Hi all, Below is a graphical view of a xtal's // resonance. What challenge=20 plotting like this! In a nutshell, parallel resonance, which I believe is a coined term, occurs= =20 between the series and anti-resonant frequencies. Within this area, the=20 series C will set the frequency. Low C values will result in frequencies=20 near anti-resonance, Higher C values will put the frequency closer to=20 series resonance. The phase between series and antiresonance will swing=20 -180 degrees. The inverter amplifier will make up the remainder of the 180= =20 degrees to meet Barkhausen's criterion for oscillation, 0 or n360 degrees=20 with gain greater than 1. Parallel resonant crystals are calibrated with= =20 a known load capacitance like 12 pf for example. The user ckt needs to=20 duplicate this as with 2 -24 pf PI caps which are really in series with the= =20 crystal. Once oscillation is achieved and easy way to set frequency is to=20 tweek the cap values or use a trimmer. Usually you get many ppm per pf of= =20 capacitance change. fa Xtal reactance curve - -- - - Inductive - - - - fs - - - - - - - - - - - - - -= =20 - - - - - - - freq >>> - - - - capacitive -- - - ^ // res area 0 ---------------------------- \/ = ------------------------------- - - Phase plot - - - - -180 ---------------- I hope this helps, Ed Miguel Connor Winfield At 12:50 PM 1/14/03 +0800, =3D?gb2312?q?Bi=3D20Han?=3D wrote: >The phase shift is most mentioned in ring oscillators. > > Parthasarathy Sampath <parthsv@xxxxxxxxx> wrote: >Hi all, >I have a question regarding crystall oscillator >operating at parallel resonance. >At parallel resonance, the impedance offered by >series resonant ckt within crystal oscillator is >inductive. This inductive reactance is cancelled by >the capacitive reactance offered by parallel >capacitance in the crystall oscillator and the load >capacitance. So there should not be any phase in the >circuit since the reactances get cancelled. However a >lot of articles say load capacitance provide a phase >shift of 180 in order to oscillate in closed loop. >Since the load capacitance is included in the parallel >resonance to cancel inductive reactance, how can it >contribute 180 degress phase shift. > >Thanks in advance, >Partha > >__________________________________________________ >Do you Yahoo!? >Yahoo! Mail Plus - Powerful. Affordable. Sign up now. >http://mailplus.yahoo.com >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List archives are viewable at: >//www.freelists.org/archives/si-list >or at our remote archives: >http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: >http://www.qsl.net/wb6tpu > > > > >--------------------------------- >Do You Yahoo!? >"=D6=D0=B9=FA=D2=C6=B6=AF=CA=D6=BB=FA=BD=BB=D3=D1=D6=D0=D0=C4=A3=BA=D5=E6= =C8=CB=A3=AC=D5=E6=C9=F9=A3=AC=D5=E6=BD=BB=D3=D1=A3=A1" > >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List archives are viewable at: > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu