13. TRANSISTOR CONFIGURATION SUMMARY TABLE
TRANSISTOR CONFIGURATION COMMON BASE COMMON
COLLECTOR
(EMITTER
FOLLOWER)
COMMON EMITTER
Voltage gain High Low Medium
Current gain Low High Medium
Power gain Low Medium High
Input / output phase relationship 0° 0° 180°
Input resistance Low High Medium
Output resistance High Low Medium
Transistor is considered one of the most important invention of the 20th century replacing the vaccum tubes. Invented at the Bell Labs, United state by John Bardeen, Wesley Brattain and William Shockley in 1947 a transistor is used to amplify signals and acts as a switch in electronic devices
It consists of a lightly doped n type material called the Base which is sandwiched between two heavily doped P type material. Upper p type material is made physically larger so as to handle a large amount of current and this constitutes the collector. The lower semiconductor material constitutes the emitter. This is the basic construction of a pnp type transistor which is usually represented by a round symbol consisting of three terminals with an arrow pointing towards the base in the emitter section signifying that it is a pnp type transistor
Similarly we can have an NPN type transistor as shown in the illustration. In this case the p type material is sandwiched between two N-type material. This is again represented by the round symbol consisting of three terminals with an arrow pointing out of the base in the emitter section signifying that it is an npn-type transistor