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. -- Bill Sloman, Sydney
inductor tempco
Started by ●December 13, 2015
Reply by ●December 14, 20152015-12-14
Reply by ●December 14, 20152015-12-14
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
Reply by ●December 14, 20152015-12-14
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> piglet
Reply by ●December 14, 20152015-12-14
On Monday, 14 December 2015 18:53:32 UTC+11, Chris Jones 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.The multipliers are injecting small adjusting currents, not the whole signal, and the scheme can - in principle - generate a pretty clean sine wave. The Colpitts oscillator is a class-C oscillator so the current that sustains the oscillation is essentially a Dirac spike, with every harmonic up to the limit imposed by the width of the spike. A feedback stabilised oscillator can use linear amplifier to supply the bulk of the power required to sustain the oscillation, which isn't much with a high-Q inductor, and the amplitude control multiplier is just a tweak around that. The frequency adjusting multiplier has to inject (or subtract) an appropriate proportion of the current circulating in the tank circuit, which would get nasty for large frequency shifts, but not as nasty as Class-C spike. -- Bill Sloman, Sydney
Reply by ●December 14, 20152015-12-14
>In the circuit that I posted, amplitude is limited by conduction of >the transistor c-b junction. That probably has costs.Sure does--collector limiting will hurt the phase noise. Cutoff is way cleaner than saturation. Since the gain is so high, you'll be loading down the tank, too, which will not do good things to the Q. Cheers Phil Hobbs
Reply by ●December 14, 20152015-12-14
OP I don't understand your orignal question. Is the coil for the PLL VCO? Most modern PLL ICs have on chip VCOs. Mark
Reply by ●December 14, 20152015-12-14
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 -- 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 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 HobbsYes, 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.
Reply by ●December 14, 20152015-12-14
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. > >ChrisA BFT25 costs us 36 cents.
Reply by ●December 14, 20152015-12-14
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 -- 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
