THE DESIGN OF TETRODE TRANSISTOR AMPLIFIERS 821 



The output power can be readily evaluated in terms of L and M. 



h = /l/i21 + ^2/i22 (9) 



/2 = (1 + mn + (L + jM)h,, tM (10) 



I Powerout = Po = fl«(-^2/!) (11) 



^ ^^ [- (L -jM)h, ^^ _ , ^ ^j,^ ^^^ (12) 



L 2/i22r 4/i22r J 



'21 r /t2 , tit2\ ^21 



|2 



On the basis of (13) the power output plotted as a function of L and 

 M is a paraboloid as shown in Fig. 5, having the pertinent dimensions 

 indicated there. Only within the circle centered at L = 1, ikf = and 

 passing through the origin does one obtain positive power output. The 

 apex of the paraboloid corresponds to 



P, = P,„ = IM (14) 



4/i22r 



The input power can similarly be evaluated in terms of L and M. 



El = hhn + E^hn (15) 



= (1 + jO)hn +{L+ jM) t^ hn (16) 



Power in = Pi = Re[E,h] (17) 



{ — h2^)hn 



Pi = Re 



hn + (L + jM) 



2h 



22r 



(18) 



7 T Ti (^12^2l) , Tirr \h\2h2V f-,rs\ 



= hur - LRe — T — + MIm -— — (19) 



where /m[(/ii2/i2i)/2/i22r] means the imaginary part of the expression in 

 parenthesis. 



On the basis of Eq. 19 the input power plotted as a function of L and 

 M is simply an inclined plane having the properties indicated on Figure 6. 



Since Figures 5 and 6 turn out to be such simple geometrical figures 

 the problem of finding the point of maximum ratio of Po to P, is very 

 simple and other interpretations are easy to make. First, a negative value 

 of Pio{Pi at 1, 0) certainly indicates potential instability for both input 

 and output terminations receive power from the two-port. Even if the 

 plane of P.- intersects the L-M plane within the unit circle centered at 



