HP3458 ADC integrator
Why do you think that the datasheet is wrong?
Its the same as the 1989 version.
A lot of the early wideband opamps didn't have high open loop gain.
Even the LT1220 only has about 7 - 15x more gain at rated load.
The LT1220 has a a pair of cascaded complementary symmetry emitter followers in its output stage compared to the single complementary symmetry emitter follower output stage of the LM6361.
Bruce
On 24 February 2018 at 11:05 "David C. Partridge" <david.partridge@perdrix.co.uk> wrote:
The datasheet I have found (Natsemi Sept 1995) lists 550 V/V = 0.55 V/mV.
Which I think is a bit low, but then, the opamp is old.
Check other datasheets, that's definitely wrong
David
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- Reverse the supplies on U4 (in real circuit reversed supplies will fry the chip.)
- Add 10k in series with reset switch
- Swap connections to U4 inputs.
- Use series shunt switch for reset switch as used in an actual 3458A.
Once done together with swapping in LT1220 for LT1225 rest works as expected and output slews due to gate current of J1 and input bias current of U1
Bruce
On 24 February 2018 at 10:23 Attila Kinali attila@kinali.ch wrote:
On Fri, 23 Feb 2018 18:48:24 -0000
"David C. Partridge" david.partridge@perdrix.co.uk wrote:
Looking your schematic, I see that you are using LT1225 for both U2 (U111) and U3 (U112)
Why did you use those rather than LM6361 and AD848? Was it just because
LTSpice didn't have models for them? It can make a difference ...
Yes. LTSpice doesn't have an LM6361 or AD848. Linear lists the LT1225
as replacement for LM6361, so I thought this was safe. I deemed the AD848
to be close enough.
But as Bruce mentioned, the LT1225 is not unity gain stable, while the
LM6361 is. That might explain the oscillations.
BTW LM6361 is 550V/mv not .55V (I assume that was a mistake in your post) ...
Slew rates seem a bit different at +/- 15V supply as well.
The datasheet I have found (Natsemi Sept 1995) lists 550 V/V = 0.55 V/mV.
Which I think is a bit low, but then, the opamp is old.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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I eat humble pie - I re-checked the datasheets low limit of 550V/V it is (wow that's really low)
David
-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces@febo.com] On Behalf Of David C. Partridge
Sent: 23 February 2018 22:06
To: 'Discussion of precise voltage measurement'
Subject: Re: [volt-nuts] HP3458 ADC integrator
The datasheet I have found (Natsemi Sept 1995) lists 550 V/V = 0.55 V/mV.
Which I think is a bit low, but then, the opamp is old.
Check other datasheets, that's definitely wrong
David
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On Sat, 24 Feb 2018 12:59:21 +1300 (NZDT)
Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
- Reverse the supplies on U4 (in real circuit reversed supplies will fry the chip.)
- Add 10k in series with reset switch
- Swap connections to U4 inputs.
- Use series shunt switch for reset switch as used in an actual 3458A.
Once done together with swapping in LT1220 for LT1225 rest works as expected and output slews due to gate current of J1 and input bias current of U1
Ok, I played around a bit more and I think I now mostly understand what's
going on. The main problem was really the stability of the opamps chosen.
For the integrator to work, the added up gain and phase shift must still
fulfill the stability condition (obvious, yes, but.. well I am stupid at times)
I am not sure how the intermediate steps in a 3 opamp integrator work,
but I guess that should imediatly be obvious once a complete stability
analyis is done.
Thanks everyone who provided insight and feedback.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
Can you make use of an LM3900? I have one here somewhere.
I think its a quad Norton, not sure how long its been there for.
also have a few canned op-amps etc
-Andre
From: volt-nuts volt-nuts-bounces@febo.com on behalf of Attila Kinali attila@kinali.ch
Sent: 27 February 2018 18:25
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] HP3458 ADC integrator
On Sat, 24 Feb 2018 12:59:21 +1300 (NZDT)
Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
- Reverse the supplies on U4 (in real circuit reversed supplies will fry the chip.)
- Add 10k in series with reset switch
- Swap connections to U4 inputs.
- Use series shunt switch for reset switch as used in an actual 3458A.
Once done together with swapping in LT1220 for LT1225 rest works as expected and output slews due to gate current of J1 and input bias current of U1
Ok, I played around a bit more and I think I now mostly understand what's
going on. The main problem was really the stability of the opamps chosen.
For the integrator to work, the added up gain and phase shift must still
fulfill the stability condition (obvious, yes, but.. well I am stupid at times)
I am not sure how the intermediate steps in a 3 opamp integrator work,
but I guess that should imediatly be obvious once a complete stability
analyis is done.
Thanks everyone who provided insight and feedback.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
volt-nuts mailing list -- volt-nuts@febo.com
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and follow the instructions there.
Hi, is there a guide anywhere on "good bits" to salvage from ancient Panabrickic (tm) GSM phones please?
I found one here, the display is fandango'd but other than that it did turn on very briefly with a "jump start" to its
circa 1998 NiCad pack.
I understand that there are often OCXO and other interesting bits, recall vaguely salvaging some of these from ancient
cell base station boards that got flooded out.
kind regards, -Andre
#include "CTC101.h"
From: volt-nuts volt-nuts-bounces@febo.com on behalf of Andre Andre@Lanoe.net
Sent: 28 February 2018 06:32
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] HP3458 ADC integrator (SPARES)
Can you make use of an LM3900? I have one here somewhere.
I think its a quad Norton, not sure how long its been there for.
also have a few canned op-amps etc
-Andre
From: volt-nuts volt-nuts-bounces@febo.com on behalf of Attila Kinali attila@kinali.ch
Sent: 27 February 2018 18:25
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] HP3458 ADC integrator
On Sat, 24 Feb 2018 12:59:21 +1300 (NZDT)
Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
- Reverse the supplies on U4 (in real circuit reversed supplies will fry the chip.)
- Add 10k in series with reset switch
- Swap connections to U4 inputs.
- Use series shunt switch for reset switch as used in an actual 3458A.
Once done together with swapping in LT1220 for LT1225 rest works as expected and output slews due to gate current of J1 and input bias current of U1
Ok, I played around a bit more and I think I now mostly understand what's
going on. The main problem was really the stability of the opamps chosen.
For the integrator to work, the added up gain and phase shift must still
fulfill the stability condition (obvious, yes, but.. well I am stupid at times)
I am not sure how the intermediate steps in a 3 opamp integrator work,
but I guess that should imediatly be obvious once a complete stability
analyis is done.
Thanks everyone who provided insight and feedback.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
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On Wed, 28 Feb 2018 06:32:58 +0000
Andre Andre@Lanoe.net wrote:
Can you make use of an LM3900? I have one here somewhere.
I think its a quad Norton, not sure how long its been there for.
Theoretically yes, in practice you are better off using an opamp
that is not 40 years old and not as quirky as a Norton opamp.
You can buy standard bipolar opamps that beat those old beats
at all metrics, and they only cost little more, if at all.
The only place where these beasts really excell is that the
inputs are basically independent of the supply voltage, given
the maximum input current is not exceeded. Linear has a few
opamps that can do the same trick (though in a slightly different
manner), but they also cost a bit more.
Attila Kinali
--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
Attila wrote:
Theoretically yes, in practice you are better off using an opamp
that is not 40 years old and not as quirky as a Norton opamp.
They are also perhaps the noisiest op-amps ever marketed. They invite
one to add the missing PNP differential input pair externally, but even
this is very disappointing due to the extremely low internal currents in
the 3900. Of course, this also makes them very slow.
There is one semi-clever trick 3900s will play -- with one section and
no diodes, you can make a half-wave rectifier, and with three sections
and no diodes, you can make a full-wave rectifier (the Tracor 900A uses
them this way). But again, extremely, miserably, intolerably noisy.
Best regards,
Charles
Hi, also have three AD623(?) IA's I purchased for a heart rate monitor.
Can find them as and when needed, pretty sure they are the ones featured in the Hackaday article.
At the time if the ECG worked the same circuit would get cloned and used for an EEG as the signals are a lot smaller but
in this case I'd use a Pi Zero or Arduino as the input as its already got onboard A-D's.
For this project the isolation requirements are insane, 0.1mA permitted leakage means you're limited to battery power and
even wireless charging is verboten. One big problem is the brain really does not like excess electricity, permanent damage is
quite likely even with careless use of a TENS machine etc.
Its feasible to use EM sensors based on old atomic clock "cores" to measure brain magnetic fields (maybe thats what DOC BROWN used)
but try getting more than one of them or disciplining them in the presence of Earth's magnetic field to make measurements.
Alas this project is going to have to wait until technology radically improves, as all the SQUID sensors I've run into use liquid helium and there are very few ways to get a piece of niobium-titanium that cold even using laser cooling and Linde refrigerators etc.
Ironically this is the main reason why quantum computers suchnas D-wave 2 or the IBM one are so heinously £xpen$iv£ as they need to get down to millikelvins so sit upside-down in the LHe vat with all the sensors far away from that little chip.
-A
From: volt-nuts volt-nuts-bounces@febo.com on behalf of Attila Kinali attila@kinali.ch
Sent: 01 March 2018 19:57
To: Discussion of precise voltage measurement
Subject: [volt-nuts] LM3900 (was: HP3458 ADC integrator)
On Wed, 28 Feb 2018 06:32:58 +0000
Andre Andre@Lanoe.net wrote:
Can you make use of an LM3900? I have one here somewhere.
I think its a quad Norton, not sure how long its been there for.
Theoretically yes, in practice you are better off using an opamp
that is not 40 years old and not as quirky as a Norton opamp.
You can buy standard bipolar opamps that beat those old beats
at all metrics, and they only cost little more, if at all.
The only place where these beasts really excell is that the
inputs are basically independent of the supply voltage, given
the maximum input current is not exceeded. Linear has a few
opamps that can do the same trick (though in a slightly different
manner), but they also cost a bit more.
Attila Kinali
--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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