TRF2050_00 Datasheet, PDF (27/34 Pages) Texas Instruments – LOW-VOLTAGE 1.2-GHz FRACTIONAL-N/INTEGER-N SYNTHESIZER

TRF2050
LOW-VOLTAGE 1.2-GHz FRACTIONAL-N/INTEGER-N SYNTHESIZER
SLWS030E– JUNE 1996 – REVISED OCTOBER 2000
PRINCIPLES OF OPERATION
main divider – fractional-N sidebands and compensation (continued)
Table 5. Main PHP Fractional-N Pulse-Widths and Areas for 3/8 Channel
ACCUMULATOR
STATE
3
6
1
4
7
2
5
0
NF = 3, FMOD = 8
MAIN PHP FRACTIONAL PULSE WIDTH
(ps)
3 x PW–Mean = 393.558
6 x PW–Mean = 787.116
1 x PW–Mean = 131.186
4 x PW–Mean = 524.744
7 x PW–Mean = 918.302
2 x PW–Mean = 262.372
5 x PW–Mean = 655.930
0 x PW–Mean = 0
MAIN PHP FRACTIONAL AREA
(ps X AMPS)
393.558 ps x 500 µA = .196779
787.116 ps x 500 µA = .393558
131.186 ps x 500 µA = .065593
524.744 ps x 500 µA = .262372
918.302 ps x 500 µA = .459151
262.372 ps x 500 µA = .131186
655.930 ps x 500 µA = .327965
0 ps x 500 µA = 0
Table 5 also shows the area of the fractional-N portion of the main PHP charge-pump waveform.1
D Determine the pulse width of the compensation charge-pump output waveform.
+ + + CompPW
1
fRef
1
19.44 MHz
51.440 ns
D Determine the fundamental compensation charge-pump current magnitude using the fundamental main
PHP fractional area.
+ + + CompMag
FracArea
CompPW
0.065593 psA
51.440 ns
1.275 mA
Table 6 shows the magnitude of the compensation pulse as a function of the fractional accumulator.
Table 6. Compensation Pulse Magnitudes for 3/8 Channel
NF = 3, FMOD = 8
Accumulator Compensation Pulse
Numerator
Magnitude (µA)
3
3 x 1.275 = 3.825
6
6 x 1.275 = 7.651
1
1 x 1.275 = 1.275
4
4 x 1.275 = 5.101
7
7 x 1.275 = 8.926
2
2 x 1.275 = 2.550
5
5 x 1.275 = 6.376
0
0 x 1.275 = 0
D Using the result of step 3, determine the value of RF to give the fundamental compensation pulse
magnitude.
+ + + RF (kW)
m ²⁵
CompMag( A)
25
1.275
19.6 kW.
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