• Resolved

TINA/Spice/OPA860: Mismatch between Transient and AC analysis of OPA860

Prodigy 90 points

Replies: 4

Views: 88

Part Number: OPA860

Tool/software: TINA-TI or Spice Models

Hello all 

I have problem of OPA860 response in Transient and AC analysis. 

In particular, the Gain ~ 2 V/V at f = 16,250,440 Hz as indicated in AC analysis. 

However, when I did a Transient analysis ( Vsin = 16,025,440, 100mV ), the AC output voltage ~ 10mV.

Could anyone please help me to fix this problem ? 

16MHz_OPA_Remove C0.TSC

AC Analysis result

Transient Analysis result

  • Hello user3925438,

    When running an AC simulation, TINA runs a "small-signal" analysis in order to provide an appropriate response. The AC analysis does not account for changes in bias points or any slew limitations in the circuit outside of the initial DC bias. You will see different results if you significantly lower the amplitude of your AC signal. What is it that you are trying to achieve?

    Best,
    Hasan Babiker
  • In reply to Hasan Babiker31:

    Hello Hasan Babiker

    I am clear now. Even if i still want to apply large input voltage ( ~400mV). Is there any way for this ?

    thank you.
  • In reply to user3925438:

    Hello,

    What is it that you are trying to achieve? An active bandpass filter using an amplifier may be more suited for your design.

    Best,
    Hasan Babiker
  • Hi,

    the L1/C1/R7 resonance in your simulation is much too sharp. With the standard settings TINA-TI isn't capable to run the transient analysis precisely enough to exactly hit the resonance. Another issue is that you should allow the output signal to settle. Remember: Sharp resonance = Long settling time!

    I have broadened the resonance by modifying L1 and C1. Now the transient analysis looks much better. But the resonance frequency of transient analysis 16.118MHz still doesn't fit the resonance frequency of AC analysis (16.25MHz) and the gain is incorrect either:

    opa860.TSC

    You could try to modify the analysis parameters to increase the precision of simulation. But I guess TINA-TI is not designed to run such sharp resonances.

    Kai