Differential output amplifier input stage with rail-to-rail common mode input range

An amplifier having a rail-to-rail common mode input range, comprising:

• a differential input stage;
• a differential output stage having first and second current paths;
• first and second current mirror input circuits respectively connected in parallel with said first and second current paths in said differential output stage to duplicate the differential output of said differential output stage;
• a circuit for detecting a common-mode voltage difference between nodes of said first and second current mirror input circuits for developing a current related to said common-mode voltage difference;
• and
• a current mirror output circuit connected to receive said current related to said common-mode voltage difference for controlling the current in said first and second current paths in said differential output stage.

A bipolar differential amplifier having a rail-to-rail common mode input range, comprising:

• a differential input stage including first and second pairs of complementary bipolar transistors, each pair receiving a respective differential input, and first and second input stage current sources to bias transistors of respective first and second conductivity types;
• a differential output stage including third and fourth pairs of complementary transistors, the transistors of each pair respectively providing said first and second output current paths;
• first and second output stage current sources connected to provide current respectively to said first and second output current paths;
• fifth and sixth pairs of complementary transistors, respectively connected in parallel with said third and fourth pairs of complementary transistors in said differential output stage to duplicate the current of said first and second output current paths;
• a circuit for detecting a common-mode voltage difference between nodes between transistors of said fifth and sixth pairs of complementary transistors;
• and
• a current mirror circuit connected to receive said detected common-mode voltage difference for controlling the common mode currents in said first and second current paths in said differential output stage.