SKY74038 Datasheet, PDF (5/12 Pages) Skyworks Solutions Inc. – 2.6 GHz/800 MHz Dual Fractional-N/lnteger-N Frequency Synthesizer

DATA SHEET • SKY74038 FREQUENCY SYNTHESIZER
Case 1: To achieve a desired FVCO_RF frequency of 2440.2 MHz using a crystal frequency of 24 MHz with operation
of the synthesizer in RF mode using the 16/17 prescaler (PS = 1). R1 is set to divide by 3 to achieve a
comparison frequency of 8 MHz, since the maximum internal reference frequency is 9 MHz. Divide the operating
frequency by the internal reference frequency to determine the value of NTotal:
N_Total
= 2440.2 MHz
8 MHz
= 305.025
Subtract 3.5 from NTotal and remove the fractional portion of the result to determine N1:
305.025 – 3.5 = 301.525
N1 = 301 (decimal)
Fractional portion = 0.525 (decimal)
N1 = 000100101101 (binary)
D21 -----------D10 Register Address 112
Multiply the fractional portion of N1 by 256 and remove the fractional portion of the result to determine FN:
0.525 × 256 = 134.4
FN = 134 (decimal)
FN = 10000110 (binary)
D9 -------D2 Register Address 112
Divide FN by 256 to determine the actual fractional portion:
134 = 0.5234375
256
Subtract this result from the fractional portion of N1:
0.525 – 0.5234375 = 0.0015625
Multiply this result by 2097152 (the 21-bit ∆Σ modulator value 2²¹) and remove the fractional portion to determine
the ME:
0.0015625 × 2097152 = 3276.8
ME = 3276 (decimal)
ME = 0110011001100 (binary)
D21 --------------D9 Register Address 012
In this example, N1 is greater than 256, the minimum divide ratio for the 16/17 prescaler.
C1454
Figure 5. Fractional-N Applications: Sample Calculation (1 of 2)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
101075M • Skyworks Proprietary and Confidential information • Products and Product Information are Subject to Change Without Notice • June 4, 2007
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