strabush
Joined: 10 Apr 2002
Posts: 83
Helped: 6
|
 06 Jan 2005 10:23 Re: crystal osc, for help |
|
|
|
M1 and M2 are the main differential amplifier. Its output is amplified by the second differential pair M3 and M4. Its output is taken from M4, through two Emitter followers M10 and M11 and fed back to the two differential inputs of the main differential amplifier M1 and M2.
If you follow the polarity of the feedback you will find that the feedback to M1 input is positive feedback, and the feedback to M2 input is negative feedback.
The crystal shorts to ground the negative feedback at M2 input only at its series resonance, so the net feedback left is positive, and if its magnitude is large enough, the circuit will oscillate.
|
|
