From Design and Development of Medical Electronic Instrumentation
As they operate, digital circuits constantly switch the state of lines between a high-voltage
level and a low-voltage level to represent binary states. As shown in Figure 4.1a, the resulting
time-domain waveform on any single line of a digital circuit can thus be idealized as
a train of trapezoidal pulses of amplitude (either current I or voltage V) A, rise time tr, fall
time tf(between 10 and 90% of the amplitude), pulse width τ (at 50% of the amplitude),
and period T.
The Fourier envelope of all frequency-domain components generated by such a periodic
pulse train can be approximated by the nomogram of Figure 4.1b. The frequency spectrum
is composed mainly of a series of discrete sine-wave harmonics starting at the fundamental
frequency f0 = 1/T and continuing for all integer multiples of f0. The nomogram
identifies two frequencies of interest. The first is f1, above which the locus of the maximum
amplitudes rolls off with a 1/f slope. The second, f2, is the limit above which the locus rolls
off at a more abrupt rate of 1/f2...
Products & Services
Topics of Interest
EMI standards establish that radiated-emissions test measurements should be performed at a distance of 10 to 30 m, depending on the device’s classification. For compliance testing, the device...
Susceptibility to Radiated Electromagnetic Interference IEC-61000-4-3 specifies a modulated RFI test of 3 V/m as representative of the radiated electromagnetic interference that may be caused on a...
CONDUCTED EMISSIONS Conducted emissions measurements are made to determine the line-to-ground radio noise from each power-input terminal of a line-powered medical device. Measurements are taken using...
The importance of effective EMI shielding of medical devices continues to escalate, due in large part to two European regulatory requirements that apply to all medical equipment manufacturers that...
GOOD DESIGN PRACTICES, REMEDIES, AND DUCT TAPE No cure for EMC problems is better than prevention. Trouble avoidance in EMC is accomplished by considering the emissions and susceptibility aspects of...