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John Larkin
Guest
Guest
Thu Sep 02, 2010 5:04 am
On Tue, 31 Aug 2010 21:29:17 -0700, John Larkin
<jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:
Quote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
OK, this is weird,
ftp://jjlarkin.lmi.net/Bessel_3+7c.jpg
pretty much just instinct and fiddling. It only uses 4 inductors, so
it's not outrageous to actually do. It hardly has any tail, so I could
slow down the filters a bit and stretch the output a little wider.
TAP is pretty far from F2, which means that most of the delay in the
second filter happens in the last LC. Maybe I can flip ends on this
filter and pretty things up a little. Or use something more like a
classic delay line for the second section. Interesting, and mildly
tedious.
T-coils make better delay lines, but it's hard to get the tapped
inductors.
John
whit3rd
Guest
Guest
Thu Sep 02, 2010 8:39 am
On Sep 1, 7:24 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Quote:
The bad news is that few people still make analog delay lines, and
they want 4 weeks to come up with a sample. I don't have 4 weeks. So
either I make my own tapped LC delay line from parts, or try cascading
and summing Bessel filters.
they want 4 weeks to come up with a sample. I don't have 4 weeks. So
either I make my own tapped LC delay line from parts, or try cascading
and summing Bessel filters.
For 5 ns, you need about five feet of twinlead or coax cable to make a
delay line.
Probably there's a way to get it without a four week wait.
You can make a short pulse have a long tail by feeding it to a
termination
network with a diode, and the resulting (fast-rise, slow-fall) pulse
can be shortened
by using a delay line stub (the reflection is a fast-fall slow-rise
pulse that, added to the long-tail original, has a fast-rise and fast-
fall
with nearly zero straggle).
miso@sushi.com
Guest
Guest
Thu Sep 02, 2010 9:20 am
On Sep 1, 7:44 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Quote:
On Wed, 1 Sep 2010 18:04:58 -0700 (PDT), "m...@sushi.com"
m...@sushi.com> wrote:
On Sep 1, 4:15 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Tue, 31 Aug 2010 21:44:07 -0700 (PDT), "m...@sushi.com"
m...@sushi.com> wrote:
On Aug 31, 9:29 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
Why wouldn't you just stretch the pulses with logic circuits? Your
delay element would be a string of inverters.
It has to be analog and linear. Downstream will be amplifiers and
comparators, as noted.
Another possibility is two cascaded Bessel filters. The first shapes
the 2 ns pulse into, say, a 6 ns gaussian pulse, and the second pretty
much just delays that. The sum of the filter outputs will be pretty
much flat and will settle out fast.
John
John
I claim pulse stretching is not a linear operation.
What I want to do certainly is. A passive LC filter is linear. The
output is strictly proportional to the input.
John
m...@sushi.com> wrote:
On Sep 1, 4:15 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Tue, 31 Aug 2010 21:44:07 -0700 (PDT), "m...@sushi.com"
m...@sushi.com> wrote:
On Aug 31, 9:29 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
Why wouldn't you just stretch the pulses with logic circuits? Your
delay element would be a string of inverters.
It has to be analog and linear. Downstream will be amplifiers and
comparators, as noted.
Another possibility is two cascaded Bessel filters. The first shapes
the 2 ns pulse into, say, a 6 ns gaussian pulse, and the second pretty
much just delays that. The sum of the filter outputs will be pretty
much flat and will settle out fast.
John
John
I claim pulse stretching is not a linear operation.
What I want to do certainly is. A passive LC filter is linear. The
output is strictly proportional to the input.
John
Then you are not stretching the pulse. Think of it this way. The input
pulse is of amplitude A and width W. The output pulse is of amplitude
A and width Y, where Y>W. The energy of the output is greater than
that of the input, hence my reference to Parseval.
Oh, eh yeah, QED.
Sylvia Else
Guest
Guest
Thu Sep 02, 2010 10:04 am
On 2/09/2010 2:04 PM, John Larkin wrote:
Quote:
On Tue, 31 Aug 2010 21:29:17 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
OK, this is weird,
ftp://jjlarkin.lmi.net/Bessel_3+7c.jpg
pretty much just instinct and fiddling. It only uses 4 inductors, so
it's not outrageous to actually do. It hardly has any tail, so I could
slow down the filters a bit and stretch the output a little wider.
TAP is pretty far from F2, which means that most of the delay in the
second filter happens in the last LC. Maybe I can flip ends on this
filter and pretty things up a little. Or use something more like a
classic delay line for the second section. Interesting, and mildly
tedious.
T-coils make better delay lines, but it's hard to get the tapped
inductors.
John
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
OK, this is weird,
ftp://jjlarkin.lmi.net/Bessel_3+7c.jpg
pretty much just instinct and fiddling. It only uses 4 inductors, so
it's not outrageous to actually do. It hardly has any tail, so I could
slow down the filters a bit and stretch the output a little wider.
TAP is pretty far from F2, which means that most of the delay in the
second filter happens in the last LC. Maybe I can flip ends on this
filter and pretty things up a little. Or use something more like a
classic delay line for the second section. Interesting, and mildly
tedious.
T-coils make better delay lines, but it's hard to get the tapped
inductors.
John
Taps on a few feet of suitable coax?
Sylvia.
Tim Williams
Guest
Guest
Thu Sep 02, 2010 11:16 am
<miso_at_sushi.com> wrote in message
news:828ee989-7afd-4fe8-8a9b-a60aadf46cd4_at_n3g2000yqb.googlegroups.com...
Quote:
Then you are not stretching the pulse. Think of it this way. The input
pulse is of amplitude A and width W. The output pulse is of amplitude
A and width Y, where Y>W. The energy of the output is greater than
that of the input, hence my reference to Parseval.
pulse is of amplitude A and width W. The output pulse is of amplitude
A and width Y, where Y>W. The energy of the output is greater than
that of the input, hence my reference to Parseval.
*Unless* you put it on narrower traces at the output (high Z). Then you
get the same amplitude (voltage) but less power (since the energy is
spread out) and a lot less current.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Tim Williams
Guest
Guest
Thu Sep 02, 2010 11:22 am
"whit3rd" <whit3rd_at_gmail.com> wrote in message
news:82357e93-0609-424b-8297-d640573f8dc3_at_f6g2000yqa.googlegroups.com...
Quote:
For 5 ns, you need about five feet of twinlead or coax cable to make a
delay line.
Probably there's a way to get it without a four week wait.
delay line.
Probably there's a way to get it without a four week wait.
Or if you don't like the bulk of coax, take a piece of copper tubing and
wrap with bifilar magnet wire (make sure the wires never cross). Or just
squiggle back and forth over a few layers on your PCB, if it's not too
cramped.
Last time I saw such a delay line, it was in a color TV, to compensate for
the delay between the luminance amp (going to the CRT cathodes) and
chrominance amps (going to the grids). The propagation delay of a tube
stage was something like 50ns.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
brent
Guest
Guest
Thu Sep 02, 2010 1:39 pm
On Sep 1, 1:06 am, Bill Sloman <bill.slo...@ieee.org> wrote:
Quote:
An infinitely long FIR filter, for one.
Isn't that an oxymoron?
John Larkin
Guest
Guest
Thu Sep 02, 2010 2:59 pm
On Wed, 1 Sep 2010 23:20:38 -0700 (PDT), "miso_at_sushi.com"
<miso_at_sushi.com> wrote:
Quote:
On Sep 1, 7:44 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Wed, 1 Sep 2010 18:04:58 -0700 (PDT), "m...@sushi.com"
m...@sushi.com> wrote:
On Sep 1, 4:15 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Tue, 31 Aug 2010 21:44:07 -0700 (PDT), "m...@sushi.com"
m...@sushi.com> wrote:
On Aug 31, 9:29 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
Why wouldn't you just stretch the pulses with logic circuits? Your
delay element would be a string of inverters.
It has to be analog and linear. Downstream will be amplifiers and
comparators, as noted.
Another possibility is two cascaded Bessel filters. The first shapes
the 2 ns pulse into, say, a 6 ns gaussian pulse, and the second pretty
much just delays that. The sum of the filter outputs will be pretty
much flat and will settle out fast.
John
John
I claim pulse stretching is not a linear operation.
What I want to do certainly is. A passive LC filter is linear. The
output is strictly proportional to the input.
John
Then you are not stretching the pulse. Think of it this way. The input
pulse is of amplitude A and width W. The output pulse is of amplitude
A and width Y, where Y>W. The energy of the output is greater than
that of the input, hence my reference to Parseval.
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Wed, 1 Sep 2010 18:04:58 -0700 (PDT), "m...@sushi.com"
m...@sushi.com> wrote:
On Sep 1, 4:15 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Tue, 31 Aug 2010 21:44:07 -0700 (PDT), "m...@sushi.com"
m...@sushi.com> wrote:
On Aug 31, 9:29 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
Why wouldn't you just stretch the pulses with logic circuits? Your
delay element would be a string of inverters.
It has to be analog and linear. Downstream will be amplifiers and
comparators, as noted.
Another possibility is two cascaded Bessel filters. The first shapes
the 2 ns pulse into, say, a 6 ns gaussian pulse, and the second pretty
much just delays that. The sum of the filter outputs will be pretty
much flat and will settle out fast.
John
John
I claim pulse stretching is not a linear operation.
What I want to do certainly is. A passive LC filter is linear. The
output is strictly proportional to the input.
John
Then you are not stretching the pulse. Think of it this way. The input
pulse is of amplitude A and width W. The output pulse is of amplitude
A and width Y, where Y>W. The energy of the output is greater than
that of the input, hence my reference to Parseval.
Why would the output amplitude be unchanged? That's your assumption,
not mine. COE is meaningless here anyhow, since the network, even if
passive, even if the output amplitude is unchanged, could impedance
scale. Voltage is not energy.
Quote:
Oh, eh yeah, QED.
By your reasoning, any lowpass filter (which my stretcher is) is
nonlinear. And a coaxial cable must be nonlinear. Only a Brickenbox
network is linear.
I guess you have your own working definition of "nonlinear", which
isn't the one they taught us in engineering school.
We thought a network was linear if the output scales exactly with the
amplitude of the input.
John
Bill Sloman
Guest
Guest
Thu Sep 02, 2010 4:53 pm
On Sep 2, 8:39 pm, brent <buleg...@columbus.rr.com> wrote:
Quote:
On Sep 1, 1:06 am, Bill Sloman <bill.slo...@ieee.org> wrote:
An infinitely long FIR filter, for one.
Isn't that an oxymoron?
An infinitely long FIR filter, for one.
Isn't that an oxymoron?
Absolutely. A rectangular pulse response is equally unattainable.
--
Bill Sloman, Nijmegen
Bill Sloman
Guest
Guest
Thu Sep 02, 2010 5:02 pm
On Sep 2, 3:39 pm, whit3rd <whit...@gmail.com> wrote:
Quote:
On Sep 1, 7:24 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
The bad news is that few people still make analog delay lines, and
they want 4 weeks to come up with a sample. I don't have 4 weeks. So
either I make my own tapped LC delay line from parts, or try cascading
and summing Bessel filters.
For 5 ns, you need about five feet of twinlead or coax cable to make a
delay line.
Probably there's a way to get it without a four week wait.
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
The bad news is that few people still make analog delay lines, and
they want 4 weeks to come up with a sample. I don't have 4 weeks. So
either I make my own tapped LC delay line from parts, or try cascading
and summing Bessel filters.
For 5 ns, you need about five feet of twinlead or coax cable to make a
delay line.
Probably there's a way to get it without a four week wait.
The propagation delay of light in air (or vacuum) is about 1nsec per
foot. The propagation delay in the dielelctric of coaxial cable is
slower, at about 1.5nsec per foot. You can get 1.1mm OD teflon
dielecric minature coax, and three feet of that can be coiled into a
reasonably compact bundle (and I've used that as a delay line).
Twisted pair is going to have a mixed dielectric and experiment would
seem to be called for. Twisted transformer wire - with enamel
insulation - makes a remarkably compact transmission line, but I've no
idea of the propagation delay, beyond that it too has a mixed
dielectric (air plus enamel).
<snip>
--
Bill Sloman, Nijmegen
John Larkin
Guest
Guest
Thu Sep 02, 2010 5:07 pm
On Thu, 2 Sep 2010 06:53:29 -0700 (PDT), Bill Sloman
<bill.sloman_at_ieee.org> wrote:
Quote:
On Sep 2, 8:39 pm, brent <buleg...@columbus.rr.com> wrote:
On Sep 1, 1:06 am, Bill Sloman <bill.slo...@ieee.org> wrote:
An infinitely long FIR filter, for one.
Isn't that an oxymoron?
Absolutely. A rectangular pulse response is equally unattainable.
On Sep 1, 1:06 am, Bill Sloman <bill.slo...@ieee.org> wrote:
An infinitely long FIR filter, for one.
Isn't that an oxymoron?
Absolutely. A rectangular pulse response is equally unattainable.
What about this?
in----+-----delay line------------+
| |
| sum -----integrate----out
| |
+-----------(-1)------------+
Its impulse response is a rectangular pulse and it's linear.
John
tm
Guest
Guest
Thu Sep 02, 2010 5:18 pm
"John Larkin" <jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote in message
news:rakr76tpoiph198ldaiq5uvjpneebuvlbt_at_4ax.com...
Quote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
How about a short piece of transmission line open on the far end. It will
reflect
back with twice the delay and add to the original pulse.
That would double the pulse length.
tm
--- news://freenews.netfront.net/ - complaints: news_at_netfront.net ---
Richard Henry
Guest
Guest
Thu Sep 02, 2010 7:32 pm
On Sep 1, 4:15 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Quote:
On Tue, 31 Aug 2010 21:44:07 -0700 (PDT), "m...@sushi.com"
m...@sushi.com> wrote:
On Aug 31, 9:29 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
Why wouldn't you just stretch the pulses with logic circuits? Your
delay element would be a string of inverters.
It has to be analog and linear. Downstream will be amplifiers and
comparators, as noted.
Another possibility is two cascaded Bessel filters. The first shapes
the 2 ns pulse into, say, a 6 ns gaussian pulse, and the second pretty
much just delays that. The sum of the filter outputs will be pretty
much flat and will settle out fast.
John
John
m...@sushi.com> wrote:
On Aug 31, 9:29 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
Why wouldn't you just stretch the pulses with logic circuits? Your
delay element would be a string of inverters.
It has to be analog and linear. Downstream will be amplifiers and
comparators, as noted.
Another possibility is two cascaded Bessel filters. The first shapes
the 2 ns pulse into, say, a 6 ns gaussian pulse, and the second pretty
much just delays that. The sum of the filter outputs will be pretty
much flat and will settle out fast.
John
John
If the pulses are always the same height and polarity, there is no
need for such complexity.
John Larkin
Guest
Guest
Thu Sep 02, 2010 7:49 pm
On Thu, 2 Sep 2010 12:18:08 -0400, "tm" <the_obamunist_at_whitehouse.gov>
wrote:
Quote:
"John Larkin" <jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote in message
news:rakr76tpoiph198ldaiq5uvjpneebuvlbt_at_4ax.com...
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
How about a short piece of transmission line open on the far end. It will
reflect
back with twice the delay and add to the original pulse.
That would double the pulse length.
tm
That almost works.
I think this works:
input----50r-----+-------integrator----out
|
|
|
|
| 50r transmission
| line
|
|
gnd
It has the ideal transfer function, impulse in and rectangular pulse
out.
John
Quote:
--- news://freenews.netfront.net/ - complaints: news_at_netfront.net ---
John Larkin
Guest
Guest
Thu Sep 02, 2010 7:52 pm
On Thu, 2 Sep 2010 09:32:53 -0700 (PDT), Richard Henry
<pomerado_at_hotmail.com> wrote:
Quote:
On Sep 1, 4:15 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Tue, 31 Aug 2010 21:44:07 -0700 (PDT), "m...@sushi.com"
m...@sushi.com> wrote:
On Aug 31, 9:29 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
Why wouldn't you just stretch the pulses with logic circuits? Your
delay element would be a string of inverters.
It has to be analog and linear. Downstream will be amplifiers and
comparators, as noted.
Another possibility is two cascaded Bessel filters. The first shapes
the 2 ns pulse into, say, a 6 ns gaussian pulse, and the second pretty
much just delays that. The sum of the filter outputs will be pretty
much flat and will settle out fast.
John
John
If the pulses are always the same height and polarity, there is no
need for such complexity.
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Tue, 31 Aug 2010 21:44:07 -0700 (PDT), "m...@sushi.com"
m...@sushi.com> wrote:
On Aug 31, 9:29 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
I'm expecting to get some photodiode pulses that are just a bit too
fast to handle with cheapish amps and comparators and such. It would
be nice to have an analog filter that would accept a roughly gaussian
pulse, maybe 2 ns wide, and stretch it to, say, 5 or 6 ns wide,
substantially flat on top if possible. Rep-rate might go up to 40 MHz
maybe.
An LC phase-linear lowpass filter with a reasonable number of poles
would make a slower sorta gaussian blip, not very flat, with a
substantial tail, which would limit my rep-rate to some extent.
If I run the pulse through a tapped analog delay line, maybe five 1 ns
taps, and sum the signals that appears at each tap, I can get a pretty
flat pulse. That amounts to a FIR/transversal filter with all
coefficients = 1, tweakable a little maybe. That's OK if I can get and
afford such a delay line and can sum the tap signals without great
hassles.
We were playing around with using a 3 or maybe 5 pole LC lowpass
filter, but summing the signals from intermediate nodes, instead of
just taking the last one. This looks promising but mathematically
messy to do really well, a "lost in space" situation maybe. A filter
that makes a beautiful output pulse can have some ghastly intermediate
waveforms.
Any ideas? What sort of filter has a rectangular-pulse impulse
response?
John
Why wouldn't you just stretch the pulses with logic circuits? Your
delay element would be a string of inverters.
It has to be analog and linear. Downstream will be amplifiers and
comparators, as noted.
Another possibility is two cascaded Bessel filters. The first shapes
the 2 ns pulse into, say, a 6 ns gaussian pulse, and the second pretty
much just delays that. The sum of the filter outputs will be pretty
much flat and will settle out fast.
John
John
If the pulses are always the same height and polarity, there is no
need for such complexity.
If the pulses were always the same height, I wouldn't have to measure
them.
John
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