lmx2505lq1321 National Semiconductor Corporation, lmx2505lq1321 Datasheet - Page 13

• Manufacturer Part Number: lmx2505lq1321
• Description: Pllatinu Dual Frequency Synthesizer System With Integrated Vcos
• Manufacturer: National Semiconductor Corporation

Programming Description
PULSE SWALLOW FUNCTION
f
f
f
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: Preset denominator for modulus counter (FD = f
f
R: Internal reference oscillator frequency divider
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.
VCO
VCO
VCO
OSC
Rx/Tx
: Output frequency of voltage controlled oscillator (VCO)
: Reference oscillator frequency
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
= {8 x RF_B + RF_A + (RF_FN / FD)} x f
= {4 x RF_B + RF_A + (RF_FN / FD)} x f
OSC_FREQ [1:0]
BS
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
00
01
10
11
OSC_FREQ [1:0]
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Reference Oscillator Frequency (MHz)
(Continued)
OSC
OSC
Reference Oscillator Frequency (MHz)
TABLE 6. Demonimator Values
/ R where (RF_A
/ R where (RF_A
OSC
/(R x f
12.6
14.4
25.2
26.0
12.6
14.4
25.2
26.0
12.6
14.4
25.2
26.0
12.6
14.4
25.2
26.0
CH
13
12.6
14.4
25.2
26.0
) where f
<
<
RF_B) for PDC1500
RF_B) for PDC800
<
CH
FD)
is the channel spacing)
R
1
1
2
2
1
1
2
2
1
1
2
2
1
1
2
2
f
CH
22.22
22.22
22.22
22.22
25.0
25.0
25.0
25.0
25.0
25.0
25.0
25.0
20.0
20.0
20.0
20.0
(kHz)
Denominator (FD)
R Divider
1
1
2
2
504
576
504
520
504
576
504
520
630
720
630
650
567
648
567
585
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