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Riposte Ivor Catt. 18june02
. More nonsense about the so-called “self-resonant frequency” of a
capacitor. http://www.ivorcatt.com/em_test04.htm
Scandals in Electromagnetic Theory http://www.ivorcatt.com/28scan.htm http://www.ultracad.com/seminar_caps.htm Generally,
this is nonsense. In particular, This approach depends critically on the self resonant
frequencies of the particular bypass caps chosen, and also on the ESR
(Equivalent Series Resistance.) It turns out, many of the assumptions
designers routinely make regarding these issues are not true, as we
demonstrate in this seminar is nonsense. Did
the author ever do experiments with capacitors, and is he capable of wiring a
circuit together competently in order to avoid strays? http://www.ivorcatt.com/em_test04.htm This brings a score of 0/10 for Douglas
Brooks - Ivor Catt 22apr02 http://www.capacitors.com/consider/consider.htm The point of minimum impedance (ESR) marks
the frequency at which L and C form a series-resonant circuit, where the
inductive reactance equals the capacitive reactance. Above this resonant
frequency, the capacitor functions as an inductor. For many applications, the
capacitor's series resonant frequency will be a circuit's useful upper
frequency limit, especially where the phase angle of the capacitor is
expected to maintain a 90-degree (tan ð = 0) or near 90-degree
voltage/current relationship. This is a common assumption in filter network
design. Nonsense. The fact that this nonsense has been trotted out for nearly a century does not stop it from being nonsense. Ivor Catt 22apr02. http://hsi.web.cern.ch/HSI/s-link/devices/g-ldc/decouple.pdf This has some nonsense in it about two capacitors in parallel being
worse for voltage decoupling than a single capacitor. He is a mess, even
though he says that a 1uF capacitor will do fine. He does not understand the
nature of voltage decoupling, thinking that each frequency component is
individually decoupled. The truth is, the C is an energy source. Frequency is
irrelevant. Ivor Catt 22apr02 Ivor
Catt 22apr02 In
1963 I bought the EH-125 pulse generator. This delivered a –10v step with a
100psec fall time into a 50 ohm load (e.g. 50 ohm coax.). The
pulse generator could also deliver a –ve 10v spike with a width of 150psec. I
decided to try to create a positive 10v spike. I cut into the 50 ohm coax, and
joined the incoming inner to the outgoing outer via a red 1uF tantalum
capacitor. I also joined the incoming outer to the outgoing inner via another
1uF tantalum capacitor. Further downstream I found that I had a positive
150psec spike with no discernable degradation (in rise time or pulse width)
compared with the initial –ve spike. That is, I had a +ve 10v spike with a
width of 150psec. It
is interesting to calculate the physical width of a 150v spike travelling
down normal coax, which has a dielectric with a dielectric constant of 2.
Whereas light travels one foot in vacuo in one nsec, it would travel 8 inches
in material with a dielectric constant of 2. Thus, a 150psec spike in the
coax has a width of about one inch. So I sent a TEM spike with a width of 1
inch through these 1uF capacitors. [Note 1] Obviously, I kept their legs
short. It is sad that during the ensuing 40 years the New York IEEE and the
London IEE prevented me from informing electronic engineers that they did not
have to add “high frequency” decoupling capacitors to their logic boards,
that the 1uF would do perfectly well on its own. This obstruction has cost
the industry many millions of pounds. However, a bolshie IEEE and a bolshie
IEE cost us a lot more than that in other ways. Ivor Catt 22apr02 Note 1. Anyone
who wants to play with frequencies can be told that the fundamental of the
150psec spike will be around 3GHz. Put that in your “self-resonant” pipe and
smoke it! IC |
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