Page "Differential amplifier" Paragraph 14

The long-tailed pair was developed from earlier knowledge of push-pull circuit techniques and measurement bridges.

The earliest circuit that is truly recognizable as a long-tailed pair in its conventional form is given by Matthews ( 1934 ) and the same circuit form appears in a patent submitted by Alan Blumlein in 1936.

By the end of the 1930s the topology was well established and had been described by various authors including Offner ( 1937 ), Schmitt ( 1937 ) and Toennies ( 1938 ) and It was particularly used for detection and measurement of physiological impulses.