# colpitts oscillator circuit

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#### ymmen

##### Member level 1
how to find the range of inductance for which the circuit will function well in following circuit?

#### FvM

##### Super Moderator
Staff member
Talking about an exact solution, you'll derive the circuit loop gain and determine the L range for that the Barkhausen oscillation condition can be fulfilled. Deriving the exact loop gain in a hand calculation is rather complex, even with a circuit simulator it's not really easy.

A more practical approach is to estimate a useful range of LC circuit characteristic impedance √L/C related to the common emitter stage input- and output impedances.

Besides finding a reasonable L value for the given circuit, it should be also checked if the other circuit parameters haven been chosen suitably. How did you derive it?

#### ymmen

##### Member level 1
Talking about an exact solution, you'll derive the circuit loop gain and determine the L range for that the Barkhausen oscillation condition can be fulfilled. Deriving the exact loop gain in a hand calculation is rather complex, even with a circuit simulator it's not really easy.

A more practical approach is to estimate a useful range of LC circuit characteristic impedance √L/C related to the common emitter stage input- and output impedances.

Besides finding a reasonable L value for the given circuit, it should be also checked if the other circuit parameters haven been chosen suitably. How did you derive it?

As i have read, in colpitts oscillator if A>C2/C1 the circuit is capable of oscillating at resonant frequency. but how does the change in value of inductor affect this stability criteria?

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this was the frequency response of the circuit, and with the current circuit my inductance value is ranging from 10uH to 1mH. How can I increase this range

##### Super Moderator
Staff member
A larger Henry value creates greater impedance to a given frequency.

If you increase Henry value, then you must reduce capacitor value, if you wish to keep a given frequency. You will have reduced current flow back and forth in the LC loop. This may require re-adjusting other component values.

In general, a greater Henry value is associated with:
* lower frequency
* lesser current flow
* larger voltage swings

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