Operational amplifier output stage driven by a single ended gain stage

Claim 1

In an operational amplifier of the type which includes a differential first state, an output circuit having an intput and an output, comprising: a voltage gain transistor having a base electrode coupled to the output of said differential first stage, an emitter adapted to be coupled to a first source of supply voltage, and having a collector; a current source coupled to the collector of said voltage gain transistor and adapted to be coupled to a second source of supply voltage; first means coupled to said collector of said voltage gain transistor and to said output and responsive to current flowing from said current source for establishing a quiescent voltage at said output, said first means including: diode means coupled between said current source and the collector of said voltage gain transistor; a first junction field effect transistor having gate and source electrodes coupled to the collector of said voltage gain transistor and having a drain electrode; a second junction field effect transistor having a gate electrode coupled to the collector of said voltage gain transistor, a source electrode coupled to said output and a drain electrode; and current mirror means coupled between the drain electrode of said first junction field effect transistor and a drain electrode of said second junction field effect transistor; voltage pull-up means coupled between said current source and said output for producing a first output voltage at said output when a first input voltage appears on said base electrode of said voltage gain transistor; and voltage pull-down means coupled to said output and to said first means for producing a second output voltage at said output when a second input voltage is applied to the base electrode of said voltage gain transistor.