oscillation of Clapp LC circuit

Discussion in 'Electronic Basics' started by jason, Mar 19, 2005.

1. Hello All

I am studying about Clapp LC oscillator.
Given below link is the circuit of interests
http://www.geocities.com/jason_class/ClappLC.jpg

May I know how do we calculate by hand if this circuit gonna oscillate
or not?

I learnt in lecture that I must find Av multiply by beta(feedback
factor). Av is always given by gm multiply by R efficient , which is
gmReff
Reff is the sum of series and parallel resistances of all emitter
resistance, ac emitter resistance , load resistance and also reflected
resistances from the tap of capacitors. Emitter is mentioned here
because I learnt about bipolar transistor configuration.

For the circuit in the link given, I do not understand why the same
approach is use?
Why we can use gmReff as the Av since it is a common drain
configuration? Is it because we have already sum all the net
resistances in Reff , therefore we can use gmReff as the Av?

So for other type of configuration of mosfet such as common gate and
common source? We can use the same Av=gmReff ?
If possible show me the correct way of checking if the circuit can
oscillate by manual calculation..at least the steps or methodology.  