High frequency paragraph of test FAIL, why?
[introduction] noise signal has two kinds of main forms, also namely periodic signal and aperiodic signal. Periodic signal every sampling paragraph spectrum is same, so its spectrum shows disperse model, but strength is great, call tape noise normally; Signal of cycle of and rather than every sampling paragraph spectrum is different, its spectrum is very broad, but intensity is weaker, call broadband noise normally. The periodic signal on circuit board is the signal with generation the strongest radiate, the concussion in circuit implement, the power circuit with undee cycle of clock circuit, generation (the switch frequency in be like switch power source) etc is strong radiate circuit, the spectrum of common and periodic signal is as follows:
Any signal can establish the relationship of meantime region and frequency domain through Fourier commutation, following plan institute show the spectrum of echelon pulse function.
It by advocate valve and composition of countless deputy valve, although every deputy valve also has maximum, but total trend is drop as the heighten of frequency, the bag of peak value of echelon pulse spectrum that rise time is T for Tr, width contains two turning point, one is 1/πt, another is 1/πtr. End of spectrum extent low frequency is invariable, via the first turning point later with – times frequency of 20dB/10 Cheng drops, via the 2nd turning point hind with – times frequency of 40dB/10 Cheng drops. Following graphs are the graph of near field spectrum of clock of multimedia product screen, total trend also is drop as the heighten of frequency.
Where is the phenomenon that why checks the on the high side of Gao Cixie wave that periodic signal often appears in the process actually in us then?
To screen clock, its radiate basically is divided for signal electric current (wrong standard electric current) the wrong standard radiation that loop produces and in all loop of modular electric current arises in all modular radiate. It is OK to need character of modular radiant frequency among them according to formulary EdB = 20lg (K I A /D) + 40lg F reachs as frequency elevatory increase, increase rate to be 40dB / Dec.
The spectrum of pulse signal includes line of subsidiary channels in the human body through which vital energy: Cent is 3 paragraphs, evenness paragraph, 20dB / Dec drops paragraph, 40dB / Dec drops paragraph.
The spectrum bag sth resembling a net pulse signal and union of character of frequency of wrong standard radiant rise, can get pulse signal differs modular radiant spectrum to include line of subsidiary channels in the human body through which vital energy (the ③ curve in pursueing as follows) .
Accordingly, see in the sth resembling a net of radiation spectrum bag from pulse signal, although the range of heft of Gao Cixie wave of pulse signal is lesser, but the strength that radiation comes out is very great however, this also is a when the Gao Cixie wave that why has some of clock can exceed bid easily main reason.
The article is reprinted from EMC of military strategy science and technology