Patent ID: 7737784
Filing Date: 2010-06-15
Classification: H03F

Abstract:
1. An amplifier output stage for operating from a positive rail and an amplifier ground rail, comprising: first pull-up circuitry and second pull-down circuitry coupled to an output stage output; the first pull-up circuitry being coupled to the positive rail through third circuitry, and the second pull-down circuitry being coupled to the amplifier ground rail through fourth circuitry; the fourth circuitry being configured to gradually turn off current to the pull-down circuitry when the output stage output approaches a voltage of the amplifier ground rail from a positive voltage relative to the amplifier ground rail, and to turn off current to the pull-down circuitry before the output stage output reaches a voltage of the amplifier ground rail; the third circuitry, including amplification, coupled to the pull-up circuitry to gradually turn off current to the pull-up circuitry responsive to an input to the output stage to maintain output stage gain at progressively lower output stage outputs as the output stage output is approaching the voltage of the ground reference, and to turn off current to the pull-up circuitry responsive to a corresponding input to the output stage to allow an output stage output voltage equal to that of a ground reference that is less than the amplifier ground rail; whereby the amplifier has a self configuring output stage operable with either a mid-rail or ground reference that may be below the amplifier ground rail.