# Current Mirror - Supply Dependence

I have a question about one of the current mirrors introduced in the "Bandgap References" chapter of Razavi's Design of Analog ICs.

He has this:

My confusion is about Equation 12.1.

I know that for a basic current mirror, $$I_{out} = (W/L)(M_2)/(W/L)(M_1) * I_{ref}$$ is valid.

From the looks of it, he seems to have ignored the voltage drop across R1 and just taken it to be the supply voltage Vdd. Shouldn't there be another term?