On Wednesday, October 25, 2023 at 2:22:37 PM UTC-4, john larkin wrote:> On Wed, 25 Oct 2023 09:23:20 -0700 (PDT), Fred Bloggs > <bloggs.fred...@gmail.com> wrote: > >On Wednesday, October 25, 2023 at 6:40:17?AM UTC-4, John Larkin wrote: > >> On Wed, 25 Oct 2023 07:18:58 +0300, Dimiter_Popoff <d...@tgi-sci.com> > >> wrote: > >> > >> >On 10/25/2023 1:51, john larkin wrote: > >> >> On Wed, 25 Oct 2023 01:12:21 +0300, Dimiter_Popoff <d...@tgi-sci.com> > >> >> wrote: > >> >> > >> >>> On 10/25/2023 0:34, john larkin wrote: > >> >>>> Tww it the dimensionless factor > >> >>>> > >> >>>> (how many parts you tidly-wink and lose) / (how many parts you want) > >> >>>> > >> >>>> which, for 0603's, runs 0.6 or so. > >> >>>> > >> >>> > >> >>> Not sure I got what tww is (looked it up, some domino thing so I > >> >>> guess I get it if so) but 0402 are significantly worse, a lot more > >> >>> than twice worse. And I have not yet done any 0201... > >> >> > >> >> When I first saw 1206's, I thought they were tiny. Ha! > >> >> > >> >> I refuse to use 0402's. I default to 0805s. > >> >> > >> >> I'm tuning the tempco of a 50 MHz triggrered Colpitts oscillator. What > >> >> a nuisance. It should have a 3.3 pF N4700 0805 cap, but the layout guy > >> >> used all 0603s, so some engineer (who shall not be named) substituted > >> >> an 0603 NP0. "NTC" does sound a lot like "NPO" I guess. > >> >> > >> >> The proper 0805 cap was custom brewed for us by Capax. > >> >> > >> > > >> >I often do it the other way around,the 0805 pads I make can also hold > >> >0603. Took me a while to grasp I could do it the first time I could > >> >not find the 0805 I needed... > >> > > >> >The temp compensations I typically have to deal with are resistor > >> >tracking. Meanwhile I know which batch of which supply I have > >> >does not track too well with which other. > >> What I'm fighting right now is the positive TC of the Coilcraft > >> Midi-spring inductor (typically +100 PPM/c or so) and the positive TC > >> of the PCB FR4, typically +900. The combo makes the oscillator have a > >> serious negative TC, which the N4700 cap compensates. I have a series > >> padder cap, in series with the NTC cap, to trim the oscillator tempco > >> to near zero, down to the 2nd order parabola. > >> > >> It's tedious. Tuning takes about an hour per iteration. We have a > >> gigantic environmental oven in the basement, but using that would take > >> more like a day per iteration. I made my own benchtop chamber, a > >> cardboard box with a USB fan inside, used with a heat gun and freeze > >> spray. > >> > >> My $5000 Rigol scope is the frequncy counter and USB fan supply. > > > >You're using an LC tuned Colpitts? > Yes. It uses a SAV551 phemt as a source follower driving the usual two > caps back into the tank. > > Here's my temp chamber. > > https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1 > > I blast it with a heat gun or freeze spray to evaluate tempco. This > gadget has a pretty narrow pull range PLL to lock the triggered LC > oscillator to a crystal oscillator, and it will fail lock if > temperature changes the LC osc frequency more than maybe 1000 PPM. > > We use a digital capacitor to center the frequency to close to 50 MHz > at powerup, but then it's usually cold, and can't drift more than the > 1000 PPM after that.You need to re-examine your lock-in idea and make it a coarse/fine tuning one. Are you using some digital discriminator in an FPGA or something minimal like that?> > Tedious. > > DOGBERRY: But truly, if I were as tedious as a king, I would find it > in my heart to give it all to you, your Worship. LEONATO: All thy > tediousness on me, ah?
Tww
Started by ●October 24, 2023
Reply by ●October 25, 20232023-10-25
Reply by ●October 25, 20232023-10-25
On Wednesday, October 25, 2023 at 2:22:37 PM UTC-4, john larkin wrote:> On Wed, 25 Oct 2023 09:23:20 -0700 (PDT), Fred Bloggs > <bloggs.fred...@gmail.com> wrote: > >On Wednesday, October 25, 2023 at 6:40:17?AM UTC-4, John Larkin wrote: > >> On Wed, 25 Oct 2023 07:18:58 +0300, Dimiter_Popoff <d...@tgi-sci.com> > >> wrote: > >> > >> >On 10/25/2023 1:51, john larkin wrote: > >> >> On Wed, 25 Oct 2023 01:12:21 +0300, Dimiter_Popoff <d...@tgi-sci.com> > >> >> wrote: > >> >> > >> >>> On 10/25/2023 0:34, john larkin wrote: > >> >>>> Tww it the dimensionless factor > >> >>>> > >> >>>> (how many parts you tidly-wink and lose) / (how many parts you want) > >> >>>> > >> >>>> which, for 0603's, runs 0.6 or so. > >> >>>> > >> >>> > >> >>> Not sure I got what tww is (looked it up, some domino thing so I > >> >>> guess I get it if so) but 0402 are significantly worse, a lot more > >> >>> than twice worse. And I have not yet done any 0201... > >> >> > >> >> When I first saw 1206's, I thought they were tiny. Ha! > >> >> > >> >> I refuse to use 0402's. I default to 0805s. > >> >> > >> >> I'm tuning the tempco of a 50 MHz triggrered Colpitts oscillator. What > >> >> a nuisance. It should have a 3.3 pF N4700 0805 cap, but the layout guy > >> >> used all 0603s, so some engineer (who shall not be named) substituted > >> >> an 0603 NP0. "NTC" does sound a lot like "NPO" I guess. > >> >> > >> >> The proper 0805 cap was custom brewed for us by Capax. > >> >> > >> > > >> >I often do it the other way around,the 0805 pads I make can also hold > >> >0603. Took me a while to grasp I could do it the first time I could > >> >not find the 0805 I needed... > >> > > >> >The temp compensations I typically have to deal with are resistor > >> >tracking. Meanwhile I know which batch of which supply I have > >> >does not track too well with which other. > >> What I'm fighting right now is the positive TC of the Coilcraft > >> Midi-spring inductor (typically +100 PPM/c or so) and the positive TC > >> of the PCB FR4, typically +900. The combo makes the oscillator have a > >> serious negative TC, which the N4700 cap compensates. I have a series > >> padder cap, in series with the NTC cap, to trim the oscillator tempco > >> to near zero, down to the 2nd order parabola. > >> > >> It's tedious. Tuning takes about an hour per iteration. We have a > >> gigantic environmental oven in the basement, but using that would take > >> more like a day per iteration. I made my own benchtop chamber, a > >> cardboard box with a USB fan inside, used with a heat gun and freeze > >> spray. > >> > >> My $5000 Rigol scope is the frequncy counter and USB fan supply. > > > >You're using an LC tuned Colpitts? > Yes. It uses a SAV551 phemt as a source follower driving the usual two > caps back into the tank. > > Here's my temp chamber. > > https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1 > > I blast it with a heat gun or freeze spray to evaluate tempco. This > gadget has a pretty narrow pull range PLL to lock the triggered LC > oscillator to a crystal oscillator, and it will fail lock if > temperature changes the LC osc frequency more than maybe 1000 PPM. > > We use a digital capacitor to center the frequency to close to 50 MHz > at powerup, but then it's usually cold, and can't drift more than the > 1000 PPM after that. > > Tedious. > > DOGBERRY: But truly, if I were as tedious as a king, I would find it > in my heart to give it all to you, your Worship. LEONATO: All thy > tediousness on me, ah?I found this after an exhausting 15-second search. There are tons of others: https://www.sciencedirect.com/science/article/abs/pii/S0026269216306036
Reply by ●October 26, 20232023-10-26
On Wed, 25 Oct 2023 21:02:50 +0100, piglet <erichpwagner@hotmail.com> wrote:>On 25/10/2023 19:22, john larkin wrote: >> On Wed, 25 Oct 2023 09:23:20 -0700 (PDT), Fred Bloggs >> <bloggs.fredbloggs.fred@gmail.com> wrote: >> >>> On Wednesday, October 25, 2023 at 6:40:17?AM UTC-4, John Larkin wrote: >>>> On Wed, 25 Oct 2023 07:18:58 +0300, Dimiter_Popoff <d...@tgi-sci.com> >>>> wrote: >>>> >>>>> On 10/25/2023 1:51, john larkin wrote: >>>>>> On Wed, 25 Oct 2023 01:12:21 +0300, Dimiter_Popoff <d...@tgi-sci.com> >>>>>> wrote: >>>>>> >>>>>>> On 10/25/2023 0:34, john larkin wrote: >>>>>>>> Tww it the dimensionless factor >>>>>>>> >>>>>>>> (how many parts you tidly-wink and lose) / (how many parts you want) >>>>>>>> >>>>>>>> which, for 0603's, runs 0.6 or so. >>>>>>>> >>>>>>> >>>>>>> Not sure I got what tww is (looked it up, some domino thing so I >>>>>>> guess I get it if so) but 0402 are significantly worse, a lot more >>>>>>> than twice worse. And I have not yet done any 0201... >>>>>> >>>>>> When I first saw 1206's, I thought they were tiny. Ha! >>>>>> >>>>>> I refuse to use 0402's. I default to 0805s. >>>>>> >>>>>> I'm tuning the tempco of a 50 MHz triggrered Colpitts oscillator. What >>>>>> a nuisance. It should have a 3.3 pF N4700 0805 cap, but the layout guy >>>>>> used all 0603s, so some engineer (who shall not be named) substituted >>>>>> an 0603 NP0. "NTC" does sound a lot like "NPO" I guess. >>>>>> >>>>>> The proper 0805 cap was custom brewed for us by Capax. >>>>>> >>>>> >>>>> I often do it the other way around,the 0805 pads I make can also hold >>>>> 0603. Took me a while to grasp I could do it the first time I could >>>>> not find the 0805 I needed... >>>>> >>>>> The temp compensations I typically have to deal with are resistor >>>>> tracking. Meanwhile I know which batch of which supply I have >>>>> does not track too well with which other. >>>> What I'm fighting right now is the positive TC of the Coilcraft >>>> Midi-spring inductor (typically +100 PPM/c or so) and the positive TC >>>> of the PCB FR4, typically +900. The combo makes the oscillator have a >>>> serious negative TC, which the N4700 cap compensates. I have a series >>>> padder cap, in series with the NTC cap, to trim the oscillator tempco >>>> to near zero, down to the 2nd order parabola. >>>> >>>> It's tedious. Tuning takes about an hour per iteration. We have a >>>> gigantic environmental oven in the basement, but using that would take >>>> more like a day per iteration. I made my own benchtop chamber, a >>>> cardboard box with a USB fan inside, used with a heat gun and freeze >>>> spray. >>>> >>>> My $5000 Rigol scope is the frequncy counter and USB fan supply. >>> >>> You're using an LC tuned Colpitts? >> >> Yes. It uses a SAV551 phemt as a source follower driving the usual two >> caps back into the tank. >> >> Here's my temp chamber. >> >> https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1 >> >> I blast it with a heat gun or freeze spray to evaluate tempco. This >> gadget has a pretty narrow pull range PLL to lock the triggered LC >> oscillator to a crystal oscillator, and it will fail lock if >> temperature changes the LC osc frequency more than maybe 1000 PPM. >> >> We use a digital capacitor to center the frequency to close to 50 MHz >> at powerup, but then it's usually cold, and can't drift more than the >> 1000 PPM after that. >> >> Tedious. >> >> DOGBERRY: But truly, if I were as tedious as a king, I would find it >> in my heart to give it all to you, your Worship. LEONATO: All thy >> tediousness on me, ah? >> > >I assume that board has an MCU and with many now including on chip >temperature measurement can you use the digital capacitor to do the temp >compensation in software? > >piglet > >No. We don't know when we might get a trigger, and tuning the digital cap would disrupt a timing cycle. There is a dac+varicap for fine tuning, and that is used for locking the LC oscillator to the XO. The trick in a digital delay generator is to get crystal oscillator accuracy, but not quantize timings to the clock edges. There's a wikipedia article about various ways to accomplish that trick; I wrote some of it.
Reply by ●October 26, 20232023-10-26
On Wed, 25 Oct 2023 13:50:35 -0700 (PDT), Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote:>On Wednesday, October 25, 2023 at 2:22:37?PM UTC-4, john larkin wrote: >> On Wed, 25 Oct 2023 09:23:20 -0700 (PDT), Fred Bloggs >> <bloggs.fred...@gmail.com> wrote: >> >On Wednesday, October 25, 2023 at 6:40:17?AM UTC-4, John Larkin wrote: >> >> On Wed, 25 Oct 2023 07:18:58 +0300, Dimiter_Popoff <d...@tgi-sci.com> >> >> wrote: >> >> >> >> >On 10/25/2023 1:51, john larkin wrote: >> >> >> On Wed, 25 Oct 2023 01:12:21 +0300, Dimiter_Popoff <d...@tgi-sci.com> >> >> >> wrote: >> >> >> >> >> >>> On 10/25/2023 0:34, john larkin wrote: >> >> >>>> Tww it the dimensionless factor >> >> >>>> >> >> >>>> (how many parts you tidly-wink and lose) / (how many parts you want) >> >> >>>> >> >> >>>> which, for 0603's, runs 0.6 or so. >> >> >>>> >> >> >>> >> >> >>> Not sure I got what tww is (looked it up, some domino thing so I >> >> >>> guess I get it if so) but 0402 are significantly worse, a lot more >> >> >>> than twice worse. And I have not yet done any 0201... >> >> >> >> >> >> When I first saw 1206's, I thought they were tiny. Ha! >> >> >> >> >> >> I refuse to use 0402's. I default to 0805s. >> >> >> >> >> >> I'm tuning the tempco of a 50 MHz triggrered Colpitts oscillator. What >> >> >> a nuisance. It should have a 3.3 pF N4700 0805 cap, but the layout guy >> >> >> used all 0603s, so some engineer (who shall not be named) substituted >> >> >> an 0603 NP0. "NTC" does sound a lot like "NPO" I guess. >> >> >> >> >> >> The proper 0805 cap was custom brewed for us by Capax. >> >> >> >> >> > >> >> >I often do it the other way around,the 0805 pads I make can also hold >> >> >0603. Took me a while to grasp I could do it the first time I could >> >> >not find the 0805 I needed... >> >> > >> >> >The temp compensations I typically have to deal with are resistor >> >> >tracking. Meanwhile I know which batch of which supply I have >> >> >does not track too well with which other. >> >> What I'm fighting right now is the positive TC of the Coilcraft >> >> Midi-spring inductor (typically +100 PPM/c or so) and the positive TC >> >> of the PCB FR4, typically +900. The combo makes the oscillator have a >> >> serious negative TC, which the N4700 cap compensates. I have a series >> >> padder cap, in series with the NTC cap, to trim the oscillator tempco >> >> to near zero, down to the 2nd order parabola. >> >> >> >> It's tedious. Tuning takes about an hour per iteration. We have a >> >> gigantic environmental oven in the basement, but using that would take >> >> more like a day per iteration. I made my own benchtop chamber, a >> >> cardboard box with a USB fan inside, used with a heat gun and freeze >> >> spray. >> >> >> >> My $5000 Rigol scope is the frequncy counter and USB fan supply. >> > >> >You're using an LC tuned Colpitts? >> Yes. It uses a SAV551 phemt as a source follower driving the usual two >> caps back into the tank. >> >> Here's my temp chamber. >> >> https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1 >> >> I blast it with a heat gun or freeze spray to evaluate tempco. This >> gadget has a pretty narrow pull range PLL to lock the triggered LC >> oscillator to a crystal oscillator, and it will fail lock if >> temperature changes the LC osc frequency more than maybe 1000 PPM. >> >> We use a digital capacitor to center the frequency to close to 50 MHz >> at powerup, but then it's usually cold, and can't drift more than the >> 1000 PPM after that. >> >> Tedious. >> >> DOGBERRY: But truly, if I were as tedious as a king, I would find it >> in my heart to give it all to you, your Worship. LEONATO: All thy >> tediousness on me, ah? > >I found this after an exhausting 15-second search. There are tons of others: > >https://www.sciencedirect.com/science/article/abs/pii/S0026269216306036The trick in a digital delay generator, or at least ours, is to stop an LC oscillator and start it when we get an external trigger, and then use it as our timebase. But lock it to an crystal oscillator to keep long delays accurate. To do that, I need a pretty stable LC oscillator, hence the tempco tuning. Capex made us a reel of custom N4700 ceramic caps, which can be used to compensate the pretty awful inductor and FR4 tempcos. HP made one delay generator that actually started and stopped a crystal oscillator. It didn't work very well. A quartz crystal is hard to kick start and is even worse to stop; it rings like a bell.
Reply by ●October 26, 20232023-10-26
On Wed, 25 Oct 2023 13:45:19 -0700 (PDT), Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote:>On Wednesday, October 25, 2023 at 2:22:37?PM UTC-4, john larkin wrote: >> On Wed, 25 Oct 2023 09:23:20 -0700 (PDT), Fred Bloggs >> <bloggs.fred...@gmail.com> wrote: >> >On Wednesday, October 25, 2023 at 6:40:17?AM UTC-4, John Larkin wrote: >> >> On Wed, 25 Oct 2023 07:18:58 +0300, Dimiter_Popoff <d...@tgi-sci.com> >> >> wrote: >> >> >> >> >On 10/25/2023 1:51, john larkin wrote: >> >> >> On Wed, 25 Oct 2023 01:12:21 +0300, Dimiter_Popoff <d...@tgi-sci.com> >> >> >> wrote: >> >> >> >> >> >>> On 10/25/2023 0:34, john larkin wrote: >> >> >>>> Tww it the dimensionless factor >> >> >>>> >> >> >>>> (how many parts you tidly-wink and lose) / (how many parts you want) >> >> >>>> >> >> >>>> which, for 0603's, runs 0.6 or so. >> >> >>>> >> >> >>> >> >> >>> Not sure I got what tww is (looked it up, some domino thing so I >> >> >>> guess I get it if so) but 0402 are significantly worse, a lot more >> >> >>> than twice worse. And I have not yet done any 0201... >> >> >> >> >> >> When I first saw 1206's, I thought they were tiny. Ha! >> >> >> >> >> >> I refuse to use 0402's. I default to 0805s. >> >> >> >> >> >> I'm tuning the tempco of a 50 MHz triggrered Colpitts oscillator. What >> >> >> a nuisance. It should have a 3.3 pF N4700 0805 cap, but the layout guy >> >> >> used all 0603s, so some engineer (who shall not be named) substituted >> >> >> an 0603 NP0. "NTC" does sound a lot like "NPO" I guess. >> >> >> >> >> >> The proper 0805 cap was custom brewed for us by Capax. >> >> >> >> >> > >> >> >I often do it the other way around,the 0805 pads I make can also hold >> >> >0603. Took me a while to grasp I could do it the first time I could >> >> >not find the 0805 I needed... >> >> > >> >> >The temp compensations I typically have to deal with are resistor >> >> >tracking. Meanwhile I know which batch of which supply I have >> >> >does not track too well with which other. >> >> What I'm fighting right now is the positive TC of the Coilcraft >> >> Midi-spring inductor (typically +100 PPM/c or so) and the positive TC >> >> of the PCB FR4, typically +900. The combo makes the oscillator have a >> >> serious negative TC, which the N4700 cap compensates. I have a series >> >> padder cap, in series with the NTC cap, to trim the oscillator tempco >> >> to near zero, down to the 2nd order parabola. >> >> >> >> It's tedious. Tuning takes about an hour per iteration. We have a >> >> gigantic environmental oven in the basement, but using that would take >> >> more like a day per iteration. I made my own benchtop chamber, a >> >> cardboard box with a USB fan inside, used with a heat gun and freeze >> >> spray. >> >> >> >> My $5000 Rigol scope is the frequncy counter and USB fan supply. >> > >> >You're using an LC tuned Colpitts? >> Yes. It uses a SAV551 phemt as a source follower driving the usual two >> caps back into the tank. >> >> Here's my temp chamber. >> >> https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1 >> >> I blast it with a heat gun or freeze spray to evaluate tempco. This >> gadget has a pretty narrow pull range PLL to lock the triggered LC >> oscillator to a crystal oscillator, and it will fail lock if >> temperature changes the LC osc frequency more than maybe 1000 PPM. >> >> We use a digital capacitor to center the frequency to close to 50 MHz >> at powerup, but then it's usually cold, and can't drift more than the >> 1000 PPM after that. > >You need to re-examine your lock-in idea and make it a coarse/fine tuning one.Well, no.> >Are you using some digital discriminator in an FPGA or something minimal like that?When we get a trigger, we measure the phase (actually time) difference between the triggered LC oscillator and a continuous-running crystal oscillator, and lock that difference in. The logic is in an FPGA, but the fun parts are analog.
Reply by ●October 26, 20232023-10-26
On Tue, 24 Oct 2023 22:40:39 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Dimiter_Popoff <dp@tgi-sci.com> wrote: >> On 10/25/2023 0:34, john larkin wrote: >>> Tww it the dimensionless factor >>> >>> (how many parts you tidly-wink and lose) / (how many parts you want) >>> >>> which, for 0603's, runs 0.6 or so. >>> >> >> Not sure I got what tww is (looked it up, some domino thing so I >> guess I get it if so) but 0402 are significantly worse, a lot more >> than twice worse. And I have not yet done any 0201... >> > >I highly recommend a good set of curved jaw tweezers, with a tiny binder >clip on the hinge end. That lets you micro-adjust the tension by sliding >the clip, so that they open when you squeeze them edgeways, and close very >gently when you release. > >Good Medicine. > >Cheers > >Phil HobbsMy Tww:0603 factor is above unity today. Must have been something I ate. I do have curved tweezers. I'll try the binder clip thing.
Reply by ●October 26, 20232023-10-26
On a sunny day (Wed, 25 Oct 2023 20:45:52 -0700) it happened John Larkin <jl@997PotHill.com> wrote in <hknjjih3rp87naoq2o2pefergou2deg7i4@4ax.com>:>The trick in a digital delay generator, or at least ours, is to stop >an LC oscillator and start it when we get an external trigger, and >then use it as our timebase. But lock it to an crystal oscillator to >keep long delays accurate. > >To do that, I need a pretty stable LC oscillator, hence the tempco >tuning. Capex made us a reel of custom N4700 ceramic caps, which can >be used to compensate the pretty awful inductor and FR4 tempcos. > >HP made one delay generator that actually started and stopped a >crystal oscillator. It didn't work very well. A quartz crystal is hard >to kick start and is even worse to stop; it rings like a bell.All this makes me think about a 4046 and PLL.
Reply by ●October 26, 20232023-10-26
On 26/10/2023 04:34, John Larkin wrote:> On Wed, 25 Oct 2023 21:02:50 +0100, piglet <erichpwagner@hotmail.com> > wrote: > >> On 25/10/2023 19:22, john larkin wrote: >>> On Wed, 25 Oct 2023 09:23:20 -0700 (PDT), Fred Bloggs >>> <bloggs.fredbloggs.fred@gmail.com> wrote: >>> >>>> On Wednesday, October 25, 2023 at 6:40:17?AM UTC-4, John Larkin wrote: >>>>> On Wed, 25 Oct 2023 07:18:58 +0300, Dimiter_Popoff <d...@tgi-sci.com> >>>>> wrote: >>>>> >>>>>> On 10/25/2023 1:51, john larkin wrote: >>>>>>> On Wed, 25 Oct 2023 01:12:21 +0300, Dimiter_Popoff <d...@tgi-sci.com> >>>>>>> wrote: >>>>>>> >>>>>>>> On 10/25/2023 0:34, john larkin wrote: >>>>>>>>> Tww it the dimensionless factor >>>>>>>>> >>>>>>>>> (how many parts you tidly-wink and lose) / (how many parts you want) >>>>>>>>> >>>>>>>>> which, for 0603's, runs 0.6 or so. >>>>>>>>> >>>>>>>> >>>>>>>> Not sure I got what tww is (looked it up, some domino thing so I >>>>>>>> guess I get it if so) but 0402 are significantly worse, a lot more >>>>>>>> than twice worse. And I have not yet done any 0201... >>>>>>> >>>>>>> When I first saw 1206's, I thought they were tiny. Ha! >>>>>>> >>>>>>> I refuse to use 0402's. I default to 0805s. >>>>>>> >>>>>>> I'm tuning the tempco of a 50 MHz triggrered Colpitts oscillator. What >>>>>>> a nuisance. It should have a 3.3 pF N4700 0805 cap, but the layout guy >>>>>>> used all 0603s, so some engineer (who shall not be named) substituted >>>>>>> an 0603 NP0. "NTC" does sound a lot like "NPO" I guess. >>>>>>> >>>>>>> The proper 0805 cap was custom brewed for us by Capax. >>>>>>> >>>>>> >>>>>> I often do it the other way around,the 0805 pads I make can also hold >>>>>> 0603. Took me a while to grasp I could do it the first time I could >>>>>> not find the 0805 I needed... >>>>>> >>>>>> The temp compensations I typically have to deal with are resistor >>>>>> tracking. Meanwhile I know which batch of which supply I have >>>>>> does not track too well with which other. >>>>> What I'm fighting right now is the positive TC of the Coilcraft >>>>> Midi-spring inductor (typically +100 PPM/c or so) and the positive TC >>>>> of the PCB FR4, typically +900. The combo makes the oscillator have a >>>>> serious negative TC, which the N4700 cap compensates. I have a series >>>>> padder cap, in series with the NTC cap, to trim the oscillator tempco >>>>> to near zero, down to the 2nd order parabola. >>>>> >>>>> It's tedious. Tuning takes about an hour per iteration. We have a >>>>> gigantic environmental oven in the basement, but using that would take >>>>> more like a day per iteration. I made my own benchtop chamber, a >>>>> cardboard box with a USB fan inside, used with a heat gun and freeze >>>>> spray. >>>>> >>>>> My $5000 Rigol scope is the frequncy counter and USB fan supply. >>>> >>>> You're using an LC tuned Colpitts? >>> >>> Yes. It uses a SAV551 phemt as a source follower driving the usual two >>> caps back into the tank. >>> >>> Here's my temp chamber. >>> >>> https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1 >>> >>> I blast it with a heat gun or freeze spray to evaluate tempco. This >>> gadget has a pretty narrow pull range PLL to lock the triggered LC >>> oscillator to a crystal oscillator, and it will fail lock if >>> temperature changes the LC osc frequency more than maybe 1000 PPM. >>> >>> We use a digital capacitor to center the frequency to close to 50 MHz >>> at powerup, but then it's usually cold, and can't drift more than the >>> 1000 PPM after that. >>> >>> Tedious. >>> >>> DOGBERRY: But truly, if I were as tedious as a king, I would find it >>> in my heart to give it all to you, your Worship. LEONATO: All thy >>> tediousness on me, ah? >>> >> >> I assume that board has an MCU and with many now including on chip >> temperature measurement can you use the digital capacitor to do the temp >> compensation in software? >> >> piglet >> >> > > No. We don't know when we might get a trigger, and tuning the digital > cap would disrupt a timing cycle. There is a dac+varicap for fine > tuning, and that is used for locking the LC oscillator to the XO. > > The trick in a digital delay generator is to get crystal oscillator > accuracy, but not quantize timings to the clock edges. > > There's a wikipedia article about various ways to accomplish that > trick; I wrote some of it. >You know your project far better than me but I don't understand why the temp tuning varicap or digi-cap can't make tiny slow changes while the oscillator is running - after all you can't very well stop the N4700 cap from shifting value during an oscillator run? piglet
Reply by ●October 26, 20232023-10-26
On Thursday, October 26, 2023 at 9:05:29 PM UTC+11, piglet wrote:> On 26/10/2023 04:34, John Larkin wrote: > > On Wed, 25 Oct 2023 21:02:50 +0100, piglet <erichp...@hotmail.com> > > wrote: > > > >> On 25/10/2023 19:22, john larkin wrote: > >>> On Wed, 25 Oct 2023 09:23:20 -0700 (PDT), Fred Bloggs > >>> <bloggs.fred...@gmail.com> wrote: > >>> > >>>> On Wednesday, October 25, 2023 at 6:40:17?AM UTC-4, John Larkin wrote: > >>>>> On Wed, 25 Oct 2023 07:18:58 +0300, Dimiter_Popoff <d...@tgi-sci.com> > >>>>> wrote: > >>>>> > >>>>>> On 10/25/2023 1:51, john larkin wrote: > >>>>>>> On Wed, 25 Oct 2023 01:12:21 +0300, Dimiter_Popoff <d...@tgi-sci.com> > >>>>>>> wrote: > >>>>>>> > >>>>>>>> On 10/25/2023 0:34, john larkin wrote: > >>>>>>>>> Tww it the dimensionless factor > >>>>>>>>> > >>>>>>>>> (how many parts you tidly-wink and lose) / (how many parts you want) > >>>>>>>>> > >>>>>>>>> which, for 0603's, runs 0.6 or so. > >>>>>>>>> > >>>>>>>> > >>>>>>>> Not sure I got what tww is (looked it up, some domino thing so I > >>>>>>>> guess I get it if so) but 0402 are significantly worse, a lot more > >>>>>>>> than twice worse. And I have not yet done any 0201... > >>>>>>> > >>>>>>> When I first saw 1206's, I thought they were tiny. Ha! > >>>>>>> > >>>>>>> I refuse to use 0402's. I default to 0805s. > >>>>>>> > >>>>>>> I'm tuning the tempco of a 50 MHz triggrered Colpitts oscillator. What > >>>>>>> a nuisance. It should have a 3.3 pF N4700 0805 cap, but the layout guy > >>>>>>> used all 0603s, so some engineer (who shall not be named) substituted > >>>>>>> an 0603 NP0. "NTC" does sound a lot like "NPO" I guess. > >>>>>>> > >>>>>>> The proper 0805 cap was custom brewed for us by Capax. > >>>>>>> > >>>>>> > >>>>>> I often do it the other way around,the 0805 pads I make can also hold > >>>>>> 0603. Took me a while to grasp I could do it the first time I could > >>>>>> not find the 0805 I needed... > >>>>>> > >>>>>> The temp compensations I typically have to deal with are resistor > >>>>>> tracking. Meanwhile I know which batch of which supply I have > >>>>>> does not track too well with which other. > >>>>> What I'm fighting right now is the positive TC of the Coilcraft > >>>>> Midi-spring inductor (typically +100 PPM/c or so) and the positive TC > >>>>> of the PCB FR4, typically +900. The combo makes the oscillator have a > >>>>> serious negative TC, which the N4700 cap compensates. I have a series > >>>>> padder cap, in series with the NTC cap, to trim the oscillator tempco > >>>>> to near zero, down to the 2nd order parabola. > >>>>> > >>>>> It's tedious. Tuning takes about an hour per iteration. We have a > >>>>> gigantic environmental oven in the basement, but using that would take > >>>>> more like a day per iteration. I made my own benchtop chamber, a > >>>>> cardboard box with a USB fan inside, used with a heat gun and freeze > >>>>> spray. > >>>>> > >>>>> My $5000 Rigol scope is the frequncy counter and USB fan supply. > >>>> > >>>> You're using an LC tuned Colpitts? > >>> > >>> Yes. It uses a SAV551 phemt as a source follower driving the usual two > >>> caps back into the tank. > >>> > >>> Here's my temp chamber. > >>> > >>> https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1 > >>> > >>> I blast it with a heat gun or freeze spray to evaluate tempco. This > >>> gadget has a pretty narrow pull range PLL to lock the triggered LC > >>> oscillator to a crystal oscillator, and it will fail lock if > >>> temperature changes the LC osc frequency more than maybe 1000 PPM. > >>> > >>> We use a digital capacitor to center the frequency to close to 50 MHz > >>> at powerup, but then it's usually cold, and can't drift more than the > >>> 1000 PPM after that. > >>> > >>> Tedious.<snip>> >> I assume that board has an MCU and with many now including on chip temperature measurement can you use the digital capacitor to do the temp compensation in software?> > No. We don't know when we might get a trigger, and tuning the digital > > cap would disrupt a timing cycle. There is a dac+varicap for fine > > tuning, and that is used for locking the LC oscillator to the XO. > > > > The trick in a digital delay generator is to get crystal oscillator > > accuracy, but not quantize timings to the clock edges. > > > > There's a wikipedia article about various ways to accomplish that > > trick; I wrote some of it. > > > You know your project far better than me but I don't understand why the > temp tuning varicap or digi-cap can't make tiny slow changes while the > oscillator is running - after all you can't very well stop the N4700 cap > from shifting value during an oscillator run?I imagine that this his time delay generator for the US laser Ignition set up. It has always struck me as as odd scheme. If you use a continuously running clock you can have a much better clock running much faster. When we did something similar at Cambridge Instruments back around 1989, we used a an 800MHz clock and recorded when the trigger came to about 10psec, and added the offset to the desired delay in ECL to set up the output pulse. It worked fine - it did need a fast ADC to digitise the ramp that the trigger edge started, but that wasn't difficult, even back then. -- Bill Sloman, Sydney
Reply by ●October 26, 20232023-10-26
On Thu, 26 Oct 2023 11:05:20 +0100, piglet <erichpwagner@hotmail.com> wrote:>On 26/10/2023 04:34, John Larkin wrote: >> On Wed, 25 Oct 2023 21:02:50 +0100, piglet <erichpwagner@hotmail.com> >> wrote: >> >>> On 25/10/2023 19:22, john larkin wrote: >>>> On Wed, 25 Oct 2023 09:23:20 -0700 (PDT), Fred Bloggs >>>> <bloggs.fredbloggs.fred@gmail.com> wrote: >>>> >>>>> On Wednesday, October 25, 2023 at 6:40:17?AM UTC-4, John Larkin wrote: >>>>>> On Wed, 25 Oct 2023 07:18:58 +0300, Dimiter_Popoff <d...@tgi-sci.com> >>>>>> wrote: >>>>>> >>>>>>> On 10/25/2023 1:51, john larkin wrote: >>>>>>>> On Wed, 25 Oct 2023 01:12:21 +0300, Dimiter_Popoff <d...@tgi-sci.com> >>>>>>>> wrote: >>>>>>>> >>>>>>>>> On 10/25/2023 0:34, john larkin wrote: >>>>>>>>>> Tww it the dimensionless factor >>>>>>>>>> >>>>>>>>>> (how many parts you tidly-wink and lose) / (how many parts you want) >>>>>>>>>> >>>>>>>>>> which, for 0603's, runs 0.6 or so. >>>>>>>>>> >>>>>>>>> >>>>>>>>> Not sure I got what tww is (looked it up, some domino thing so I >>>>>>>>> guess I get it if so) but 0402 are significantly worse, a lot more >>>>>>>>> than twice worse. And I have not yet done any 0201... >>>>>>>> >>>>>>>> When I first saw 1206's, I thought they were tiny. Ha! >>>>>>>> >>>>>>>> I refuse to use 0402's. I default to 0805s. >>>>>>>> >>>>>>>> I'm tuning the tempco of a 50 MHz triggrered Colpitts oscillator. What >>>>>>>> a nuisance. It should have a 3.3 pF N4700 0805 cap, but the layout guy >>>>>>>> used all 0603s, so some engineer (who shall not be named) substituted >>>>>>>> an 0603 NP0. "NTC" does sound a lot like "NPO" I guess. >>>>>>>> >>>>>>>> The proper 0805 cap was custom brewed for us by Capax. >>>>>>>> >>>>>>> >>>>>>> I often do it the other way around,the 0805 pads I make can also hold >>>>>>> 0603. Took me a while to grasp I could do it the first time I could >>>>>>> not find the 0805 I needed... >>>>>>> >>>>>>> The temp compensations I typically have to deal with are resistor >>>>>>> tracking. Meanwhile I know which batch of which supply I have >>>>>>> does not track too well with which other. >>>>>> What I'm fighting right now is the positive TC of the Coilcraft >>>>>> Midi-spring inductor (typically +100 PPM/c or so) and the positive TC >>>>>> of the PCB FR4, typically +900. The combo makes the oscillator have a >>>>>> serious negative TC, which the N4700 cap compensates. I have a series >>>>>> padder cap, in series with the NTC cap, to trim the oscillator tempco >>>>>> to near zero, down to the 2nd order parabola. >>>>>> >>>>>> It's tedious. Tuning takes about an hour per iteration. We have a >>>>>> gigantic environmental oven in the basement, but using that would take >>>>>> more like a day per iteration. I made my own benchtop chamber, a >>>>>> cardboard box with a USB fan inside, used with a heat gun and freeze >>>>>> spray. >>>>>> >>>>>> My $5000 Rigol scope is the frequncy counter and USB fan supply. >>>>> >>>>> You're using an LC tuned Colpitts? >>>> >>>> Yes. It uses a SAV551 phemt as a source follower driving the usual two >>>> caps back into the tank. >>>> >>>> Here's my temp chamber. >>>> >>>> https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1 >>>> >>>> I blast it with a heat gun or freeze spray to evaluate tempco. This >>>> gadget has a pretty narrow pull range PLL to lock the triggered LC >>>> oscillator to a crystal oscillator, and it will fail lock if >>>> temperature changes the LC osc frequency more than maybe 1000 PPM. >>>> >>>> We use a digital capacitor to center the frequency to close to 50 MHz >>>> at powerup, but then it's usually cold, and can't drift more than the >>>> 1000 PPM after that. >>>> >>>> Tedious. >>>> >>>> DOGBERRY: But truly, if I were as tedious as a king, I would find it >>>> in my heart to give it all to you, your Worship. LEONATO: All thy >>>> tediousness on me, ah? >>>> >>> >>> I assume that board has an MCU and with many now including on chip >>> temperature measurement can you use the digital capacitor to do the temp >>> compensation in software? >>> >>> piglet >>> >>> >> >> No. We don't know when we might get a trigger, and tuning the digital >> cap would disrupt a timing cycle. There is a dac+varicap for fine >> tuning, and that is used for locking the LC oscillator to the XO. >> >> The trick in a digital delay generator is to get crystal oscillator >> accuracy, but not quantize timings to the clock edges. >> >> There's a wikipedia article about various ways to accomplish that >> trick; I wrote some of it. >> > >You know your project far better than me but I don't understand why the >temp tuning varicap or digi-cap can't make tiny slow changes while the >oscillator is running - after all you can't very well stop the N4700 cap >from shifting value during an oscillator run? > >piglet >At powerup time, we center the varicap voltage and step through all the possible digital cap values, and pick the one that's closest to 50 MHz. After that, we don't change the digital cap value, and expect the oscillator to not drift more than a couple hundred PPM. Programming the digital cap is too violent to do while timing shots are running. It's a slow SPI interface. We used to use a piston cap to set the oscillator center frequency, but that's a one-time manual operation and piston caps cost something crazy like $20 nowadays. The digital capacitors are very cool. We used to use a Maxim part but of course they discontinued it without notice. We use an IXYS part now. It could be used to tune filters and such too, or as a phase shifter or something.
