hey guys, my 1st attempted thread,

just wondering if anybody could explain in a little detail how a transistor would create harmonics in a circuit. i read up a bit in a john bird text book but cant find a complete answer. any help would be greatly recieved cheers

 

One simple case in which the presence of harmonics would represent an undesirable condition is where a typical common emitter transistor amplifier is driven into cut-off or saturation distortion by excessive input. If the input is a pure sine wave of sufficient amplitude it is possible to imagine the output looking something like a square wave which (as you may be aware) would be "rich" in harmonic content.

 

There are also many intentional situations where harmonic generation is essential in circuit operation - take the case of RF mixers. The attached pdf includes some theory for bipolar transistor harmonic generation in mixer applications. Not sure how deep you want to go into this.

http://rfic.eecs.berkeley.edu/142/pdf/lect19.pdf