BE Multiplier Circuit Working Principle

The forward voltage drop of D1 and D2 in the original ClassAB may be mismatched with the VBE of T1 and T2, resulting in crossover distortion that cannot be completely eliminated or overthrough. in order to be able to arbitrarily adjust the voltage compensated to the two VBEs of T1 and T2, a VBE multiplier circuit is used. (b) In the figure, the VBE of NPN can be considered as a constant 0.7V, the voltage on R4 is equal to VBE, ignoring IB, then I1=I2=VBE/R4, then the voltage on R3 is equal to VBE*(R3/R4), so that the voltages on R3 and R4 are used instead of the voltages of D1 and D2, and by changing the values of R3 and R4, arbitrary voltages are obtained to compensate the VBE of T1 and T2, respectively. and T2 VBE, because the VBE is multiplied by (R3 + R4)/R4 times, so it is called VBE multiplier circuit.