On Sun, 26 Jul 2015 13:00:01 -0400, Phil Hobbs <hobbs@electrooptical.net> wrote:>On 7/26/2015 12:30 PM, Jim Thompson wrote: >> On Sun, 26 Jul 2015 12:26:21 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>[snip]>>>> >>>> My favorite crystal oscillator structure... >>>> >>>> <http://www.analog-innovations.com/SED/XtalSeriesOsc.pdf> >>>> >>>> No fiddle, no fuss, no critical matching... always works. >>>> >>>> First used it to get to 144MHz (2m) by X3 (transistor), X3 (varactor), >>>> from 16MHz crystal for my first (and last ;-) 2m rig... when in my mid >>>> '20's. >>>> >>>> ...Jim Thompson >>>> >>> I tend not to put DC on crystals, though modern ones may be less sensitive. >> >> No DC there... each end of the XTAL is 1*Vbe down from rail >>[snip]>>> >>> Cheers >>> >>> Phil Hobbs >> >> ...Jim Thompson >> >Ah, right, quite so. You IC guys and your weird-ass biasing schemes. ;) > >Cheers > >Phil HobbsI think our _brains_ are "biased" differently >:-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | 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.
Colpitts crystal oscillator in LTSPICE
Started by ●July 25, 2015
Reply by ●July 26, 20152015-07-26
Reply by ●July 26, 20152015-07-26
On Sun, 26 Jul 2015 19:59:27 +0300, upsidedown@downunder.com wrote: [snip]> >I have seen oscillator designs with some kick-start pulse delivered >through a diode or some kind of power on reset type circuit that slams >on the Vcc when a sufficient voltage has been stabilized from the >mains PSU, simulating the turn on transient from battery powered >devices :-) >[snip] I know a low-power IC designer who relies on kick-start schemes initiated by a uP... but no check for success. I think he's an idiot>:-}...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | 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.
Reply by ●July 26, 20152015-07-26
On Sun, 26 Jul 2015 13:00:01 -0400, Phil Hobbs <hobbs@electrooptical.net> wrote:>On 7/26/2015 12:30 PM, Jim Thompson wrote: >> On Sun, 26 Jul 2015 12:26:21 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 7/26/2015 12:02 PM, Jim Thompson wrote: >>>> On Sat, 25 Jul 2015 10:56:05 -0400, bitrex >>>> <bitrex@de.lete.earthlink.net> wrote: >>>> >>>>> I'm trying to simulate a low frequency Colpitts oscillator in LTSpice >>>>> using an NPN darlington and a crystal, and I'm having a lot of trouble >>>>> getting it to start up. Does anyone have a working one of these? I'm >>>>> just using a capacitor to simulate the crystal, the parameters I am >>>>> working with are something like: >>>>> >>>>> motional capacitance: 5.3ff >>>>> ESR = 11k >>>>> ESI ~ 4500 henries >>>>> EPR = 100 meg >>>>> EPC = 1.5pf >>>>> >>>>> Does this seem plausible? >>>> >>>> My favorite crystal oscillator structure... >>>> >>>> <http://www.analog-innovations.com/SED/XtalSeriesOsc.pdf> >>>> >>>> No fiddle, no fuss, no critical matching... always works. >>>> >>>> First used it to get to 144MHz (2m) by X3 (transistor), X3 (varactor), >>>> from 16MHz crystal for my first (and last ;-) 2m rig... when in my mid >>>> '20's. >>>> >>>> ...Jim Thompson >>>> >>> I tend not to put DC on crystals, though modern ones may be less sensitive. >> >> No DC there... each end of the XTAL is 1*Vbe down from rail >> >>> >>> One thing that series resonant oscillators are especially good for is >>> ring-down calibrators for logarithmic amplitude detectors (DLVAs). >>> Exponential envelope decay -> linear ramp output (ideally). >>> >>> Running at series resonance maximizes the initial amplitude of the >>> envelope when the oscillator switches off. One of those will calibrate >>> an SA615 good to at least 12 bits, usually more. >>> >>> Cheers >>> >>> Phil Hobbs >> >> ...Jim Thompson >> >Ah, right, quite so. You IC guys and your weird-ass biasing schemes. ;) > >Cheers > >Phil HobbsYou can do a lot of fun stuff if you don't mind using 70 transistors to do it. Sometimes an IC data sheet will have a transistor count. The numbers can be amazing. -- John Larkin Highland Technology, Inc lunatic fringe electronics jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●July 26, 20152015-07-26
On 7/26/2015 1:11 PM, Jim Thompson wrote:> On Sun, 26 Jul 2015 19:59:27 +0300, upsidedown@downunder.com wrote: > > [snip] >> >> I have seen oscillator designs with some kick-start pulse delivered >> through a diode or some kind of power on reset type circuit that slams >> on the Vcc when a sufficient voltage has been stabilized from the >> mains PSU, simulating the turn on transient from battery powered >> devices :-) >> > [snip] > > I know a low-power IC designer who relies on kick-start schemes > initiated by a uP... but no check for success. I think he's an idiot >> :-}Sounds like it. There are enough non-obvious ways to fail that there's no reason to include the obvious ones. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 26, 20152015-07-26
On 7/26/2015 1:07 PM, Jim Thompson wrote:> On Sun, 26 Jul 2015 13:00:01 -0400, Phil Hobbs > <hobbs@electrooptical.net> wrote: > >> On 7/26/2015 12:30 PM, Jim Thompson wrote: >>> On Sun, 26 Jul 2015 12:26:21 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> > [snip] >>>>> >>>>> My favorite crystal oscillator structure... >>>>> >>>>> <http://www.analog-innovations.com/SED/XtalSeriesOsc.pdf> >>>>> >>>>> No fiddle, no fuss, no critical matching... always works. >>>>> >>>>> First used it to get to 144MHz (2m) by X3 (transistor), X3 (varactor), >>>>> from 16MHz crystal for my first (and last ;-) 2m rig... when in my mid >>>>> '20's. >>>>> >>>>> ...Jim Thompson >>>>> >>>> I tend not to put DC on crystals, though modern ones may be less sensitive. >>> >>> No DC there... each end of the XTAL is 1*Vbe down from rail >>> > [snip] >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> ...Jim Thompson >>> >> Ah, right, quite so. You IC guys and your weird-ass biasing schemes. ;) >> >> Cheers >> >> Phil Hobbs > > I think our _brains_ are "biased" differently >:-} > > ...Jim Thompson >Within an ace of saturation, like the oscillator. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 26, 20152015-07-26
On 7/26/2015 1:23 PM, John Larkin wrote:> On Sun, 26 Jul 2015 13:00:01 -0400, Phil Hobbs > <hobbs@electrooptical.net> wrote: > >> On 7/26/2015 12:30 PM, Jim Thompson wrote: >>> On Sun, 26 Jul 2015 12:26:21 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 7/26/2015 12:02 PM, Jim Thompson wrote: >>>>> On Sat, 25 Jul 2015 10:56:05 -0400, bitrex >>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>> >>>>>> I'm trying to simulate a low frequency Colpitts oscillator in LTSpice >>>>>> using an NPN darlington and a crystal, and I'm having a lot of trouble >>>>>> getting it to start up. Does anyone have a working one of these? I'm >>>>>> just using a capacitor to simulate the crystal, the parameters I am >>>>>> working with are something like: >>>>>> >>>>>> motional capacitance: 5.3ff >>>>>> ESR = 11k >>>>>> ESI ~ 4500 henries >>>>>> EPR = 100 meg >>>>>> EPC = 1.5pf >>>>>> >>>>>> Does this seem plausible? >>>>> >>>>> My favorite crystal oscillator structure... >>>>> >>>>> <http://www.analog-innovations.com/SED/XtalSeriesOsc.pdf> >>>>> >>>>> No fiddle, no fuss, no critical matching... always works. >>>>> >>>>> First used it to get to 144MHz (2m) by X3 (transistor), X3 (varactor), >>>>> from 16MHz crystal for my first (and last ;-) 2m rig... when in my mid >>>>> '20's. >>>>> >>>>> ...Jim Thompson >>>>> >>>> I tend not to put DC on crystals, though modern ones may be less sensitive. >>> >>> No DC there... each end of the XTAL is 1*Vbe down from rail >>> >>>> >>>> One thing that series resonant oscillators are especially good for is >>>> ring-down calibrators for logarithmic amplitude detectors (DLVAs). >>>> Exponential envelope decay -> linear ramp output (ideally). >>>> >>>> Running at series resonance maximizes the initial amplitude of the >>>> envelope when the oscillator switches off. One of those will calibrate >>>> an SA615 good to at least 12 bits, usually more. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> ...Jim Thompson >>> >> Ah, right, quite so. You IC guys and your weird-ass biasing schemes. ;) >> >> Cheers >> >> Phil Hobbs > > You can do a lot of fun stuff if you don't mind using 70 transistors > to do it. > > Sometimes an IC data sheet will have a transistor count. The numbers > can be amazing. > >It's really important to avoid saturating BJT oscillators. The bias-dependent time delay alone is enough to ruin the stability and phase noise, not counting limit cycles and so on. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 26, 20152015-07-26
On 7/26/2015 8:02 AM, Phil Hobbs wrote:> On 7/26/2015 12:17 AM, John Larkin wrote: >> On Sat, 25 Jul 2015 23:53:34 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> On 7/25/2015 11:07 PM, John Larkin wrote: >>>> On Sat, 25 Jul 2015 21:17:32 -0400, bitrex >>>> <bitrex@de.lete.earthlink.net> wrote: >>>> >>>>> On 7/25/2015 7:46 PM, John Larkin wrote: >>>>>> On Sat, 25 Jul 2015 17:14:35 -0400, bitrex >>>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>>> >>>>>>> On 7/25/2015 12:12 PM, John Larkin wrote: >>>>>>>> On Sat, 25 Jul 2015 10:56:05 -0400, bitrex >>>>>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>>>>> >>>>>>>>> I'm trying to simulate a low frequency Colpitts oscillator in LTSpice >>>>>>>>> using an NPN darlington and a crystal, and I'm having a lot of trouble >>>>>>>>> getting it to start up. Does anyone have a working one of these? I'm >>>>>>>>> just using a capacitor to simulate the crystal, the parameters I am >>>>>>>>> working with are something like: >>>>>>>>> >>>>>>>>> motional capacitance: 5.3ff >>>>>>>>> ESR = 11k >>>>>>>>> ESI ~ 4500 henries >>>>>>>>> EPR = 100 meg >>>>>>>>> EPC = 1.5pf >>>>>>>>> >>>>>>>>> Does this seem plausible? >>>>>>>> >>>>>>>> Select "skip initial operating point" in the transient analysis, or it >>>>>>>> will never start. Or goose it as Phil suggests. >>>>>>>> >>>>>>>> XOs are terrible to sim in time domain. The sims take forever and >>>>>>>> there's no reasonable way to measure the frequency to PPM resolution. >>>>>>>> Once I get one running, I cut over to AC loop analysis to fine-tune >>>>>>>> things. >>>>>>>> >>>>>>>> Post your netlist so people can play with it. >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> Here's a Dropbox link to the files: >>>>>>> >>>>>>> https://www.dropbox.com/sh/txmcmhn6p7fhuh2/AACKLnAh-41bI2jO7UT4wjCza?dl=0 >>>>>>> >>>>>>> I'm actually attempting to use the Darlington buffer inside a LM13700 >>>>>>> section to build a Colpitts crystal oscillator, which will then be 2 >>>>>>> quadrant multiplied by an external signal within the transconductance >>>>>>> amp itself... >>>>>> >>>>>> I'd guess that C2 and C3 are way too big. >>>>>> >>>>>> >>>>> >>>>> Lowering C2 and C3 to 470p, making the emitter resistor 4.7k, keeping >>>>> the feedback cap the same and setting the crystal resonant frequency to >>>>> 500kHz makes it start up. >>>> >>>> Don't quit now; keep going. >>>> >>>> And maybe make the upper one a bit smaller than the lower one. But I >>>> never understood Colpitts oscillators. >>>> >>>> I did recently design one using a coaxial ceramic resonator, at 600 >>>> MHz. It works fine even if I don't understand it. >>> >>> Wes Hayward's book "Radio Frequency Design" has a pretty good section on >>> analysis of the various LC oscillator topologies on pages 265-290, and >>> how to plot the gain and phase angle as a function of emitter current. >>> >>> The book is very math-heavy in general, it's like the anti-AoE. >> >> Spice has made all sorts of math unnecessary. Math tends to sputter >> out when things get nonlinear anyhow. >> >> > > Oscillator and high frequency amplifier design are special cases, where > grinding out the math is important. Even in a classical Colpitts, the > choice of collector current, tank impedance, the ratio of the tank caps, > and the size of the emitter and base coupling caps have a lot of > influence on frequency stability and phase noise. > > That's a 5-D search space, so getting it right can take awhile > numerically, and you can never really be sure you're not on a local optimum. > > You only have to do it once for each topology, then you just use Mathcad > or Mathematica or something to apply it to the case at hand. > > Cheers > > Phil Hobbs >I'm pretty skilled with Numpy and SciPy. Do you have an interesting set of equations I can set it to work grinding on?
Reply by ●July 26, 20152015-07-26
On 7/26/2015 2:15 PM, bitrex wrote:> On 7/26/2015 8:02 AM, Phil Hobbs wrote: >> On 7/26/2015 12:17 AM, John Larkin wrote: >>> On Sat, 25 Jul 2015 23:53:34 -0400, bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> On 7/25/2015 11:07 PM, John Larkin wrote: >>>>> On Sat, 25 Jul 2015 21:17:32 -0400, bitrex >>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>> >>>>>> On 7/25/2015 7:46 PM, John Larkin wrote: >>>>>>> On Sat, 25 Jul 2015 17:14:35 -0400, bitrex >>>>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>>>> >>>>>>>> On 7/25/2015 12:12 PM, John Larkin wrote: >>>>>>>>> On Sat, 25 Jul 2015 10:56:05 -0400, bitrex >>>>>>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>>>>>> >>>>>>>>>> I'm trying to simulate a low frequency Colpitts oscillator in >>>>>>>>>> LTSpice >>>>>>>>>> using an NPN darlington and a crystal, and I'm having a lot of >>>>>>>>>> trouble >>>>>>>>>> getting it to start up. Does anyone have a working one of >>>>>>>>>> these? I'm >>>>>>>>>> just using a capacitor to simulate the crystal, the parameters >>>>>>>>>> I am >>>>>>>>>> working with are something like: >>>>>>>>>> >>>>>>>>>> motional capacitance: 5.3ff >>>>>>>>>> ESR = 11k >>>>>>>>>> ESI ~ 4500 henries >>>>>>>>>> EPR = 100 meg >>>>>>>>>> EPC = 1.5pf >>>>>>>>>> >>>>>>>>>> Does this seem plausible? >>>>>>>>> >>>>>>>>> Select "skip initial operating point" in the transient >>>>>>>>> analysis, or it >>>>>>>>> will never start. Or goose it as Phil suggests. >>>>>>>>> >>>>>>>>> XOs are terrible to sim in time domain. The sims take forever and >>>>>>>>> there's no reasonable way to measure the frequency to PPM >>>>>>>>> resolution. >>>>>>>>> Once I get one running, I cut over to AC loop analysis to >>>>>>>>> fine-tune >>>>>>>>> things. >>>>>>>>> >>>>>>>>> Post your netlist so people can play with it. >>>>>>>>> >>>>>>>>> >>>>>>>> >>>>>>>> Here's a Dropbox link to the files: >>>>>>>> >>>>>>>> https://www.dropbox.com/sh/txmcmhn6p7fhuh2/AACKLnAh-41bI2jO7UT4wjCza?dl=0 >>>>>>>> >>>>>>>> >>>>>>>> I'm actually attempting to use the Darlington buffer inside a >>>>>>>> LM13700 >>>>>>>> section to build a Colpitts crystal oscillator, which will then >>>>>>>> be 2 >>>>>>>> quadrant multiplied by an external signal within the >>>>>>>> transconductance >>>>>>>> amp itself... >>>>>>> >>>>>>> I'd guess that C2 and C3 are way too big. >>>>>>> >>>>>>> >>>>>> >>>>>> Lowering C2 and C3 to 470p, making the emitter resistor 4.7k, keeping >>>>>> the feedback cap the same and setting the crystal resonant >>>>>> frequency to >>>>>> 500kHz makes it start up. >>>>> >>>>> Don't quit now; keep going. >>>>> >>>>> And maybe make the upper one a bit smaller than the lower one. But I >>>>> never understood Colpitts oscillators. >>>>> >>>>> I did recently design one using a coaxial ceramic resonator, at 600 >>>>> MHz. It works fine even if I don't understand it. >>>> >>>> Wes Hayward's book "Radio Frequency Design" has a pretty good >>>> section on >>>> analysis of the various LC oscillator topologies on pages 265-290, and >>>> how to plot the gain and phase angle as a function of emitter current. >>>> >>>> The book is very math-heavy in general, it's like the anti-AoE. >>> >>> Spice has made all sorts of math unnecessary. Math tends to sputter >>> out when things get nonlinear anyhow. >>> >>> >> >> Oscillator and high frequency amplifier design are special cases, where >> grinding out the math is important. Even in a classical Colpitts, the >> choice of collector current, tank impedance, the ratio of the tank caps, >> and the size of the emitter and base coupling caps have a lot of >> influence on frequency stability and phase noise. >> >> That's a 5-D search space, so getting it right can take awhile >> numerically, and you can never really be sure you're not on a local >> optimum. >> >> You only have to do it once for each topology, then you just use Mathcad >> or Mathematica or something to apply it to the case at hand. >> >> Cheers >> >> Phil Hobbs >> > > I'm pretty skilled with Numpy and SciPy. Do you have an interesting set > of equations I can set it to work grinding on?Not right handy--I haven't done a crystal oscillator in years. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 26, 20152015-07-26
On Sun, 26 Jul 2015 13:34:57 -0400, Phil Hobbs <hobbs@electrooptical.net> wrote:>On 7/26/2015 1:07 PM, Jim Thompson wrote: >> On Sun, 26 Jul 2015 13:00:01 -0400, Phil Hobbs >> <hobbs@electrooptical.net> wrote: >> >>> On 7/26/2015 12:30 PM, Jim Thompson wrote: >>>> On Sun, 26 Jul 2015 12:26:21 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >> [snip] >>>>>> >>>>>> My favorite crystal oscillator structure... >>>>>> >>>>>> <http://www.analog-innovations.com/SED/XtalSeriesOsc.pdf> >>>>>> >>>>>> No fiddle, no fuss, no critical matching... always works. >>>>>> >>>>>> First used it to get to 144MHz (2m) by X3 (transistor), X3 (varactor), >>>>>> from 16MHz crystal for my first (and last ;-) 2m rig... when in my mid >>>>>> '20's. >>>>>> >>>>>> ...Jim Thompson >>>>>> >>>>> I tend not to put DC on crystals, though modern ones may be less sensitive. >>>> >>>> No DC there... each end of the XTAL is 1*Vbe down from rail >>>> >> [snip] >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> ...Jim Thompson >>>> >>> Ah, right, quite so. You IC guys and your weird-ass biasing schemes. ;) >>> >>> Cheers >>> >>> Phil Hobbs >> >> I think our _brains_ are "biased" differently >:-} >> >> ...Jim Thompson >> >Within an ace of saturation, like the oscillator. ;) > >Cheers > >Phil HobbsThat's why the gold-doped 2N2369's. My chip versions use level measurement and current source control... much better spectral purity. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | 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.
Reply by ●July 27, 20152015-07-27
On Sun, 26 Jul 2015 14:20:19 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 7/26/2015 2:15 PM, bitrex wrote: >> On 7/26/2015 8:02 AM, Phil Hobbs wrote: >>> On 7/26/2015 12:17 AM, John Larkin wrote: >>>> On Sat, 25 Jul 2015 23:53:34 -0400, bitrex >>>> <bitrex@de.lete.earthlink.net> wrote: >>>> >>>>> On 7/25/2015 11:07 PM, John Larkin wrote: >>>>>> On Sat, 25 Jul 2015 21:17:32 -0400, bitrex >>>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>>> >>>>>>> On 7/25/2015 7:46 PM, John Larkin wrote: >>>>>>>> On Sat, 25 Jul 2015 17:14:35 -0400, bitrex >>>>>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>>>>> >>>>>>>>> On 7/25/2015 12:12 PM, John Larkin wrote: >>>>>>>>>> On Sat, 25 Jul 2015 10:56:05 -0400, bitrex >>>>>>>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>>>>>>> >>>>>>>>>>> I'm trying to simulate a low frequency Colpitts oscillator in >>>>>>>>>>> LTSpice >>>>>>>>>>> using an NPN darlington and a crystal, and I'm having a lot of >>>>>>>>>>> trouble >>>>>>>>>>> getting it to start up. Does anyone have a working one of >>>>>>>>>>> these? I'm >>>>>>>>>>> just using a capacitor to simulate the crystal, the parameters >>>>>>>>>>> I am >>>>>>>>>>> working with are something like: >>>>>>>>>>> >>>>>>>>>>> motional capacitance: 5.3ff >>>>>>>>>>> ESR = 11k >>>>>>>>>>> ESI ~ 4500 henries >>>>>>>>>>> EPR = 100 meg >>>>>>>>>>> EPC = 1.5pf >>>>>>>>>>> >>>>>>>>>>> Does this seem plausible? >>>>>>>>>> >>>>>>>>>> Select "skip initial operating point" in the transient >>>>>>>>>> analysis, or it >>>>>>>>>> will never start. Or goose it as Phil suggests. >>>>>>>>>> >>>>>>>>>> XOs are terrible to sim in time domain. The sims take forever and >>>>>>>>>> there's no reasonable way to measure the frequency to PPM >>>>>>>>>> resolution. >>>>>>>>>> Once I get one running, I cut over to AC loop analysis to >>>>>>>>>> fine-tune >>>>>>>>>> things. >>>>>>>>>> >>>>>>>>>> Post your netlist so people can play with it. >>>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>> Here's a Dropbox link to the files: >>>>>>>>> >>>>>>>>> https://www.dropbox.com/sh/txmcmhn6p7fhuh2/AACKLnAh-41bI2jO7UT4wjCza?dl=0 >>>>>>>>> >>>>>>>>> >>>>>>>>> I'm actually attempting to use the Darlington buffer inside a >>>>>>>>> LM13700 >>>>>>>>> section to build a Colpitts crystal oscillator, which will then >>>>>>>>> be 2 >>>>>>>>> quadrant multiplied by an external signal within the >>>>>>>>> transconductance >>>>>>>>> amp itself... >>>>>>>> >>>>>>>> I'd guess that C2 and C3 are way too big. >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> Lowering C2 and C3 to 470p, making the emitter resistor 4.7k, keeping >>>>>>> the feedback cap the same and setting the crystal resonant >>>>>>> frequency to >>>>>>> 500kHz makes it start up. >>>>>> >>>>>> Don't quit now; keep going. >>>>>> >>>>>> And maybe make the upper one a bit smaller than the lower one. But I >>>>>> never understood Colpitts oscillators. >>>>>> >>>>>> I did recently design one using a coaxial ceramic resonator, at 600 >>>>>> MHz. It works fine even if I don't understand it. >>>>> >>>>> Wes Hayward's book "Radio Frequency Design" has a pretty good >>>>> section on >>>>> analysis of the various LC oscillator topologies on pages 265-290, and >>>>> how to plot the gain and phase angle as a function of emitter current. >>>>> >>>>> The book is very math-heavy in general, it's like the anti-AoE. >>>> >>>> Spice has made all sorts of math unnecessary. Math tends to sputter >>>> out when things get nonlinear anyhow. >>>> >>>> >>> >>> Oscillator and high frequency amplifier design are special cases, where >>> grinding out the math is important. Even in a classical Colpitts, the >>> choice of collector current, tank impedance, the ratio of the tank caps, >>> and the size of the emitter and base coupling caps have a lot of >>> influence on frequency stability and phase noise. >>> >>> That's a 5-D search space, so getting it right can take awhile >>> numerically, and you can never really be sure you're not on a local >>> optimum. >>> >>> You only have to do it once for each topology, then you just use Mathcad >>> or Mathematica or something to apply it to the case at hand. >>> >>> Cheers >>> >>> Phil Hobbs >>> >> >> I'm pretty skilled with Numpy and SciPy. Do you have an interesting set >> of equations I can set it to work grinding on? > >Not right handy--I haven't done a crystal oscillator in years. >It's really easier to buy oscillators. The phase noise and suchlike specs are right there already. A pretty good OCXO can be cheaper than buying just an SC-cut crystal. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
