Driver to drive?

John Larkin · Nov 3, 2004

On Wed, 3 Nov 2004 18:07:02 +0000 (UTC), kensmith@green.rahul.net (Ken
Smith) wrote:

Making a low noise high performance analog filter near 0.05 is next to
imposible. The capacitors you need to use are large and costly. If this
is just a one-off or cost is no object, There are 2 and 3 op-amp circuits
you may want to consider.

0.05 Hz is an omega of 0.3, so 1 uF and 3 megs is the ballpark RC. Or
0.33 uF and 10M. Those are perfectly happy numbers to work around a
fet opamp. Sounds easy to me.

John

If the cost is an object, I'd suggest you try to find a way to not need
the filter. A micro controller with an ADC and DAC could implement a very
sharp filter, but there you have the LSB rattling issue to deal with.

If I was going with the micro method I'd do this:

If needed add some high frequency noise to the signal to ensure that the
noise is at least 2 LSBs RMS. Run the ADC circuit at as high of a
frequency as you can. Construct a multi-stage IIR filter in software.
Pump the output values to the DAC much faster than the Nyquist. Add a
high frequency dithering (PWM to fake more bits) to the data for the DAC
that is large enough to blur out the dif-nonlinearities. Follow the DAC
with a low pass filter to remove the dithering.

--

John Larkin · Nov 3, 2004

On Wed, 03 Nov 2004 18:12:20 GMT, "Ban" <bansuri@web.de> wrote:

the passband.
It doesn't matter which topology you implement the filters, because the
performance will be the same. Sallen-Key is indeed the most suitable
topology, but keep resistors low and (unfortunately) capacitors high.

Why?

Fet- and CMos
opamps are unsuitable because of their low-frequency unstability.

What? Fet opamps don't work at DC?

John

Jim Thompson · Nov 3, 2004

On Wed, 03 Nov 2004 15:46:00 -0800, John Larkin
<jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:

On Wed, 03 Nov 2004 09:58:23 -0700, Jim Thompson
thegreatone@example.com> wrote:

On 3 Nov 2004 08:46:17 -0800, convertino@deemail.poliba.it (Alessandro
Convertino) wrote:

Hi to all,
I would like to know some informations about bandpass filtering on
frequency range between 0.05-30 Hz. In the past I've used a Sallen-key
active filter, and I would like to find a more performing solution.
What IC can I use to implement it?

Thanks for your attention.

Alessandro

VERY LOW FREQUENCY filters are difficult since the dissipation factor
of typical capacitors dominates (and deteriorates) the performance,
particularly in a production environment where repeatability is
important.

How so? I'd suspect a polycarb or something decent would have a very
low df in the sub-Hz range. Numbers like 1 uF and 10 megohms seem
perfectly nice to me, with fet opamps.

John

John,

What kind of df do you get with polycarb caps?

My experience is primarily with (NPO) chip caps for hybrids, which is
why I utilized the "p+1" method... then you can tolerate horrible df
before it even tweaks you a dB.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice

480)460-2350 | |
| E-mail Address at Website Fax

Terry Given · Nov 3, 2004

Joerg wrote:

Hi Terry,

ps yay the Red Sox!

Aren't you located in New Zealand? If so, how come you are a Red Sox fan?

Regards, Joerg

Hi Joerg,

Yep. But I lived in Boston MA for 3 years - in the South end - well it
was just about Roxbury really. I went to a few games at Fenway park, its
a great way to drink beer. Although my first game was watching the
Yankees kick the hell out of the Orioles (sp?) at Oriole stadium (or
something like that) in Baltimore, when I went there for a PCIM
conference in 1997 (at which point someone offered me a job...pissed my
boss off in NZ when I quit immediately after a junket)

I watched the 2nd-to-last match at a pub in Auckland, NZ (and was the
only person doing so), but alas missed the final.

Cheers
Terry

John Larkin · Nov 3, 2004

On Wed, 03 Nov 2004 16:54:31 -0700, Jim Thompson
<thegreatone@example.com> wrote:

On Wed, 03 Nov 2004 15:46:00 -0800, John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:

On Wed, 03 Nov 2004 09:58:23 -0700, Jim Thompson
thegreatone@example.com> wrote:

On 3 Nov 2004 08:46:17 -0800, convertino@deemail.poliba.it (Alessandro
Convertino) wrote:

Hi to all,
I would like to know some informations about bandpass filtering on
frequency range between 0.05-30 Hz. In the past I've used a Sallen-key
active filter, and I would like to find a more performing solution.
What IC can I use to implement it?

Thanks for your attention.

Alessandro

VERY LOW FREQUENCY filters are difficult since the dissipation factor
of typical capacitors dominates (and deteriorates) the performance,
particularly in a production environment where repeatability is
important.

How so? I'd suspect a polycarb or something decent would have a very
low df in the sub-Hz range. Numbers like 1 uF and 10 megohms seem
perfectly nice to me, with fet opamps.

John

John,

What kind of df do you get with polycarb caps?

My experience is primarily with (NPO) chip caps for hybrids, which is
why I utilized the "p+1" method... then you can tolerate horrible df
before it even tweaks you a dB.

...Jim Thompson

I've used them in sample-hold and precision integrator circuits, and
the DFs are tiny, below 0.1% I'm guessing. Polypropylene is good too,
polysulfone (hard to find nowadays) is better. Mylar sucks.

Larger ceramics are terrible, and even NPOs are mediocre. The biggest
NPO I've ever seen was only 22 nF.

Right, there are filter designs that adjust for lossy caps.

John

Scott Stephens · Nov 3, 2004

Rich Grise wrote:

On Wed, 03 Nov 2004 08:52:05 +0000, Scott Stephens wrote:

Using force to override another
person's will is evil. It's that simple.

Its not that simple. What about overriding the will of children?

That's the most insidious evil of all, perpetrated, of course, in
the name of "god".

Not always. What about libertarians that coerce their children into
doing things that are ultimately for their own good?

The criminally insane?

Who defines "criminally insane?" These days, apparently, the punishment
for the criminally insane is to elect them to office.

I define it as people who think their good ideas entitle them to coerce
you to live for them, by serving them in some way or surrendering your
property to them.

I think peacenicks should refrain from burning or using petroleum
products, which means they should be living like Amish, to not be
hypocrites.

Well, OK, that's what you think "they" "should" do.

They don't have to live like the Amish. They could buy solar cells and
wind mills and use bio-diesel fuel. Of course, all these things are made
from petroleum. But at least their unplugging from the world system,
rather than plugging in.

Its a moral issue. Peacenicks bitch and moan about circumstances they
create by their own consumption. You are paying people to fight for your
petroleum when you purchase it with dollars, simple as that. You are, in
effect, contracting a mercenary force to stabilize the global economy
whenever you spend a dollar. If you can't see that, you are myopic.

Reality doesn't change just because you dont want to see it.

Well, I'm not going to live by your limitations, and if you want
to force me to, you're going to have to have the courage to come
over here and physically use force on me.

No, I'll just laugh at how ignorant you are. Truth is self-evident,
stupidity reaps its own rewards.

That's the way your

religion works, isn't it? You're gonna save their souls if you
have to burn them at the stake?

I'm doing my best to worship the God of Reality, of Existence. Currently
I'm studying Peikoff's "Objectivism: The Philosophy Of Ayn Rand".
Hard-core materialistic atheism.

Not that I endorse it, her or him, but they have a profound grasp of
reality you seem to lack, as evidenced by your ability to only
criticize, citing failing policy but not any effective policy. And you
think magically, as evidenced by the religious beliefs you've stated,
and thinking that a run of sporting events could predict a political
election without citing causal rather than merely correlating factors.

My God doesn't need to burn anyone for not worshiping, Rich, those that
transgress my God burn themselves. You think when you spend your dollars
and live in a community, you don't motivate others in that community to
do evil? You do understand market capitalism?

Perhaps we can say we voted Libertarian - we didn't endorse direct
initiation of violence and advocate peace. But we spend dollars for
petroleum products, and we must realize the consequence on others of
motivating them thus.

A Libertarian must recognize the plight of his neighbors, and not "game"
and make "excuses" to avoid responsibility for influencing environment
and contexts of actions.

You are responsible for educating your children right and wrong, so they
don't rob others for you. Or don't get together in a mob to enslave
others, as socialists do.

I would recommend other of Rand/Peikoffs books, but your technically
minded enough to handle the one I cited. Read it, and see if you can
keep faith in your God

It may challenge what you think of as your head and heart, spirit and
soul. Perhaps Objectivism lacks a context of faith, to believe the
universe is worth honoring it by living a life in it.

And so, in your little speech here, you have completely evaded my
question as to when I ever claimed to be a "good little hippy."

You like weed, you criticize war you are indirectly causing and is being
waged for your benefit, you live an unconventional existance, so I
identified you as a "hippy". I don't remember you claiming to be one.
Sorry if I offend.

But you didn't pass up the opportunity to spew forth your personal
ideology, did you?

Do I ever? Does anyone care? Have I ever gotten any rational, useful
feedback? When I resolve and integrate my love/hatred for society, I
wont bother spewing forth any more pearls before undeserving swine.

--
Scott

**********************************

DIY Piezo-Gyro, PCB Drill Bot & More Soon!

http://home.comcast.net/~scottxs/

POLITICS, n.
A strife of interests masquerading as a contest of principles.
The conduct of public affairs for private advantage. - Ambrose Bierce

**********************************

Terry Given · Nov 3, 2004

Jim Thompson wrote:

On Wed, 03 Nov 2004 15:46:00 -0800, John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:

On Wed, 03 Nov 2004 09:58:23 -0700, Jim Thompson
thegreatone@example.com> wrote:

On 3 Nov 2004 08:46:17 -0800, convertino@deemail.poliba.it (Alessandro
Convertino) wrote:

Hi to all,
I would like to know some informations about bandpass filtering on
frequency range between 0.05-30 Hz. In the past I've used a Sallen-key
active filter, and I would like to find a more performing solution.
What IC can I use to implement it?

Thanks for your attention.

Alessandro

VERY LOW FREQUENCY filters are difficult since the dissipation factor
of typical capacitors dominates (and deteriorates) the performance,
particularly in a production environment where repeatability is
important.

How so? I'd suspect a polycarb or something decent would have a very
low df in the sub-Hz range. Numbers like 1 uF and 10 megohms seem
perfectly nice to me, with fet opamps.

John

John,

What kind of df do you get with polycarb caps?

My experience is primarily with (NPO) chip caps for hybrids, which is
why I utilized the "p+1" method... then you can tolerate horrible df
before it even tweaks you a dB.

...Jim Thompson

Hi Jim,

whats the "p+1" method?

Cheers
Terry

James Meyer · Nov 3, 2004

On Wed, 03 Nov 2004 13:06:59 -0700, Jim Thompson <thegreatone@example.com>
wroth:

On Wed, 03 Nov 2004 18:12:20 GMT, "Ban" <bansuri@web.de> wrote:

With this broad range you can only cascade a highpass with a lowpass filter.

"...only..."?? Not so.

[snip]

Sallen-Key is indeed the most suitable
topology, but keep resistors low and (unfortunately) capacitors high.

[snip]

Sallen-Key sucks... why do you declare it "most suitable topology"?

...Jim Thompson

If all you have in your toolbox is a hammer, every problem begins to
look like a nail.

Jim "The other one."

Tim Wescott · Nov 3, 2004

Joerg wrote:

Hello Alessandro,

This could be nicely done with a DSP. ADC and DAC for data conversion
are cheap and plentiful, and so are DSP.

A microcontroller solution might work as well if it has to be rock
bottom in cost. Some MSP430 versions contain a 16 bit multiplier.
However, it can be a hassle to pipe the data in and out through the ports.

Ciao, Joerg

http://www.analogconsultants.com

Sampling at 150Hz will make the anti-aliasing easy, and even an 8051
ought to be able to make a pretty credible filter at that sample rate.
There are some very good 24-bit Sigma-Delta ADCs that have output sample
rates that fast, and input sample rates high enough that you anti-alias
with any R and C you find kicking around on the floor.

You still need an anti-aliasing filter, though. The advantage to doing
it with digital hardware is your frequencies are set by the uP
oscillator frequency, which will be pretty darn stable.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Jim Thompson · Nov 3, 2004

On Thu, 04 Nov 2004 00:34:04 GMT, James Meyer <jmeyer@nowhere.net>
wrote:

On Wed, 03 Nov 2004 13:06:59 -0700, Jim Thompson <thegreatone@example.com
wroth:

On Wed, 03 Nov 2004 18:12:20 GMT, "Ban" <bansuri@web.de> wrote:

With this broad range you can only cascade a highpass with a lowpass filter.

"...only..."?? Not so.

[snip]

Sallen-Key is indeed the most suitable
topology, but keep resistors low and (unfortunately) capacitors high.

[snip]

Sallen-Key sucks... why do you declare it "most suitable topology"?

...Jim Thompson

If all you have in your toolbox is a hammer, every problem begins to
look like a nail.

Jim "The other one."

480)460-2350 | |
| E-mail Address at Website Fax

Joerg · Nov 3, 2004

Hello Alessandro,

In case all the other methods are not to your liking here is another: Switched capacitor filters. They are not so much 'en vogue' anymore these days since everyone uses DSP but I believe LTC and National still offer these chips. In case this is for series production you'd have to make sure the chips stay around for a while though.

That gets you around most of the large capacitor tolerance issues.

Regards, Joerg

http://www.analogconsultants.com

Rich Grise · Nov 3, 2004

On Thu, 04 Nov 2004 00:26:26 +0000, Scott Stephens wrote:

Rich Grise wrote:

I'm more interested in, howcome evolution works the way it does?

OK, what induces subatomic particles to coalesce into atoms just the way
they do?
What induces these atoms to spontaneously form complex molecules, which
requires an input of energy?
What makes these molecules decide to get together and cooperate, building
even more complex molecules, that then cooperate, building organelles
and cell structures, and so on?

These are the kinds of questions I'm looking for the answer to.

Path of least *action*. "Action" is power - energy * time. If the
universe is a hyper-geometric space-time manifold, it seeks to conserve
what it is, like a soap bubble likes to be round to conserve what it is.

We experience "living" as a point moving along our "psychological arrow
of time".

I've heard time defined as the direction along which things have a
probability of occurring. If this perspective is true, and the universe'
dimensions fluctuate, are twisted about relative to each other, then
some spooky dynamics (from our "time" perspective) are probable. Our
space-time tensors are just a projection of our conscious experience of
time onto a chaotic manifold we can't know. Hawkings said he feared time
itself may be a complex quantity.

Cool!

Thanks!
Rich

john jardine · Nov 3, 2004

"Ban" <bansuri@web.de> wrote in message
news:8c9id.256803$35.11976599@news4.tin.it...

Alessandro Convertino wrote:
Hi to all,
I would like to know some informations about bandpass filtering on
frequency range between 0.05-30 Hz. In the past I've used a Sallen-key
active filter, and I would like to find a more performing solution.
What IC can I use to implement it?

Thanks for your attention.

Alessandro

With this broad range you can only cascade a highpass with a lowpass
filter.
With two filters of second order with maybe Bessel-characteristic you will
get a very good performance with very small overshoot and constant delay
in
the passband.
It doesn't matter which topology you implement the filters, because the
performance will be the same. Sallen-Key is indeed the most suitable
topology, but keep resistors low and (unfortunately) capacitors high. If
you
need steeper filter characteristic, you will have to increase the filter
order.
It is very important to choose the right opamps for this low frequency
task.
I recommend the AD797 or if it has to be cheap the NE5532. Fet- and CMos
opamps are unsuitable because of their low-frequency unstability. Use caps
of at least 1000uF for the high-pass. I think the noise performance will
be
the most important issue, as well as THD. But it all depends on your
application.
--
ciao Ban
Bordighera, Italy

(My Krohn-Hite 3342 switched, lo-pass hi-pass, lab filter goes down to

0.001Hz. Biggest caps in there seem 10uF polyprops, using discrete semis!)
regards
john

Joerg · Nov 4, 2004

Hi Tim,

Sampling at 150Hz will make the anti-aliasing easy, and even an 8051
ought to be able to make a pretty credible filter at that sample rate.
There are some very good 24-bit Sigma-Delta ADCs that have output
sample rates that fast, and input sample rates high enough that you
anti-alias with any R and C you find kicking around on the floor.

You still need an anti-aliasing filter, though. The advantage to
doing it with digital hardware is your frequencies are set by the uP
oscillator frequency, which will be pretty darn stable.

The only chore would be to pipe the data in and out. With a typical
limitation of two or three 8bit ports where some pins need to be shared
for JTAG programming it almost boils down to serial interfacing, or at
least muxed data tranfer.

BTW, I think your new paper on your web site about block diagrams in
control systems is great.

Regards, Joerg

http://www.analogconsultants.com

Mook Johnson · Nov 4, 2004

The 450k/.1uF filter would have even more spike killing effect. Something
more nonlinear than a spike was happening. I'd suspect a voltage breakdown
or coupling or something.

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:9umfo0157dd4rr9q4b07de6h3e2hj5uo23@4ax.com...

On 2 Nov 2004 10:46:32 -0800, the renowned
david.pariseau@sbcglobal.net (David Pariseau) wrote:

The problem was actually a voltage spike on startup (switching on the
Variac) that was large enough (>9000v) to toast the reference. I
guess it makes sense that the auto-transformer might have such an
excursion initially with such light load.

I added a 10K resistor in series with my 450K resistor and added a TVS
from this new node to ground and voila...

Thanks to all for your input.

Dave.

I would have thought the 3.3uF would have killed any such spikes. Do
you actually have that part installed?

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com

Joerg · Nov 4, 2004

Hi John,

(My Krohn-Hite 3342 switched, lo-pass hi-pass, lab filter goes down to
0.001Hz. Biggest caps in there seem 10uF polyprops, using discrete semis!)
regards

Weren't these hand-built and the size of a Radio Flyer cart?

Regards, Joerg

http://www.analogconsultants.com

Terry Given · Nov 4, 2004

Spehro Pefhany wrote:

On Thu, 04 Nov 2004 00:09:02 +1300, the renowned Terry Given
my_name@ieee.org> wrote:

Robert Baer wrote:

Electrolytics are traditionally poor on HF bypass - which degrades
over time.

It was presumably a brand-new capacitor.

and lets not forget if he bought a shitty electrolytic, it could easily
have 30+ Ohms ESR.

snip

So it forms a voltage divider with the 1K- that still doesn't leave
enough voltage to do damage to a LM4040 through an almost 1/2M
resistor.

Either the resistors were all breaking over or the schematic was not
as presented in some way.

Best regards,
Spehro Pefhany

sounds like the resistors were breaking over - rated for 200V
continuous, 400V peak each.

Cheers
Terry

Terry Given · Nov 4, 2004

Jim Thompson wrote:

On Thu, 04 Nov 2004 13:34:01 +1300, Terry Given <my_name@ieee.org
wrote:

Jim Thompson wrote:

[snip]

My experience is primarily with (NPO) chip caps for hybrids, which is
why I utilized the "p+1" method... then you can tolerate horrible df
before it even tweaks you a dB.

...Jim Thompson

Hi Jim,

whats the "p+1" method?

Cheers
Terry

For a way to swamp out dissipation effects, look over
"StateVariableFilter(P+1).pdf" on the SED/Schematics page of my
website.

...Jim Thompson

Thanks. nice.

Cheers
Terry

Jim Thompson · Nov 4, 2004

On Thu, 04 Nov 2004 01:45:31 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hi John,

(My Krohn-Hite 3342 switched, lo-pass hi-pass, lab filter goes down to
0.001Hz. Biggest caps in there seem 10uF polyprops, using discrete semis!)
regards

Weren't these hand-built and the size of a Radio Flyer cart?

Regards, Joerg

http://www.analogconsultants.com

480)460-2350 | |
| E-mail Address at Website Fax

Jim Thompson · Oct 31, 2004

On 31 Oct 2004 07:28:02 -0800, shoppa@trailing-edge.com (Tim Shoppa)
wrote:

Jim Thompson <thegreatone@example.com> wrote in message news:<cubqn0tp4a4dbr150m12ist196p31i9e11@4ax.com>...
3,649,929 Sine and Square-Wave Oscillator with AGC - MC1648

Wow, that's a good read. I did much better with that than I do
with most patents. I feel like taking some CA3046's or discrete
transistors and playing around with the ideas!

The MC1648 data sheet says it only works with LC tanks and not with
crystals, but if I built one out of transistors it would probably
oscillate with a series-resonant crystal where the wire is between
the collector of one Q and the base of the other Q? (A resistor or
RFC from the collector to Vcc too).

Tim.

It should, though my favorite approach is emitter-coupled... XTAL
between emitters, resistors to ground from each emitter, tank in one
collector, direct to VCC for the other collector. Connect "tank
collector" to base of other device, base of device with tank to VCC.

Hope that's clear... I despise ASCII schematics

480)460-2350 | |
| E-mail Address at Website Fax

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