INA819: Simulation of two INA819 in series fails

Patrik Rusterholz

Part Number: INA819

Hi
I would like to connect two INA819 amplifiers in series to achieve high bandwidth and high gain. Attached is the Tina simulation.

Side notes:
R3 and R5 put some load on the OpAmps. I thought at best this was necessary. But it doesn't seem to change anything.
The gain is set to about 28.7 for each OpAmp.

If there is no connection between the two INAs, everything works as expected. However, the series connection leads to distortions in the simulation. Is this just simulation artefacts or a problem? Solutions?
It seems the simulation is somewhat unstable anyway. If I add low-pass filters, I often get convergence errors.

Your help is much appreciated.

Thanks and best regards

PatrikINA819_Offset_v1.TSC

over 1 year ago

+1 Marek Lis over 1 year ago

TI__Guru 64140 points

Patrik,

That is correct - the resistive loading does not effect the gain unless resulting the output current exceeds the short-circuit limit.

In AC simulation I see expected -3dB and -6dB bandwidth of around 1MHz - similar what datasheet shows (see below).

As far as 'distortion' of the cascaded INA819's, I believe they are transient simulation artifacts - see below.

0 Patrik Rusterholz over 1 year ago in reply to Marek Lis

Prodigy 10 points

Hi Marek
Thanks for your fast help! Great job!

Best regards
Patrik

0 Marek Lis over 1 year ago in reply to Patrik Rusterholz

TI__Guru 64140 points

No problem. Running discrete transient simulation using ideal op amps shows all nodes operating in linear region well within the supply voltage - see below.

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INA819: Simulation of two INA819 in series fails