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AK1590 Datasheet(PDF) 11 Page - Asahi Kasei Microsystems |
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AK1590 Datasheet(HTML) 11 Page - Asahi Kasei Microsystems |
11 / 36 page [AK1590] MS1478-E-01 11 2013/2 8. Block Functional Descriptions 1. Frequency Setup AK1590 is a Fractional-N type synthesizer that takes 2 18 as the denominator, which calculates the integer and numerator to be set using the following formulas: Frequency setting = FPFD × (Integer + Numerator / 2 18) Integer = ROUND (Target Frequency / FPFD) Numerator = ROUND {(Target Frequency – Integer × FPFD) / (FPFD / 2 18)} Note) ROUND: Rounded off to the nearest integer FPFD : Phase Frequency Detector comparative Frequency (= [REFIN] input frequency / R divider ratio) Calculation examples Example 1) The numerator is positive; when the target frequency is 950.0375MHz and FPFD is 1MHz. Integer = 950.0375MHz / 1MHz = 950.0375 It is rounded off to 950 (decimal) = 3B6 (hexadecimal) = 0011 1011 0110 (binary) Numerator = (950.0375MHz - 950 × 1MHz) / (1MHz / 2 18) = 9830.4 It is rounded off to 9830 (decimal) = 2666 (hexadecimal) = 10 0110 0110 0110 (binary) Frequency setting =1MHz × (950 + 9830 / 2 18) = 950.0374985MHz (In this case the frequency error is 1.5Hz.) Example 2) The numerator is negative; when the target frequency is 950.550MHz and FPFD is 1MHz. Integer = 950.550MHz / 1MHz = 950.550 It is rounded off to 951 (decimal) = 3B7 (hexadecimal) = 0011 1011 0111 (binary) Numerator = (950.550MHz - 951 × 1MHz) / (1MHz / 2 18) = -117964.8 It is rounded off to -117965 (decimal), which is reduced from 2 18 to be converted into binary for 2's complementary expression. 2 18 - 117965 (decimal) = 144179 (decimal) = 23333 (hexadecimal) = 10 0011 0011 0011 0011 (binary) Frequency setting =1MHz × (951 + (-117965/2 18)) = 950.5499992MHz (In this case the frequency error is 0.8Hz.) Calculation of 2’s complement representation 1) Positive number: Binary expression (Unmanipulated) exp. 100 (decimal) 64 (hexadecimal) = 110 0100 (binary) 2) Negative number: 2 18 minus this number in binary expression exp. –100 (decimal) 2 18 - 100 = 262044 (decimal) = 3FF9C (hexadecimal) = 11 1111 1111 1001 1100 (binary) |
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