I've got quick question about the input resistance for this particular circuit.

The input resistance is looking in from the white node to the right of Rsig right?

Why doesn't his calculations for Rin include that 0.1MΩ resistor as well? Is there a mistake?

Can someone clarify?

 

I do not see any 0.1M Ohm resistor.

 

The .1 ma refers to an unknown current source. Did you mistake it for a resistor?

 

No, the 1M ohm resistor to the right first of the capacitor that couples the signal voltage.

 

Still looking for some clarification on this one. My test is soon!

 

Strictly speaking the 1MΩ should be included - maybe the person who wrote the solution thought it wouldn't change things by that much.

With the 1MΩ included Rin=50.5k||1M=48.07k which is about a 5% change and probably shouldn't be disregarded.

 

Strictly speaking the 1MΩ should be included - maybe the person who wrote the solution thought it wouldn't change things by that much.

With the 1MΩ included Rin=50.5k||1M=48.07k which is about a 5% change and probably shouldn't be disregarded.

Ah so that's the best way to deal with the 1MΩ being in there, find the input resistance to the right of it (say Rib), and combine that in parallel with the 1MΩ to get the actual input resistance(Rin).

Where, Rin = (Rib//1MΩ)

Thank you for clearing this up!