In the circuit shown below, the transistors $M_{1}$ and $M_{2}$ are biased in saturation. Their small signal transconductances are $g_{m 1}$ and $g_{m 2}$ respectively. Neglect body effect, channel length modulation and intrinsic device capacitances.
Assuming that capacitor $C_{1}$ is a short circuit for $\mathrm{AC}$ analysis, the exact magnitude of small signal voltage gain $\left|\frac{v_{\text {out }}}{v_{\text {in }}}\right|$ is
- $g_{m 2} R_{D}$
- $\frac{g_{m 2} R_{D}\left(R_{B}+\frac{1}{g_{m 1}}\right)}{R_{B}+\frac{1}{g_{m 1}}+R_{s}}$
- $\frac{g_{m 2} R_{D}\left(R_{B}+\frac{1}{g_{m 1}}+R_{s}\right)}{R_{B}+\frac{1}{g_{m 1}}}$
- $\frac{g_{m 2} R_{D}\left(\frac{1}{g_{m 1}}\right)}{\frac{1}{g_{m 1}}+R_{s}}$