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SPICE simulation -- how to bias a crystal oscillatoir

Started by Unknown November 6, 2015
Could some electronics/SPICE guru please help ? I have a
simple model of a quartz crystal, as used in an oscillator.
With my SPICE simulation, I can measure both the parallel 
and series resonant frequencies of the "pure" crystal.
However, when I attach the same crystal to a biasing 
circuit, and run the simulation, the output is a flat DC
offset. The biasing circuit involves two CMOS(1.0u micron
gate length) inverters, as well as the large value feedback
resistor, capacitirs etc. Is there anything special I need
to do ? Any hints/suggestions would be helpful. Thanks in 
advance.
On Fri, 6 Nov 2015 19:31:46 -0800 (PST), dakupoto@gmail.com wrote:

>Could some electronics/SPICE guru please help ? I have a >simple model of a quartz crystal, as used in an oscillator. >With my SPICE simulation, I can measure both the parallel >and series resonant frequencies of the "pure" crystal. >However, when I attach the same crystal to a biasing >circuit, and run the simulation, the output is a flat DC >offset. The biasing circuit involves two CMOS(1.0u micron >gate length) inverters, as well as the large value feedback >resistor, capacitirs etc. Is there anything special I need >to do ? Any hints/suggestions would be helpful. Thanks in >advance.
Crystal oscillators can be very tricky to simulate. They _always_ need a "kick-start" of some sort to initiate the oscillation. This can be by inserting a current pulse or skewing the normal bias with a .IC statement. You will also need to set a very small timestep. If you are using LTspice, be sure to use the "Alternate" solver... the "Normal" solver takes simplification liberties that will produce false results on most anything but switchers. ...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.
On Fri, 6 Nov 2015 19:31:46 -0800 (PST), dakupoto@gmail.com wrote:

>Could some electronics/SPICE guru please help ? I have a >simple model of a quartz crystal, as used in an oscillator. >With my SPICE simulation, I can measure both the parallel >and series resonant frequencies of the "pure" crystal. >However, when I attach the same crystal to a biasing >circuit, and run the simulation, the output is a flat DC >offset. The biasing circuit involves two CMOS(1.0u micron >gate length) inverters, as well as the large value feedback >resistor, capacitirs etc. Is there anything special I need >to do ? Any hints/suggestions would be helpful. Thanks in >advance.
Remember that an oscillator is just an noise amplification stage with a frequency dependent feedback. When the oscillator active element works in Class-A/AB/B, the thermal noise of the active element is amplified and fed back through the frequency selective network into the input. Doing this a few times, the amplitude of the frequency selective network (in this case crystal) is amplified and other frequencies severely attenuated each time through. Finally the amplitude is limited by saturation of the active device. Look for the Barkhausen criterion. For active elements working in Class-C. you need some kind of kick-start, such as _rapid_ power application. This explains why the oscillator starts well when battery powered, but fails when powered by a mains power supply. In the first case, turning the power switch on, will create a sharp power transient, while using mains, it takes some time to charge the power supply capacitors.
On Sat, 07 Nov 2015 07:38:36 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Fri, 6 Nov 2015 19:31:46 -0800 (PST), dakupoto@gmail.com wrote: > >>Could some electronics/SPICE guru please help ? I have a >>simple model of a quartz crystal, as used in an oscillator. >>With my SPICE simulation, I can measure both the parallel >>and series resonant frequencies of the "pure" crystal. >>However, when I attach the same crystal to a biasing >>circuit, and run the simulation, the output is a flat DC >>offset. The biasing circuit involves two CMOS(1.0u micron >>gate length) inverters, as well as the large value feedback >>resistor, capacitirs etc. Is there anything special I need >>to do ? Any hints/suggestions would be helpful. Thanks in >>advance. > >Crystal oscillators can be very tricky to simulate. > >They _always_ need a "kick-start" of some sort to initiate the >oscillation. This can be by inserting a current pulse or skewing the >normal bias with a .IC statement. > >You will also need to set a very small timestep. > >If you are using LTspice, be sure to use the "Alternate" solver... the >"Normal" solver takes simplification liberties that will produce false >results on most anything but switchers. > > ...Jim Thompson
An example... <http://www.analog-innovations.com/SED/XtalOscillatorExample.png> Several things to note: IKS is the "kick-start" current pulse. MaxTimeStep is set at 100ps SOLVER=0 is equivalent to LTspice's "Alternate" solver (Used to be PSpice's default solver until they decided to take liberties to speed-up simulation... not as bad as Mikey's "Normal", but loose enough not to handle crystal oscillators). What's with the Kiwi Semi? I am the "ghost designer" for a number of fabless design houses and they like their names on the drawings ;-) ...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.
On Sat, 07 Nov 2015 17:09:05 +0200, upsidedown@downunder.com wrote:

>On Fri, 6 Nov 2015 19:31:46 -0800 (PST), dakupoto@gmail.com wrote: > >>Could some electronics/SPICE guru please help ? I have a >>simple model of a quartz crystal, as used in an oscillator. >>With my SPICE simulation, I can measure both the parallel >>and series resonant frequencies of the "pure" crystal. >>However, when I attach the same crystal to a biasing >>circuit, and run the simulation, the output is a flat DC >>offset. The biasing circuit involves two CMOS(1.0u micron >>gate length) inverters, as well as the large value feedback >>resistor, capacitirs etc. Is there anything special I need >>to do ? Any hints/suggestions would be helpful. Thanks in >>advance. > >Remember that an oscillator is just an noise amplification stage with >a frequency dependent feedback. > >When the oscillator active element works in Class-A/AB/B, the thermal >noise of the active element is amplified and fed back through the >frequency selective network into the input. Doing this a few times, >the amplitude of the frequency selective network (in this case >crystal) is amplified and other frequencies severely attenuated each >time through. Finally the amplitude is limited by saturation of the >active device. > >Look for the Barkhausen criterion. > >For active elements working in Class-C. you need some kind of >kick-start, such as _rapid_ power application. This explains why the >oscillator starts well when battery powered, but fails when powered by >a mains power supply. In the first case, turning the power switch on, >will create a sharp power transient, while using mains, it takes some >time to charge the power supply capacitors. >
Transient simulators don't know about noise starts... noise only exists in AC analyses. ...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.
On 11/07/2015 10:34 AM, Jim Thompson wrote:
> On Sat, 07 Nov 2015 07:38:36 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >> On Fri, 6 Nov 2015 19:31:46 -0800 (PST), dakupoto@gmail.com wrote: >> >>> Could some electronics/SPICE guru please help ? I have a >>> simple model of a quartz crystal, as used in an oscillator. >>> With my SPICE simulation, I can measure both the parallel >>> and series resonant frequencies of the "pure" crystal. >>> However, when I attach the same crystal to a biasing >>> circuit, and run the simulation, the output is a flat DC >>> offset. The biasing circuit involves two CMOS(1.0u micron >>> gate length) inverters, as well as the large value feedback >>> resistor, capacitirs etc. Is there anything special I need >>> to do ? Any hints/suggestions would be helpful. Thanks in >>> advance. >> >> Crystal oscillators can be very tricky to simulate. >> >> They _always_ need a "kick-start" of some sort to initiate the >> oscillation. This can be by inserting a current pulse or skewing the >> normal bias with a .IC statement. >> >> You will also need to set a very small timestep. >> >> If you are using LTspice, be sure to use the "Alternate" solver... the >> "Normal" solver takes simplification liberties that will produce false >> results on most anything but switchers. >> >> ...Jim Thompson > > An example... > > <http://www.analog-innovations.com/SED/XtalOscillatorExample.png> > > Several things to note: > > IKS is the "kick-start" current pulse. > > MaxTimeStep is set at 100ps > > SOLVER=0 is equivalent to LTspice's "Alternate" solver (Used to be > PSpice's default solver until they decided to take liberties to > speed-up simulation... not as bad as Mikey's "Normal", but loose > enough not to handle crystal oscillators). > > What's with the Kiwi Semi? I am the "ghost designer" for a number of > fabless design houses and they like their names on the drawings ;-) > > > > ...Jim Thompson >
One caution is that the kickstart has to be _small_, not much more than rounding error. A nanoamp is often a good value. Putting the current source in parallel with the crystal inductance will make sure that it starts off ringing at its natural frequency, which helps a lot. 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
On Sat, 7 Nov 2015 10:40:25 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 11/07/2015 10:34 AM, Jim Thompson wrote: >> On Sat, 07 Nov 2015 07:38:36 -0700, Jim Thompson >> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >> >>> On Fri, 6 Nov 2015 19:31:46 -0800 (PST), dakupoto@gmail.com wrote: >>> >>>> Could some electronics/SPICE guru please help ? I have a >>>> simple model of a quartz crystal, as used in an oscillator. >>>> With my SPICE simulation, I can measure both the parallel >>>> and series resonant frequencies of the "pure" crystal. >>>> However, when I attach the same crystal to a biasing >>>> circuit, and run the simulation, the output is a flat DC >>>> offset. The biasing circuit involves two CMOS(1.0u micron >>>> gate length) inverters, as well as the large value feedback >>>> resistor, capacitirs etc. Is there anything special I need >>>> to do ? Any hints/suggestions would be helpful. Thanks in >>>> advance. >>> >>> Crystal oscillators can be very tricky to simulate. >>> >>> They _always_ need a "kick-start" of some sort to initiate the >>> oscillation. This can be by inserting a current pulse or skewing the >>> normal bias with a .IC statement. >>> >>> You will also need to set a very small timestep. >>> >>> If you are using LTspice, be sure to use the "Alternate" solver... the >>> "Normal" solver takes simplification liberties that will produce false >>> results on most anything but switchers. >>> >>> ...Jim Thompson >> >> An example... >> >> <http://www.analog-innovations.com/SED/XtalOscillatorExample.png> >> >> Several things to note: >> >> IKS is the "kick-start" current pulse. >> >> MaxTimeStep is set at 100ps >> >> SOLVER=0 is equivalent to LTspice's "Alternate" solver (Used to be >> PSpice's default solver until they decided to take liberties to >> speed-up simulation... not as bad as Mikey's "Normal", but loose >> enough not to handle crystal oscillators). >> >> What's with the Kiwi Semi? I am the "ghost designer" for a number of >> fabless design houses and they like their names on the drawings ;-) >> >> >> >> ...Jim Thompson >> >One caution is that the kickstart has to be _small_, not much more than >rounding error. A nanoamp is often a good value. Putting the current >source in parallel with the crystal inductance will make sure that it >starts off ringing at its natural frequency, which helps a lot. > >Cheers > >Phil Hobbs
No. It has to be sufficient enough to significantly perturb the quiescent operating point. The example has a 10ns wide x 1mA pulse. ...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.
On 11/07/2015 10:59 AM, Jim Thompson wrote:
> On Sat, 7 Nov 2015 10:40:25 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 11/07/2015 10:34 AM, Jim Thompson wrote: >>> On Sat, 07 Nov 2015 07:38:36 -0700, Jim Thompson >>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >>> >>>> On Fri, 6 Nov 2015 19:31:46 -0800 (PST), dakupoto@gmail.com wrote: >>>> >>>>> Could some electronics/SPICE guru please help ? I have a >>>>> simple model of a quartz crystal, as used in an oscillator. >>>>> With my SPICE simulation, I can measure both the parallel >>>>> and series resonant frequencies of the "pure" crystal. >>>>> However, when I attach the same crystal to a biasing >>>>> circuit, and run the simulation, the output is a flat DC >>>>> offset. The biasing circuit involves two CMOS(1.0u micron >>>>> gate length) inverters, as well as the large value feedback >>>>> resistor, capacitirs etc. Is there anything special I need >>>>> to do ? Any hints/suggestions would be helpful. Thanks in >>>>> advance. >>>> >>>> Crystal oscillators can be very tricky to simulate. >>>> >>>> They _always_ need a "kick-start" of some sort to initiate the >>>> oscillation. This can be by inserting a current pulse or skewing the >>>> normal bias with a .IC statement. >>>> >>>> You will also need to set a very small timestep. >>>> >>>> If you are using LTspice, be sure to use the "Alternate" solver... the >>>> "Normal" solver takes simplification liberties that will produce false >>>> results on most anything but switchers. >>>> >>>> ...Jim Thompson >>> >>> An example... >>> >>> <http://www.analog-innovations.com/SED/XtalOscillatorExample.png> >>> >>> Several things to note: >>> >>> IKS is the "kick-start" current pulse. >>> >>> MaxTimeStep is set at 100ps >>> >>> SOLVER=0 is equivalent to LTspice's "Alternate" solver (Used to be >>> PSpice's default solver until they decided to take liberties to >>> speed-up simulation... not as bad as Mikey's "Normal", but loose >>> enough not to handle crystal oscillators). >>> >>> What's with the Kiwi Semi? I am the "ghost designer" for a number of >>> fabless design houses and they like their names on the drawings ;-) >>> >>> >>> >>> ...Jim Thompson >>> >> One caution is that the kickstart has to be _small_, not much more than >> rounding error. A nanoamp is often a good value. Putting the current >> source in parallel with the crystal inductance will make sure that it >> starts off ringing at its natural frequency, which helps a lot. >> >> Cheers >> >> Phil Hobbs > > No. It has to be sufficient enough to significantly perturb the > quiescent operating point. The example has a 10ns wide x 1mA pulse.
The danger with that approach is that you can easily mask startup problems. I doubt that would happen to you very often, but as a piece of general advice to noobs it's not beneficial. Setting the tank ringing gently, so that it the circuit starts up in the small signal limit, is the ticket. A nanoamp is lots for that, if you put it in the right place, i.e. across the inductor. 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
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On 11/07/2015 11:47 AM, Phil Hobbs wrote:
> On 11/07/2015 10:59 AM, Jim Thompson wrote: >> On Sat, 7 Nov 2015 10:40:25 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 11/07/2015 10:34 AM, Jim Thompson wrote: >>>> On Sat, 07 Nov 2015 07:38:36 -0700, Jim Thompson >>>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >>>> >>>>> On Fri, 6 Nov 2015 19:31:46 -0800 (PST), dakupoto@gmail.com wrote: >>>>> >>>>>> Could some electronics/SPICE guru please help ? I have a >>>>>> simple model of a quartz crystal, as used in an oscillator. >>>>>> With my SPICE simulation, I can measure both the parallel >>>>>> and series resonant frequencies of the "pure" crystal. >>>>>> However, when I attach the same crystal to a biasing >>>>>> circuit, and run the simulation, the output is a flat DC >>>>>> offset. The biasing circuit involves two CMOS(1.0u micron >>>>>> gate length) inverters, as well as the large value feedback >>>>>> resistor, capacitirs etc. Is there anything special I need >>>>>> to do ? Any hints/suggestions would be helpful. Thanks in >>>>>> advance. >>>>> >>>>> Crystal oscillators can be very tricky to simulate. >>>>> >>>>> They _always_ need a "kick-start" of some sort to initiate the >>>>> oscillation. This can be by inserting a current pulse or skewing the >>>>> normal bias with a .IC statement. >>>>> >>>>> You will also need to set a very small timestep. >>>>> >>>>> If you are using LTspice, be sure to use the "Alternate" solver... the >>>>> "Normal" solver takes simplification liberties that will produce false >>>>> results on most anything but switchers. >>>>> >>>>> ...Jim Thompson >>>> >>>> An example... >>>> >>>> <http://www.analog-innovations.com/SED/XtalOscillatorExample.png> >>>> >>>> Several things to note: >>>> >>>> IKS is the "kick-start" current pulse. >>>> >>>> MaxTimeStep is set at 100ps >>>> >>>> SOLVER=0 is equivalent to LTspice's "Alternate" solver (Used to be >>>> PSpice's default solver until they decided to take liberties to >>>> speed-up simulation... not as bad as Mikey's "Normal", but loose >>>> enough not to handle crystal oscillators). >>>> >>>> What's with the Kiwi Semi? I am the "ghost designer" for a number of >>>> fabless design houses and they like their names on the drawings ;-) >>>> >>>> >>>> >>>> ...Jim Thompson >>>> >>> One caution is that the kickstart has to be _small_, not much more than >>> rounding error. A nanoamp is often a good value. Putting the current >>> source in parallel with the crystal inductance will make sure that it >>> starts off ringing at its natural frequency, which helps a lot. >>> >>> Cheers >>> >>> Phil Hobbs >> >> No. It has to be sufficient enough to significantly perturb the >> quiescent operating point. The example has a 10ns wide x 1mA pulse. > > The danger with that approach is that you can easily mask startup > problems. I doubt that would happen to you very often, but as a piece > of general advice to noobs it's not beneficial. > > Setting the tank ringing gently, so that it the circuit starts up in the > small signal limit, is the ticket. A nanoamp is lots for that, if you > put it in the right place, i.e. across the inductor. >
Like so. (Two posts, one with the schematic inline, the other as an attachment.) 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 --------------040003080400080306070608 Content-Type: application/pgp-encrypted; name="GentleKickstartOscillator.asc" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="GentleKickstartOscillator.asc" VmVyc2lvbiA0ClNIRUVUIDEgODgwIDY4MApXSVJFIDY0MCAtMTYwIDQ4MCAtMTYwCldJUkUg NDgwIC0xNDQgNDgwIC0xNjAKV0lSRSAyMjQgLTgwIDgwIC04MApXSVJFIDM2OCAtODAgMjI0 IC04MApXSVJFIDQzMiAtODAgMzY4IC04MApXSVJFIDY0MCAtODAgNjQwIC0xNjAKV0lSRSA4 MCAwIDgwIC04MApXSVJFIDgwIDAgMzIgMApXSVJFIDExMiAwIDgwIDAKV0lSRSAyMjQgMCAy MjQgLTgwCldJUkUgMzIgMTYgMzIgMApXSVJFIDM2OCAzMiAzNjggLTgwCldJUkUgNjQwIDgw IDY0MCAwCldJUkUgMzIgMTEyIDMyIDk2CldJUkUgMzIgMTEyIC0xMTIgMTEyCldJUkUgLTEx MiAxNDQgLTExMiAxMTIKV0lSRSAzMiAxNDQgMzIgMTEyCldJUkUgMjI0IDE0NCAyMjQgODAK V0lSRSAyNTYgMTQ0IDIyNCAxNDQKV0lSRSAzNjggMTQ0IDM2OCA5NgpXSVJFIDM2OCAxNDQg MzIwIDE0NApXSVJFIDQ4MCAxNDQgNDgwIC00OApXSVJFIDQ4MCAxNDQgMzY4IDE0NApXSVJF IDExMiAxNjAgMTEyIDAKV0lSRSA0ODAgMTkyIDQ4MCAxNDQKV0lSRSAyMjQgMjQwIDIyNCAx NDQKV0lSRSAtMTEyIDI1NiAtMTEyIDIyNApXSVJFIDMyIDI1NiAzMiAyMjQKV0lSRSAzMiAy NTYgLTExMiAyNTYKV0lSRSAzNjggMjU2IDM2OCAxNDQKV0lSRSAzMiAyNzIgMzIgMjU2CldJ UkUgNDgwIDMwNCA0ODAgMjcyCldJUkUgMzIgMzUyIDMyIDMzNgpXSVJFIDExMiAzNTIgMTEy IDIyNApXSVJFIDExMiAzNTIgMzIgMzUyCldJUkUgMTEyIDQxNiAxMTIgMzUyCldJUkUgMjI0 IDQxNiAyMjQgMzIwCldJUkUgMzY4IDQxNiAzNjggMzIwCldJUkUgNDgwIDQxNiA0ODAgMzg0 CkZMQUcgMTEyIDQxNiAwCkZMQUcgNDgwIDQxNiAwCkZMQUcgNjQwIDgwIDAKRkxBRyAyMjQg NDE2IDAKRkxBRyAzNjggNDE2IDAKU1lNQk9MIGluZCA0OCAyNDAgUjE4MApXSU5ET1cgMCAz NiA4MCBMZWZ0IDIKV0lORE9XIDMgMzYgNDAgTGVmdCAyClNZTUFUVFIgSW5zdE5hbWUgTDEK U1lNQVRUUiBWYWx1ZSAwLjMKU1lNQk9MIGNhcCAxNiAyNzIgUjAKU1lNQVRUUiBJbnN0TmFt ZSBDMQpTWU1BVFRSIFZhbHVlIDEuM2YKU1lNQk9MIGNhcCA5NiAxNjAgUjAKU1lNQVRUUiBJ bnN0TmFtZSBDMgpTWU1BVFRSIFZhbHVlIDJwClNZTUJPTCByZXMgMTYgMCBSMApTWU1BVFRS IEluc3ROYW1lIFIxClNZTUFUVFIgVmFsdWUgMjAKU1lNQk9MIG5qZiA0MzIgLTE0NCBSMApT WU1BVFRSIEluc3ROYW1lIEoxClNZTUFUVFIgVmFsdWUgMk40NDE2ClNZTUJPTCByZXMgNDY0 IDE3NiBSMApTWU1BVFRSIEluc3ROYW1lIFIyClNZTUFUVFIgVmFsdWUgMWsKU1lNQk9MIGNh cCAzNTIgMjU2IFIwCldJTkRPVyAzIDI4IDU4IExlZnQgMgpTWU1BVFRSIEluc3ROYW1lIEM0 ClNZTUFUVFIgVmFsdWUgMzlwClNZTUJPTCBjYXAgMzUyIDMyIFIwClNZTUFUVFIgSW5zdE5h bWUgQzUKU1lNQVRUUiBWYWx1ZSAxMHAKU1lNQk9MIHZvbHRhZ2UgNjQwIC05NiBSMApTWU1B VFRSIEluc3ROYW1lIFYxClNZTUFUVFIgVmFsdWUgMwpTWU1CT0wgcmVzIDIwOCAtMTYgUjAK U1lNQVRUUiBJbnN0TmFtZSBSMwpTWU1BVFRSIFZhbHVlIDFtZWcKU1lNQk9MIGN1cnJlbnQg LTExMiAxNDQgUjAKV0lORE9XIDMgLTExMSAtMTk5IExlZnQgMgpXSU5ET1cgMTIzIDAgMCBM ZWZ0IDIKV0lORE9XIDM5IDAgMCBMZWZ0IDIKU1lNQVRUUiBJbnN0TmFtZSBJMQpTWU1BVFRS IFZhbHVlIFBVTFNFKHtJa2lja30gMCAxMG4gMW4pClNZTUJPTCByZXMgMjA4IDIyNCBSMApT WU1BVFRSIEluc3ROYW1lIFI0ClNZTUFUVFIgVmFsdWUgMW1lZwpTWU1CT0wgY2FwIDI1NiAx NjAgUjI3MApXSU5ET1cgMCAzMiAzMiBWVG9wIDIKV0lORE9XIDMgMCAzMiBWQm90dG9tIDIK U1lNQVRUUiBJbnN0TmFtZSBDMwpTWU1BVFRSIFZhbHVlIDFuClNZTUJPTCBpbmQgNDY0IDI4 OCBSMApTWU1BVFRSIEluc3ROYW1lIEwyClNZTUFUVFIgVmFsdWUgMQpURVhUIC0yMDggMzIw IExlZnQgMiAhLnRyYW4gNTBtClRFWFQgLTE3NiAtMjAwIExlZnQgMiA7OCBNSHogQ3J5c3Rh bCBPc2NpbGxhdG9yIFdpdGgvV2l0aG91dCAgU21hbGwtU2lnbmFsIEtpY2tzdGFydApURVhU IC0yODAgNDAwIExlZnQgMiAhLnN0ZXAgcGFyYW0gSWtpY2sgbGlzdCAwLjAwMWYgMW4KVEVY VCAtMTY4IC0xNTIgTGVmdCAyIDtQaGlsIEhvYmJzLCAyMDE1LTExLTA3ClJFQ1RBTkdMRSBO b3JtYWwgMTc2IDM2OCAtMzIgLTMyIDIK --------------040003080400080306070608--
On 11/07/2015 11:47 AM, Phil Hobbs wrote:
> On 11/07/2015 10:59 AM, Jim Thompson wrote: >> On Sat, 7 Nov 2015 10:40:25 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 11/07/2015 10:34 AM, Jim Thompson wrote: >>>> On Sat, 07 Nov 2015 07:38:36 -0700, Jim Thompson >>>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >>>> >>>>> On Fri, 6 Nov 2015 19:31:46 -0800 (PST), dakupoto@gmail.com wrote: >>>>> >>>>>> Could some electronics/SPICE guru please help ? I have a >>>>>> simple model of a quartz crystal, as used in an oscillator. >>>>>> With my SPICE simulation, I can measure both the parallel >>>>>> and series resonant frequencies of the "pure" crystal. >>>>>> However, when I attach the same crystal to a biasing >>>>>> circuit, and run the simulation, the output is a flat DC >>>>>> offset. The biasing circuit involves two CMOS(1.0u micron >>>>>> gate length) inverters, as well as the large value feedback >>>>>> resistor, capacitirs etc. Is there anything special I need >>>>>> to do ? Any hints/suggestions would be helpful. Thanks in >>>>>> advance. >>>>> >>>>> Crystal oscillators can be very tricky to simulate. >>>>> >>>>> They _always_ need a "kick-start" of some sort to initiate the >>>>> oscillation. This can be by inserting a current pulse or skewing the >>>>> normal bias with a .IC statement. >>>>> >>>>> You will also need to set a very small timestep. >>>>> >>>>> If you are using LTspice, be sure to use the "Alternate" solver... the >>>>> "Normal" solver takes simplification liberties that will produce false >>>>> results on most anything but switchers. >>>>> >>>>> ...Jim Thompson >>>> >>>> An example... >>>> >>>> <http://www.analog-innovations.com/SED/XtalOscillatorExample.png> >>>> >>>> Several things to note: >>>> >>>> IKS is the "kick-start" current pulse. >>>> >>>> MaxTimeStep is set at 100ps >>>> >>>> SOLVER=0 is equivalent to LTspice's "Alternate" solver (Used to be >>>> PSpice's default solver until they decided to take liberties to >>>> speed-up simulation... not as bad as Mikey's "Normal", but loose >>>> enough not to handle crystal oscillators). >>>> >>>> What's with the Kiwi Semi? I am the "ghost designer" for a number of >>>> fabless design houses and they like their names on the drawings ;-) >>>> >>>> >>>> >>>> ...Jim Thompson >>>> >>> One caution is that the kickstart has to be _small_, not much more than >>> rounding error. A nanoamp is often a good value. Putting the current >>> source in parallel with the crystal inductance will make sure that it >>> starts off ringing at its natural frequency, which helps a lot. >>> >>> Cheers >>> >>> Phil Hobbs >> >> No. It has to be sufficient enough to significantly perturb the >> quiescent operating point. The example has a 10ns wide x 1mA pulse. > > The danger with that approach is that you can easily mask startup > problems. I doubt that would happen to you very often, but as a piece > of general advice to noobs it's not beneficial. > > Setting the tank ringing gently, so that it the circuit starts up in the > small signal limit, is the ticket. A nanoamp is lots for that, if you > put it in the right place, i.e. across the inductor. >
Like so. (Two posts, one with the schematic inline, the other as an attachment.) Cheers Phil Hobbs ============ Version 4 SHEET 1 880 680 WIRE 640 -160 480 -160 WIRE 480 -144 480 -160 WIRE 224 -80 80 -80 WIRE 368 -80 224 -80 WIRE 432 -80 368 -80 WIRE 640 -80 640 -160 WIRE 80 0 80 -80 WIRE 80 0 32 0 WIRE 112 0 80 0 WIRE 224 0 224 -80 WIRE 32 16 32 0 WIRE 368 32 368 -80 WIRE 640 80 640 0 WIRE 32 112 32 96 WIRE 32 112 -112 112 WIRE -112 144 -112 112 WIRE 32 144 32 112 WIRE 224 144 224 80 WIRE 256 144 224 144 WIRE 368 144 368 96 WIRE 368 144 320 144 WIRE 480 144 480 -48 WIRE 480 144 368 144 WIRE 112 160 112 0 WIRE 480 192 480 144 WIRE 224 240 224 144 WIRE -112 256 -112 224 WIRE 32 256 32 224 WIRE 32 256 -112 256 WIRE 368 256 368 144 WIRE 32 272 32 256 WIRE 480 304 480 272 WIRE 32 352 32 336 WIRE 112 352 112 224 WIRE 112 352 32 352 WIRE 112 416 112 352 WIRE 224 416 224 320 WIRE 368 416 368 320 WIRE 480 416 480 384 FLAG 112 416 0 FLAG 480 416 0 FLAG 640 80 0 FLAG 224 416 0 FLAG 368 416 0 SYMBOL ind 48 240 R180 WINDOW 0 36 80 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName L1 SYMATTR Value 0.3 SYMBOL cap 16 272 R0 SYMATTR InstName C1 SYMATTR Value 1.3f SYMBOL cap 96 160 R0 SYMATTR InstName C2 SYMATTR Value 2p SYMBOL res 16 0 R0 SYMATTR InstName R1 SYMATTR Value 20 SYMBOL njf 432 -144 R0 SYMATTR InstName J1 SYMATTR Value 2N4416 SYMBOL res 464 176 R0 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL cap 352 256 R0 WINDOW 3 28 58 Left 2 SYMATTR InstName C4 SYMATTR Value 39p SYMBOL cap 352 32 R0 SYMATTR InstName C5 SYMATTR Value 10p SYMBOL voltage 640 -96 R0 SYMATTR InstName V1 SYMATTR Value 3 SYMBOL res 208 -16 R0 SYMATTR InstName R3 SYMATTR Value 1meg SYMBOL current -112 144 R0 WINDOW 3 -111 -199 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName I1 SYMATTR Value PULSE({Ikick} 0 10n 1n) SYMBOL res 208 224 R0 SYMATTR InstName R4 SYMATTR Value 1meg SYMBOL cap 256 160 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName C3 SYMATTR Value 1n SYMBOL ind 464 288 R0 SYMATTR InstName L2 SYMATTR Value 1 TEXT -208 320 Left 2 !.tran 50m TEXT -176 -200 Left 2 ;8 MHz Crystal Oscillator With/Without Small-Signal Kickstart TEXT -280 400 Left 2 !.step param Ikick list 0.001f 1n TEXT -168 -152 Left 2 ;Phil Hobbs, 2015-11-07 RECTANGLE Normal 176 368 -32 -32 2 -- 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