stcd2400 STMicroelectronics, stcd2400 Datasheet - Page 15

• Manufacturer Part Number: stcd2400
• Description: Multichannel Clock Distribution Circuit
• Manufacturer: STMicroelectronics

STCD22x0, STCD23x0, STCD24x0
4.5
Phase noise
Phase noise is a frequency domain phenomenon and is a critical specification in reference
clocks. It is illustrated by a continuous spreading of the energy of the wave mainly caused by
random noise. The phase noise is normally specified with a unit of dBc/Hz at a given offset
in frequency (for example, 10 kHz) from the carrier wave (for example, 26 MHz). The value
of the phase noise is the difference of the power contained within 1 Hz bandwidth of the
offset frequency to the power at the carrier frequency. The total phase noise of the clock tree
is obtained by adding the additive phase noise of STCD22x0, STCD23x0 and STCD24x0
and the phase noise of the clock source (for example, TCXO) in power which is illustrated in
Equation
Equation 1
where:
PN
PN
PN
Make sure the total phase noise is kept within the phase noise requirement of each
application PN
the requirement.
T
C
X
is the total phase noise in dBc/Hz
is the phase noise of clock source
is the additive phase noise of STCD22x0, STCD23x0 and STCD24x0 and
1.
A
. The user should choose the right TCXO with proper phase noise to meet
PN
Doc ID 15400 Rev 2
T
=
10
log(
10
PN
10
C
+
10
PN
10
X
)
<
PN
A
Application information
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