DUALITY AS GUIDE IN TRANSISTOR CIRCUIT DESIGN 



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carrier harmonics, so also does the circuit of Fig. 9. When these are added 

 the circuit of Fig. 10 is obtained. 



Doherty shows that there are two basic circuit arrangements for obtain- 

 ing the high efficiency hnear amphfier action which he describes. One of them 

 has been discussed above. By starting with Doherty's other arrangement, 



Fig. 9 — The basic circuit of a Doherty-type amplifier using a transistor to replace a vac- 

 uum tube and two impedance inverting networks. 



Fig. 10 — A Doherty-type amplifier in which low level signals are amplified by the tran- 

 sistor alone. 



one arrives at the circuit of Fig. 11. In this case, it is the vacuum tube which 

 operates class B and the transistor which helps to supply the peaks by class 

 C operation. At low input levels the transistor behaves as a short circuit 

 and the vacuum tube works into an impedance just twice the value into 

 which it can deliver maximum power. As the input signal increases above 

 the carrier level the transistor begins to operate, contributing in two ways 



