George Herold wrote:> On Sep 28, 4:33 pm, me0...@yahoo.com wrote: >> On Sep 28, 12:34 pm, George Herold <gher...@teachspin.com> wrote: >> >> >> >> >> >>> On Sep 28, 1:38 pm, Tim Wescott <t...@seemywebsite.com> wrote: > <big snip> >>> - Show quoted text - >> Hey George, >> >> Here�s some more food for thought re the downconverter approach: > > Hi MeO >> (you�ve never said what you�re looking for in Frequency stability, but >> I�m assuming you want accuracy set by your XOSC and phase noise is >> really not an issue) > > Hmm, this is a small part of a new project. I'm still trying to get a > handle on the specs I need. >> If you�ve never done this before I would discourage you: >> >> 1) Unless you�ve got the time to put into the learning curve, not >> only RF but the Freq Synth part >> 2) You have access to a decent SA or FFT analyzer that can cover your >> frequency of interest >> 3) A low frequency network analyzer would also make the job a lot >> easier > > Well, an RF amplifier design ~20 years ago. (would have been nice to > have a spectrum analyzer at the time, I had some ring down issues in > one of the amp stages.) The only RF recently is a few watt oscillator > for a Rubidium discharge lamp. (Where frequency stability is not much > of an issue.) I've got a 'new' SRS770 spectrum analyzer, (DC-100kHz) > which should tell me all I need to know about what's happening after > the mixer. >I wouldn't be so sure. A client was trying to find a noise/instability issue with one of those SRS analyzers. Couldn't, so they called me in. I couldn't find it either so I whipped out my trusty Durabook laptop. It has a fairly low-key sound chip, IIRC only 18 bits. Lo and behold, _that_ found it. Some jaws dropped.>> You�ve got another potential problem when you attempt this kind of >> frequency translation. The low �Q� VCO is going to have a tendency to >> be pulled around by the high �Q� XOSC. They �sniff� each other when >> they get close frequency wise. > > Hmm a bit of padding should take care of that... I'll just burn > power!Decouple the power rails well, that usually takes care of unwanted injection locking effects. [...]>> Btw, you do want to go with frequencies up over 10MHz. Get far away >> from your baseband, just makes the IF filtering all that much >> easier.Only if you don't have to adjust the VCO by hand. Because that would get iffy. -- Regards, Joerg http://www.analogconsultants.com/
50 kHz VCO w/sine output
Started by ●September 27, 2011
Reply by ●September 29, 20112011-09-29
Reply by ●September 29, 20112011-09-29
On Tue, 27 Sep 2011 12:44:44 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:> On Sep 27, 2:17 pm, Tim Wescott <t...@seemywebsite.com> wrote: >> On Tue, 27 Sep 2011 09:54:36 -0700, George Herold wrote:>> > 30kHz to 100kHz VCO with sine wave output.[...]> Hi Tim, I've got a spice simulation with just diode limiting for the > varible gain. ~1.2 Vp-p on the output. I couldn't find any varactors > in LTspice so I just used a diode and added some more C in parallel.George, You may have already achieved a useful solution, but I did run across a numnber of potential models using the following search string: +spice|ltspice +model varactor|vvc including these: Varactor SPICE Models for RF VCO Applications - Skyworks http://www.skyworksinc.com/uploads/documents/200315B.pdf Spice Models for Aeroflex / Metelics GaAs Hyperabrupt Varactor http://www.aeroflex.com/ams/Metelics/pdfiles/MGV_spice_models.pdf and Infineon has some spice models for (e.g.) its BB535 varactor. Got to: http://http://www.infineon.com/ and search for BB535. Hope one of these helps. Frank McKenney -- "Expecting the world to treat you fairly because you are good is like expecting the bull not to charge because you are a vegetarian." -- Dennis Wholey -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney aatt mindspring ddoott com
Reply by ●September 29, 20112011-09-29
On Thu, 29 Sep 2011 10:28:43 -0700, Joerg wrote:> George Herold wrote: >> On Sep 28, 4:33 pm, me0...@yahoo.com wrote: >>> On Sep 28, 12:34 pm, George Herold <gher...@teachspin.com> wrote: >>> >>> >>> >>> >>> >>>> On Sep 28, 1:38 pm, Tim Wescott <t...@seemywebsite.com> wrote: >> <big snip> >>>> - Show quoted text - >>> Hey George, >>> >>> Here’s some more food for thought re the downconverter approach: >> >> Hi MeO >>> (you’ve never said what you’re looking for in Frequency stability, but >>> I’m assuming you want accuracy set by your XOSC and phase noise is >>> really not an issue) >> >> Hmm, this is a small part of a new project. I'm still trying to get a >> handle on the specs I need. >>> If you’ve never done this before I would discourage you: >>> >>> 1) Unless you’ve got the time to put into the learning curve, >>> not only RF but the Freq Synth part >>> 2) You have access to a decent SA or FFT analyzer that can cover >>> your frequency of interest >>> 3) A low frequency network analyzer would also make the job a lot >>> easier >> >> Well, an RF amplifier design ~20 years ago. (would have been nice to >> have a spectrum analyzer at the time, I had some ring down issues in >> one of the amp stages.) The only RF recently is a few watt oscillator >> for a Rubidium discharge lamp. (Where frequency stability is not much >> of an issue.) I've got a 'new' SRS770 spectrum analyzer, (DC-100kHz) >> which should tell me all I need to know about what's happening after >> the mixer. >> >> > I wouldn't be so sure. A client was trying to find a noise/instability > issue with one of those SRS analyzers. Couldn't, so they called me in. I > couldn't find it either so I whipped out my trusty Durabook laptop. It > has a fairly low-key sound chip, IIRC only 18 bits. Lo and behold, > _that_ found it. Some jaws dropped. > > >>> You’ve got another potential problem when you attempt this kind of >>> frequency translation. The low “Q” VCO is going to have a tendency to >>> be pulled around by the high “Q” XOSC. They “sniff” each other when >>> they get close frequency wise. >> >> Hmm a bit of padding should take care of that... I'll just burn power! > > > Decouple the power rails well, that usually takes care of unwanted > injection locking effects.Note that if you _do_ have mild injection locking problems they'll show up as harmonic distortion in your sine wave long before they show up as your VCO snapping to the reference frequency. Good decoupling will help lots, dividing your VCO frequency down by some convenient factor may help a lot more (and if you're careful about your transformers, you can get 7dBm out of a 74HCxx flip-flop with complementary outputs). I think that me0 is overstating the case -- but that depends a lot on just what you need, and you say you don't know the specifications exactly, so... -- www.wescottdesign.com
Reply by ●September 29, 20112011-09-29
On Wednesday, September 28, 2011 11:57:41 AM UTC-7, John Larkin wrote: [on making a sinewave VCO]> For shaping a triangle into a sine, what should be optimized is the > harmonic distortion, not the RMS error, I guess. Fiddling in Spice is > probably as good a way as any.It's arguable that, for a VCO, you want to know if/how it'll be phase-locked (i.e. it's the sensitivity of the intended use, not the energy in the total harmonics, that will matter). The little corner of the remnant of the triangle wave might be a lot less important than other measures of sine compliance, or might be MORE important.
Reply by ●September 29, 20112011-09-29
On Sep 29, 9:11=A0am, George Herold <gher...@teachspin.com> wrote:> On Sep 28, 5:38=A0pm, Bill Sloman <bill.slo...@ieee.org> wrote: > > > > > > > On Sep 28, 9:41=A0pm, George Herold <gher...@teachspin.com> wrote: > > > > On Sep 28, 1:41=A0pm, "Michael A. Terrell" <mike.terr...@earthlink.ne=t>> > > wrote: > > > > > George Herold wrote: > > > > > > Yeah DDS from a micro looks like the 'best' path. =A0It's just ou=tside> > > > > my present comfort zone and so hard to predict how long it will > > > > > take. > > > > > =A0 =A0You can get a "AD9850 Module DDS Signal Generator with Circu=it> > > > Diagram" in ebay for about $13 and demo software on the Analog Devi=ces> > > > website. =A0There is also VB source code & 80*51 source code availi=ble for> > > > free. > > > > > =A0 =A0I just bought a couple for a project I'm working on. > > > > > -- > > > > You can't have a sense of humor, if you have no sense. > > > > Thanks Michael, =A0there's so many DDS chips. =A0Which ones will stil=l be> > > around in ten years? > > > The first mention of the AD9850 I can find here dates back to 2000, so > > it has been around for more than ten years already - always a good > > sign - and I think that it had been around for a while then. IIRR it > > was the first of Analog Devices DDS chips, and it seems to have been > > designed into a lot of applications, so it may be around for a while > > yet. > > > -- > > Bill Sloman, Nijmegen- Hide quoted text - > > > - Show quoted text - > > Thanks Bill, that's good to know. > > George H.- Hide quoted text - > > - Show quoted text -George, What kind of tuning resolution do you need?
Reply by ●September 29, 20112011-09-29
Frnak McKenney wrote: [...]> You may have already achieved a useful solution, but I did run > across a numnber of potential models using the following search > string: > > +spice|ltspice +model varactor|vvc > > including these: > > Varactor SPICE Models for RF VCO Applications - Skyworks > http://www.skyworksinc.com/uploads/documents/200315B.pdf > > Spice Models for Aeroflex / Metelics GaAs Hyperabrupt Varactor > http://www.aeroflex.com/ams/Metelics/pdfiles/MGV_spice_models.pdf > > and Infineon has some spice models for (e.g.) its BB535 varactor. > Got to: > > http://http://www.infineon.com/ > > and search for BB535. > > Hope one of these helps. >Amazing. It all started out at 100kHz and below, and now we are already into gigeehoitz-capable products :-) -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●September 29, 20112011-09-29
On 09/29/2011 12:11 PM, George Herold wrote:> On Sep 28, 4:33 pm, me0...@yahoo.com wrote: >> On Sep 28, 12:34 pm, George Herold<gher...@teachspin.com> wrote: >> >> >> >> >> >>> On Sep 28, 1:38 pm, Tim Wescott<t...@seemywebsite.com> wrote: >> > <big snip> >>> - Show quoted text - >> >> Hey George, >> >> Here�s some more food for thought re the downconverter approach: > > Hi MeO >> >> (you�ve never said what you�re looking for in Frequency stability, but >> I�m assuming you want accuracy set by your XOSC and phase noise is >> really not an issue) > > Hmm, this is a small part of a new project. I'm still trying to get a > handle on the specs I need. >> >> If you�ve never done this before I would discourage you: >> >> 1) Unless you�ve got the time to put into the learning curve, not >> only RF but the Freq Synth part >> 2) You have access to a decent SA or FFT analyzer that can cover your >> frequency of interest >> 3) A low frequency network analyzer would also make the job a lot >> easier > > Well, an RF amplifier design ~20 years ago. (would have been nice to > have a spectrum analyzer at the time, I had some ring down issues in > one of the amp stages.) The only RF recently is a few watt oscillator > for a Rubidium discharge lamp. (Where frequency stability is not much > of an issue.) I've got a 'new' SRS770 spectrum analyzer, (DC-100kHz) > which should tell me all I need to know about what's happening after > the mixer. > >> >> You�ve got another potential problem when you attempt this kind of >> frequency translation. The low �Q� VCO is going to have a tendency to >> be pulled around by the high �Q� XOSC. They �sniff� each other when >> they get close frequency wise. > > Hmm a bit of padding should take care of that... I'll just burn > power! >> >> So you have to make sure your system has enough isolation between the >> two oscillators. You need to take into account things like LO to RF >> isolation when looking at the mixer. In �S� parameter terms it will >> be the S12 term of the VCO chain. >> >> Again I will state, I really believe your VCO will have to be phased >> locked. Otherwise it�ll be hit and miss when trying to set it�s >> freq. Each one of those gain curves will be slightly different from >> part to part. >> >> I don�t mean to discourage you. In fact, for somebody that does synth >> design this is pretty trivial. >> >> But for a first timer it will be daunting, and could really end up >> being a big waste of time. The digital approach is just a matter of >> ramping up and not equipment intensive. And software is comparatively >> easier to change then hardware. > > Thanks, I'd like to do a DDS design sometime, but right now that > looks like a longer learning curve/ time sink. (strange as that may > sound.) >> >> I�m just trying to be helpful and I wish you the best of luck. > > Thanks again. At the moment I'm just going to order some VCO's from > minicirciuts... (throw some money at the problem.) and see what the > output looks like. I'll also push forward on the triangle wave/ sine > shaper idea. > > This is a nice app note, > http://www.national.com/an/AN/AN-263.pdf > > > George H. > >> >> Btw, you do want to go with frequencies up over 10MHz. Get far away >> from your baseband, just makes the IF filtering all that much >> easier.- Hide quoted text - >> >> - Show quoted text - >As I posted to the sample-hold thread by mistake: Using a CD4017 and some resistors will get rid of all harmonics up to the ninth, so a fixed LPF will make a nice sine wave with 3:1 tunability. 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 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●September 29, 20112011-09-29
George Herold wrote:> > Bill Sloman wrote: > > > > The first mention of the AD9850 I can find here dates back to 2000, so > > it has been around for more than ten years already - always a good > > sign - and I think that it had been around for a while then. IIRR it > > was the first of Analog Devices DDS chips, and it seems to have been > > designed into a lot of applications, so it may be around for a while > > yet. > > Thanks Bill, that's good to know.Here is the evaluation software for the 9850/9851 DDS chips. <ftp://ftp.analog.com/pub/www/techSupport/designTools/evaluationBoards/downloads/AD9850_51_V2.41_Win2KXP.exe> You can install it and look at it without the DDS chip connected. One of the $13 modules, a couple of 74HCT574 octal latch ICs and a few other parts will let you connect it to a standard parallel printer port. The 72 MHz lowpass filter is on the module, along with the 125 MHz oscillator module. That software has the interface schematic. It was released in 2003. We were already using the AD9850 early in 2001. <http://www.analog.com/en/rfif-components/direct-digital-synthesis-dds/ad9850/products/evaluation-boardstools/CU_AD9850_evaluation_tools/resources/fca.html> has versions for older versions of Windows. -- You can't have a sense of humor, if you have no sense.
Reply by ●September 29, 20112011-09-29
On Thu, 29 Sep 2011 12:40:32 -0500, Frnak McKenney <frnak@far.from.the.madding.crowd.com> wrote:>On Tue, 27 Sep 2011 12:44:44 -0700 (PDT), George Herold <gherold@teachspin.com> wrote: >> On Sep 27, 2:17�pm, Tim Wescott <t...@seemywebsite.com> wrote: >>> On Tue, 27 Sep 2011 09:54:36 -0700, George Herold wrote: > >>> > 30kHz to 100kHz VCO with sine wave output. > > [...] > >> Hi Tim, I've got a spice simulation with just diode limiting for the >> varible gain. ~1.2 Vp-p on the output. I couldn't find any varactors >> in LTspice so I just used a diode and added some more C in parallel. > >George, > >You may have already achieved a useful solution, but I did run >across a numnber of potential models using the following search >string: > > +spice|ltspice +model varactor|vvc > >including these: > > Varactor SPICE Models for RF VCO Applications - Skyworks > http://www.skyworksinc.com/uploads/documents/200315B.pdf > > Spice Models for Aeroflex / Metelics GaAs Hyperabrupt Varactor > http://www.aeroflex.com/ams/Metelics/pdfiles/MGV_spice_models.pdf > >and Infineon has some spice models for (e.g.) its BB535 varactor. >Got to: > > http://http://www.infineon.com/ > >and search for BB535. > >Hope one of these helps. > > >Frank McKenney >-- > "Expecting the world to treat you fairly because you are good is > like expecting the bull not to charge because you are a > vegetarian." -- Dennis WholeyDo it with the exact data... www.analog-innovations.com/VVC.zip ...Jim Thompson -- [On the Road, in New York] | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●September 30, 20112011-09-30
On Sep 29, 1:40=A0pm, Frnak McKenney <fr...@far.from.the.madding.crowd.com> wrote:> On Tue, 27 Sep 2011 12:44:44 -0700 (PDT), George Herold <gher...@teachspi=n.com> wrote:> > On Sep 27, 2:17=A0pm, Tim Wescott <t...@seemywebsite.com> wrote: > >> On Tue, 27 Sep 2011 09:54:36 -0700, George Herold wrote: > >> > 30kHz to 100kHz VCO with sine wave output. > > =A0 =A0[...] > > > Hi Tim, =A0I've got a spice simulation with just diode limiting for the > > varible gain. =A0~1.2 Vp-p on the output. =A0I couldn't find any varact=ors> > in LTspice so I just used a diode and added some more C in parallel. > > George, > > You may have already achieved a useful solution, but I did run > across a numnber of potential models using the following search > string: > > =A0 +spice|ltspice +model varactor|vvc > > including these: > > =A0 Varactor SPICE Models for RF VCO Applications - Skyworks > =A0http://www.skyworksinc.com/uploads/documents/200315B.pdf > > =A0 Spice Models for Aeroflex / Metelics GaAs Hyperabrupt Varactor > =A0http://www.aeroflex.com/ams/Metelics/pdfiles/MGV_spice_models.pdf > > and Infineon has some spice models for (e.g.) its BB535 varactor. > Got to: > > =A0http://http://www.infineon.com/ > > and search for BB535. > > Hope one of these helps. > > Frank McKenney > -- > =A0 "Expecting the world to treat you fairly because you are good is > =A0 =A0like expecting the bull not to charge because you are a > =A0 =A0vegetarian." =A0 =A0 =A0 =A0 =A0 =A0 =A0-- Dennis Wholey > -- > Frank McKenney, McKenney Associates > Richmond, Virginia / (804) 320-4887 > Munged E-mail: frank uscore mckenney aatt mindspring ddoott comThanks Frank, If I go the varactor route I'll just bread board it. George H.
