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 HobbsMy 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. Spice is not useful in simulating this, and I don't have the budget or the learning time to use fancy RF tools. It's solder-and-fiddle time, I guess. I really need to do that anyhow, for tempcos and such. The actual design needs to leave lots of knobs to turn, to allow tweaking.
inductor tempco
Started by ●December 13, 2015
Reply by ●December 14, 20152015-12-14
Reply by ●December 14, 20152015-12-14
On Sun, 13 Dec 2015 23:10:24 -0800, 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.Resonant time bases (like an LC tank) provide better phase noise and stability characteristics than non-resonant solutions (even, I'm pretty sure, your 1/4-wave line). Not knowing what JL is planning I can't say which approach is better, but if he needs good stability and phase noise characteristics, than building something around a good LC oscillator is the way to go. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●December 14, 20152015-12-14
On Monday, December 14, 2015 at 8:22:18 AM UTC-8, John Larkin wrote:> Yes, it is an instant-start oscillator that is eventually phase locked > to an OCXO. ... > The inductor is a big part of the problem. Nasty things, inductors.If you waste some current, it can also be the solution: instead of an instant-start by applied voltage spike, you can 'idle' the tank by switching a high regulated current through the coil. When you unclamp the coil and the loop amplification takes over, it's already got stored energy in I-squared-L, so it doesn't need to accelerate up to full amplitude.
Reply by ●December 14, 20152015-12-14
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." "The opposite of current limiting is called voltage limiting. In that case, clipping limits the amplitude of oscillation. This is undesirable because it generates a lot of harmonic distortion plus the low impedance state when the device is driven into saturation or the ohmic region kills the tank Q for part of the cycle and is bad for FM or phase noise." IOW E-B cutoff is your friend if you want a simple oscillator with low phase noise. The tank gain is only about 1.1, which is probably fine. I initially misread the schematic--I was thinking of a CC Colpitts, which is what I usually make. In your CB case, I should have read the tank the other way up, i.e. a gain of 10. 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 14, 20152015-12-14
On 12/14/2015 02:52 PM, Phil Hobbs 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." > > "The opposite of current limiting is called voltage limiting. In that > case, clipping limits the amplitude of oscillation. This is undesirable > because it generates a lot of harmonic distortion plus the low impedance > state when the device is driven into saturation or the ohmic region > kills the tank Q for part of the cycle and is bad for FM or phase noise." > > IOW E-B cutoff is your friend if you want a simple oscillator with low > phase noise. > > The tank gain is only about 1.1, which is probably fine. I initially > misread the schematic--I was thinking of a CC Colpitts, which is what I > usually make. In your CB case, I should have read the tank the other > way up, i.e. a gain of1.1:1, not 10:1. .> > 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 14, 20152015-12-14
On 12/14/2015 02:46 PM, whit3rd wrote:> On Monday, December 14, 2015 at 8:22:18 AM UTC-8, John Larkin wrote: > >> Yes, it is an instant-start oscillator that is eventually phase locked >> to an OCXO. ... >> The inductor is a big part of the problem. Nasty things, inductors. > > If you waste some current, it can also be the solution: instead of > an instant-start by applied voltage spike, you can 'idle' the tank > by switching a high regulated current through the coil. > When you unclamp the coil and the loop amplification takes > over, it's already got stored energy in I-squared-L, so it > doesn't need to accelerate up to full amplitude. >Right, that's how you do it. 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 14, 20152015-12-14
On 12/14/2015 02:04 PM, Tim Wescott wrote:> On Sun, 13 Dec 2015 23:10:24 -0800, 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. > > Resonant time bases (like an LC tank) provide better phase noise and > stability characteristics than non-resonant solutions (even, I'm pretty > sure, your 1/4-wave line).A 1/4 wave line is a resonant solution.> > Not knowing what JL is planning I can't say which approach is better, but > if he needs good stability and phase noise characteristics, than building > something around a good LC oscillator is the way to go. >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 14, 20152015-12-14
On Mon, 14 Dec 2015 15:04:03 -0500, Phil Hobbs wrote:> On 12/14/2015 02:04 PM, Tim Wescott wrote: >> On Sun, 13 Dec 2015 23:10:24 -0800, 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. >> >> Resonant time bases (like an LC tank) provide better phase noise and >> stability characteristics than non-resonant solutions (even, I'm pretty >> sure, your 1/4-wave line). > > A 1/4 wave line is a resonant solution.I don't think it is the way that Bill is proposing to use it. When properly terminated for the job a 1/4-wave line is resonant, but Bill's talking about using it as nothing more than a 90 degree delay line, not as a resonant element. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●December 14, 20152015-12-14
Cliff: your clock appears to be about a half day behind everyone... Tim Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com "Clifford Heath" wrote in message news:JArby.179832$og6.43850@fx06.iad... On 14/12/15 14:15, John S wrote:> On 12/13/2015 8:38 PM, John Larkin wrote: >> On Sun, 13 Dec 2015 19:56:02 -0600, John S <Sophi.2@invalid.org> >>> On 12/13/2015 7:26 PM, 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'm thinking about... >> https://dl.dropboxusercontent.com/u/53724080/Circuits/Oscillators/Colpitts.JPG >> It's a clock generator, so distortion doesn't matter much. Low tempco >> and low phase noise are good. >> I guess I'll build one and try it. > Good idea. I LTSpiced it and it looks okay, but the amplitude is only > +/- .8V. Is that enough?The amplitude at the BFT25A's base is about 40mV, based on the capacitive divider ratio. Without having Spice'd it, there should be enough gain headroom to double the output by increasing the divider ratio, which will probably increase the signal purity also (more tank energy, same base bleed). Clifford Heath.
Reply by ●December 14, 20152015-12-14
On 12/14/2015 03:13 PM, Tim Wescott wrote:> On Mon, 14 Dec 2015 15:04:03 -0500, Phil Hobbs wrote: > >> On 12/14/2015 02:04 PM, Tim Wescott wrote: >>> On Sun, 13 Dec 2015 23:10:24 -0800, 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. >>> >>> Resonant time bases (like an LC tank) provide better phase noise and >>> stability characteristics than non-resonant solutions (even, I'm pretty >>> sure, your 1/4-wave line). >> >> A 1/4 wave line is a resonant solution. > > I don't think it is the way that Bill is proposing to use it.Ah, right you are, thanks. I was thinking about JL's fave coaxial resonators.> When properly terminated for the job a 1/4-wave line is resonant, but > Bill's talking about using it as nothing more than a 90 degree delay > line, not as a resonant element.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
