This circuit outputs the maximum (or the minimum) of the four input voltages Vv V2, V3, and V4. Each of these input voltages is in the range 0 to 5 V. The output of the unit is the maximum of Vv V2, V3, and V4 if the control voltage input is 5 V (i.e., logical 1). The output is the minimum of Vv V2, V3, and V4 if the control input is zero. By cascading TV such units, one can select the maximum (or the minimum) of 3N + 1 input voltages.
Thus if k is the number of input voltages, we need [(/c+l)/3] units.