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LMX2331ATM Datasheet(PDF) 11 Page - National Semiconductor (TI) |
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LMX2331ATM Datasheet(HTML) 11 Page - National Semiconductor (TI) |
11 / 17 page Functional Description (Continued) PROGRAMMABLE DIVIDER (N COUNTER) The N counter consists of the 7-bit swallow counter (A counter) and the 11-bit programmable counter (B counter). If the Control Bits are 10 or 11 (10 for IF counter and 11 for RF counter) data is transferred from the 22-bit shift register into a 4-bit or 7-bit latch (which sets the Swallow (A) Counter) and an 11-bit latch (which sets the 11-bit programmable (B) Counter), MSB first. Serial data format is shown below. For the IF N counter bits 5, 6, and 7 are don’t care bits. The RF N counter does not have don’t care bits. 7-BIT SWALLOW COUNTER DIVIDE RATIO (A COUNTER) RF Divide Ratio A N 7 N 6 N 5 N 4 N 3 N 2 N 1 0 0000000 1 0000001 • ••••••• 127 1111111 Note: Divide ratio: 0 to 127 B ≥ A IF Divide Ratio A N 7 N 6 N 5 N 4 N 3 N 2 N 1 0 X X X 0000 1 X X X 0001 • ••••••• 15 X X X 1111 X = DON’T CARE condition 11-BIT PROGRAMMABLE COUNTER DIVIDE RATIO (B COUNTER) Divide Ratio B N 18 N 17 N 16 N 15 N 14 N 13 N 12 N 11 N 10 N 9 N 8 3 00000000011 4 00000000100 • ••••••••••• 2047 11111111111 Note: Divide ratio: 3 to 2047 (Divide ratios less than 3 are prohibited) B ≥ A PULSE SWALLOW FUNCTION f VCO = [(P xB)+ A]xfOSC/R f VCO: Output frequency of external voltage controlled oscillator (VCO) B: Preset divide ratio of binary 11-bit programmable counter (3 to 2047) A: Preset divide ratio of binary 7-bit swallow counter (0 ≤ A ≤ 127 {RF}, 0 ≤ A ≤ 15 {IF}, A ≤ B) f OSC: Output frequency of the external reference frequency oscillator R: Preset divide ratio of binary 15-bit programmable reference counter (3 to 32767) P: Preset modulus of dual moduIus prescaler (for IF ;P = 8or16; for RF ; LMX2330A: P = 32 or 64 LMX2331A/32A: P = 64 or 128) PROGRAMMABLE MODES Several modes of operation can be programmed with bits R16–R20 including the phase detector polarity, charge pump TRI-STATE and the output of the F oLD pin. The prescaler and powerdown modes are selected with bits N19 and N20. The pro- grammable modes are shown in Table 1. Truth table for the programmable modes and F oLD output are shown in Table 2 and Table 3. DS012331-15 www.national.com 11 |
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