filters

[John Larkin]

This cool. Click on a box on one of the surfaces.

http://tinyurl.com/3jyxpke

Click "filter expert" then "dual supplies." Then click on a box on one
of the surfaces.




I came up with a new-to-me filter architecture that *almost* works for
me. It's a degenerated MFB lowpass, where the opamp itself replaces
the usual opamp-r-c integrator.

http://dl.dropbox.com/u/53724080/Circuits/MFB_hack.JPG

This is freaky because it's weird to see a cap from an opamp inverting
output to ground. But the opamp is acting like an integrator, not an
opamp. Its input is *not* a summing point.

Unfortunately, this circuit has too few parts, so not enough degrees
of freedom to give me the gain I need (gotta have -5) and a decent
filter response: I seem to be stuck with a +14 dB peak. Cute, though.


--

John Larkin, President
Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation

 

[George Herold]

On Mar 5, 6:54 pm, John Larkin <jlar...@highlandtechnology.com> wrote:

This cool. Click on a box on one of the surfaces.

http://tinyurl.com/3jyxpke

Click "filter expert" then "dual supplies." Then click on a box on one
of the surfaces.

I came up with a new-to-me filter architecture that *almost* works for
me. It's a degenerated MFB lowpass, where the opamp itself replaces
the usual opamp-r-c integrator.

http://dl.dropbox.com/u/53724080/Circuits/MFB_hack.JPG

That top one looks like a low pass, with a bit coming back from the
output.

This is freaky because it's weird to see a cap from an opamp inverting
output to ground. But the opamp is acting like an integrator, not an
opamp. Its input is *not* a summing point.

Unfortunately, this circuit has too few parts, so not enough degrees
of freedom to give me the gain I need (gotta have -5) and a decent
filter response: I seem to be stuck with a +14 dB peak. Cute, though.

DC gain or just at the peak?

Maybe some DC gain will add to the peak?
George H.

--

John Larkin, President
Highland Technology, Inc

jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

 

[John Larkin]

On Mon, 5 Mar 2012 20:04:22 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

On Mar 5, 6:54 pm, John Larkin <jlar...@highlandtechnology.com> wrote:
This cool. Click on a box on one of the surfaces.

http://tinyurl.com/3jyxpke

Click "filter expert" then "dual supplies." Then click on a box on one
of the surfaces.

I came up with a new-to-me filter architecture that *almost* works for
me. It's a degenerated MFB lowpass, where the opamp itself replaces
the usual opamp-r-c integrator.

http://dl.dropbox.com/u/53724080/Circuits/MFB_hack.JPG

That top one looks like a low pass, with a bit coming back from the
output.

It's a textbook 2-pole MFB lowpass.

This is freaky because it's weird to see a cap from an opamp inverting
output to ground. But the opamp is acting like an integrator, not an
opamp. Its input is *not* a summing point.

Unfortunately, this circuit has too few parts, so not enough degrees
of freedom to give me the gain I need (gotta have -5) and a decent
filter response: I seem to be stuck with a +14 dB peak. Cute, though.

DC gain or just at the peak?

Maybe some DC gain will add to the peak?
George H.

DC gain has to be -5. The lower circuit has an additional gain bump,
14 dB roughly, at the high and of the passband.

(I posted this to s.e.b. by mistake, should have been s.e.d.)


--

John Larkin, President Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[George Herold]

On Mar 6, 11:48 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 5 Mar 2012 20:04:22 -0800 (PST), George Herold





gher...@teachspin.com> wrote:
On Mar 5, 6:54 pm, John Larkin <jlar...@highlandtechnology.com> wrote:
This cool. Click on a box on one of the surfaces.

http://tinyurl.com/3jyxpke

Click "filter expert" then "dual supplies." Then click on a box on one
of the surfaces.

I came up with a new-to-me filter architecture that *almost* works for
me. It's a degenerated MFB lowpass, where the opamp itself replaces
the usual opamp-r-c integrator.

http://dl.dropbox.com/u/53724080/Circuits/MFB_hack.JPG

That top one looks like a low pass, with a bit coming back from the
output.

It's a textbook 2-pole MFB lowpass.



This is freaky because it's weird to see a cap from an opamp inverting
output to ground. But the opamp is acting like an integrator, not an
opamp. Its input is *not* a summing point.

Unfortunately, this circuit has too few parts, so not enough degrees
of freedom to give me the gain I need (gotta have -5) and a decent
filter response: I seem to be stuck with a +14 dB peak. Cute, though.

DC gain or just at the peak?

Maybe some DC gain will add to the peak?
George H.

DC gain has to be -5. The lower circuit has an additional gain bump,
14 dB roughly, at the high and of the passband.

OK... the bottom one is like a PD TIA... you can hang a bit of C on
the inverting input.

Is the gain peak at the mean of the opamp GBW and the Rf/Cin
frequency?

Would it help to split the input R in half and put the C in the
middle?

(I posted this to s.e.b. by mistake, should have been s.e.d.)
Oh... well too late now.

George H.

--

John Larkin, President       Highland Technology Incwww.highlandtechnology.com  jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators- Hide quoted text -

- Show quoted text -