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Stability Simulation: Open loop gain does not cross 0dB

Category: Software
Product Number: LTspice; LTC6268
Software Version: 17.1.6

Hello,

I am designing a transimpedance amplifier for a rangefinder application. I am checking the Op Amp stability through the LTspice simulation. However, the open loop gain does not cross 0dB which is where we check the phase margin. The circuit is the following.

The closer from the 0dB is at 4dB with a phase of 163 degrees. Below are the open loop and phase waveforms.

So, why the open loop gain does not cross 0dB? Is this normal? Is it because of the feedback capacitor?

Thank you in advance.

Best regards,

João Rego

81441.LTC6268_Stability.asc

Parents Reply
  • Hi Joao,

    I checked the LTC6268 if it is really properly modelled for open loop gain by simulating the output impedance and it seems that it is not properly modelled that's why we are not getting the accurate results. The plot below shows the simulated output impedance for gain of 1, 10, and 100. 

    I will raise this to our LTspice team so we could revise the model. Thank you for understanding.

    Regards,

    Mae

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