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参数资料
| 型号： | TRF2050PW |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | PLL合成/DDS/VCOs |
| 英文描述： | PLL FREQUENCY SYNTHESIZER, 1200 MHz, PDSO20 |
| 封装： | PLASTIC, SO-20 |
| 文件页数： | 17/34页 |
| 文件大小： | 543K |
| 代理商： | TRF2050PW |
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TRF2050
LOW-VOLTAGE 1.2-GHz FRACTIONAL-N/INTEGER-N SYNTHESIZER
SLWS030E– JUNE 1996 – REVISED OCTOBER 2000
24
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
PRINCIPLES OF OPERATION
main divider – fractional accumulator (continued)
Table 4. Fractional Accumulator Operation
NF = 3, FMOD = 8
NF = 6, FMOD = 8
ACCUMULATOR
NUMERATOR
STATE
ACCUMULATOR
NUMERATOR
STATE
3
÷ N
6
÷ N
6
÷ N
4
÷ N + 1, overflow
1
÷ N + 1, overflow
2
÷ N + 1, overflow
4
÷ N
0
÷ N + 1, overflow
7
÷ N
6
÷ N
2
÷ N + 1, overflow
4
÷ N + 1, overflow
5
÷ N
2
÷ N + 1, overflow
0
÷ N + 1, overflow
0
÷ N + 1, overflow
For example, suppose that a typical AMPS channel of 953.25 MHz is desired. Because AMPS channel spacing
is 30 kHz, for fractional-N operation the main phase detector reference frequency must be a multiple of 30 kHz;
240 kHz is typical. A value of FMOD = 8 is selected because 240 kHz / 30 kHz = 8. Dividing the channel frequency
by the reference frequency results in 953.13
÷ 240 kHz = 3971.375 = 3971 + 3/8. This example is shown in
Table 4 where NF = 3 and FMOD = 8. The table shows that over the period of a complete fractional accumulator
cycle, the fractional accumulator overflows three times for every eight main divider cycles. Figure 21 illustrates
the division by N or N+1 for this 3/8 fractional channel example.
N
(3971)
N
(3971)
N + 1
(3972)
N
(3971)
N
(3971)
N + 1
(3972)
N
(3971)
N + 1
(3972)
Number of Main
Divider Pulses
RF Input
Main Divider Out
Figure 21. 3/8 Fractional Channel Main Divider Operation
The mean division over the complete fractional accumulator cycle as shown in Figure 21 is:
N
MEAN +
3971
) 3971 ) 3972 ) 3971 ) 3971 ) 3972 ) 3971 ) 3972
8
+ 3971.375
+ 3971 ) 3 8
Therefore, fractional channels are available every 30 kHz or 240 kHz
1
FMOD
+ 240 kHz
8
.
main divider – integer channels
In the case where NF = 0, only division by N occurs, and the fractional accumulator is essentially in a steady
state with a numerator of 0. It never increments or overflows. A channel that requires NF = 0 is a pure integer
channel because the fractional term of
NF
FMOD
is zero.
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