THE DESIGN OF TETRODE TRANSISTOR AMPLIFIERS 815 



determines the potentialities of amplifiers employing the transistor and 

 designs a suitable amplifier circuit. This step in^'olves answering two 

 (luestions: What performance, maximum power gain for instance, is it 

 possible to obtain? What source and loatl impedances should the tran- 

 sistor be associated with? 



Two-Port Parameters of Transistors 



For circuit applications, the two-port parameters are the most con- 

 venient for characterization of the transistor. These parameters implicitly 

 but completely characterize the device from the performance standpoint. 



Four sets of two-port parameters are illustrated in Fig. 1. Any set can 

 be calculated from any other set, and the choice of the set to employ is 

 determined only by convenience in the use of available measuring eciuip- 

 ment and the preference of the designer. The relationships between 

 parameters, input and output impedances, voltage and current ratios 

 are summarized on Fig. 1. The same expressions given there for /i's can 

 be used for any parameter set so long as one uses the corresponding 

 quantities applicable to the desired parameter set. 



Though the transistor can be operated as an amplifier with the base, 

 emitter or collector common between the input and output terminal 

 pairs, the two-port parameters for any of the connections can be used 

 to calculate the parameters for any other connection. 



For determination of the two-port parameters of tetrode transistors, 

 R. L. Wallace suggested the use of two-terminal impedance measure- 

 ments with subsec^uent calculation of the two-port parameters of in- 

 terest from these. The impedances indicated in Fig. 2 have proved 

 simple to measure at typical operating points with conventional high- 

 : frecjuency bridges. These impedances have been measured at a set of 

 frequencies extending to 30 mc. Because of the number of transistors 

 measured it has been economical to program a digital computer to cal- 

 culate two-port parameters and other ciuantities of interest from the 

 measured two-terminal impedances. 



THE RELATIONSHIPS OF TRANSISTOR PARAMETERS TO AMPLIFIER PER- 

 FORMANCE 



Any of the sets of two-port parameters implicitly characterize all of 



I the linear properties of the transistor for the range of frequencies for 



which the parameters ha\'e been measured. As mentioned before, it is 



necessary to translate the parameters into answers to the following 



questions. How much amplification can the transistor give at a particular 



