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TINA/Spice/LF353: Simulation of 2 cascaded integrators

Part Number: LF353
Other Parts Discussed in Thread: TINA-TI

Tool/software: TINA-TI or Spice Models

Hello,

I'd like to simulate 2 cascaded integrators inTINA with an ac-simulation (picture shows schematic). The attached bode plot shows the transfer function after the first stage and after the second.

The result suprises me,  because the gain at low frequencies, like  1 Hz, isn't doubled. Is there anything wrong with my simulation?

Thanks in advance!

Alexander

CascadedIntegratorsLF353.TSC

  • Hi Alexander,

    When I ran simulation on your attached test bench, the dc output is railed hitting the maximum or minimum output range of the amplifier.

    To be able to run ac simulation (small signal analysis), we need to stabilize the output so that it will be ideally around it's mid range.

    Since you are using the opamp as pure integrator, it will be difficult to put resistor on the feedback path. So an alternative for ac analysis in this case is by putting high value inductor of 1 Tera H so that at 0 Hz it will be like a dc short stabilizing the dc operating point of the output, but at other frequencies it will be like open circuit on the feedback path.

    Hope it helps.

    Attached:

    CascadedIntegratorsLF353_Debug2.TSC

    Herman