DUALITY AS GUIDE IN TRANSISTOR CIRCUIT DESIGN 



395 



since the gyrator gives a phase reversal or not, depending on the direction 

 of transmission, a transistor plus two gyxators can be made the equivalent 

 of a vacuum tube triode by pohng the gyrators in such a way as to take 

 care of the phase reversal. 



Ideal gyrators are not yet available but passive circuit elements having 

 very similar properties over a narrow frequency range are available and 

 are used in certain vacuum tube circuits. A quarter-wave line or its lumped- 

 constant equivalent (which amounts to a full section of low- or high-pass 

 filter) has the property of impedance inversion at a single frequency. Instead 

 of giving zero or 180° phase change as does the ideal gyrator discussed 

 above, this single frequency gyrator can be designed to give either -|-90° 

 or —90° phase change. In either case, the phase shift is independent of the 



+ eci 



.'I/-.. 





1-624 ' .i.e2 



eu'^Li Ves: 



ki' 



/pi 



Cl-E, = 

 Ei + eL-ea-eR=o 

 Vg2 - ep = 



-Lci-Lc'-Ii =0 



I, + Ic'- Ll,'- Ir'= 

 -i.e2-i-R= 

 eL= ec Lc'= Ll' 



Lpi + Ici + Lu + i-c = -Vci + eu'H- ec'+ Bl' = o 



lg2 + i-R - Ici = (a) -Ve2 + eR/-eu'= 



Fig. 4 — A tuned amplifier stage and the transistor dual. 



(b) 



direction of transmission. This leads to the possibility of exchanging a 

 transistor for a vacuum tube plus two quarter wave lines. An application 

 of this sort will be discussed in a later section. 



The Dual or an Amplifier with Shunt Tuned Interstage 



Figure 4(a) shows a vacuum tube amplifier with the Kirchoff equations 

 which apply to it. Figure 4(b) shows the transformed equations and a transis- 

 tor circuit which satisfies them. 



The ideal transformer in this circuit has no effect on any aspect of the 

 circuit performance except the phase of the output and, if this is not impor- 

 tant, the transformer may be left out. The curved arrows represent constant 

 current suppUes. All the element values in the transistor circuit may be 



