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Linear Technology's FilterCAD
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paul@burridge8333.fsbusin
electronics forum beginner


Joined: 20 Mar 2006
Posts: 31

PostPosted: Sun May 21, 2006 2:01 pm    Post subject: Linear Technology's FilterCAD Reply with quote

Anyone had any success in using this program? Every time I enter any
parameters (even for the most basic bandpass Butterworth, for example)
the thing just seems to complain and won't come up with any valid
result. Neutral
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Tom Bruhns
electronics forum addict


Joined: 28 Feb 2005
Posts: 94

PostPosted: Sun May 21, 2006 4:15 pm    Post subject: Re: Linear Technology's FilterCAD Reply with quote

Works fine for me. Are you giving it parameters that lead to an order
greater than 16? Look at the "order" box, assuming you're using the
"enhanced design". What _exactly_ is the complaint it registers?
Perhaps it's telling you that you are asking to implement an
impractical design, and it refuses.
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Jim Thompson
electronics forum Guru


Joined: 06 May 2005
Posts: 5440

PostPosted: Sun May 21, 2006 4:36 pm    Post subject: Re: Linear Technology's FilterCAD Reply with quote

On 21 May 2006 09:15:01 -0700, "Tom Bruhns" <k7itm@msn.com> wrote:

Quote:
Works fine for me. Are you giving it parameters that lead to an order
greater than 16? Look at the "order" box, assuming you're using the
"enhanced design". What _exactly_ is the complaint it registers?
Perhaps it's telling you that you are asking to implement an
impractical design, and it refuses.

It's Burridge, what do you expect ?:-)

...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:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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paul@burridge8333.fsbusin
electronics forum beginner


Joined: 20 Mar 2006
Posts: 31

PostPosted: Sun May 21, 2006 9:01 pm    Post subject: Re: Linear Technology's FilterCAD Reply with quote

Thanks, Tom.
I was simply (initially) trying to get it to come up with design values
for a L/C notch filter centered on 153Mhz with -30dB attenation at the
centre and *passband* 3dB corners at 147Mhz and 159Mhz at < 4dB overall
insertion loss. Is that really so difficult???
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Ben Jackson
electronics forum beginner


Joined: 19 Sep 2005
Posts: 48

PostPosted: Sun May 21, 2006 11:07 pm    Post subject: Re: Linear Technology's FilterCAD Reply with quote

On 2006-05-21, paul@burridge8333.fsbusiness.co.uk <paul@burridge8333.fsbusiness.co.uk> wrote:
Quote:
Anyone had any success in using this program? Every time I enter any
parameters (even for the most basic bandpass Butterworth, for example)
the thing just seems to complain and won't come up with any valid
result. Neutral

I had it choke on 'quick", but then when I went back to "enhanced" it
even carried over the parameters from quick and produced results.

--
Ben Jackson
<ben@ben.com>
http://www.ben.com/
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Tom Bruhns
electronics forum addict


Joined: 28 Feb 2005
Posts: 94

PostPosted: Mon May 22, 2006 12:37 am    Post subject: Re: Linear Technology's FilterCAD Reply with quote

Well, yes, Paul, it is very difficult for an active filter circuit.
Remember, the Linear Technology software is for designing filters with
their active filter parts.

You should go to some LC filter design software such as Elsie, the
filter software from AADE, or the filter design stuff in RFSim99. Be
sure to include inductor Q in your design. You have to do that "by
hand" by adding resistance to the inductances in RFSim99. The AADE
software lets you enter coil Q, and I think Elsie does too. And
depending on what you REALLY want to do, it may be quite inappropriate
to ask for a symmetrical notch and passband flat from DC to close to
the notch.
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Jim
electronics forum beginner


Joined: 11 May 2006
Posts: 7

PostPosted: Mon May 22, 2006 2:36 am    Post subject: Re: Linear Technology's FilterCAD Reply with quote

I have found that RFSIMM99 seems to incorporate Q when I click on USE
PHYSICAL MODEL.

This works for capacitors and inductors. For resistors, I have to add
the parasitic capacitance and inductance as separate components, but that
may, or may not, be required depending mainly on frequency and what sort of
physical component will be used.

Now, in the circuit Paul wants, I'd use the Monte Carlo tolerance sweep to
see if the circuit is too critical to be reasonable to build. To get that
notch, and narrow response, is probably not going to be easy.


Jim
N6BIU
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Tom Bruhns
electronics forum addict


Joined: 28 Feb 2005
Posts: 94

PostPosted: Mon May 22, 2006 6:26 am    Post subject: Re: Linear Technology's FilterCAD Reply with quote

Yes, you're right that it's more automatic than I suggested, though
AFAIK you have to set the Q and SRF parameters for each component
individually after doing the design. Plus of course RFSim99 won't do
notch filter designs as Paul is looking for.

I suppose Paul is wanting to make a one-off filter, so using tuning
caps should let him make the notch be where he wants.

Thanks for pointing out the "use physical model" thing.

Cheers,
Tom
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paul@burridge8333.fsbusin
electronics forum beginner


Joined: 20 Mar 2006
Posts: 31

PostPosted: Mon May 22, 2006 10:53 pm    Post subject: Re: Linear Technology's FilterCAD Reply with quote

Oh! Thanks for that info, Tom. Yeah, I'm only interested in L/C
passives and had no idea about that LTFC was built around their ICs.
Thanks for the heads up! Thanks to everyone else who chipped in their
2p worth, btw.
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