LMX2525 datasheet(14/17 Pages) NSC

14 / 17 page

Programming Description (Continued)

PULSE SWALLOW FUNCTION

VCO = {8 x RF_B + RF_A + (RF_FN / FD)} x fOSC / R where (RF_A < RF_B) for PDC1500

VCO = {4 x RF_B + RF_A + (RF_FN / FD)} x fOSC / R where (RF_A < RF_B) for PDC800

VCO: Output frequency of voltage controlled oscillator (VCO)

RF_B: Preset divide ratio of binary 4-bit programmable counter (2

≤ RF_B≤ 15)

RF_A: Preset divide ratio of binary 3-bit swallow counter (0

≤ RF_A ≤ 7 for PDC1500 and 0 ≤ RF_A ≤ 3 for PDC800)

RF_FN: Preset numerator of binary 10-bit modulus counter (0

≤ RF_FN < FD)

FD: Preset denominator for modulus counter (FD = f

OSC/(RxfCH) where fCH is the channel spacing)

OSC: Reference oscillator frequency

R: Internal reference oscillator frequency divider

OSC_FREQ [1:0]

Reference Oscillator Frequency (MHz)

R Divider

12.6

14.4

25.2

26.0

The value of the denominator (FD) is depended on the channel spacing and reference oscillator frequency. Table 6 summarizes

the denominator values based on the settings of the Rx/Tx, BS, and OSC_FREQ [1:0] bits.

TABLE 6. Demonimator Values

Rx/Tx

OSC_FREQ [1:0]

Reference Oscillator Frequency (MHz)

CH (kHz)

Denominator(FD)

12.6

25.0

504

14.4

25.0

576

25.2

25.0

504

26.0

25.0

520

12.6

25.0

504

14.4

25.0

576

25.2

25.0

504

26.0

25.0

520

12.6

20.0

630

14.4

20.0

720

25.2

20.0

630

26.0

20.0

650

12.6

22.22

567

14.4

22.22

648

25.2

22.22

567

26.0

22.22

585

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