Voltage at the output/Parallel resistors

[dalarev]

Homework Statement

Reading the voltage taken at the output, Vo.

Homework Equations

Resistors in parallel carry the same voltage.

The Attempt at a Solution

The circuit shown in the diagram, the output is taken directly in parallel with R_o, so shouldn't that mean that:

V_RL = V_RD = V_ro ?

In calculating the output, they combine all those 3 resistors in parallel into R_L', I don't understand why.


In other words, why doesn't V_o = V_RL ?

 

[berkeman]

The output voltage is indeed the voltage across those three parallel resistor components. It doesn't matter if they are drawn as 3 resistors or the equivalent single resistor, unless some individual current is needed for some other part of the model calculation.

 

[rootX]

I might be repeating the above post:

The circuit shown in the diagram, the output is taken directly in parallel with Ro, so shouldn't that mean that:

VRL = VRD = Vro ?

Yes

In calculating the output, they combine all those 3 resistors in parallel into RL', I don't understand why.

You don't know the voltage across either of those three. But the total current passing through all three resistors is g_m*V_gs which is known as I am assuming. You can go solve the circuit in either way: it's a simple circuit with three resistors in parallel and one current source. Simplest possible method is to combine all three ll resistors and find the voltage.