Integrated
Circuit
Systems, Inc.
Product Data Sheet
M2020/21
VCSO B
ASED
C
LOCK
PLL
G
ENERAL
D
ESCRIPTION
The M2020/21 is a VCSO (Voltage Controlled SAW
Oscillator) based clock jitter
attenuator PLL designed for clock
jitter attenuation and frequency
translation. The device is ideal for
generating the transmit reference
clock for optical network systems
supporting 2.5-10 GB data rates.
It can serve to jitter attenuate a
stratum reference clock or a recovered clock in loop
timing mode. The M2020/21 module includes a
proprietary SAW (surface acoustic wave) delay line as
part of the VCSO. This results in a high frequency,
high-Q, low phase noise oscillator that assures low
intrinsic output jitter.
P
IN
A
SSIGNMENT
(9 x 9 mm SMT)
FIN_SEL1
GND
P_SEL2
DIF_REF0
nDIF_REF0
REF_SEL
DIF_REF1
nDIF_REF1
VCC
FIN_SEL0
MR_SEL0
MR_SEL1
LOL
NBW
VCC
DNC
DNC
DNC
27
26
25
24
23
22
21
20
19
28
29
30
31
32
33
34
35
36
M2020
M2021
(Top View)
18
17
16
15
14
13
12
11
10
P_SEL0
P_SEL1
nFOUT0
FOUT0
GND
nFOUT1
FOUT1
VCC
GND
F
EATURES
◆
Integrated SAW (surface acoustic wave) delay line;
low phase jitter of < 0.5ps rms, typical (12kHz to 20MHz
or 50kHz to 80MHz)
◆
Output frequencies of 15 to 700 MHz
*
◆
LVPECL clock output (CML and LVDS options available)
◆
Reference clock inputs support differential LVDS,
LVPECL, as well as single-ended LVCMOS, LVTTL
◆
Loss of Lock (LOL) output pin
◆
Narrow Bandwidth control input (NBW pin)
◆
Hitless Switching (HS) options with or without Phase
Build-out (PBO) available for SONET (GR-253) /
SDH (G.813) MTIE and TDEV compliance during
reference clock reselection
◆
Industrial temperature grade available
◆
Single 3.3V power supply
◆
Small 9 x 9 mm SMT (surface mount) package
Figure 1: Pin Assignment
Example I/O Clock Frequency Combinations
Using
M2020-11-622.0800 or M2021-11-622.0800
Input Reference
Clock
(MHz)
(M2020)
(M2021)
GND
GND
GND
OP_IN
nOP_OUT
nVC
VC
OP_OUT
nOP_IN
1
2
3
4
5
6
7
8
9
PLL Ratio
(Pin Selectable)
(M2020)
(M2021)
Output Clock
(MHz)
19.44 or 38.88
77.76
155.52
622.08
32 or 16
8
4
1
622.08
Table 1: Example I/O Clock Frequency Combinations
* Specify VCSO center frequency at time of order.
S
IMPLIFIED
B
LOCK
D
IAGRAM
Loop
Filter
M2020/21
NBW
LOL
MUX
DIF_REF0
nDIF_REF0
DIF_REF1
nDIF_REF1
REF_SEL
MR_SEL1:0
2
0
1
R Div
(1, 4,
16, 64)
Phase
Detector
VCSO
M Divider
(1, 4, 16, 64)
(1, 4, 8, 32)
or
( 1, 4, 8, 16)
Mfin Div
M / R Divider
LUT
Mfin Divider
LUT
P Divider
LUT
P Divider
FOUT0: 1, 4, 8, 32 or TriState
FOUT1: 1, 4, 8 or TriState
TriState
FOUT0
nFOUT0
FOUT1
nFOUT1
FIN_SEL1:0
P_SEL2:0
2
3
Figure 2: Simplified Block Diagram
M2020/21 Datasheet Rev 1.0
M2020/21 VCSO Based Clock PLL
Revised 30Jul2004
●
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 .
Networking & Communications
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M2020/21
VCSO B
ASED
C
LOCK
PLL
Product Data Sheet
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
25
20
21
22
23
24
27
28
29
30
31
Name
GND
OP_IN
nOP_IN
nOP_OUT
OP_OUT
nVC
VC
VCC
FOUT1
nFOUT1
FOUT0
nFOUT0
P_SEL1
P_SEL0
P_SEL2
nDIF_REF1
DIF_REF1
REF_SEL
nDIF_REF0
DIF_REF0
FIN_SEL1
FIN_SEL0
MR_SEL0
MR_SEL1
LOL
I/O
Configuration
Description
Ground
Input
Output
Input
Power
Output
Output
Input
Input
Input
Input
Input
Input
No internal terminator
No internal terminator
Power supply ground connections.
External loop filter connections.
See Figure 5, External Loop Filter, on pg. 6.
Power supply connection, connect to +
3.3
V.
Clock output pair 1. Differential LVPECL.
Clock output pair 0. Differential LVPECL.
, P divider selection. LVCMOS/LVTTL. See Table 5,
Internal pull-down resistor
1
Post-PLL Look-Up Table (LUT), on pg. 3.
P Divider
Biased to Vcc/2
2
Internal pull-down resistor
1
Internal pull-down resistor
1
Biased to Vcc/2
2
Internal pull-down resistor
1
Reference clock input pair 1. Differential LVPECL or LVDS.
Resistor bias on inverting terminal supports TTL or LVCMOS.
Reference clock input selection. LVCMOS/LVTTL:
Logic
1
selects
DIF_REF1, nDIF_REF1.
Logic
0
selects
DIF_REF0, nDIF_REF0
.
Reference clock input pair 0. Differential LVPECL or LVDS.
Resistor bias on inverting terminal supports TTL or LVCMOS.
I
nput clock frequency selection. LVCMOS/LVTTL.
Internal pull-down resistor
1
See Table
3,
Mfin Divider Look-Up Table (LUT) on pg. 3.
M and R divider value selection. LVCMOS/ LVTTL.
Internal pull-down resistor
1
See Table 4, M and R Divider Look-Up Table (LUT)
on pg. 3.
Output
32
34, 35, 36
NBW
DNC
Input
Internal pull-UP resistor
1
Do Not Connect.
Loss of Lock indicator output. Asserted when internal PLL is
not tracking the input reference for frequency and phase.
3
Logic
1
indicates loss of lock.
Logic
0
indicates locked condition.
Narrow Bandwidth enable. LVCMOS/LVTTL:
Logic
1
- Narrow loop bandwidth
, R
IN
= 2100kΩ
.
Logic
0
- Wide bandwidth
, R
IN
= 100kΩ
.
Internal nodes. Connection to these pins can cause erratic
device operation.
Table 2: Pin Descriptions
Note 1: For typical values of internal pull-down and pull-UP resistors, see
DC Characteristics
on pg. 8.
Note 2: Biased toVcc/2, with 50kΩ to Vcc and 50kΩ to ground. See
Differential Inputs Biased to VCC/2
on pg. 8.
Note 3: See
LVCMOS Output
in
DC Characteristics
on pg. 8.
M2020/21 Datasheet Rev 1.0
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M2020/21
VCSO B
ASED
C
LOCK
PLL
Product Data Sheet
D
ETAILED
B
LOCK
D
IAGRAM
R
LOOP
C
LOOP
R
POST
C
POST
C
POST
R
LOOP
C
LOOP
OP_OUT
R
POST
nOP_OUT
nVC
VC
External
Loop Filter
Components
M2020/21
NBW
LOL
MUX
OP_IN
nOP_IN
Hitless Switching (HS) Opt.
HS with Phase Build-out Opt.
Phase
Detector
DIF_REF0
nDIF_REF0
DIF_REF1
nDIF_REF1
REF_SEL
MR_SEL1:0
FIN_SEL1:0
P_SEL2:0
2
0
R Div
(1, 4,
16, 64)
R
IN
Loop Filter
Amplifier
1
Phase
Locked
Loop
(PLL)
(1, 4, 8, 32
or
1, 4, 8, 16)
SAW Delay Line
Phase
Shifter
M Div
(1, 4, 16, 64)
Mfin Divider
VCSO
M and R Divider
LUT
Mfin Divider
LUT
P Divider
LUT
P Divider
(for FOUT0: 1, 4, 8, or 32),
(for FOUT1: 1, 4, or 8)
TriState
FOUT0
nFOUT0
FOUT1
nFOUT1
2
3
Figure 3: Detailed Block Diagram
D
IVIDER
S
ELECTION
T
ABLES
Mfin Divider Look-Up Table (LUT)
The
FIN_SEL1:0
pins select the Mfin divider value, which
establishes the PLL clock multiplication ratio. Since the
VCSO frequency is fixed, this allows input reference
selection.
FIN_SEL1:0
P Divider Look-Up Table (LUT)
The
P_SEL2:0
pins select the P divider values, which set
the output clock frequencies. A P divider of value of
1
will provide a
622.08MHz
output when using a
622.08MHz
VCSO, for example. P divider values of
4
,
8
, or
32
are
also available, plus a TriState mode. The outputs can be
placed into the valid state combinations as listed in
Table 5. (The outputs cannot each be placed into any of
the five available states independently.)
P_SEL2:0
Mfin Value
(M2020) (M2021)
Input Ref. Freq. (MHz)
1
M2020-yz-622.0800 or M2021-yz-622.0800
0
0
1
1
0
1
0
1
32 or 16
8
4
1
19.44 or 38.88
77.76
155.52
622.08
Table 3: Mfin Divider Look-Up Table (LUT)
P Value
for
for
FOUT0
FOUT1
M2020-yz-622.0800 or M2021-yz-622.0800
Output Frequency (MHz)
FOUT0
FOUT1
Note 1: Example with
M2020-yz-622.0800 or M2021-yz-622.0800
M and R Divider Look-Up Table (LUT)
The
MR_SEL1:0
pins select the M and R divider values,
which establish phase detector frequency. A lower
phase detector frequency improves jitter tolerance and
lowers loop bandwidth.
MR_SEL1:0
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
32
1
0
32
4
1
0
1
1
1
4
1
0
8
8
4
4
1
8
4
0
1 TriState TriState
19.44
19.44
622.08
155.52
77.76
155.52
77.76
N/A
622.08
155.52
622.08
622.08
77.76
155.52
155.52
N/A
Table 5: P Divider Look-Up Table (LUT)
M
1
4
16
64
R
1
4
16
64
Description
General Guidelines for M and R Divider Selection
•
A lower phase detector frequency should be used for
loop timing applications to assure PLL tracking,
especially during GR-253 jitter tolerance testing. The
recommended maximum phase detector frequency
for loop timing mode is
19.44MHz
.
When
LOL
is to be used for system health monitoring,
the phase detector frequency should be 5MHz or
greater. Low phase detector frequencies make
LOL
overly sensitive, and higher phase detector
frequencies make
LOL
less sensitive. The
LOL
pin
should not be used during loop timing mode.
Revised 30Jul2004
●
0
0
1
1
0
1
0
1
1
Four sets of divider values to enable
adjustment of bandwidth and jitter
tolerance
•
Table 4: M and R Divider Look-Up Table (LUT)
Note 1: Do not use with
FIN_SEL1:0=11;
Maximum Phase Detector
Frequency=175MHz
M2020/21 Datasheet Rev 1.0
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M2020/21
VCSO B
ASED
C
LOCK
PLL
Product Data Sheet
Configuration of a single-ended input has been
facilitated by biasing
nDIF_REF0
and
nDEF_REF1
to Vcc/2,
with 50kΩ to Vcc and 50kΩ to ground. The input clock
structure, and how it is used with either
LVCMOS/LVTTL inputs or a DC- coupled LVPECL
clock, is shown in Figure 4
.
DIF_REF0
50k
Ω
VCC
50k
Ω
X
50k
Ω
MUX
F
UNCTIONAL
D
ESCRIPTION
The M2020/21 is a PLL (Phase Locked Loop) based
clock generator that generates output clocks synchro-
nized to one of two selectable input reference clocks.
An internal high "Q" SAW delay line provides low jitter
signal performance and establishes the output
frequency of the VCSO (Voltage Controlled SAW
Oscillator). In a given M2020/21 device, the VCSO
center frequency is fixed. A common center frequency
is
622.08MHz,
for SONET for SDH optical network
applications. The VCSO center frequency is specified at
time of order (see “Ordering Information” on pg. 10).
The VCSO has a guaranteed tuning range of
±120
ppm
(commercial temperature grade).
Pin selectable dividers are used within the PLL and
for the output clock. This enables tailoring of device
functionality and performance. The Mfin divider controls
the overall PLL multiplication ratio and thus determines
the input reference clock (see Table 3, on pg. 3). The
M and R dividers control the phase detector frequency
(see Table 4). The P divider scales the VCSO output
enabling lower output frequency selections (Table 5).
The M2020/21 includes a Loss of Lock (
LOL
) indicator,
which provides status information to system
management software. A Narrow Bandwidth (
NBW
)
control pin is provided as an additional mechanism for
adjusting PLL loop bandwidth without affecting the
phase detector frequency.
Options are available for Hitless Switching (HS) with or
without Phase Build-out (PBO). They provide
SONET/SDH MTIE and TDEV compliance during a
reference clock reselection.
Allowance for a single-ended input has been facilitated
by a unique input resistor bias scheme, which is
described next and shown in Figure 4.
Input Reference Clocks
Two clock reference inputs and a selection mux are
provided. Either reference clock input can accept a
differential clock signal (such as LVPECL or LVDS) or
a single-ended clock input (LVCMOS or LVTTL on the
non-inverting input).
A single-ended reference clock on the unselected
reference input can cause an increase in output
clock jitter. For this reason, differential reference
inputs are preferred; interference from a differential
input on the non-selected input is minimal.
LVCMOS/
LVTTL
nDIF_REF0
VCC
0
DIF_REF1
LVPECL
127
Ω
VCC
127
Ω
VCC
50k
Ω
1
82
Ω
50k
Ω
nDIF_REF1
REF_SEL
82
Ω
50k
Ω
M2020/21
Figure 4: Input Reference Clocks
Differential Inputs
Differential LVPECL inputs are connected to both
reference input pins in the usual manner. The external
load termination resistors shown in Figure 4 (the 127Ω
and 82Ω resistors) is ideally suited for both AC and DC
coupled LVPECL reference clock lines. These provide
the 50Ω load termination and the V
TT
bias voltage.
Single-ended Inputs
Single-ended inputs (LVCMOS or LVTTL) are
connected to the non-inverting reference input pin
(
DIF_REF0
or
DIF_REF1
). The inverting reference input pin
(
nDIF_REF0
or
nDIF_REF1
) must be left unconnected.
In single-ended operation, when the unused inverting
input pin (nDIF_REF0 or
nDEF_REF1)
is left floating (not
connected), the input will self-bias at VCC/2.
PLL Operation
The M2020/21 is a complete clock PLL. It uses a phase
detector and configurable dividers to synchronize the
output of the VCSO with the selected reference clock.
The PLL will work correctly, meaning it will phase-lock
the VCSO output to the input reference clock, when the
internal phase detector inputs are able to run at the
same frequency. This means the PLL dividers must be
set appropriately and a suitable reference frequency
must be chosen for the intended output frequency.
When the PLL is not set up appropriately, the VCSO is
forced to its upper or lower operating limit which is
typically about 250 ppm above or below the VCSO
center frequency (no more than 500 ppm above or
below).
4 of 10
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In normal phase-locked condition, the instantaneous
phase error is measured by the phase detector and is
converted to charge pump current pulses. These
current pulses are then integrated by the external loop
filter to create a VCSO control voltage. The loop filter
acts as a low pass filter to remove unwanted reference
clock jitter above a determined frequency or PLL
bandwidth. For reference phase jitter frequencies within
the loop bandwidth, phase jitter amplitude is passed on
to the output clock according to the PLL loop frequency
response curve.
The relationship between the nominal VCSO center
frequency (Fvcso), the M divider, and the input
reference frequency (Fin) is:
-
Fvcso
=
Fin
×
Mfin
×
---
R
Example Frequency and Divider Combinations
Using M2021-yz-622.0800
Fvcso
=
Fin
38.88
77.76
155.52
622.08
x
Mfin
x
M/R
16 x (1/1, 4/4, etc.)
8 x (1/1, 4/4, etc.)
4 x (1/1, 4/4, etc.)
1 x (1/1, 4/4, etc.)
M
M2020/21
VCSO B
ASED
C
LOCK
PLL
Product Data Sheet
TriState
The TriState feature puts the LVPECL output driver into
a high impedance state, effectively disconnecting the
driver from the
FOUT
and
nFOUT
pins of the device. A
logic
0
is then present on the clock net. The impedance
of the clock net is then set to 50Ω by the external circuit
resistors. (This is in distinction to a CMOS output in
TriState, in which case the net goes to a high
impedance and the logic value floats.) The 50Ω
impedance level of the LVPECL TriState allows
manufacturing In-circuit Test to drive the clock net with
an external 50Ω generator to validate the integrity of
clock net and the clock load.
Any unused output (single-ended or differential) should
be left unconnected (floating) in system application.
This minimizes output switching current and therefore
minimizes noise modulation of the VCSO.
622.08
Table 6: Example I/O Clock Frequency Combinations
The M, R, and Mfin dividers can be set by pin configura-
tion using the input pins
MR_SEL1
,
MR_SEL0
,
FIN_SEL1
, and
FIN_SEL0
.
Post-PLL Divider
The M2020/21 also features a post-PLL (P) divider.
Through use of the P divider, the device’s output
frequency (Fout) can be that of the VCSO (such as
622.08MHz
) or the VCSO frequency divided by
4
,
8
or
32
(common optical reference clocks in SONET and SDH
systems).
The
P_SEL2:0
pins select the value for the P divider. (See
Table 5 on pg. 3.)
Accounting for the P divider, the complete relationship
between the input clock reference frequency (Fin) and
output clock frequency (Fout) is defined as:
M
×
Mfin
Fvcso
-
Fout
=
-------------------
=
Fin
×
-------------------------
Due to the narrow tuning range of the VCSO (+120ppm
guaranteed), appropriate selection of all of the following
are required for the PLL be able to lock: VCSO center
frequency, input frequency, and divider selections.
P
R
×
P
Narrow Bandwidth (NBW) Control Pin
A Narrow Loop Bandwidth control pin (
NBW
pin) is
included to enable adjustment of the PLL loop
bandwidth. In wide bandwidth mode (
NBW
=
0
), the
internal resistor Rin is 100kΩ . With the
NBW
pin
asserted (
NBW
=
1
), the internal resistor Rin is changed to
2100kΩ . This lowers the loop bandwidth by a factor of
about 21 (2100 / 100) and lowers the damping factor by
about 4.6 (the square root of 21), assuming the same
external loop filter component values.
Loss of Lock Indicator (LOL) Output Pin
Under normal device operation, when the PLL is locked,
the LOL Phase Detector drives
LOL
to logic
0
. Under
circumstances when the VCSO cannot fully phase lock
to the input (as measured by a greater than 4 ns
discrepancy between the feedback and reference clock
rising edges at the LOL Phase Detector) the
LOL
output
goes to logic 1. The
LOL
pin will return back to logic
0
when the phase detector error is less than 2 ns. The
loss of lock indicator is a low current LVCMOS output.
Guidelines for Using LOL
In a given application, the magnitude of peak-to-peak
jitter at the phase detector will usually increase as the R
divider is increased. If the
LOL
pin will be used to detect
an unusual clock condition, or a clock fault, the
MR_SEL1:0
pins should be set to provide a phase detector
frequency of
5MHz
or greater (the phase detector
frequency is equal to Fin divided by the R divider).
Otherwise, false
LOL
indications may result. A phase
detector frequency of
10MHz
or greater is desirable
when reference jitter is over
500ps
, or when the device is
used within a noisy system environment.
LOL
should not
be used when the device is used in a loop timing
application.
M2020/21 Datasheet Rev 1.0
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 10
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Revised 30Jul2004
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