參數(shù)資料
型號(hào)： TRF2056PWR
廠商： TEXAS INSTRUMENTS INC
元件分類： PLL合成/DDS/VCOs
英文描述： PLL FREQUENCY SYNTHESIZER, 1200 MHz, PDSO20
封裝： PLASTIC, SOP-20
文件頁(yè)數(shù)： 7/24頁(yè)
文件大小： 327K
代理商： TRF2056PWR
TRF2056
LOW VOLTAGE 1.2GHz FRACTIONALN/INTEGERN SYNTHESIZER
SLWS111– NOVEMBER 2000
15
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
PRINCIPLES OF OPERATION
Table 3. 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 MHz
÷ 240 kHz = 3971.375 = 3971 3/8. This example is shown
in Table 3 where NF = 3 and FMOD = 8. The table shows that over the period of a complete fractional
accumulator cycle, the fractional accumulator overflows 3 times for every 8 main divider cycles. Figure 6
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 6. 3/8 Fractional Channel Main Divider Operation
The mean division over the complete fractional accumulator cycle as shown in Figure 6 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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