Some Circuit Aspects of the Transistor

n p H E p u r p o s e o f this n o t e i s t o discuss i n a general w a y some circuit aspects of the transistor. It is r a t h e r interesting t h a t in order to discuss its circuit aspects, little direct reference to t h e t r a n s i s t o r is necessary. O n e needs only certain properties of the transistor which are empirically obtainable by m e a s u r e m e n t ; these properties t h e n d e t e r m i n e b e h a v i o r in t h e m a n n e r prescribed by t h e m e t h o d s of general n e t w o r k theory. In principle, one needs no knowledge of the physics of t h e transistor in order to t r e a t it circuitwise; a n y " b l a c k b o x " with t h e same electrical b e h a v i o r a t its t e r m inals would act the s a m e way. I t i s r a t h e r f o r t u n a t e for our purposes t h a t t h e p r o b l e m does s e p a r a t e nicely in this w a y . T h e o p e r a t i o n of t h e t r a n s i s t o r is reasonably well u n d e r stood; b u t , for calculations of p e r f o r m a n c e f r o m physical properties, t h e numerical p a r a m e t e r s needed are s o m e w h a t inaccessible, n u m e r o u s a n d complicated. T h e p a p e r by Shockley 1 gives some calculations of this k i n d which are illuminating for theoretical u n d e r s t a n d i n g . H o w e v e r , j u s t as w i t h electron tubes, practical engineering calculations o f t e n do n o t need to go b a c k to t h e u l t i m a t e physics. S t a r t i n g f r o m the electrical properties of the transistor as empirically d e t e r m i n e d by m e a s u r e m e n t s on its terminals, we need go only to the literature of electrical engineering to find m u c h practically useful information on properties of circuits which could be built a r o u n d t h e unit.