The figure shows a MOSFET differential amplifier with an active load. Transistors $m_1$ and $m_2$ are n – channel devices and form the differential pair based with $i_q$ the load circuit consists of transistors $m_3$ and $m_4$, both p-channel devices, connected in a current mirror configuration. A one sided o/p is taken from the common drain of $m_2$ and $m_4$ when a common mode voltage of $v_1$ = $v_2$ = vcm is applied, the current IQ splits evenly between $m_1$ $m_2$ and $id_1$ = IQ/2 There is no gate current.

$\therefore$ i $d_3$ = i $d_1$ and i $d_4$ = i$d_2$

MOSFET differential amplifier with active load.