Communications Clock Jitter Attenuator
MDS 2058-01 B 3 Revision 071001
Integrated Circuit Systems, Inc. ● 525 Race Street, San Jose, CA 95126 ● tel (408) 295-9800 ● www.icst.com
MK2058-01
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.
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.
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 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 14pF. 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 shown below.
Recommended Crystal Parameters:
Operating Temperature Range
Commercial Applications 0 to 70
°C
Industrial Applications -40 to 85
°C
Initial Accuracy at 25
°C ±20 ppm
Temperature Stability ±30 ppm
Aging ±20 ppm
Load Capacitance Note 1
Shunt Capacitance, C0 7 pF Max
C0/C1 Ratio 250 Max
Equivalent Series Resistance 35 Ω Max
Note 1: For crystal frequencies between 13.5MHz and
27MHz the nominal crystal load capacitance
specification should be 14pF. Contact ICS MicroClock
applications at (408) 297-1201 regarding the use of a
crystal below 13.5MHz.
