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Sallen-Key input Z

M

miso

Jan 1, 1970
0
Miso, do you know if this approach is discussed in William's Filter
Handbook?

Is it done with All pass filters (phase shifts) and summers?

George H.

Nope. I never read Williams book. But anyone simply meditating on the
task at hand can see that IF you have enough degrees of freedom, it
makes total sense for each op amp to reach the same signal swing. If you
don't, you are simply adding more noise to the system for no good reason
other than laziness or incompetence.

Now not every topology has enough degrees of freedom to adjust the swing
of all nodes.

If you go to this power point presentation, Dr. Temes explains the
procedure of dynamic range adjustment. The discussion starts on page 21.

Google hides the direct link unfortunately. I would guess this is an
undergraduate class based on what I read.
 
M

miso

Jan 1, 1970
0
Bingo. When you crank stuff out by the millions, close isn't good enough.
 
M

miso

Jan 1, 1970
0
Has it occurred to you that some requirements need AC accuracy. Your SK
filters are simply shit for that use.

I know you have a PHD and don't like being pointed out when you are
wrong, but give it a rest here.
 
M

miso

Jan 1, 1970
0
"OK, how would you do a non-Sallen-Key lowpass filter that has a gain
tempco in the single digits of PPM? Mortgage all your property to
Vishay?"
Actually the LT1062 does that. Nello is a good filter designer.
 
M

miso

Jan 1, 1970
0
Except it costs you nothing to dynamic range the design. Hence Dr. Temes
put it in his lecture. Why do a shitty job when for no additional
components, you can do it correctly?

Further, with low noise op amps, you can make quiet active filters.
There are applications where it is best to avoid the A-D and D->A steps.
 
M

miso

Jan 1, 1970
0
It has a number of chapters on filter synthesis. Of course, with
computers, perhaps the techniques are old fashioned.

I don't recall seeing any other sources on crystal filters. I suppose
they exist.
 
M

miso

Jan 1, 1970
0
You can predistort for Q enhancement, but you run the risk of tempco
effecting the filter.

If you go for a ladder approach, the localized Qs tend to be lower. I'm
not sure if localized Q is a generally accepted term, but I learned it
from Dan Senderovich. The idea is every node is a filter, even if only
one node has the desired frequency response. If you examine the response
at intermediate nodes of a cascade of biquadratic sections versus the
nodes of a ladder, the ladder "localized" Q is lower. I don't believe
there is a strict proof of this, but anecdotal evidence shows this.

The other advantage to a ladder is that the all the components interact
in a manner where the sensitivity to an individual component is reduced.

Senderovich is quite the guru at this. I learned how to do bandpass and
highpass ladders from him, something textbooks don't cover. His approach
is totally signal flow graph. In fact, if you want to ponder dynamic
range adjustment, signal flow graph is the way to go.

In ladder design using signal flow graph, the upper nodes represent
voltage, and physically are op amp outputs. The lower nodes represent
current. Going from the upper nodes to the lower nodes is done with
integrators (physically an op amp with a cap as feedback, positive input
to ground if single ended.).

Say the node is peaking. To dynamic range adjust a filter as shown on
the signal flow graph, you scale down (attenuate) all the paths entering
the node, then scale up (amplify) all the paths leaving the node. If
you do this, the final output of the signal flow graph has remained
unchanged.
 
M

miso

Jan 1, 1970
0
I don't push polygons... that's a specialty all its own... I hire that
out.

...Jim Thompson
Often at salaries exceeding that of many engineers. ;-)
 
M

miso

Jan 1, 1970
0
Sometimes when using Zverev, you wonder why he has so few significant
figures in the tables. But then thinking of the year it was published,
it makes sense.

The book also talks about how to make physical (passive) LCR filters.
 
J

Jon Kirwan

Jan 1, 1970
0
It has a number of chapters on filter synthesis. Of course, with
computers, perhaps the techniques are old fashioned.
<snip>

No. You don't get nearly as much intuition out of using a
program to do the work. Old fashioned techniques focus
prioritize what's important and that is a good thing.

Jon
 
J

Jon Kirwan

Jan 1, 1970
0
(*) I even used an ANALOG computer to factor transfer functions.
Forgot its name... some company in Oregon... blue case like Tek, but
not Tek... cost me (company, Dickson) around $10K in 1970 :-(

I'd be interested to know its name. I did find this:

http://oregondigital.org/cdm4/item_viewer.php?CISOROOT=/archives&CISOPTR=3916&CISOBOX=1&REC=2

1957, though, and I don't think that's what you meant.

$10k was real money back then. Would get you maybe three
pretty decent new cars. A production worker made a little
more than half that much in a whole year.

Jon
 
Wait until you graduate to a quad 16QFN and 0201 :)

I don't think that's going to happen in my lifetime. We're pushing
0201s for bypass caps but corporate isn't going to buy it for
production.
Then your techs need a sign above the lab benches "No sneezing within 10
feet".

"Then stop giving us reels of pepper!" ;-)
 
On Thu, 29 Nov 2012 08:40:23 -0800, John Larkin

On Wed, 28 Nov 2012 22:19:57 -0500, [email protected] wrote:

On Wed, 28 Nov 2012 17:50:49 -0800, John Larkin

On Wed, 28 Nov 2012 17:35:43 -0800 (PST), George Herold

On Nov 28, 8:19 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:
On Wed, 28 Nov 2012 17:16:30 -0800 (PST), George Herold





On Nov 28, 4:23 pm, Spehro Pefhany <[email protected]>
wrote:
On Wed, 28 Nov 2012 12:25:00 -0800 (PST), George Herold
<snip>
Oh and about the nice idea of recomputing my first R3 to make it all
come out right.
That's a great idea, unfortunately I was trying to do a bit much with
this section of circuit and the 10k resistor is actually a pot that
adjusts the amplitude.. so I'm a bit f'ed.
George H.
Probably easiest to just buffer with an op-amp follower after the
divider. Just one part to hack in.
Yeah, driving home I figure I'll turn the first opamp into a buffer,
and then change a few resistors in the next (2) stages.. a four pole
butterworth.
No one will care but me....
George H.
Or do it right, using a quad op-amp package... Sallen-Key sucks >:-}

What transfer function are you trying to realize?

...Jim Thompson
- Hide quoted text -

- Show quoted text -
Grin... too late for that.
And I hate opamp quad packs...
I can never get things nice and tight. :^)

George H.
There's seldom a reason to go beyond duals.
The design I'm working on uses sixteen quads per board. Thirty-two
duals wouldn't cut it. Getting the design tight is simply a matter of
a little work (and two sides). In fact, thirty-two duals would be
*far* worse. You can pack a lot of 0402s in a small space.
Two duals aren't much bigger than a quad, and routing can be easier
with duals.

I used to think that but have changed my mind after using quads with
0402 discrete's.

Wait until you graduate to a quad 16QFN and 0201 :)

Then your techs need a sign above the lab benches "No sneezing within 10
feet".

[...]

Whenever I need a surfmount resistor or cap from stock, I pull 5. I
usually wind up losing or tidly-winking a couple before I get one
safely soldered down. Good thing they are so cheap.

We have binders of surface mount parts in various sizes that the
vendors give us. There are about 100 of each value and perhaps 100
values in a binder. There are a few cut tape strips in small pouches
attached to pages in each binder. It really is handy to have these
available when modifying boards. I generally have a success rate of
about 5 0402s (larger components are higher since it's harder for them
to hide) placed properly before one takes a walkabout.
 
John said:
[email protected] wrote:
On Thu, 29 Nov 2012 08:40:23 -0800, John Larkin

On Wed, 28 Nov 2012 22:19:57 -0500, [email protected] wrote:

On Wed, 28 Nov 2012 17:50:49 -0800, John Larkin

On Wed, 28 Nov 2012 17:35:43 -0800 (PST), George Herold

On Nov 28, 8:19 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:
On Wed, 28 Nov 2012 17:16:30 -0800 (PST), George Herold





On Nov 28, 4:23 pm, Spehro Pefhany <[email protected]>
wrote:
On Wed, 28 Nov 2012 12:25:00 -0800 (PST), George Herold
<snip>
Oh and about the nice idea of recomputing my first R3 to make it all
come out right.
That's a great idea, unfortunately I was trying to do a bit much with
this section of circuit and the 10k resistor is actually a pot that
adjusts the amplitude.. so I'm a bit f'ed.
George H.
Probably easiest to just buffer with an op-amp follower after the
divider. Just one part to hack in.
Yeah, driving home I figure I'll turn the first opamp into a buffer,
and then change a few resistors in the next (2) stages.. a four pole
butterworth.
No one will care but me....
George H.
Or do it right, using a quad op-amp package... Sallen-Key sucks >:-}

What transfer function are you trying to realize?

...Jim Thompson
- Hide quoted text -

- Show quoted text -
Grin... too late for that.
And I hate opamp quad packs...
I can never get things nice and tight. :^)

George H.
There's seldom a reason to go beyond duals.
The design I'm working on uses sixteen quads per board. Thirty-two
duals wouldn't cut it. Getting the design tight is simply a matter of
a little work (and two sides). In fact, thirty-two duals would be
*far* worse. You can pack a lot of 0402s in a small space.
Two duals aren't much bigger than a quad, and routing can be easier
with duals.
I used to think that but have changed my mind after using quads with
0402 discrete's.

Wait until you graduate to a quad 16QFN and 0201 :)

Then your techs need a sign above the lab benches "No sneezing within 10
feet".

[...]

Whenever I need a surfmount resistor or cap from stock, I pull 5. I
usually wind up losing or tidly-winking a couple before I get one
safely soldered down. Good thing they are so cheap.

The scare is when it snaps out of the tweezers, is nowhere to be found,
and there's your coffee mug right next to all the action. Did it land in
there?

This, too, shall pass.
Or what happened to a friend: Snip ... snap ... tchk ... *PHOOFFFF* ...
$2k worth of damage in a piece of lab equipment it had sailed into.

Never had a failure that could be attributed to a wandering 0402.
 
J

josephkk

Jan 1, 1970
0
I'm afraid not. There is simply no reason to design a filter with nodes
that don't swing at equal amplitudes at all op amps. There is no
argument here. I am 100% correct on this.
The instant anyone insists that they are 100 % correct on anything i know
that it is NOT true. Nor have i found an exception to validate that other
rule.
 
J

Joerg

Jan 1, 1970
0
I don't think that's going to happen in my lifetime. We're pushing
0201s for bypass caps but corporate isn't going to buy it for
production.


"Then stop giving us reels of pepper!" ;-)


Right now I can't solder any of this because of exactly that problem.
Serious cold, lots of *ACHOOO* ... courtesy of flight UA1015 where
almost everyone around me had a hacking cough.
 
J

Jon Kirwan

Jan 1, 1970
0
Things go easier with government money to lubricate the system.

Another of the fun problems with using a laser to trim resistors is
the width of the kerf is rather narrow. Looking at a cross section,
it looks like two vertical walls with very little space in between.
Use too much power, and the top edges melt and short across the kerf.
With square top edges, if we were sloppy in handling, the edges would
crumble, fall into the kerf, and short across the kerf. When I
widened the kerf, it took more laser power to ablate the resistor
material, which sometimes caused the substrate to shatter. Of course,
the resistor changes value as it cools down, which required slowing
down the trim rate near the end of the cut.

I think I had a nightmare last night with a laser trimmer playing a
key role.

Also, due to security clearance issues, I don't do MIL work.
<snip>

It's no fun. FBI (and whomever else they decide) talks to all
your neighbors, people you barely remember from your past,
family, you name it. And it takes a while, too. Long while.
Special access required (SAR) is painful.

Then at work you can walk in with stuff into a Faraday caged
room, but you can't walk out with it. They smash anything
electronic (and other things they feel might carry info) on
the way out. No exceptions. Scary, too, gun-toting folks;
places you are supposed to know not to walk around, yet no
signs so, easy to make mistakes that could end your life in a
moment. I made a few innocent mistakes during a lunch break,
for example, and got shaken up plenty from it.

It paid well, but I won't do it again.

Jon
 
I had an HP9100, an HP35, a PDP-11, two motorcycles, and an Austin Healey
Sprite. I guess I wasn't doing badly for a kid still in school.

I had an HP45 and a wife. At the time I thought the calculator was
expensive. ;-)
 
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