106
CHAPTER 6 CLOCK MODULATOR
6.1
Overview of Clock Modulator
This section gives an overview of the Clock Modulator.
■
Overview
The clock modulator is intended for the reduction of electromagnetic interference - EMI, by spreading the
spectrum of the clock signal over a wide range of frequencies.
The modulator offers two modes: 1) phase modulation mode and 2) frequency modulation mode
In both cases the module is fed with an unmodulated reference clock with frequency F0, provided by the
PLL circuit. This reference clock is phase modulated by a triangular waveform or frequency modulated,
controlled by a random signal.
In general, the frequency modulation mode leads to better EMI behavior than phase modulation mode.
The mean frequency of the modulated clock is equal to the reference clock frequency F0.
Figure 6.1-1 Frequency Spectrum of the Modulated Clock (Fundamentals Only)
■
Modulation Degree and Frequency Resolution in Frequency Modulation Mode
Maximum and minimum frequencies (F
max
and F
min
) of the modulated clock are well defined by the
modulation degree parameter. Furthermore the resolution of the modulation range is selectable in 7 steps
from "L" (1) to "H" (7). Higher resolution implies a finer granularity of discrete frequencies in the spectrum
of the modulated clock but less possible modulation degrees.
In general the highest possible frequency resolution combined with the highest possible modulation degree
results in the highest EMI reduction. But for some cases lower modulation degrees may result in a better
EMI behavior. Please refer to the table of possible settings in Table 6.3-4.
fre
qu
ency
F
0
F
min
F
max
mod
u
lation range
Содержание MB90390 Series
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Страница 17: ...xiii APPENDIX D List of Interrupt Vectors 690 INDEX 695 ...
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Страница 132: ...104 CHAPTER 5 CLOCKS ...
Страница 152: ...124 CHAPTER 6 CLOCK MODULATOR ...
Страница 210: ...182 CHAPTER 11 TIME BASE TIMER ...
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Страница 274: ...246 CHAPTER 15 WATCH TIMER ...
Страница 306: ...278 CHAPTER 17 DTP EXTERNAL INTERRUPTS ...
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Страница 364: ...336 CHAPTER 19 UART0 UART1 ...
Страница 398: ...370 CHAPTER 20 UART2 UART3 Figure 20 5 2 ORE Set Timing Receive data RDRF ORE ...
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Страница 632: ...604 CHAPTER 29 EXAMPLES OF SERIAL PROGRAMMING CONNECTION ...
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Страница 723: ...695 INDEX The index follows on the next page This is listed in alphabetic order ...
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