# Working out ICopy from a current mirror [Mosfet]

I'm trying to solve for $I_{copy}$, but I've looked around on the internet and cannot find an explanation. However, I know the formula:

$I_{copy} =\frac{I_{REF} * W_1/L_1}{W_{REF}/L_{REF}}$

but don't understand how to work this out from the circuit diagram.

Attached is an image explanation my problem. Answer for:

• The circuit on the left: $I_{copy}=\frac{2}{8I_{REF}}$

• The circuit on the right: $I_{copy}= 7I_{REF}$

## 1 Answer

Your formula is for one current mirror. You could use it to determine the current through the NMOS marked 2(W/L)n in the left circuit.

That current would then be 2/3 * Iref.

That same current is fed into a 2nd current mirror, the one with 2 PMOS transistors. Use the same formula again but note what the input current is: 2/3 Iref

The right schematic is slightly more complex but using the formula you can determine the currents through the NMOS marked 5(W/L)n and 3(W/L)n.

Then again solve the currents in the PMOS mirror.

At the output what happens to those 2 currents? Use the current law if you must.