL operation, and thereby a low jitter
output clock, the M908-02 requires the use of an
external loop filter. This is provided via the provided
filter pins (see
Figure 5).
R
LOOP
C
LOOP
R
POST
C
POST
C
POST
R
LOOP
OP_IN
4
9
M908-02
VCSO B
ASED
C
LOCK
G
ENERATOR
Preliminary Information
See Table 4, Example External Loop Filter Component
Values, below.
Example External Loop Filter Component Values
PLL Bandwidth Damping R loop C loop R post C post
(
kHz
)
Factor
(
kΩ
)
(
µF
)
(
kΩ
)
(
pF
)
0.395
1.2
10
1
2.0
2.9
2.4
1.5
4.7
39.0
4.70
1.00
0.01
20
20
20
3300
1000
240
Table 4: Example External Loop Filter Component Values
C
LOOP
OP_OUT
8
5
R
POST
nOP_OUT
nVC
6
7
Note 1: Recommended for minimum output jitter when
using a crystal or crystal oscillator reference.
nOP_IN
VC
Refer to the M908-02 product web page at
www.icst.com/products/summary/m908-02.htm for
additional product information.
Figure 5: External Loop Filter
The loop filter is implemented as a differential circuit
to minimize system noise interference. Due to the
differential signal path design, the implementation
requires two identical complementary RC filters as
shown here.
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.
Refer to the SAW PLL Simulator Software web page at
www.icst.com/products/calculators/m2000filterSWdesc.htm
for additional information.
A
BSOLUTE
M
AXIMUM
R
ATINGS1
Symbol Parameter
Rating
Unit
V
I
V
O
V
CC
T
S
Inputs
Outputs
Power Supply Voltage
Storage Temperature
-
0.5
to V
CC
+
0.5
-
0.5
to V
CC
+
0.5
4.6
V
V
V
o
C
-
45
to +
100
Table 5: Absolute Maximum Ratings
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the
device. These ratings are stress specifications only. Functional operation of product at these conditions
or any conditions beyond those listed in Recommended Conditions of Operation, DC Characteristics, or
AC Characteristics is not implied. Exposure to absolute maximum rating conditions for extended periods
may affect product reliability.
R
ECOMMENDED
C
ONDITIONS OF
O
PERATION
Symbol Parameter
Min
3.135
Typ
3.3
Max
3.465
Unit
V
CC
T
A
Positive Supply Voltage
Ambient Operating Temperature
Commercial
Industrial
V
o
C
o
C
0
-40
+
70
+
85
Table 6: Recommended Conditions of Operation
M908-02 Datasheet Rev 0.4
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Revised 30Jul2004
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Integrated
Circuit
Systems, Inc.
M908-02
VCSO B
ASED
C
LOCK
G
ENERATOR
Preliminary Information
E
LECTRICAL
S
PECIFICATIONS
DC Characteristics
Unless stated otherwise, V
CC
= 3.3V +5%,T
A
= 0
o
C to +70
o
C (commercial), T
A
= -40
o
C to +85
o
C (industrial), F
VCSO
= 155.52MHz,
1
LVPECL outputs terminated with 50Ω to V
CC
- 2V
Symbol Parameter
Min
3.135
Typ
3.3
375
Max
3.465
Unit
Power Supply
V
CC
I
CC
Positive Supply Voltage
Power Supply Current
Input High Voltage
Input Low Voltage
Input High Current
Input Low Current
Input Capacitance
Output High Voltage
Output Low Voltage
Peak to Peak Output Voltage
FOUT, nFOUT (0-7)
XTAL_1 / REF_IN
XTAL_1 / REF_IN
(XTAL_2 disconnected)
V
mA
Reference
Clock
Input
V
IH
V
IL
I
IH
I
IL
(V
cc
/
2
) +
0.5
V
cc
+
0.3
V
µA
µA
-
0.3
-
5.0
(V
cc
/ 2 ) +
0.5
V
150
Crystal or
Reference
Clock Input
Differential
Output
C
IN
V
OH
V
OL
V
P
-
P
4
V
cc
-
1.4
V
cc
-
2.0
0.6
V
cc
-
1.0
V
cc
-
1.7
0.85
pF
V
V
V
Note 1: For other VCSO center frequencies, contact ICS
Table 7: DC Characteristics
AC Characteristics
Unless implied otherwise, V
CC
= 3.3V +5%,T
A
= 0
o
C to +70
o
C (commercial), T
A
= -40
o
C to +85
o
C (industrial), F
VCSO
= 155.52MHz,
1
LVPECL outputs terminated with 50Ω to V
CC
- 2V
Symbol Parameter
Min
75
Typ
Max
175
Unit
Test Conditions
F
OUT
F
IN
APR
Φn
Output Frequency Range
Nominal Input Frequency,
XTAL_1 / REF_IN
VCSO Pull-Range
Single Side Band
Phase Noise
@
155.52
MHz
Jitter (rms)
Output Duty Cycle, High Time
Output Rise Time
Output Fall Time
Output Skew
FOUT, nFOUT (0-7)
FOUT, nFOUT (0-7)
1
kHz Offset
10
kHz Offset
100
kHz Offset
MHz
MHz
ppm
dBc/Hz
dBc/Hz
dBc/Hz
ps
%
ps
ps
ps
Table 8: AC Characteristics
19.44
+
100
+
150
-100
-110
-134
0.7
1.0
55
550
550
100
J(t)
t
DC
t
R
t
F
t
S
12
kHz to
20
MHz
45
350
350
50
450
450
20
% to
80
%
20
% to
80
%
Between Any Pair
Note 1: For other VCSO center frequencies, contact ICS
M908-02 Datasheet Rev 0.4
I n t e g r a t e d C i r c u i t S y s t e m s, I n c .
●
5 of 6
Networking & Communications
●
Revised 30Jul2004
w w w. i c s t . c o m
●
tel (508) 852-5400
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