In the small circuit shown, the enhancement mode $n$-channel $\text{MOSFET}$ is biased in saturation with a transconductance $g_{m}.$ A small signal low-frequency voltage $v_{d}$ injected at the supply terminal results in a small signal voltage fluctuation $v_{o}$ at the output. If the channel length modulation of the $\text{MOSFET}$ is ignored, the small signal gain $v_{o}/v_{d}$ is given by __________
- $\dfrac{-g_{m}R_{o}}{1+g_{m}R_{o}}$
- $\left(g_{m}R_{o}+1\right)^{-1}$
- $\dfrac{-g_{m}R_{o}}{1+2g_{m}R_{o}}$
- $\left(\dfrac{g_{m}R_{o}}{2} + \dfrac{3}{2}\right)^{-1}$