SKY73121-11 Datasheet, PDF (11/22 Pages) Skyworks Solutions Inc. – 1805 - 1890 MHz High Performance VCO/Synthesizer With Integrated Switch

DATA SHEET • SKY73121-11 VCO/SYNTHESIZER
The value of ME is equal to the binary representation of the
integer part of 2²³ u ME_actual, or:
ME = D₁₄ u 2¹⁴ + D₁₃ u 2¹³ + D₁₂ u 2¹² + . . .D₀
Example :
A desired synthesizer frequency of 1860 MHz is required using a
crystal frequency of 52 MHz and an 8/9 prescaler. Since the
maximum internal reference frequency is 25 MHz, the crystal
frequency needs to be divided; a reference divider ratio of 8 is
used for this example.
Restating Equation (2) as a function of D_Total:
D_Total = (1860 u 8)/52 = 286.153846153846
Where: RF = 1860
R1 = 8
F_REF = 52
Determine N_actual by subtracting 3.5 from D_Total and removing the
fractional portion:
D_Total – 3.5 = 282.653846153846
Using Equation (3):
N_actual = 282 = M_actual u P + A_actual
where: M_actual = 35
P=8
A_actual = 2
M = M_actual = 35 = 100011b (the six MSBs)
A = A_actual = 2 = 0010b (the four LSBs)
N = M u 2⁴ + A = 1000110010b (the value programmed)
Multiply the fractional portion that was removed in the previous
step by 256 and remove the fractional portion of the result to
determine FN:
0.653846153846 u 256 = 167.384615384576
FN = 167 = 10100111b (the value programmed)
Divide FN by 256 to determine the actual fractional part, FN_actual:
FN_actual = 167/256 = 0.65234375
Subtract this result from the fractional portion of D_Total – 3.5 to
determine the actual fractional modulus extender, ME_actual:
ME_actual = (D_Total – 3.5 – N_actual) – FN_actual
= 0.653846153846 – 0.65234375
= 0.001502403846
Multiply this result by 8388608 (the 23-bit '6 modulator value,
2²³) and remove the fractional portion to determine the value of
ME:
0.001502403846 u 8388608 = 12603.076921786386
ME = 12603 = 011000100111011b (the value programmed).
Refer to Tables 6 and 7 for the location of the resulting bits in the
ME parameter.
Package and Handling Information
Since the device package is sensitive to moisture absorption, it is
baked and vacuum packed before shipping. Instructions on the
shipping container label regarding exposure to moisture after the
container seal is broken must be followed. Otherwise, problems
related to moisture absorption may occur when the part is
subjected to high temperature during solder assembly.
The SKY73121-11 is rated to Moisture Sensitivity Level 3 (MSL3)
at 260 qC. It can be used for lead or lead-free soldering. For
additional information, refer to Skyworks Application Note, PCB
Design and SMT Assembly/Rework Guidelines for MCM-L
Packages, document number 101752.
Care must be taken when attaching this product, whether it is
done manually or in a production solder reflow environment.
Production quantities of this product are shipped in a standard
tape and reel format. For packaging details, refer to the Skyworks
Application Note, Tape and Reel, document number 101568.
Circuit Design Considerations
The following design considerations are general in nature and
must be followed regardless of final use or configuration
1. Paths to ground should be made as short and as low
impedance as possible.
2. The ground pad of the SKY73121-11 provides critical
electrical grounding requirements. Design the connection to
the ground pad to provide the best electrical connection to the
circuit board. Multiple vias to the grounding layer are
recommended to connect the top layer ground area to the
main ground layer.
3. Skyworks recommends including external bypass capacitors
on the VDD voltage input (pin 37) of the device. These
capacitors should be placed as close as possible to the VDD
input pin.
4. A 50 : impedance trace is needed for the RF_OUT (pin 10)
line.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
200888B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • December 1, 2009
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