MOSFET Half-Supply Voltage To Current Converter

Q1 and Q2 form a half-supply voltage generator (refer to the circuit MOSFET Half-Supply Voltage Generator). In this circuit Q1 and Q2 are identical so the voltage at the gate/drain of Q2 is ½ of the supply voltage. The voltage at the gate/drain of Q2 is also applied to the gate of Q3 so these two MOSFETs form a current mirror.