Low voltage operational amplifier input stage and method

摘要

Low voltage operational amplifier (10) operates in a voltage range of one to eight volts over a temperature range of 0 DEG to 70 DEG centigrade. Op amp input stage (12) uses N-channel depletion-mode MOSFETs to provide amplification of the differential input and maintain constant transconductance. Source follower MOSFET (13) provides unity gain in transferring the AC signal, STAGE-1 OUTPUT, to the base of current sinking transistor (18). Sink control circuit (14) and source control circuit (22) create the base drive current in transistors (18) and (24). Dependent on the input signal the AC signal path on SINK PASS THROUGH signal controls op amp output sink transistor to sink current or through current steering circuit (16) causes SOURCE PASS THROUGH signal controlling op amp output source transistor to source current. An output stage provides approximately fifty milliamps of current drive and is quiescent until the output driver is selected. <IMAGE>