Capacitor Discharging with CMOS Gate

[Joerg]

If you do, open it up to find out, let me know.

Thanks!

 

[IanM]

Is that 470R or 47R, either way, I know of at least one fairly popular
lab grade type that would not like that at all...you should have used
a constant impedance filter. See the tutorial in US6608536,
know-it-all.

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

 

[Fred Bloggs]

Our convention is that 470r means four hundred and seventy ohms.




You know of a generator that blows up when it drives a 470 ohm load?
Let me know, so I'll be sure to not buy one.

Oh, the reason to keep the input impedance high is so that one 10 MHz
source can lock a lot of modules. The bandpass/comparator makes the
thing pretty much indifferent about waveforms.

John

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.

 

[John Larkin]

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

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.

https://jeroen.web.cern.ch/jeroen/crfilter/crfilter.html

John

 

[Joerg]

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.

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 ))

Broadcom as usual patents any old crap.

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

[...]

 

[Jim Thompson]

John Larkin wrote: [snip]

Broadcom as usual patents any old crap.

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

[...]

I was the expert witness against Broadcom a few years ago... settled
against Broadcom ;-)

...Jim Thompson

 

[Dave Platt]

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 ))

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

 

[IanM]

Thanks John,

It is clearer now.

IanM

 

[Joerg]

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

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.