walid Posted April 26, 2012 Report Share Posted April 26, 2012 This circuit was intended as 27MHz colpitts oscillator:and whem simulated using multisim10 sofware I get:I have some questions:Any osci. Needs a FB to sustain oscillations, I think that this FB from collector to base path through the parallel two caps; the internal transistor capacitance b/w collector and Emitter, and the C4(=4.7p) cap.From the Fairchild datasheets of the 2n3904 transistor I get:[img width=680 height=70][img width=680 height=91]Also, there is a curve related the capacitance with REVERSE BIAS VOLTAGE (V) My questions:(1) What is the approxi. value of the internal transistor capacitance b/w collector and Emitter at 27MHz?(2) How the phase shifted from 180 degree at the collector to 0 or 360 degree at the base? Please give me a step by step illustration.(3) The freq of the osci. was 25.4MHz while my calculaed value of the resonant freq was 27MHz? what factors affect this?thanks Quote Link to comment Share on other sites More sharing options...
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