571AMC000154DG Silicon Laboratories Inc, 571AMC000154DG Datasheet - Page 13

• Manufacturer Part Number: 571AMC000154DG
• Manufacturer: Silicon Laboratories Inc

Specifications of 571AMC000154DG

• Lead Free Status / Rohs Status: Compliant

3. Functional Description
The Si570 XO and the Si571 VCXO are low-jitter
oscillators ideally suited for applications requiring
programmable
programmed to generate virtually any output clock in
the range of 10 MHz to 1.4 GHz. Output jitter
performance exceeds the strict requirements of high-
speed communication systems including OC-192/STM-
64 and 10 Gigabit Ethernet (10 GbE).
The Si57x consists of a digitally-controlled oscillator
(DCO) based on Silicon Laboratories' third-generation
DSPLL technology, which is driven by an internal fixed-
frequency crystal reference.
The device's default output frequency is set at the
factory and can be reprogrammed through the two-wire
I
return to its factory-set default output frequency.
While the Si570 outputs a fixed frequency, the Si571
has a pullable output frequency using the voltage
control input pin. This makes the Si571 an ideal choice
for high-performance, low-jitter, phase-locked loops.
3.1. Programming a New Output
Frequency
The
programming the DCO frequency (f
device's output dividers (HS_DIV, N1). The output
frequency is calculated using the following equation:
The DCO frequency is adjustable in the range of 4.85 to
5.67 GHz by setting the high-resolution 38-bit fractional
multiplier (RFREQ). The DCO frequency is the product
of the internal fixed-frequency crystal (f
RFREQ.
2
C serial port. Once the device is powered down, it will
4.85 GHz
output
f
out
=
---------------------------------------- -
Output Dividers
frequency
frequencies.
f
DCO
(f
out
=
)
The
f
------------------------------------------ -
XTAL
HSDIV N1
is

-3500 ppm
Figure 3. DCO Frequency Range
Si57x
RFREQ
determined
DCO

Configuration
Frequency
) and the
XTAL
Center
can
) and
+3500 ppm
Rev. 1.2
be
by
The 38-bit resolution of RFREQ allows the DCO
frequency to have a programmable frequency resolution
of 0.09 ppb.
As shown in Figure 3, the device allows reprogramming
of the DCO frequency up to ±3500 ppm from the center
frequency configuration without interruption to the
output clock. Changes greater than the ±3500 ppm
window will cause the device to recalibrate its internal
tuning circuitry, forcing the output clock to momentarily
stop and start at any arbitrary point during a clock cycle.
This re-calibration process establishes a new center
frequency and can take up to 10 ms. Circuitry receiving
a clock from the Si57x device that is sensitive to glitches
or runt pulses may have to be reset once the
recalibration process is complete.
3.1.1. Reconfiguring the Output Clock for a Small
Change in Frequency
For output changes less than ±3500 ppm from the
center frequency configuration, the DCO frequency is
the only value that needs reprogramming. Since
f
the DCO frequency is as simple as reconfiguring the
RFREQ value as outlined below:
1. Using the serial port, read the current RFREQ value
2. Calculate the new value of RFREQ given the change
3. Using the serial port, write the new RFREQ value
Example:
An Si570 generating a 148.35 MHz clock must be
reconfigured "on-the-fly" to generate a 148.5 MHz clock.
This represents a change of +1011.122 ppm, which is
well within the ±3500 ppm window.
DCO
small frequency changes can be made
“on-the-fly” without interruption to the
(registers 0x08–0x12).
in frequency.
(registers 0x08—0x12).
= f
XTAL
RFREQ
output clock
x RFREQ, and that f
new
=
RFREQ
Si570/Si571
current
XTAL

------------------------ -
f
is fixed, changing
out_current
f
out_new
5.67 GHz
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