Bootstrapped bias mixer with soft start POR

摘要

A biasing circuit is arranged to provide relatively well controlled startup and steady state behavior for a reference circuit such as noise immunity and reduced dependence on supplies. The biasing circuit initially employs an independent bias current for biasing the reference circuit at startup until a large enough bootstrapped (output voltage referenced) bias current can be generated that can take over the subsequent biasing of the circuit in the steady state. In one embodiment, a Power On Reset (POR) signal can be generated during the transition from an initial biasing of the reference circuit by the independent bias current to a subsequent steady state biasing provided by the bootstrapped bias current. Also, the assertion of the POR signal can be employed to turn off the transistors providing the independent bias current.