Skyworks Si5338 - Center Spread

Si5338-RM
20 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
Rev. 1.4 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 2021
8.2. Center Spread
Rev B devices do not provide native support for center-spread clocking. Center-spread clocks must be
implemented as modified down-spread clocks. For example, to implement 100 MHz ±1% on CLKx, you must
modify the associated Multisynth and R dividers to output 101 MHz (see "3.2. Calculating MultiSynth Values" on
page 8) and configure the device for 2% down-spread according to the equations in “8.1. Down Spread”. Note that
ClockBuilder Pro takes care of configuring the registers properly for center spread operation on rev B devices.
8.2.1. Center Spread Equations for Rev A Devices
The part can be configured for this mode using the following equations. The Spread Spectrum parameters are
located within Registers 288–347.
Equation 7. SSC Center-Spread Equations
MSx_SSUDP1 =
F
out
4 x sscFreq
Floor
Let x and y
down
be defined as:
x = Floor(1e12 x (128 x sscAmp x (a + b/c)))
y
down
= Floor(1e12 x (1 – sscAmp) x MSx_SSUDP1)
MSx_SSDNP1 =
Floor
x
y
down
Down Parameters:
Up Parameters:
Up/Down Parameter:
where
sscAmp = spread amplitude (e.g, for +-1.3 % center spread, sscAmp = .013)
a +b/c is the MultiSynth divider ratio from section 5
MSx_SSDNP2 =
Mod(x,y
down
)
GCD (x, y
down
)
MSx_SSDNP3 =
GCD (x, y
down
)
y
down
where
Fout = MultiSynthx output frequency in Hz)
sscFreq = spreading frequency in Hz
y
up
= Floor(1e12 x (1 + sscAmp) x MSx_SSUDP1)
Let y
up
be defined as:
MSx_SSUPP1 =
Floor
x
y
up
MSx_SSUPP2 =
Mod(x,y
up
)
GCD (x, y
up
)
MSx_SSUPP3 =
GCD (x, y
up
)
y
up