Complementary Pair Matching

DC Matching of Complementary BJT Pairs 

The emitter current at which matching is required is set up by adjusting Rb. Current meter M1 indicates this. 

Centre-zero meter M2 now displays the difference between the collector currents of the two transistors. 

The direction of deflection of M2 shows which transistor has the higher hFE. 

If the base-emitter drops can be allowed for, Rb may be calibrated in base current: this is useful information when the matched pair is transferred to a working circuit. (By G. W. Short, in “Wireless World”.)

An application is non-standard current mirrors where complementary (NPN, PNP) transistors are used.