I read in !emc-pstc that [email protected] wrote (in <17d.1b28bc2.296 [email protected]>) about 'EMC-related safety issues', on Fri, 4 Jan 2002:
>Does anyone else think that ordinary semiconductors doesn't respond to RF? Your experience has been shared by thousands. The demodulation normally occurs at the first semiconductor junction that the r.f signal 'sees', although at 10 V/m there may be propagation effects. The faulty reasoning that makes this effect surprising is 'silicon diodes and transistors need 0.6 V forward bias in order to conduct'. It isn't TRUE! If you add 'more than a few microamps' it's less untrue. But conduction occurs right down to minute signal voltages, resulting, certainly, in even more minute currents, but current enough to cause trouble. 'Underbiased' junctions act as excellent square-law detectors; for every 1 dB increase in input signal level you get 2 dB increase in level of recovered modulation. You may well find that JFET-input op-amps are far less sensitive to r.f. A test that I carried out a while back, on a very simple board with no EMC counter-measures at all, indicated a 26 dB difference between an LM324 and a TL072, the difference being substantially independent of frequency from 150 kHz to 1 GHz. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
