On Jun 8, 4:35=A0pm, rickman <gnu...@gmail.com> wrote:>> ...big snip... > Robert wrote: > > is it possible to 'pull' those crystals 1kHz with only 8pF? probably > > not. > > What does LTspice show? > > Good luck on that. =A0I don't think there are any good LTspice models for > crystals... at least not the ones I wanted to simulate. =A0I think they > just tell you to construct a cap model using the crystal parameters > which most crystal makers don't provide. =A0A model is only as good as th=e> data. > > I'd say a test is worth a lot more than a simulation in this case. > > -- > > RickI once got 'bit' by cheap suppliers that produced poorly ground crystals. talk about spurious oscillation frequencies! more than 1 1/2% off sometimes. If you could get them to oscillate at the 'right' freq they were fine, somewhat. I liked simulation to show what could happen during Production with full ranges of tolerances, and then redesign to be able to absorb anything the vendors sent, well almost. Always asked the Engineers, SAY what you're going to do, DO what you said you'd do, and then PROVE you did it. THEN designs woud smoothly transition into Production. found them! these models are based upon lower frequency crystal models included in the MicroSim's Library for Crystals representing AT cut with the inforrmative header: * Release date: September 1987 * The parameters in this model library were derived from: * * Quartz-crystal timing accuracy * Electonic Design 2, January 19, 1976; pp. 74-79 * * and: * * Electronics Designers' Handbook, Second Edition * edited by L.J. Giacoletto * McGraw-Hill Book Co., 1977, pp. 16-16 to 16-31 * Example use: X3 3 4 QZ32768 * Notes: * 1) Temperature variation of resonant frequency for properly cut * crystals is quadratic. The coefficient depends on the cut used * and is implemented in these subcircuits by giving the equivalent * inductor a temperature coefficient. The AT cut is an exception, * and has a cubic temperature dependence which is not included in * these models. * 2) The values of lqz, cs, and cp do not vary much from one crystal * to the next. The value of rqz, however, can vary as much as a * factor of 2 up or down. So the crystal's Q can vary over a * range of 4 to 1. * 3) Parallel resonant crystals can be tuned slightly by attaching an * external capacitor in parallel with the crystal. The crystal's * frequency is built assuming a value of the external capacitor, * called the "calibration capacitance". Its value is noted in * the comment at the head of each parallel resonant crystal model. and includes this one: * 10Mhz frequency standard, AT cut, parallel resonant, Q=3D25000 * calibration capacitance =3D 50pf .subckt QZP10MEG 1 2 * lqz 1 11 2.54647909e-003 cs 11 12 9.96041181e-014 rqz 12 2 6.4 cp 1 2 2.49010295e-011 .ends the following models I created based upon some samples sent to a friend of mine: * 20MHz Ethernet crystal for parallel operation * #1 Crystal * * 20Mhz frequency standard, unknown cut, parallel resonant, Q=3D?? * calibration capacitance =3D ?? 50pf * .SUBCKT QZP20A 1 2 * LQZ 1 11 3.33181E-03 CS 11 12 19.0069E-15 RQZ 12 2 6.45805 CP 1 2 4.65668E-12 .ENDS * #2 Crystal * * 20Mhz frequency standard, unknown cut, parallel resonant, Q=3D?? * calibration capacitance =3D ?? 50pf * .SUBCKT QZP20B 1 2 * LQZ 1 11 3.26998E-03 CS 11 12 19.3664E-15 RQZ 12 2 7.38786 CP 1 2 4.59108E-12 .ENDS
Capacitance value for PIC crystal
Started by ●June 6, 2013
Reply by ●June 9, 20132013-06-09
Reply by ●June 9, 20132013-06-09
On Sun, 9 Jun 2013 12:08:01 -0700 (PDT), Robert Macy <robert.a.macy@gmail.com> wrote:>On Jun 8, 4:35�pm, rickman <gnu...@gmail.com> wrote: >>> ...big snip... >> Robert wrote: >> > is it possible to 'pull' those crystals 1kHz with only 8pF? probably >> > not. >> > What does LTspice show? >> >> Good luck on that. �I don't think there are any good LTspice models for >> crystals... at least not the ones I wanted to simulate. �I think they >> just tell you to construct a cap model using the crystal parameters >> which most crystal makers don't provide. �A model is only as good as the >> data. >> >> I'd say a test is worth a lot more than a simulation in this case. >> >> -- >> >> Rick > >I once got 'bit' by cheap suppliers that produced poorly ground >crystals. talk about spurious oscillation frequencies! more than 1 >1/2% off sometimes. If you could get them to oscillate at the 'right' >freq they were fine, somewhat. > >I liked simulation to show what could happen during Production with >full ranges of tolerances, and then redesign to be able to absorb >anything the vendors sent, well almost. > >Always asked the Engineers, SAY what you're going to do, DO what you >said you'd do, and then PROVE you did it. THEN designs woud smoothly >transition into Production. > >found them! > >these models are based upon lower frequency crystal models included in >the MicroSim's Library for Crystals representing AT cut > >with the inforrmative header: >* Release date: September 1987 > >* The parameters in this model library were derived from: >* >* Quartz-crystal timing accuracy >* Electonic Design 2, January 19, 1976; pp. 74-79 >* >* and: >* >* Electronics Designers' Handbook, Second Edition >* edited by L.J. Giacoletto >* McGraw-Hill Book Co., 1977, pp. 16-16 to 16-31 > >* Example use: X3 3 4 QZ32768 > >* Notes: >* 1) Temperature variation of resonant frequency for properly cut >* crystals is quadratic. The coefficient depends on the cut used >* and is implemented in these subcircuits by giving the equivalent >* inductor a temperature coefficient. The AT cut is an exception, >* and has a cubic temperature dependence which is not included in >* these models. >* 2) The values of lqz, cs, and cp do not vary much from one crystal >* to the next. The value of rqz, however, can vary as much as a >* factor of 2 up or down. So the crystal's Q can vary over a >* range of 4 to 1. >* 3) Parallel resonant crystals can be tuned slightly by attaching an >* external capacitor in parallel with the crystal. The crystal's >* frequency is built assuming a value of the external capacitor, >* called the "calibration capacitance". Its value is noted in >* the comment at the head of each parallel resonant crystal model. >and includes this one: >* 10Mhz frequency standard, AT cut, parallel resonant, Q=25000 >* calibration capacitance = 50pf >.subckt QZP10MEG 1 2 >* > lqz 1 11 2.54647909e-003 > cs 11 12 9.96041181e-014 > rqz 12 2 6.4 > cp 1 2 2.49010295e-011 >.ends > > > > >the following models I created based upon some samples sent to a >friend of mine: > >* 20MHz Ethernet crystal for parallel operation >* #1 Crystal >* >* 20Mhz frequency standard, unknown cut, parallel resonant, Q=?? >* calibration capacitance = ?? 50pf >* >.SUBCKT QZP20A 1 2 >* > LQZ 1 11 3.33181E-03 > CS 11 12 19.0069E-15 > RQZ 12 2 6.45805 > CP 1 2 4.65668E-12 >.ENDS >* #2 Crystal >* >* 20Mhz frequency standard, unknown cut, parallel resonant, Q=?? >* calibration capacitance = ?? 50pf >* >.SUBCKT QZP20B 1 2 >* > LQZ 1 11 3.26998E-03 > CS 11 12 19.3664E-15 > RQZ 12 2 7.38786 > CP 1 2 4.59108E-12 >.ENDSBut that does not include the temperature variation. PSpice allows a linear and a quadratic TC term in-line with the instantiation, which I'd guess can be easily fit to AT-cut data. My (un-TC'd) Spice crystal model... ****************************************************************** .SUBCKT MyXTAL 1 2 PARAMS: Fo=10Meg Cp=5pF Rs=100 Q=25K Series=0 .PARAM P1={6.283185*Fo} .PARAM P2={Q*Rs} R1 1 3 {Rs} C1 1 2 {Cp} L1 4 2 {P2/P1} C2 3 4 {1/(P1*P2-(1-Series)/Cp)} .ENDS MyXTAL ****************************************************************** ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85140 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
