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ac spice model for ad8331 vga (AGC feedback stability analysis)

Question asked by quentinw on Jul 25, 2016
Latest reply on Aug 19, 2016 by quentinw

Hello,

I am designing an AGC feedback loop with an AD8331 vga.  The spice model given on your website works with the transient analysis, but I have an issue with the .ac analysis.

 

When I put an AC source on the input pin, the simulation works fine, and I can for example plot the gain for different values of Vgain.

However, when I put an AC source on the gain pin (to observe the phase margin of my feedback loop), the output of the AD8331 stays at -390dB, no matter the conditions.

 

Is there a way to study the AGC loop stability with your model ?

 

Thank you,

Quentin

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