In the circuit shown below, the transistors $M_1$ and $M_2$ are biased in saturation.
Their small signal transconductances are $g_{m1}$ and $g_{m2}$ respectively.
Neglect body effect, channel length modulation and intrinsic device capacitances. Assuming that capacitor $C_1$ is a short circuit at the signal frequency, the magnitude of small signal voltage gain $|\frac{v_{out}}{v_{in}}|$ is