DUALITY AS GUmE IN TRANSISTOR CIRCUIT DESIGN 



397 



a positive half cycle of input current, the collector voltage of the upper tran- 

 sistor goes through a negative half cycle while the collector voltage of the 

 lower transistor remains essentially zero. All the collector voltage swing of 

 the upper transistor is impressed directly on the load because, during this 

 half cycle, the lower transistor serves as a short circuit element in series 

 with the load and with the upper transistor. The next half cycle is, of course, 

 like the first except that the lower tube and the lower transistor assume the 

 active roles. 



It was this circuit which first showed the great advantage which can some- 

 times be achieved through the use of duahty. Using two type A transistors 

 in the circuit of Fig. 6(b), it has been possible to obtain 400 milHwatts of 



Lei 



\ Vei 



I Ve2 



Vc, ! 



A 



VC2 \ 



k2 



(b) 



Fig. 6 — A class B amplifier and the transistor dual. 



audio output with a collector circuit efficiency of 60%. The same two tran- 

 sistors which gave this result could not be made to deliver more than 25 

 milliwatts output when used as grounded base amplifiers in a conventional 

 circuit like that of Fig. 6(a). 



The Dual of a Bridge Stabilized Oscillator 



Figure 7(a) shows the circuit of a bridge stabihzed oscillator due to 

 Meacham,^ in which amplitude stabilization can be achieved through the 

 action of a temperature sensitive resistance Rt which has a positive tem- 



5 The Bridge-Stabilized Oscillator, L. A. Meacham, Proc. LR.E.26, 1938, p. 1278; Bell 

 Sys. Tech. Jl. 17, 1938, p. 574; U. S. Pat. 2,303,485. 



