didac
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manresa,spain
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Hi, raja.cedt by spiky you mean that the MOS switch between on/off?, then it's one of the operating point for colpitts oscillator(always in saturation, saturation and cut-off or linear and saturation). Derivation comes from a large signal analysis of that oscillator and ends with something like this: Vout≈IbiasRp(5+x)/12; where: Ibias-->bias current Rp--->equivalent resistance at the drain x--> a parameter that determines the operating region of the transistor, it varies from -1 to 1(-1 always in saturation, 1 always in cut-off). From the expression it can be seen that the duty cycle that maximizes output amplitude it's an always off transistor(although in reality it will not oscillate). Hope it helps, PD: some references about this issue “Exact calculation of oscillation amplitude and predicting power consumption for CMOS Colpitts oscillators”, Qiuting Huang; Circuits and Systems, 1997. ISCAS '97., Proceedings of 1997 IEEE International Symposium on , Volume: 2 , 9- 12 June 1997, Page(s): 1401 -1404 vol.2 “Output voltage analysis for the MOS Colpitts oscillator”, Mayaram, K.; Circuits and Systems I: Fundamental Theory and Applications, IEEE Transactions on , Volume: 47 Issue: 2 , Feb. 2000, Page(s): 260 -263
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