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參數(shù)資料
| 型號(hào)： | MK1581-01GITR |
| 元件分類： | 時(shí)鐘產(chǎn)生/分配 |
| 英文描述： | 2.048 MHz, OTHER CLOCK GENERATOR, PDSO16 |
| 封裝： | 4.40 MM, 0.65 MM PITCH, MO-153, TSSOP-16 |
| 文件頁(yè)數(shù)： | 4/10頁(yè) |
| 文件大?。?/td> | 152K |
| 代理商： | MK1581-01GITR |
Low Phase Noise T1 / E1 Clock Generator
MDS 1581-01 C
3
Revision 050803
Integrated Circuit Systems, Inc. ● 525 Race Street, San Jose, CA 95126 ● tel (408) 295-9800 ●
www.icst.com
MK1581-01
Functional Description
The MK1581-01 is a clock generator IC that generates
a T1 or E1 reference clock directly from an internal
VCXO circuit that works in conjunction with an external
quartz crystal. The VCXO output frequency and phase
is controlled by an internal PLL (Phase Locked Loop)
circuit, enabling the device to perform clock
regeneration from an 8 kHz input reference clock.
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 MK1581-01 is able to generate a low jitter, low
phase-noise output clock. The low bandwidth capability
of the PLL circuit serves to provide input clock jitter
attenuation and enables stable operation with the low
frequency input reference clock.
The internal VCXO circuit requires an external pullable
crystal for operation. External loop filter components
enable a PLL configuration with low loop bandwidth.
Application Information
Output Frequency Configuration
The MK1581-01 is configured to generate either a
1.544 MHz T1 clock or a 2.048 MHz E1 clock from an
8kHz input clock. Please refer to the Output Clock
Selection Table on Page 2. Input bit SEL is set
according to this table, as is the external crystal
frequency. Please refer to the Quartz Crystal section on
this page regarding external crystal requirements.
Quartz Crystal
It is important that the correct type of quartz crystal is
used with the MK1581-01. Failure to do so may result in
reduced frequency pullability range, inability of the loop
to lock, or excessive output phase jitter.
The MK1581-01 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 MK1581-01 incorporates variable
load capacitors on-chip which “pull”, or change, the
frequency of the crystal. The crystals specified for use
with the MK1581-01 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 MK1581-01 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 ICST web
site (www.icst.com).
PLL Loop Filter Components
A phased-locked loop (PLL) is a control system that
keeps the VCO frequency and phase locked with the
input reference clock. Like all control systems, analog
PLL circuits use a loop filter to establish operating
stability. The MK1581-01 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 page, the external loop filter is made up of
components RS, CS and CP. RSET establishes PLL
charge pump current and therefore influences loop
filter characteristics.
found at www.icst.com, including on-line and PC-based
calculators.
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