Current shutdown circuit for active bias circuit having process variation compensation

Abstract

An integrated circuit biasing network for producing .a.predetermined level of bias current. The bias network includes a field-effect transistor having a gate, a source and a drain. The transistor produces a level of bias current corresponding to a predetermined input gate-source voltage applied to the field effect transistor. A control circuit is provided. The control circuit is connected to the field effect transistor and provides a current through a control current path to produce the field effect transistor input voltage. A compensation circuit is connected to the control circuit. The compensation circuit includes a compensation transistor of the same type as the field effect transistor. The compensation circuit operates the compensation transistor to divert current from said control path whereby process variations cause the compensation transistor to draw a current of a magnitude to provide an input voltage to the field effect transistor to enable such field effect transistor to produce said predetermined level of bias current. A transistor switch is provided having a first and second electrode. Conductivity between such first and second electrodes is controlled by an “on”/“off” control signal fed to a control electrode of such transistor switch. One of such first and second electrodes is coupled to the gate of the field effect transistor and the other one of the first and second electrodes is coupled to a predetermined reference potential. The transistor switch is placed in a conductive condition by the “on”/“off ” control signal to couple the gate of the field effect transistor to such reference potential during an “off” condition of the control signal. Such coupling to the reference potential turns the field effect transistor to a non-conducting state during such “off” condition. The transistor switch is placed in a non-conductive condition to de-couple the gate of the field effect transistor from such reference potential during an “on” condition of the control signal to enable the field effect transistor to amplify a signal fed to the gate thereof during such “on” condition. The reference potential is coupled to the control circuit. The field effect transistor, the compensation transistor and the transistor switch are depletion mode field effect transistors. The compensation circuit is coupled between a second reference potential and the first-mentioned reference potential.