Capacitor Discharging with CMOS Gate

I looked up the patent, didn't understand it. I'm struggling to understand how a "constant impedance filter" filters anything? There isn't that much info on google, is this type of filter usually called something else?

IanM

Okay- well that's not the best way to do it. I never had any problem with a JFET compound follower with hardwired 1MR pulldown from gate to gnd for a daisy chained drive, and a switchable 56R for proper relatively broadband termination as required. Then follower into a series resonant bp R+L+C controlled Q around 20 or so.

Basically, an inductor or a capacitor can't dissipate power. So if you make an LC filter out of ideal inductors and caps, it has to either pass power through (in its passband) or reflect it back at the generator (in the stopband.) So the input impedance of a loaded filter is low, ideally that of the resistive load, in the pass band but becomes high or reactive in the stopband. For some systems, this is very bad.

One can design a filter that either passes or absorbs input signals, a "constant impedance" or "absorptive" filter. Several people make and sell such filters. The must include resistors of some sort to gobble the stopband signals. Done right, the filter input looks just like a resistor at all frequencies.

Broadcom as usual patents any old crap.

Jeroen Belleman did some nice work on absorptive filters and posted about it here.

John

Those are often called "diplexers". Used in higher end comms gear where mixers expect proper termination for passband and for stopband. The unwanted stuff is diverted into a resistor. Of course nowadays some people would frown upon that, claiming that this resistor contributes to global warming. If it's pulsed stuff and you have to use carbon resistors that would really drive them up the wall :-)))

IMHO the majority of new patents these days doesn't hold water anyhow.

[...]

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Regards, Joerg

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Oh, on the contrary. You'd be sequestering a few milligrams of carbon in the resistor, and that's a Good Thing.

:-)

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Thanks John,

It is clearer now.

IanM

But while soldering it in you'd exhale at least 20 times. And nowadays our breath is considered highly toxic by the warmingists. I guess they'd really like to slap a CO2 tax on that.

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Regards, Joerg

http://www.analogconsultants.com/