On Mon, 14 Dec 2015 14:52:28 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 12/14/2015 12:39 PM, John Larkin wrote: >> On Mon, 14 Dec 2015 11:53:59 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 12/14/2015 11:22 AM, John Larkin wrote: >>>> On Mon, 14 Dec 2015 09:59:01 -0500, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 12/14/2015 09:51 AM, makolber@yahoo.com wrote: >>>>>> OP >>>>>> >>>>>> I don't understand your orignal question. >>>>>> >>>>>> Is the coil for the PLL VCO? >>>>>> >>>>>> Most modern PLL ICs have on chip VCOs. >>>>>> >>>>>> Mark >>>>>> >>>>>> >>>>> >>>>> John is usually doing something weird like instant-on VCOs that are >>>>> phase locked eventually. His stuff is pretty much all time-domain. You >>>>> could instant-on that Colpitts by putting a Schottky across the top >>>>> capacitor and swinging the supply from +5 to -5. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> Yes, it is an instant-start oscillator that is eventually phase locked >>>> to an OCXO. So any slow loop, like an ALC, or any inherent slow >>>> amplitude limiting mechanism isn't good. I want steady-state as soon >>>> as possible. It's a messy crossover between time domain and RF-type >>>> issues. >>>> >>>> The inductor is a big part of the problem. Nasty things, inductors. >>>> >>>> >>> >>> Just dropping the gain some and moving the bias so that it clips at the >>> emitter would go a long way. A third cap, from the top of the tank to >>> the base, lets you optimize the loaded Q. >>> >>> Cheers >>> >>> Phil Hobbs >> >> My Colpitts will be amplitude limited by clipping, either the c-b >> junction of the BFT25 or by the startup circuit. Either way, the gain >> (emitter current) determines how hard it clips, and that is easily >> tuned. Amplitude stabilizes in a couple of cycles. I have no idea how >> clipping (as opposed to some delicate AGC mechanism) affects things >> like phase noise. > >Like this (a tutorial by a friend of mine from grad school, Mark Rodwell): > <http://www.ece.ucsb.edu/Faculty/rodwell/Classes/ece218b/notes/Oscillators2.pdf> > >As he says on the first page, >"...a well designed LC oscillator like the Colpitts must be current >limited: that is, we allow the active device to go into cutoff for part >of the period of oscillation. This reduces the effective gm of the >device, averaged over the period, and thus gives the needed gain >compression. It also benefits phase noise as we will later see. The >simulated drain current for a common collector Colpitts oscillator below >illustrates that the device can be in cutoff for much of the period."OK, that implies a much lower C ratio, to give enough swing at the emitter to turn off the transistor some of the time. Some variation on that. I'll sim that and see if it works. I wanted to keep the C ratio high so the ohmic input of the emitter didn't kill that Q. And I went common-base so the base didn't load the top of the tank. This is complicated. Spice works fine for analyzing the gross oscillation, but it's not useful for close-in phase noise. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
inductor tempco
Started by ●December 13, 2015
Reply by ●December 14, 20152015-12-14
Reply by ●December 14, 20152015-12-14
> OK, that implies a much lower C ratio, to give enough swing at the > emitter to turn off the transistor some of the time. Some variation on >that. I'll sim that and see if it works.>I wanted to keep the C ratio high so the ohmic input of the emitter >didn't kill that Q. And I went common-base so the base didn't load the >top of the tank.Apart from bias details and strays, it doesn't matter which terminal you ground. I usually use CC, with the output taken from the top of the tank via a BF862 follower, or occasionally via a common base stage tapped way down on the tank. Connecting the collector to VCC, using an emitter resistor, and applying base bias via the inductor makes it easy to use BE limiting. (I did a couple like that earlier this year--needed an octave-band VCO for a heterodyne interference microscope.) Works pretty well for me. Cheers Phil Hobbs
Reply by ●December 15, 20152015-12-15
On 12/14/2015 04:56 AM, piglet wrote:> On 14/12/2015 04:40, John Larkin wrote: >> >> In the circuit that I posted, amplitude is limited by conduction of >> the transistor c-b junction. That probably has costs. >> > > Adding a one-transistor ALC loop may fix that. As in: > > <https://www.dropbox.com/s/ltmihwc0gnaaxdd/ALC_JLcolpitts.jpg> > > pigletCute. I might be more inclined to turn the ALC transistor upside down and use a PNP. That would avoid loading the emitter of the oscillator transistor. 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 ●December 15, 20152015-12-15
On Sun, 13 Dec 2015 17:26:05 -0800, John Larkin <jjlarkin@highlandtechnology.com> wrote:> >These look great, very high Q. I'm thinking about a 50 or maybe 100 >MHz Colpitts oscillator PLL. > >http://www.coilcraft.com/1515sq.cfm > >I wonder if the thermal expansion tempco of the FR4 board will stretch >the coil and change its native tempco. FR4 is variously cited as being >around +5 to +17 ppm/K, which isn't bad. That might even reduce the >tempco of the inductor. > >I also wonder how a PCB ground plane effects L and Q. I guess I'll >order a kit and try it. > >Coilcraft says that the tempco is indeed tested while soldered to an FR4 board.
Reply by ●December 15, 20152015-12-15
>Cute. �I might be more inclined to turn the ALC transistor upside down >and use a PNP. �That would avoid loading the emitter of the oscillator >transistor.Come to think about it, by omitting the diode and cap, connecting the PNP's base to the NPN's collector, and putting a bit of positive bias on the PNP's emitter, it could kill the NPN's collector current before saturation occurs. That wouldn't have any slow bias TCs. Cheers Phil Hobbs
Reply by ●December 15, 20152015-12-15
On 15/12/2015 03:24, John Larkin wrote:> On Mon, 14 Dec 2015 18:46:06 +1100, Chris Jones > <lugnut808@spam.yahoo.com> wrote: > >> On 14/12/2015 18:10, Bill Sloman wrote: >>> On Monday, 14 December 2015 12:26:17 UTC+11, John Larkin wrote: >>>> These look great, very high Q. I'm thinking about a 50 or maybe 100 >>>> MHz Colpitts oscillator PLL. >>>> >>>> http://www.coilcraft.com/1515sq.cfm >>>> >>>> I wonder if the thermal expansion tempco of the FR4 board will stretch >>>> the coil and change its native tempco. FR4 is variously cited as being >>>> around +5 to +17 ppm/K, which isn't bad. That might even reduce the >>>> tempco of the inductor. >>>> >>>> I also wonder how a PCB ground plane effects L and Q. I guess I'll >>>> order a kit and try it. >>> >>> Why a Colpitts? If you wanted a clean and reasonably fast tuneable sine wave oscillator you could use a pair of Analog Devices fast multipliers - the AD834, AD835 or ADL5391 are all fast enough for a 100MHz oscillator. >>> >>> One multiplier would provide the adjustable in-phase feedback to keep the amplitude where you wanted it, and the other would provide adjustable (positive or negative) quadrature input to allow you to pull the frequency up or down. At 100MHz, half a metre of coax could provide the quadrature component to be fed into the second multiplier. A coax delay line isn't a broad-band solution, but sufficiently broad-band for something you might otherwise fine-tune with a varicap. >>> >>> It's a more complicated solution than you'd come up with on your own, but it would be easier to explain to customers than the traditional approach. >>> >> >> It might be quite noisy though. Multipliers tend to be noisy because the >> "LO port" is in small-signal operation all the time, and therefore the >> devices contribute noise. If you replace the multipliers in your scheme >> with hard-driven mixers then it would be less noisy as the switching >> devices in the mixer core don't contribute to the current noise when >> they are fully on or fully off. The harmonic content in the mixer output >> current should not matter as the tank will filter it out, and even if it >> didn't, filtering out 3rd and higher harmonics is not very difficult >> unless the tuning range approaches an octave. >> >> Chris > > A BFT25 costs us 36 cents. > >I didn't say that the scheme with mixers would be cost-effective or good, just that doing it with analogue multipliers would give worse phase noise than doing it with mixers. If I were doing it, I would probably try to avoid the instant-start oscillator entirely, but then I would need to know what is the higher-level problem that you are solving which I can only guess at for now. Chris
Reply by ●December 15, 20152015-12-15
On Wednesday, 16 December 2015 11:57:35 UTC+11, Chris Jones wrote:> On 15/12/2015 03:24, John Larkin wrote: > > On Mon, 14 Dec 2015 18:46:06 +1100, Chris Jones > > <lugnut808@spam.yahoo.com> wrote: > > > >> On 14/12/2015 18:10, Bill Sloman wrote: > >>> On Monday, 14 December 2015 12:26:17 UTC+11, John Larkin wrote: > >>>> These look great, very high Q. I'm thinking about a 50 or maybe 100 > >>>> MHz Colpitts oscillator PLL. > >>>> > >>>> http://www.coilcraft.com/1515sq.cfm > >>>> > >>>> I wonder if the thermal expansion tempco of the FR4 board will stretch > >>>> the coil and change its native tempco. FR4 is variously cited as being > >>>> around +5 to +17 ppm/K, which isn't bad. That might even reduce the > >>>> tempco of the inductor. > >>>> > >>>> I also wonder how a PCB ground plane effects L and Q. I guess I'll > >>>> order a kit and try it. > >>> > >>> Why a Colpitts? If you wanted a clean and reasonably fast tuneable sine wave oscillator you could use a pair of Analog Devices fast multipliers - the AD834, AD835 or ADL5391 are all fast enough for a 100MHz oscillator. > >>> > >>> One multiplier would provide the adjustable in-phase feedback to keep the amplitude where you wanted it, and the other would provide adjustable (positive or negative) quadrature input to allow you to pull the frequency up or down. At 100MHz, half a metre of coax could provide the quadrature component to be fed into the second multiplier. A coax delay line isn't a broad-band solution, but sufficiently broad-band for something you might otherwise fine-tune with a varicap. > >>> > >>> It's a more complicated solution than you'd come up with on your own, but it would be easier to explain to customers than the traditional approach. > >>> > >> > >> It might be quite noisy though. Multipliers tend to be noisy because the > >> "LO port" is in small-signal operation all the time, and therefore the > >> devices contribute noise. If you replace the multipliers in your scheme > >> with hard-driven mixers then it would be less noisy as the switching > >> devices in the mixer core don't contribute to the current noise when > >> they are fully on or fully off. The harmonic content in the mixer output > >> current should not matter as the tank will filter it out, and even if it > >> didn't, filtering out 3rd and higher harmonics is not very difficult > >> unless the tuning range approaches an octave. > > > > A BFT25 costs us 36 cents. > > I didn't say that the scheme with mixers would be cost-effective or > good, just that doing it with analogue multipliers would give worse > phase noise than doing it with mixers.But much more harmonic content. and you missed the point that the multipliers weren't inject much current - of the order of a percent of of the tank current.> If I were doing it, I would probably try to avoid the instant-start > oscillator entirely, but then I would need to know what is the > higher-level problem that you are solving which I can only guess at for now.You can sample and digitise the phase of a continuous running clock quite accurately, and add that to whatever delay you need to generate - as we did back in 1990, with a granularity of 10psec. The system involved gets moderately complicated, much more complicated than anything that John Larkin wants to contemplate. -- Bill Sloman, Sydney
Reply by ●December 15, 20152015-12-15
On Wed, 16 Dec 2015 11:57:26 +1100, Chris Jones <lugnut808@spam.yahoo.com> wrote:>On 15/12/2015 03:24, John Larkin wrote: >> On Mon, 14 Dec 2015 18:46:06 +1100, Chris Jones >> <lugnut808@spam.yahoo.com> wrote: >> >>> On 14/12/2015 18:10, Bill Sloman wrote: >>>> On Monday, 14 December 2015 12:26:17 UTC+11, John Larkin wrote: >>>>> These look great, very high Q. I'm thinking about a 50 or maybe 100 >>>>> MHz Colpitts oscillator PLL. >>>>> >>>>> http://www.coilcraft.com/1515sq.cfm >>>>> >>>>> I wonder if the thermal expansion tempco of the FR4 board will stretch >>>>> the coil and change its native tempco. FR4 is variously cited as being >>>>> around +5 to +17 ppm/K, which isn't bad. That might even reduce the >>>>> tempco of the inductor. >>>>> >>>>> I also wonder how a PCB ground plane effects L and Q. I guess I'll >>>>> order a kit and try it. >>>> >>>> Why a Colpitts? If you wanted a clean and reasonably fast tuneable sine wave oscillator you could use a pair of Analog Devices fast multipliers - the AD834, AD835 or ADL5391 are all fast enough for a 100MHz oscillator. >>>> >>>> One multiplier would provide the adjustable in-phase feedback to keep the amplitude where you wanted it, and the other would provide adjustable (positive or negative) quadrature input to allow you to pull the frequency up or down. At 100MHz, half a metre of coax could provide the quadrature component to be fed into the second multiplier. A coax delay line isn't a broad-band solution, but sufficiently broad-band for something you might otherwise fine-tune with a varicap. >>>> >>>> It's a more complicated solution than you'd come up with on your own, but it would be easier to explain to customers than the traditional approach. >>>> >>> >>> It might be quite noisy though. Multipliers tend to be noisy because the >>> "LO port" is in small-signal operation all the time, and therefore the >>> devices contribute noise. If you replace the multipliers in your scheme >>> with hard-driven mixers then it would be less noisy as the switching >>> devices in the mixer core don't contribute to the current noise when >>> they are fully on or fully off. The harmonic content in the mixer output >>> current should not matter as the tank will filter it out, and even if it >>> didn't, filtering out 3rd and higher harmonics is not very difficult >>> unless the tuning range approaches an octave. >>> >>> Chris >> >> A BFT25 costs us 36 cents. >> >> > >I didn't say that the scheme with mixers would be cost-effective or >good, just that doing it with analogue multipliers would give worse >phase noise than doing it with mixers. > >If I were doing it, I would probably try to avoid the instant-start >oscillator entirely, but then I would need to know what is the >higher-level problem that you are solving which I can only guess at for now. > >ChrisI'm generating time delays from a trigger. The oscillator counts out coarse ticks and then an analog interpolator gets resolution down to picoseconds.
Reply by ●December 16, 20152015-12-16
On 16/12/2015 14:28, John Larkin wrote:> On Wed, 16 Dec 2015 11:57:26 +1100, Chris Jones > <lugnut808@spam.yahoo.com> wrote: > >> On 15/12/2015 03:24, John Larkin wrote: >>> On Mon, 14 Dec 2015 18:46:06 +1100, Chris Jones >>> <lugnut808@spam.yahoo.com> wrote: >>> >>>> On 14/12/2015 18:10, Bill Sloman wrote: >>>>> On Monday, 14 December 2015 12:26:17 UTC+11, John Larkin wrote: >>>>>> These look great, very high Q. I'm thinking about a 50 or maybe 100 >>>>>> MHz Colpitts oscillator PLL. >>>>>> >>>>>> http://www.coilcraft.com/1515sq.cfm >>>>>> >>>>>> I wonder if the thermal expansion tempco of the FR4 board will stretch >>>>>> the coil and change its native tempco. FR4 is variously cited as being >>>>>> around +5 to +17 ppm/K, which isn't bad. That might even reduce the >>>>>> tempco of the inductor. >>>>>> >>>>>> I also wonder how a PCB ground plane effects L and Q. I guess I'll >>>>>> order a kit and try it. >>>>> >>>>> Why a Colpitts? If you wanted a clean and reasonably fast tuneable sine wave oscillator you could use a pair of Analog Devices fast multipliers - the AD834, AD835 or ADL5391 are all fast enough for a 100MHz oscillator. >>>>> >>>>> One multiplier would provide the adjustable in-phase feedback to keep the amplitude where you wanted it, and the other would provide adjustable (positive or negative) quadrature input to allow you to pull the frequency up or down. At 100MHz, half a metre of coax could provide the quadrature component to be fed into the second multiplier. A coax delay line isn't a broad-band solution, but sufficiently broad-band for something you might otherwise fine-tune with a varicap. >>>>> >>>>> It's a more complicated solution than you'd come up with on your own, but it would be easier to explain to customers than the traditional approach. >>>>> >>>> >>>> It might be quite noisy though. Multipliers tend to be noisy because the >>>> "LO port" is in small-signal operation all the time, and therefore the >>>> devices contribute noise. If you replace the multipliers in your scheme >>>> with hard-driven mixers then it would be less noisy as the switching >>>> devices in the mixer core don't contribute to the current noise when >>>> they are fully on or fully off. The harmonic content in the mixer output >>>> current should not matter as the tank will filter it out, and even if it >>>> didn't, filtering out 3rd and higher harmonics is not very difficult >>>> unless the tuning range approaches an octave. >>>> >>>> Chris >>> >>> A BFT25 costs us 36 cents. >>> >>> >> >> I didn't say that the scheme with mixers would be cost-effective or >> good, just that doing it with analogue multipliers would give worse >> phase noise than doing it with mixers. >> >> If I were doing it, I would probably try to avoid the instant-start >> oscillator entirely, but then I would need to know what is the >> higher-level problem that you are solving which I can only guess at for now. >> >> Chris > > I'm generating time delays from a trigger. The oscillator counts out > coarse ticks and then an analog interpolator gets resolution down to > picoseconds. > >Ok, that is what I guessed. Someone should make an ASIC to do that. It would be fun to design. Chris
Reply by ●December 16, 20152015-12-16
On Wed, 16 Dec 2015 16:06:47 +1100, Chris Jones <lugnut808@spam.yahoo.com> wrote:>On 16/12/2015 14:28, John Larkin wrote: >> On Wed, 16 Dec 2015 11:57:26 +1100, Chris Jones >> <lugnut808@spam.yahoo.com> wrote: >> >>> On 15/12/2015 03:24, John Larkin wrote: >>>> On Mon, 14 Dec 2015 18:46:06 +1100, Chris Jones >>>> <lugnut808@spam.yahoo.com> wrote: >>>> >>>>> On 14/12/2015 18:10, Bill Sloman wrote: >>>>>> On Monday, 14 December 2015 12:26:17 UTC+11, John Larkin wrote: >>>>>>> These look great, very high Q. I'm thinking about a 50 or maybe 100 >>>>>>> MHz Colpitts oscillator PLL. >>>>>>> >>>>>>> http://www.coilcraft.com/1515sq.cfm >>>>>>> >>>>>>> I wonder if the thermal expansion tempco of the FR4 board will stretch >>>>>>> the coil and change its native tempco. FR4 is variously cited as being >>>>>>> around +5 to +17 ppm/K, which isn't bad. That might even reduce the >>>>>>> tempco of the inductor. >>>>>>> >>>>>>> I also wonder how a PCB ground plane effects L and Q. I guess I'll >>>>>>> order a kit and try it. >>>>>> >>>>>> Why a Colpitts? If you wanted a clean and reasonably fast tuneable sine wave oscillator you could use a pair of Analog Devices fast multipliers - the AD834, AD835 or ADL5391 are all fast enough for a 100MHz oscillator. >>>>>> >>>>>> One multiplier would provide the adjustable in-phase feedback to keep the amplitude where you wanted it, and the other would provide adjustable (positive or negative) quadrature input to allow you to pull the frequency up or down. At 100MHz, half a metre of coax could provide the quadrature component to be fed into the second multiplier. A coax delay line isn't a broad-band solution, but sufficiently broad-band for something you might otherwise fine-tune with a varicap. >>>>>> >>>>>> It's a more complicated solution than you'd come up with on your own, but it would be easier to explain to customers than the traditional approach. >>>>>> >>>>> >>>>> It might be quite noisy though. Multipliers tend to be noisy because the >>>>> "LO port" is in small-signal operation all the time, and therefore the >>>>> devices contribute noise. If you replace the multipliers in your scheme >>>>> with hard-driven mixers then it would be less noisy as the switching >>>>> devices in the mixer core don't contribute to the current noise when >>>>> they are fully on or fully off. The harmonic content in the mixer output >>>>> current should not matter as the tank will filter it out, and even if it >>>>> didn't, filtering out 3rd and higher harmonics is not very difficult >>>>> unless the tuning range approaches an octave. >>>>> >>>>> Chris >>>> >>>> A BFT25 costs us 36 cents. >>>> >>>> >>> >>> I didn't say that the scheme with mixers would be cost-effective or >>> good, just that doing it with analogue multipliers would give worse >>> phase noise than doing it with mixers. >>> >>> If I were doing it, I would probably try to avoid the instant-start >>> oscillator entirely, but then I would need to know what is the >>> higher-level problem that you are solving which I can only guess at for now. >>> >>> Chris >> >> I'm generating time delays from a trigger. The oscillator counts out >> coarse ticks and then an analog interpolator gets resolution down to >> picoseconds. >> >> > >Ok, that is what I guessed. > >Someone should make an ASIC to do that. It would be fun to design. > >Chris >There are asics that do picosecond time stamping, sort of the reverse of what I'm doing. My delay generator architecture wouldn't integrate very well, but some might. SERDES blocks are getting awfully fast these days, so something could probably be done with that. We've done SERDES-based timing generators, but only at 1 ns resolution. There are faster things around lately.
