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TINA/Spice/OPA860: Difference in gain when I change frequency range in TINA AC analysis

user3925438
Prodigy 110 points
Part Number: OPA860
Other Parts Discussed in Thread: TINA-TI

Tool/software: TINA-TI or Spice Models

Hi all 

I am doing an AC analysis as my attached file. 

For frequency range: 4.95MEG - 5.15MEG, I got a peak gain ~ 8dB 

However, for frequency range: 4MEG - 7MEGSUNNY OPA 860-No Diode.TSC, I got a peak gain ~1dB. 

I am so confused why I got this difference. 

Any one please helps me to clear this 

Thanks in advanced.

  • 0
    TI__Genius 9775 points
    Hi,

    It seems it has something to do with the inductor and capacitor network that you put in your schematic.

    What do you try to do here? Do you try to create bandpass filter or other type of circuit?

    Herman
  • 0 in reply to Herman Theodorus
    Prodigy 110 points
    Hello Herman
    thanks for feedbacks.
    Yes. I try to create a bandpass filter with LC tank.
    But i do not know why circuit gain was change when I change the frequency range ?
    Could you plz give some opinions about my situation.
    Best regards
  • 0 in reply to user3925438
    TI__Genius 9775 points
    Hi,

    It's the nature of bandpass filter especially LC tank. LC tank has a high Q resonant where it has high peak and smaller bandwidth around that peak that can maintain about the same gain. This is why when you try to sweep it across frequency, the gain quickly drops off.

    You need to see your equations of the LC tank so that you can get lower Q resonant which will translates to lower peak and wider bandwidth. In this kind of situation, don't try to do trial and error of changing the component values, but work out your circuit mathematics and then change the values accordingly. It will be much easier that way.

    Herman