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Ti stability video series question.

wenyue Chuang
Prodigy 40 points

Does anyone know the equation 1/B=1/Vfb?

I've checked Ti precision lab stability video series. I didn't figure out this equation. 

Is this AOL curve by Vo(s)/Vfb(s) ?  Assume this AOL curve is processed by Vo(s)/Vfb(s). It makes sense to me.

  • +1
    TI__Genius 10746 points

    Hello, 

    This is the equivalent feedback diagram for a closed loop amplifier where A is open loop gain, and B is beta (feedback factor)

    In this case, we break the loop at the output of the amplifier, and use a 1V ac signal source defined by Vin. 

    We can define the transfer function of the amplifier as Vout/Vin = AOL/(1+ AOL(B)). Assuming we have a large AOL, the transfer function simplifies to : Vout/Vin = 1/B

    Beta can be calculated as Vfb/Vin With Vin=1V AC, this simplifies in this case to 1/Beta equaling 1/Vfb.

    In other words, the formula listed in the TIPL presentation is simplified as most simulators default to use a 1V AC sine source by default. 

    Please let me know if you have any questions.

    Best,

    Jacob

  • 0 in reply to Jacob Nogaj
    Prodigy 40 points

    Thanks for your information. I got it.

    I think it might be 1V for Vin when reading and it makes sense to me.