DATA SHEET • SKY73126-31 VCO/SYNTHESIZER
Phase Detector and Charge Pump
Round the value of Ndiv to the nearest integer and then convert to
binary:
The phase detector and charge pump detect and integrate the
phase and frequency errors of the divided-down VCO output
versus the reference clock. This results in a feedback adjustment
of the control voltage for the VCO.
Ndiv[15:0] = 19384 = 0001111110100000b
Since the VCO output frequency (fVCO) is lower than 2000 MHz and
Ndiv is less than 215, the 8/9 prescaler mode could be used.
Lock Detect
Package and Handling Information
Lock detection circuitry provides a CMOS logic level indication
when the PLL is frequency locked (high when locked).
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.
Reference Input Divider
The R-counter (reference input clock divider) consists of 10-bit
dividers controlled by the rdiv parameter in Word 1 (Operation
Mode Register, bits [27:18]). The R-counter divides the clock
signal from the reference input buffer by 1, 2, 4, or 1023 (approx.)
and sends the rdiv output to the Phase Frequency Detector (PFD).
The SKY73126-31 is rated to Moisture Sensitivity Level 3 (MSL3)
at 260 C. 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.
Synthesizer Programming
The SKY73126-31 has selectable VCO prescalers to divide the
VCO output signal by either 16/17 or 8/9. The prescaler mode is
determined by the prescale_sel parameter (Word 1, bit [17], of
the Operation Mode Register).
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.
To program the synthesizer to the correct frequency, the N-divider
and R-divider ratios need to be determined. The N-divider ratio is
the result of dividing the VCO output frequency by the phase
comparison frequency:
Circuit Design Considerations
The following design considerations are general in nature and
must be followed regardless of final use or configuration
f
f
VCO
PFD
Ndiv
1. Paths to ground should be made as short and as low
impedance as possible.
The VCO output frequency is four times greater than the
synthesizer RF output frequency. The value of Ndiv is rounded to
the nearest integer and then converted into a binary number
which is written to the serial bus. The maximum Ndiv for the 8/9
prescaler mode is 215 or 32768. For the 16/17 prescaler mode,
the maximum Ndiv is 216 or 65536.
2. The ground pad of the SKY73126-31 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.
The R-divider ratio is the result of dividing the reference input
frequency by the phase comparison frequency:
3. Skyworks recommends including external bypass capacitors
on the VCC voltage input (pin 1) of the device. These
capacitors should be placed as close as possible to the VCC
input pin.
fref
Rdiv
fPFD
Example:
4. A 50 impedance trace is needed for the RF_OUT (pin 3)
A synthesizer frequency of 161.92 MHz is required using a crystal
frequency of 10 MHz. The minimum frequency step is 80 kHz.
Determine the R-divider ratio:
line.
Rdiv[9:0] = 10 MHz/80 kHz = 125 = 1111101b
Divide the VCO output frequency, which is four times the RF
output frequency, by the phase comparison frequency (minimum
frequency step in this example) to obtain the N-divider ratio:
Ndiv[15:0] = (161.92 MHz × 4)/80 kHz = 8096
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
February 24, 2010 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201112C
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