Mark Rages wrote:
> Hi,
> 
> The circuit I've attached is a staightforward op-amp amplifier with a
> gain of -10.
> 
> For reasons outside the scope of this question*, I needed to add the
> resistor I've called Ra.
> 
> In the traditional "virtual ground" method of analysis, Ra doesn't
> appear in the gain equation.  I tried Ra=10k in my circuit, and indeed
> it continued to work unchanged.  But I'm pretty sure if I set Ra=0 the
> circuit would stop working!
> 
> To analyze this, I guess I will need a non-ideal op-amp model.  What
> is the important parameter to include?  Finite gain?  Offset voltage?
> 
> Regards,
> Mark
> markrages@gmail
> 
> * Because someone will want to know, it's to limit the voltage swing
> at an analog switch IC (not pictured).
> 

How will Ra limit the voltage swing?

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