An amplifier having an input stage with inverting and non-inverting input terminals, a voltage amplifier stage with relay terminals and being operatively connected to the input stage, a SEPP output stage with transistors and an output terminal, and a constant-current bias circuit between the relay terminals...http://www.google.de/patents/US5049834?utm_source=gb-gplus-sharePatent US5049834 - Amplifier having a constant-current bias circuit
