On 7/25/2015 11:56 PM, bitrex 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. >> >> > > There's also apparently a variation on the Colpitts where the crystal is > inserted in the feedback path instead of parallel to the capacitors, to > resonate at the series resonant frequency. I may try that one as well.I like the standard Colpitts, because you can take the output right from the crystal, which gives you a nice wave shape for the second stage, and less broadband noise. Also capacitors are more stable than inductors, and you can't pull the oscillator off the crystal resonance the way you can with a separate tank. One good use of inductors is as overtone selectors: you resonate one of the tank caps so that it looks like the right size capacitor at only one of the overtones. Parzen's crystal oscillator book is a good read on that sort of thing. 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
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 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 -- | 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 7/25/2015 9:56 AM, bitrex 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?See if this works for you Version 4 SHEET 1 1560 740 WIRE 176 -192 -1056 -192 WIRE 416 -144 -816 -144 WIRE 784 -144 416 -144 WIRE -1056 -112 -1056 -192 WIRE 784 -112 784 -144 WIRE 416 -80 416 -144 WIRE 784 -16 784 -32 WIRE -816 16 -816 -144 WIRE -528 16 -624 16 WIRE -368 16 -448 16 WIRE -224 16 -304 16 WIRE -64 16 -144 16 WIRE 176 64 176 -192 WIRE 416 64 416 0 WIRE 416 64 176 64 WIRE -816 144 -816 96 WIRE -624 144 -624 16 WIRE -624 144 -816 144 WIRE -816 160 -816 144 WIRE 416 160 416 64 WIRE -1056 208 -1056 -48 WIRE -960 208 -1056 208 WIRE -880 208 -960 208 WIRE -624 208 -624 144 WIRE -352 208 -624 208 WIRE -64 208 -64 16 WIRE -64 208 -288 208 WIRE 176 208 -64 208 WIRE 272 208 176 208 WIRE 352 208 272 208 WIRE -880 224 -880 208 WIRE -864 224 -880 224 WIRE 352 224 352 208 WIRE 368 224 352 224 WIRE -960 240 -960 208 WIRE 272 240 272 208 WIRE -1056 320 -1056 208 WIRE 176 320 176 208 WIRE 416 320 416 256 WIRE -816 368 -816 256 WIRE 416 464 416 400 WIRE 416 464 336 464 WIRE -1056 480 -1056 400 WIRE -960 480 -960 304 WIRE -960 480 -1056 480 WIRE 176 480 176 400 WIRE 272 480 272 304 WIRE 272 480 176 480 WIRE 336 496 336 464 WIRE 416 496 416 464 WIRE 176 512 176 480 WIRE -1056 528 -1056 480 WIRE -816 544 -816 448 WIRE 336 624 336 560 WIRE 416 624 416 576 WIRE 416 624 336 624 WIRE 416 672 416 624 FLAG 416 672 0 FLAG 784 -16 0 FLAG -816 544 0 FLAG -1056 528 0 FLAG 176 512 0 SYMBOL ind -240 32 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName Lm SYMATTR Value 1701.17Hy SYMBOL res -544 32 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName Rs SYMATTR Value 15k SYMBOL cap -368 32 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName Cm SYMATTR Value 1.489fF SYMBOL cap -352 224 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName Cs SYMATTR Value 1.743pF SYMBOL voltage 784 -128 R0 WINDOW 123 24 132 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 9 SYMBOL res 400 -96 R0 SYMATTR InstName R1 SYMATTR Value 2.2k SYMBOL njf 368 160 R0 SYMATTR InstName J1 SYMATTR Value U309 SYMBOL res 400 480 R0 SYMATTR InstName R2 SYMATTR Value 680 SYMBOL cap 320 496 R0 SYMATTR InstName C2 SYMATTR Value .01u SYMBOL res 160 304 R0 SYMATTR InstName R3 SYMATTR Value 10meg SYMBOL cap -1072 -112 R0 SYMATTR InstName C4 SYMATTR Value .01u SYMBOL diode 256 240 R0 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL njf -864 160 R0 SYMATTR InstName J2 SYMATTR Value U309 SYMBOL res -832 352 R0 SYMATTR InstName R4 SYMATTR Value 1.8k SYMBOL res -1072 304 R0 SYMATTR InstName R5 SYMATTR Value 10meg SYMBOL diode -976 240 R0 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL res -832 0 R0 SYMATTR InstName R6 SYMATTR Value 1.8k SYMBOL res 400 304 R0 SYMATTR InstName R7 SYMATTR Value 470 TEXT -392 -128 Left 2 ;Crystal TEXT 1200 200 Left 2 !.tran 0 2 1.9 startup RECTANGLE Normal -48 320 -656 -96 2
Reply by ●July 26, 20152015-07-26
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. 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 -- 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 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 -- | 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 08:02:55 -0400, Phil Hobbs <hobbs@electrooptical.net> 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.I can usually find a paper or a book, where someone has done the math for me. It's amazing how little serious math I need to do electronic design; not much past algebra. The only really hairy stuff that we do is digital filter design, in FPGAs, and quantization issues make accurate analytical solutions impossible, so we wind up simulating the final filters anyhow. -- 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 Sun, 26 Jul 2015 09:02:04 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> 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 ThompsonThat is essentially the "two transistor Butler" topology. I think I've seen it with an inductor across the crystal to null out the parallel capacitance. For high precision, you have to keep the xtal current low, which is a compromise. -- 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 Sun, 26 Jul 2015 07:55:27 -0400, Phil Hobbs <hobbs@electrooptical.net> wrote:>On 7/26/2015 6:57 AM, upsidedown@downunder.com wrote: >> On Sun, 26 Jul 2015 01:48:27 -0700 (PDT), Phil Hobbs >> <pcdhobbs@gmail.com> wrote: >> >>> >>>> To satisfy the Barkhausen requirements, shouldn't you model the >>>> startup condition as a linear amplifier and a frequency >>>> selective feedback network ? >>> >>> Sure. That's why I suggested using a much smaller current step omce >>> the sim looks OK, to check for startup problems. >> >> Trying to start a (simulated) oscillator with external transient >> either relies on: >> >> a.) the transient puts the amplifier momentarily from Class-C to >> Class-A and amplifies everything during startup > >It had better be Class A at startup, or you're guaranteed a lot of >midnight phone calls. Have you ever shipped an oscillator that wasn't >Class A in quiescent conditions?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 :-)> >> >> b.) the startup transient contains so steep waveforms containing >> frequencies in the feedback filter bandwidth that then can be >> amplified >> >>> If the initial transient dies away rather than continuing, the gain >>> is too low. >> >> In case b.) the amplifier gain would have to be as high as 100 dB, >> if you have a crystal in the feedback path :-) > >No, you misunderstand what I'm proposing. If you put a current source >in parallel with the inductor, then at t=0 the full current is going >through the crystal inductance. When you turn that off, the crystal >rings strongly at its series resonance. A microamp of crystal current >in a watch crystal is probably full amplitude, or nearly. > >> >> >>> Thing is, being an iterative ODE solver, SPICE uses all sorts of >>> heuristics and fairly coarse convergence checks that make it flaky >>> and unreliable for very small signals. You have to supply an >>> initial amplitude big enough to not get ignored if you want >>> reliable (simulated) startup. >> >> Have you tried to "unwind" the startup with a number of cascaded >> stages ? > >No. What would I learn from that?At least it would educational to those that haven't thought about oscillators as amplifiers with positive frequency selective feedback.>> You would require a noise source (say a resistor at room temperature >> generating -174 dBm/Hz noise temperature) followed by your >> amplification stage (transistor with fT limitations) followed by >> your oscillator feedback frequency response. Instead of using >> feedback, connect the output of the filter to the next identical >> amplifier/filter stages. > >But they wouldn't be indentical. The phases would be independent, so >there would be nothing to enforce the oscillation criterion. All you'd >get would be filtered white noise, whereas a good oscillator has a much, >much narrower line width than the crystal.Yes, I pointed out that in my follow-up message.
Reply by ●July 26, 20152015-07-26
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 -- 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 12:53 PM, John Larkin wrote:> On Sun, 26 Jul 2015 09:02:04 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> 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 > > That is essentially the "two transistor Butler" topology. I think I've > seen it with an inductor across the crystal to null out the parallel > capacitance. For high precision, you have to keep the xtal current > low, which is a compromise. > >The parallel inductor is very helpful if you want to run at a high overtone. 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
