Two identical $\text{NMOS}$ transistors $\text{M1}$ and $\text{M2}$ are connected as shown below. $\mathrm{V}_{\text {bias }}$ is chosen so that both transistors are in saturation. The equivalent $g_{m}$ of the pair is defined to be $\frac{\partial I_{\text {out }}}{\partial V_{i}}$ at constant $V_{\text {out }}$.
The equivalent $g_{m}$ of the pair is
- the sum of individual $g_{m}$ 's of the transistors
- the product of individual $g_{m}$ 's of the transistors
- nearly equal to the $g_{m}$ of $\mathrm{Ml}$
- nearly equal to $g_{m} / g_{o}$ of $\mathrm{M} 2$