LMX2364 Datasheet, PDF (26/39 Pages) National Semiconductor (TI) – 2.6 GHz PLLatinum Fractional RF Frequency Synthesizer with 850 MHz Integer IF Frequency Synthesizer

Programming Description (Continued)
2.4 R1 REGISTER
This register is used to configure the N divider for the IF synthesizer. A single word write to this register is all that is required to
power up and tune the synthesizer to the desired frequency.
Reg 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
DATA[20:0]
C2 C1 C0
R1
IF_
PD
0
0
0
IF_N[16:0]
001
2.4.1 IF_N[16:0] — N Divider Ratio,IF Synthesizer
The IF_N[16:0] word is used to setup up the N Divider Ratio for the IF synthesizer. The IF N counter is actually a combination of
an IF A counter, IF B counter, and an IF 8/9 prescaler. The relationship between IF_N, IF_B, and IF_A is shown below.
IF_N = 8 x IF_B + IF_A
Although the IF_N counter value can created by programming the IF_B and IF_A values, it is easier to simply convert the IF N
counter value into binary and program the entire IF_N[16:0] word in this manner. The fact that the IF N counter has a prescaler
is what puts restrictions on IF_N values less than 56.
IF_N[16:0]
IF_B[13:0]
IF_A[2:0]
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0-23
Divide ratios of less than 24 are not allowed.
24-55
Legal divide ratios in this range are: 24-27, 32-36, 40-45, and 48-54.
56
0
0
0
0
0
0
0
0
0
0
0
1
1
1
0
0
0
57
0
0
0
0
0
0
0
0
0
0
0
1
1
1
0
0
1
...
...
...
...
...
...
...
...
...
...
...
...
...
...
...
...
...
...
131071
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2.4.2 IF_PD — Power Down, IF Synthesizer
Activation of the IF Synthesizer power down bit results in the disabling of the respective N divider and de-biasing of its respective
Fin inputs (to a high impedance state). The respective R divider functionality also becomes disabled when the power down bit is
activated. The OSCinIF pin reverts to a high impedance state when both RF and IF power down bits are asserted. Power down
forces the respective charge pump and phase comparator logic to a TRI-STATE condition. The MICROWIRE control register
remains active and capable of loading and latching in data during all of the power down modes.
Both synchronous and asynchronous power down modes are supported. The power down mode bit R6[8] is used to select
between synchronous and asynchronous power down. The MICROWIRE control register remains active and capable of loading
and latching in data in either power down mode.
Synchronous Power Down Mode: The IF synthesizer can be synchronously powered down by first setting the power down
mode bit HIGH (R6[8] = 1) and then asserting its power down bit (R1[23] = 1). The power down function is gated by the charge
pump. Once the power down bit is loaded, the part will go into power down mode upon the completion of a charge pump pulse
event.
Asynchronous Power Down Mode: The IF synthesizer can be asynchronously powered down by first setting the power down
mode bit LOW (R6[8] = 0) and then asserting its power down bit (R1[23]] = 1). The power down function is NOT gated by the
charge pump. Once the power down bit is loaded, the part will go into power down mode immediately
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