The transistor parameters are: $K_{n1} = K_{n2} = 0.1 mA/V^2, K_{n3} = K_{n4} = 0.3 mA/V^2$ and for all transistors, $\lambda = 0$ and $V_{TN} = 1V$. Determine the maximum range of common-mode input voltage.

The reference current can be determined from,

$I_1 = \dfrac {20 - V_{GS4}}{R_1}$

and from,

$I_1 = K_{N3}(V_{GS4} - V_{TN})^2$

Combining these two equations and substituting the parameter values, we obtain

$9V_{GS4}^2 - 17 V_{GS4} - 11 = 0$

which yields

$V_{GS4} = 2.40V$ and $I_1 = 0.587 mA$

Since …