Hint: start by looking at the summing junction voltage of a single opamp integrator with R = 50k, C = 330pF.
NB the LT1225 isnt unity gain stable so its use for any of U2, U3 and U4 is questionable. They will all likely oscillate on their own. Bruce > > On 24 February 2018 at 08:45 Bruce Griffiths <[email protected]> > wrote: > > Moin attila > > I'd start with simulating and understanding the integrator in the 34401A, > its a little simpler but still has a coupe of opamps in the integrator. Then > analysing the GBW requirements of the various opamps used in the HP3458A > shoul become somewhat clearer. > > Bruce > > > > > > On 24 February 2018 at 04:51 Attila Kinali <[email protected]> wrote: > > > > Moin, > > > > I am trying to understand how the HP 3458 integrator of its > > dual-slope ADC works, as it's a bit more complicated than > > a simple, single opamp integrator. As you can see from the > > attached picture, it consists of 3 opamps (U1-U3) for the > > integrator itself, and another for the slope amplification (U4). > > Unfortunately, I do not get what U2 and U3 are doing, much less > > why they are needed. > > > > So I tried to simulate it in LTspice. But, the circuit oscillates. > > In both, the reset state (when the integration-C shorting switch is > > closed) > > and the integration state (though, less wildly so). I guess, this > > is because I replaced the LM6361 and AD848 by the LT1225 but do not > > understand why, or respectively, which of the differing parameters > > of > > the LT1225 causes this oscillations. > > > > Would someone be so kind and give me some hints? > > > > Thanks in advance > > > > 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 -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > > > _______________________________________________ > > volt-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > > > > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
