LT Spice simulation

Hi all,

I'm simulating a DC log amplifier (as in AofE p212 fig 4.35) with LT spice, and noticed a few problems.

Firstly my application runs off a 9V battery and therefore requires micro power op amps. I intend to use 9V and 0V for the supply rails of the op amps, and apply a virtual earth point of 0.6V to the base of the transistor, and non-inverting input of op amp. R2 of the non- inverting amplifier is also connected to this virtual earth.

Running through simulations with the micro power op amps I noticed the Chopper amplifiers LTC1047, LTC1049 allow simulation to converge within minutes (although when virtual earth is raised to 0.9V or above there is no convergence). The other op amps don't converge irrespective of virtual earth value? Is this an issue because:

1) I have effectively 2 ground points 2) The type of op amp used 3) LT spice simulator

Is there any features within LT spice that reduce accuracy but improve simulation time? Hope to hear from you soon,



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Do you know how to post your netlist?

John S

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John S

"ozzy" schrieb im Newsbeitrag news:

Hello oozy,

The simulation speed can be often improved with the following command which allows greater tolerance for LTspice to converge.

.options gmin=1e-10 abstol=1e-10 reltol=0.003

The intrinsic defaults are below.

.options gmin=1e-12 abstol=1e-12 reltol=0.001

It's true that the chopper amps sometimes have problems with convergence from my experience. I would try to use another opamp for the simulation.

You can either attach the schematic file (.asc) to your next reply or you can take any text editor to copy the contents of the .asc-file into your next reply. Please do that. I guess somebody can then help you to get it running.

Best regards, Helmut

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Helmut Sennewald

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