A circuit and a method for biasing a compound cascode current mirror
(CCCM) that enables high-voltage swing at the output and accurate current
mirroring is presented. The CCCM has mirror transistors and cascode
transistors which may be of a different technology kind. The drain-source
voltage Vds of the mirror transistor on the input leg of the CCCM is held
at a voltage Vov that is generated by the biasing circuit; Vov is the
overdrive voltage of the input mirror transistor of the CCCM and the
value of Vov is maintained by the bias circuit and a feed-back amplifier
such that the mirror transistor remains on the edge of its active region,
over manufacture deviations and tracks even over operational conditions
such as temperature and supply variations. The feed-back amplifier drives
the gates of the cascode transistors and uses its feedback node to hold
the Vds at Vov.