Low voltage regulator having power down switch

Claim 1

A voltage regulator integrated circuit for high speed and high frequency applications comprising: an input terminal for receiving an unregulated voltage; an output terminal for receiving a regulated voltage; a circuit ground terminal; a first field effect transistor interconnecting said input terminal and said output terminal; a bias circuit for biasing said first field effect transistor to maintain conductance thereof and regulate a voltage on said output terminal, said bias circuit including first and second resistors serially connected between said output terminal and said circuit ground terminal and having a common terminal; a heterolunction bipolar transistor serially connected between said first field effect transistor and said circuit ground terminal and having a base region coupled to said common terminal and thereby establishing a bias voltage for said first field effect transistor; said field effect transistor and said heterojunction bipolar transistor comprising an integrated device in a unitary structure wherein said unitary structure comprises a III-V semiconductor substrate, an N+ doped subcollector region formed in said substrate, an N doped collector region formed in said N+ doped subcollector region and abutting a surface of said substrate, a P+ doped layer of III-V semiconductor material formed on said surface overlying said N doped collector region, an N doped layer overlying said P+ doped layer, and first and second spaced layers of N+ doped material overlying said N doped layer, said N doped layer functioning as an emitter of said heterojunction bipolar transistor and a channel region of said field effect transistor, and a third resistor connecting said input terminal to a common terminal of said first field effect transistor and said bipolar transistor.