High impedance circuit with four transistors

摘要

The first two transistors (Q1,2) are in differential circuit of a pair type. The third and fourth transistors (Q3,6) serve as emitter follower circuits also working as a DC shifter w.r.t. the differential circuit of the pair type, and as buffer circuits increasing the high impedance of the first two transistors, viewed from the base side of the third and fourth transistors (Q3,4). There is a pair of collector resistors (R1,2), another resistor (R3), and a pair of current source circuits. The third and fourth transistors provide current feedback w.r.t. the resistor.