DATASHEET
COMMUNICATIONS CLOCK JITTER ATTENUATOR
Description
The MK2058-01 is a VCXO (Voltage Controlled Crystal
Oscillator) based clock jitter attenuator designed for system
clock distribution applications. This monolithic IC, combined
with an external inexpensive quartz crystal, can be used to
replace a more costly hybrid VCXO retiming module. The
device accepts and outputs the same clock frequency in
selectable ranges covering 4 kHz to 27 MHz. A dual input
mux is also provided.
By controlling the VCXO frequency within a phase-locked
loop (PLL), the output clock is phase and frequency locked
to the input clock. Through selection of external loop filter
components, the PLL loop bandwidth and damping factor
can be tailored to meet system clock requirements. A loop
bandwidth down to the Hz range is possible.
MK2058-01
Features
•
Excellent jitter attenuation for telecom clocks
•
Also serves as a general purpose clock jitter attenuator
for distributed system clocks and recovered data or video
clocks
•
2:1 Input MUX for input reference clocks
•
No switching glitches on output
•
VCXO-based clock generation offers very low jitter and
phase noise generation
•
Output clock is phase and frequency locked to the
selected input reference clock
•
Fixed input to output phase relationship
•
+115ppm minimum crystal frequency pullability range,
using recommended crystal
•
•
•
•
•
Industrial temperature range
Low power CMOS technology
20-pin SOIC package
Available in Pb (lead) free package
Single 3.3 V power supply
NOTE: EOL for non-green parts to occur on 5/13/10
per PDN U-09-01
Block Diagram
Pullable Crystal
VDD
VDD
3
ISET
X1
X2
Input Clock ICLK2
Input Clock ICLK1
ISEL
1
0
Phase
Detector
Charge
Pump
VCXO
Selectable
Divider
CLK
SEL2:0
3
CHGP
VIN
GND
4
IDT™
COMMUNICATIONS CLOCK JITTER ATTENUATOR
1
MK2058-01
REV F 122109
MK2058-01
COMMUNICATIONS CLOCK JITTER ATTENUATOR
VCXO AND SYNTHESIZER
Pin Assignment
X1
VDD
VDD
VDD
VIN
GND
GND
GND
CHGP
ISET
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
X2
GND
ISEL
ICLK1
ICLK2
SEL0
CLK
NC
SEL1
SEL2
Output Clock Selection Table
SEL2 SEL1 SEL0
0
0
0
0
M
M
M
M
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
Input / Output
Range
3.3 to 8.7 kHz
0.64 to 1.68 MHz
1 to 2.7 MHz
1.7 to 4.5 MHz
5 to 13 kHz
6 to 15.75 kHz
26 to 70 kHz
70 to 210 kHz
2.5 to 6.75 MHz
3.4 to 9 MHz
5 to 13.5 MHz
10 to 27 MHz
Crystal
Frequency
3072 x ICLK
16 x ICLK
10 x ICLK
6 x ICLK
2048 x ICLK
1716 x ICLK
384 x ICLK
128 x ICLK
4 x ICLK
3 x ICLK
2 x ICLK
1 x ICLK
20-pin 300 mil SOIC
Note: For SEL input pin programming:
0 = GND, 1 = VDD, M = Floating
Pin Descriptions
Pin
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Pin
Name
X1
VDD
VDD
VDD
VIN
GND
GND
GND
CHGP
ISET
SEL2
SEL1
NC
CLK
SEL0
ICLK2
ICLK1
ISEL
GND
X2
Pin
Type
—
Power
Power
Power
Input
Power
Power
Power
Output
—
Input
Input
Input
Output
Input
Input
Input
Input
Power
—
Pin Description
Crystal Input. Connect this pin to the specified crystal.
Power Supply. Connect to +3.3 V.
Power Supply. Connect to +3.3 V.
Power Supply. Connect to +3.3 V.
VCXO Control Voltage Input. Connect this pin to CHGP pin and the external
loop filter as shown in this data sheet.
Connect to ground.
Connect to ground.
Connect to ground.
Charge Pump Output. Connect this pin to the external loop filter and to pin
VIN.
Charge pump current setting node, connection for setting resistor.
Output Frequency Selection Pin 2. Determines output frequency as per table
above. Internally biased to VDD/2.
Output Frequency Selection Pin 1. Determines output frequency as per table
above. Internal pull-up resistor.
No Internal Connection.
Clock Output.
Output Frequency Selection Pin 0. Determines output frequency as per table
above. Internal pull-up resistor.
Input Clock Connection 2. Connect an input reference clock to this pin. If
unused, connect to ground.
Input Clock Connection 1. Connect an input reference clock to this pin. If
unused, connect to ground.
Input Selection. Used to select which reference input clock is active. Low input
level selects ICLK1, high input level selects ICLK2. Internal pull-up resistor.
Connect to ground.
Crystal Output. Connect this pin to the specified crystal.
IDT™
COMMUNICATIONS CLOCK JITTER ATTENUATOR
2
MK2058-01
REV F 122109
MK2058-01
COMMUNICATIONS CLOCK JITTER ATTENUATOR
VCXO AND SYNTHESIZER
Functional Description
The MK2058-01 is a clock generator IC that generates an
output clock directly from an internal VCXO circuit which
works in conjunction with an external quartz crystal. The
VCXO is controlled by an internal PLL (Phase-Locked Loop)
circuit, enabling the device to perform clock regeneration
from an input reference clock. The MK2058-01 is configured
to provide an output clock that is the same frequency as the
input clock. There are 12 selectable input / output frequency
ranges, each of which is a submultiple of the supported
quartz crystal frequency range. Please refer to the Output
Clock Selection Table on Page 2.
Most typical PLL clock devices use an internal VCO (Voltage
Controlled Oscillator) for output clock generation. By using
a VCXO with an external crystal, the MK2058-01 is able to
generate a low jitter, low phase-noise output clock within a
low bandwidth PLL. This serves to provide input clock jitter
attenuation and enables stable operation with a
low-frequency reference clock.
The VCXO circuit requires an external pullable crystal for
operation. External loop filter components enable a PLL
configuration with low loop bandwidth.
of the newly selected input at a controlled phase slope (rate
of phase change) as influenced by the PLL loop
characteristics.
Quartz Crystal
It is important that the correct type of quartz crystal is used
with the MK2058-01. Failure to do so may result in reduced
frequency pullability range, inability of the loop to lock, or
excessive output phase jitter.
The MK2058-01 operates by phase-locking the VCXO
circuit to the input signal of the selected ICLK input. The
VCXO consists of the external crystal and the integrated
VCXO oscillator circuit. To achieve the best performance
and reliability, a crystal device with the recommended
parameters (shown below) must be used, and the layout
guidelines discussed in the PCB Layout Recommendations
section must be followed.
The frequency of oscillation of a quartz crystal is determined
by its cut and by the external load capacitance. The
MK2058-01 incorporates variable load capacitors on-chip
which “pull”, or change, the frequency of the crystal. The
crystals specified for use with the MK2058-01 are designed
to have zero frequency error when the total of on-chip +
stray capacitance is 14 pF. To achieve this, the layout should
use short traces between the MK2058-01 and the crystal.
A complete description of the recommended crystal
parameters is in application note MAN05.
A list of approved crystals is located on the IDT web site.
Application Information
Input / Output Frequency Configuration
The MK2058-01 is configured to generate an output
frequency that is equal to the input reference frequency.
Clock frequencies that are supported are those which fall
into the ranges listed in the Output Clock Selection Table on
Page 2. Input bits SEL2:0 are set according to this table, as
is the external crystal frequency. The nominal (center)
frequency of the external crystal will be an integer multiple
of the input / output clock as specified. Please refer to the
Quartz Crystal section on this page regarding external
crystal requirements.
PLL Loop Filter Components
All analog PLL circuits use a loop filter to establish operating
stability. The MK2058-01 uses external loop filter
components for the following reasons:
1) Larger loop filter capacitor values can be used, allowing
a lower loop bandwidth. This enables the use of lower input
clock reference frequencies and also input clock jitter
attenuation capabilities. Larger loop filter capacitors also
allow higher loop damping factors when less passband
peaking is desired.
2) The loop filter values can be user selected to optimize
loop response characteristics for a given application.
Referencing the External Component Schematic on this
Input Mux
The Input Mux serves to select between two alternate input
reference clocks. Upon reselection of the input clock, clock
glitches on the output clock will not be generated due to the
“fly-wheel” effect of the VCXO (the quartz crystal is a high-Q
tuned circuit). When the input clocks are not phase aligned,
the phase of the output clock will change to reflect the phase
IDT™
COMMUNICATIONS CLOCK JITTER ATTENUATOR
3
MK2058-01
REV F 122109
MK2058-01
COMMUNICATIONS CLOCK JITTER ATTENUATOR
VCXO AND SYNTHESIZER
page, the external loop filter is made up of the components
R
Z
, C
1
and C
2
. R
SET
establishes PLL charge pump current
and therefore influences loop filter characteristics.
External Component Schematic
C
L
(Refer to Crystal
Tuning section)
X1
VDD
VDD
VDD
VIN
C
L
Crystal
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
X2
GND
ISEL
ICLK1
ICLK2
SEL0
CLK
NC
SEL1
SEL2
C
P
R
S
C
S
GND
GND
GND
CHGP
ISET
R
SET
Recommended Loop Filter Values Vs. Output Frequency Range Selection
Crystal
SEL2 SEL1 SEL0
Multiplier
(N)
0
0
0
3072
0
0
1
16
0
1
0
10
0
1
1
6
M
0
0
2048
M
0
1
1716
M
1
0
384
M
1
1
128
1
0
0
4
1
0
1
3
1
1
0
2
1
1
1
1
R
SET
R
S
C
S
0.1
µF
0.1
µF
0.1
µF
0.1
µF
0.1
µF
0.1
µF
0.1
µF
0.1
µF
0.1
µF
0.1
µF
0.1
µF
0.1
µF
C
P
Loop
Bandwidth
(-3dB point)
Damping
Factor
1
1
1
1
1
1
1
1
1
1
1
1
120 kΩ
1.4 MΩ
1.4 MΩ
1.4 MΩ
540 kΩ
540 kΩ
1.4 MΩ
1.4 MΩ
1.4 MΩ
1.4 MΩ
1.4 MΩ
1.4 MΩ
750 kΩ
160 kΩ
130 kΩ
100 kΩ
1.2 MΩ
1.1 MΩ
820 kΩ
470 kΩ
82 kΩ
68 kΩ
56 kΩ
39 kΩ
4.7 nF
4.7 nF
4.7 nF
4.7 nF
4.7 nF
4.7 nF
4.7 nF
4.7 nF
4.7 nF
4.7 nF
4.7 nF
4.7 nF
14 Hz
60 Hz
75 Hz
95 Hz
8.5 Hz
9 Hz
12 Hz
20 Hz
120 Hz
130 Hz
160 Hz
225 Hz
Note: For SEL input pin programming: 0 = GND, 1 = VDD, M = Floating
IDT™
COMMUNICATIONS CLOCK JITTER ATTENUATOR
4
MK2058-01
REV F 122109
MK2058-01
COMMUNICATIONS CLOCK JITTER ATTENUATOR
VCXO AND SYNTHESIZER
A “normalized” PLL loop bandwidth may be calculated as
follows:
Special considerations must be made in choosing loop
components C
S
and C
P.
These recommendations can be
found in the design aid tools section of www.idt.com
R
S
×
I
CP
×
575
NBW
= -----------------------------------------
N
Series Termination Resistor
Clock output traces over one inch should use series
termination. To series terminate a 50Ω trace (a commonly
used trace impedance), place a 33Ω resistor in series with
the clock line, as close to the clock output pin as possible.
The nominal impedance of the clock output is 20Ω (The
.
optional series termination resistor is not shown in the
External Component Schematic.)
The “normalized” bandwidth equation above does not take
into account the effects of damping factor or the second
pole. However, it does provide a useful approximation of
filter performance.
The loop damping factor is calculated as follows:
Decoupling Capacitors
As with any high-performance mixed-signal IC, the
MK2058-01 must be isolated from system power supply
noise to perform optimally.
Decoupling capacitors of 0.01µF must be connected
between each VDD and the PCB ground plane. To further
guard against interfering system supply noise, the
MK2058-01 should use one common connection to the PCB
power plane as shown in the diagram on the next page. The
ferrite bead and bulk capacitor help reduce lower frequency
noise in the supply that can lead to output clock phase
modulation.
Damping Factor = R
S
×
625
×
I
CP
×
C
S
------------------------------------------
-
N
Where:
R
S
= Value of resistor in loop filter (Ohms)
I
CP
= Charge pump current (amps)
(refer to Charge Pump Current Table, below)
N = Crystal multiplier shown in the above table
C
S
= Value of capacitor C
1
in loop filter (Farads)
As a general rule, the following relationship should be
maintained between components C
1
and C
2
in the loop
filter:
Recommended Power Supply Connection for
Optimal Device Performance
V D D P in
C onnection to 3.3V
P ow er P lane
Ferrite
Bead
V D D P in
C
P
=
-----
-
20
C
S
B ulk D ecoupling C apacitor
(such as 1 F Tantalum )
V D D P in
Charge Pump Current Table
R
SET
1.4 MΩ
680 kΩ
540 kΩ
120 kΩ
Charge Pump Current
(I
CP
)
10
µA
20
µA
25
µA
100
µA
0.01
F D ecoupling C apacitors
Crystal Load Capacitors
The device crystal connections should include pads for
small capacitors from X1 to ground and from X2 to ground,
shown as C
L
in the External Component Schematic. These
capacitors are used to adjust the stray capacitance of the
IDT™
COMMUNICATIONS CLOCK JITTER ATTENUATOR
5
MK2058-01
REV F 122109
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