Bandpass filter with adjustable Q

[The Phantom]

There has been interest in the past concerning filters with the property that some
parameter of the filter can be adjusted (with, say, a potentiometer) without peturbing
other parameters. The latest issue of Electronic Design magazine has such a design in the
Ideas for Design section.

http://www.elecdesign.com/Articles/ArticleID/10684/10684.html

I'm not sure but what I may have seen this one before, but I thought I'd call it to the
attention of the group.

 

[john jardine]

"The Phantom" <phantom@aol.com> wrote in message
news:87f2e1tfd4u193ok3sn6sq04hin6938uh9@4ax.com...

There has been interest in the past concerning filters with the property
that some
parameter of the filter can be adjusted (with, say, a potentiometer)
without peturbing
other parameters. The latest issue of Electronic Design magazine has such
a design in the
Ideas for Design section.

http://www.elecdesign.com/Articles/ArticleID/10684/10684.html

I'm not sure but what I may have seen this one before, but I thought I'd
call it to the
attention of the group.

Used the same method with a Wein bridge network about 5 years ago. Idea came
straight out of a electronics-for-beginers' book. Also saw similar idea in a
Wireless World article from 50 years ago.
This is "trivial" stuff, why does it take 3 of 'em to reinvent a wheel?.
Have the uni's gone soft?.
regards
john

 

[Joel Kolstad]

"john jardine" <john@jjdesigns.fsnet.co.uk> wrote in message
news:dbrkpa$qn5$1@newsg3.svr.pol.co.uk...

This is "trivial" stuff, why does it take 3 of 'em to reinvent a wheel?.
Have the uni's gone soft?.

It's probably a case where the professors in question had a need for the
circuit, figured it out, and decided to share it with others. Most of what
ends up in trade magazines such as this is not meant to be new material,
rather it's meant to present useful techniques to the working engineer.
Hence, a lot of the same ideas are re-printed again and again...

 

[martin griffith]

On Fri, 22 Jul 2005 13:37:48 -0700, in sci.electronics.design "Joel
Kolstad" <JKolstad71HatesSpam@yahoo.com> wrote:

"john jardine" <john@jjdesigns.fsnet.co.uk> wrote in message
news:dbrkpa$qn5$1@newsg3.svr.pol.co.uk...
This is "trivial" stuff, why does it take 3 of 'em to reinvent a wheel?.
Have the uni's gone soft?.

It's probably a case where the professors in question had a need for the
circuit, figured it out, and decided to share it with others. Most of what
ends up in trade magazines such as this is not meant to be new material,
rather it's meant to present useful techniques to the working engineer.

Hence, a lot of the same ideas are re-printed again and again...

A bit like the US patent office then?


martin

 

[Jim Thompson]

On Fri, 22 Jul 2005 11:41:48 -0700, The Phantom <phantom@aol.com>
wrote:

There has been interest in the past concerning filters with the property that some
parameter of the filter can be adjusted (with, say, a potentiometer) without peturbing
other parameters. The latest issue of Electronic Design magazine has such a design in the
Ideas for Design section.

http://www.elecdesign.com/Articles/ArticleID/10684/10684.html

I'm not sure but what I may have seen this one before, but I thought I'd call it to the
attention of the group.

The "Twin-T" approach is the pitts. For how to do it right see all
the gyrator-based filters on the S.E.D/Schematics page of my website.
These feature independent adjustment of bandwidth and center
frequency.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[john jardine]

"Joel Kolstad" <JKolstad71HatesSpam@yahoo.com> wrote in message
news:11e2m5km0d7e3ed@corp.supernews.com...

"john jardine" <john@jjdesigns.fsnet.co.uk> wrote in message
news:dbrkpa$qn5$1@newsg3.svr.pol.co.uk...
This is "trivial" stuff, why does it take 3 of 'em to reinvent a wheel?.
Have the uni's gone soft?.

It's probably a case where the professors in question had a need for the
circuit, figured it out, and decided to share it with others. Most of
what
ends up in trade magazines such as this is not meant to be new material,
rather it's meant to present useful techniques to the working engineer.
Hence, a lot of the same ideas are re-printed again and again...


You're right of course.

If they'd generated 'original' work then for sure, they'd be publishing it
in some learned tome.
Kneejerk on my part. Ie, If I can grok what they're saying then it wasn't
worth them saying it. I'm just having a grumpy day .
regards
john

 

[Joerg]

Hello John,

Used the same method with a Wein bridge network about 5 years ago. Idea came
straight out of a electronics-for-beginers' book. Also saw similar idea in a
Wireless World article from 50 years ago.

It's probably older than that. I built Q-multipliers when I was a kid.
Not to brag about it but because I didn't have the dough for a decent
filter in those days. Or, ahem, to be honest, I didn't want to tap into
my brewsky funds for that.

Regards, Joerg

http://www.analogconsultants.com

 

[John Larkin]

On Fri, 22 Jul 2005 13:37:48 -0700, "Joel Kolstad"
<JKolstad71HatesSpam@yahoo.com> wrote:

"john jardine" <john@jjdesigns.fsnet.co.uk> wrote in message
news:dbrkpa$qn5$1@newsg3.svr.pol.co.uk...
This is "trivial" stuff, why does it take 3 of 'em to reinvent a wheel?.
Have the uni's gone soft?.

It's probably a case where the professors in question had a need for the
circuit, figured it out, and decided to share it with others. Most of what
ends up in trade magazines such as this is not meant to be new material,
rather it's meant to present useful techniques to the working engineer.
Hence, a lot of the same ideas are re-printed again and again...

There are three functions being served by articles like this:

1. For a mag to get the cheap periodicals mailing rate, they have to
have a certain percentage of "editorial content", but would rather not
pay for such, so they accept most anything. Without that requirement,
they'd be all ads.

2. Foreign engineers and academics - a huge fraction of the presenters
- get published in a "prestigious" US mag.

3. The staff of the mag, journalism majors mostly, can just cut and
paste the stuff and not have to worry their pretty heads over writing
about electronics, about which they know very little.

Hell, bootsrapped twin-tees have been around for 70 years roughly.

John

 

[Rich Grise]

On Fri, 22 Jul 2005 13:37:48 -0700, Joel Kolstad wrote:

"john jardine" <john@jjdesigns.fsnet.co.uk> wrote in message
news:dbrkpa$qn5$1@newsg3.svr.pol.co.uk...
This is "trivial" stuff, why does it take 3 of 'em to reinvent a wheel?.
Have the uni's gone soft?.

It's probably a case where the professors in question had a need for the
circuit, figured it out, and decided to share it with others. Most of
what ends up in trade magazines such as this is not meant to be new
material, rather it's meant to present useful techniques to the working
engineer. Hence, a lot of the same ideas are re-printed again and again...

Yeah ... Just like the newsgroups...

;-)
Rich

 

[Rich Grise]

On Fri, 22 Jul 2005 21:47:49 +0000, Joerg wrote:

Hello John,

Used the same method with a Wein bridge network about 5 years ago. Idea
came straight out of a electronics-for-beginers' book. Also saw similar
idea in a Wireless World article from 50 years ago.

It's probably older than that. I built Q-multipliers when I was a kid. Not
to brag about it but because I didn't have the dough for a decent filter
in those days. Or, ahem, to be honest, I didn't want to tap into my
brewsky funds for that.

But I think the point of the article is that their thing has constant
gain at the center frequency while you change the bandwidth. A Q mult.
has increasing gain as the Q, well, multiplies. IOW, it's the "constant
gain" feature that's their selling point.

At least that's how I see it.

Thanks,
Rich

 

[Joerg]

Hello Rich,

But I think the point of the article is that their thing has constant
gain at the center frequency while you change the bandwidth. A Q mult.
has increasing gain as the Q, well, multiplies. IOW, it's the "constant
gain" feature that's their selling point.

IIRC the Q multiplier also had constant gain. You just hung a gain stage
to the first filter and brought it really close to oscillation. Probably
very similar to Jim's gyrator thing. It did not amplify anything. I do
not recall having to adjust the volume when I changed the bandwidth. It
was actually a pretty cool thing but not new at all. When I built it I
basically copied from a tube based schematic in a ham radio magazine.
Judging from the type of tube the original must have been a 40's or 50's
design.

Regards, Joerg

http://www.analogconsultants.com

 

[Jim Thompson]

On Sat, 23 Jul 2005 00:16:13 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello Rich,

But I think the point of the article is that their thing has constant
gain at the center frequency while you change the bandwidth. A Q mult.
has increasing gain as the Q, well, multiplies. IOW, it's the "constant
gain" feature that's their selling point.

IIRC the Q multiplier also had constant gain. You just hung a gain stage
to the first filter and brought it really close to oscillation. Probably
very similar to Jim's gyrator thing. It did not amplify anything. I do
not recall having to adjust the volume when I changed the bandwidth. It
was actually a pretty cool thing but not new at all. When I built it I
basically copied from a tube based schematic in a ham radio magazine.
Judging from the type of tube the original must have been a 40's or 50's
design.

Regards, Joerg

http://www.analogconsultants.com

My gyrator-based filters have unity gain at fo, irrespective of
bandwidth.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.