The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl Design >> RF Design >> colpitts oscillator https://designers-guide.org/forum/YaBB.pl?num=1225781701 Message started by raja.cedt on Nov 3rd, 2008, 10:55pm |
Title: colpitts oscillator Post by raja.cedt on Nov 3rd, 2008, 10:55pm hi, can any body please explain current in mos fet in colpits oscillator? current seems like spiky.i just want to ask u guys why current is flowing only when o/p voltage is -ve?Here i am referring common gate colpits oscillator? Thank you. |
Title: Re: colpitts oscillator Post by didac on Nov 7th, 2008, 9:58am 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 |
The Designer's Guide Community Forum » Powered by YaBB 2.2.2! YaBB © 2000-2008. All Rights Reserved. |