1 GHz synthesizer
in [Design]
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From: Joerg on 25 Feb 2010 16:13 Joel Koltner wrote: > "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in > message news:gkjdo551mlj1b5t9auebvt5l18nfucubte(a)4ax.com... >> Give two returns, one in some oriental script, the other just a >> reference :-( > > This one will get you some of the flavor of the technique: > http://www.johansontechnology.com/en/technical-notes/rf-capacitors-a-inductors/dishal-bandpass-filter-tuning-using-lasertrimr-chip-caps.html > > > I've tried this at 70cm, and while it works, if you just have a bunch > of, e.g., capacitor-coupled LC resonators on FR4, it still requires some > hand-tweaking in that you're already getting to the point where there's > a little bit of coupling through "opens" and a slightly noticeable > little bit of impedance through "shorts." > In the end it's like what I have seen at an auto shop in Italy. Alfa Romeo, hot edition with four independent carburtors, needed adjusting. "O mama mia, only Giuseppe can do those, you'll have to wait until he gets back". -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 25 Feb 2010 16:44 On Thu, 25 Feb 2010 13:13:03 -0800, Joerg <invalid(a)invalid.invalid> wrote: >Joel Koltner wrote: >> "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in >> message news:gkjdo551mlj1b5t9auebvt5l18nfucubte(a)4ax.com... >>> Give two returns, one in some oriental script, the other just a >>> reference :-( >> >> This one will get you some of the flavor of the technique: >> http://www.johansontechnology.com/en/technical-notes/rf-capacitors-a-inductors/dishal-bandpass-filter-tuning-using-lasertrimr-chip-caps.html >> >> >> I've tried this at 70cm, and while it works, if you just have a bunch >> of, e.g., capacitor-coupled LC resonators on FR4, it still requires some >> hand-tweaking in that you're already getting to the point where there's >> a little bit of coupling through "opens" and a slightly noticeable >> little bit of impedance through "shorts." >> > >In the end it's like what I have seen at an auto shop in Italy. Alfa >Romeo, hot edition with four independent carburtors, needed adjusting. >"O mama mia, only Giuseppe can do those, you'll have to wait until he >gets back". I had a friend with a Spider. To reach the points, working around the hard fuel-injection lines, it helped to first break your arm about 1/3 of the way up. But it was sinful to drive. John
From: Joerg on 25 Feb 2010 16:53 John Larkin wrote: > On Thu, 25 Feb 2010 13:13:03 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> Joel Koltner wrote: >>> "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in >>> message news:gkjdo551mlj1b5t9auebvt5l18nfucubte(a)4ax.com... >>>> Give two returns, one in some oriental script, the other just a >>>> reference :-( >>> This one will get you some of the flavor of the technique: >>> http://www.johansontechnology.com/en/technical-notes/rf-capacitors-a-inductors/dishal-bandpass-filter-tuning-using-lasertrimr-chip-caps.html >>> >>> >>> I've tried this at 70cm, and while it works, if you just have a bunch >>> of, e.g., capacitor-coupled LC resonators on FR4, it still requires some >>> hand-tweaking in that you're already getting to the point where there's >>> a little bit of coupling through "opens" and a slightly noticeable >>> little bit of impedance through "shorts." >>> >> In the end it's like what I have seen at an auto shop in Italy. Alfa >> Romeo, hot edition with four independent carburtors, needed adjusting. >> "O mama mia, only Giuseppe can do those, you'll have to wait until he >> gets back". > > I had a friend with a Spider. To reach the points, working around the > hard fuel-injection lines, it helped to first break your arm about 1/3 > of the way up. But it was sinful to drive. > Oh yeah, and the design is really slick, too. This one was a Julietta but with four carbs, each having as "air filter" nothing but a stretched piece of cloth above the throat. They made a lot of very sporty cars down there. Except they rusted like crazy, at least in the 80's. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: George Herold on 25 Feb 2010 22:44 On Feb 25, 1:45 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Thu, 25 Feb 2010 10:07:22 -0800 (PST), George Herold > > > > > > <ggher...(a)gmail.com> wrote: > >On Feb 25, 12:37 pm, John Larkin > ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> On Wed, 24 Feb 2010 18:58:36 -0800, Joerg <inva...(a)invalid.invalid> > >> wrote: > > >> >John Larkin wrote: > >> >> On Wed, 24 Feb 2010 21:50:07 -0000, "Andrew Holme" <a...(a)nospam.com> > >> >> wrote: > > >> >>> "John Larkin" <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote in message > >> >>>news:u05bo5hknlma4qpda45muddb5tl5slkud2(a)4ax.com... > >> >>>> On Wed, 24 Feb 2010 20:16:15 -0000, "Andrew Holme" <a...(a)nospam.com> > >> >>>> wrote: > > >> >>>>> I'm developing a 1 GHz fractional-N synthesizer. The reference input is a > >> >>>>> 50 MHz sine wave which I'm converting to LVDS as follows: > > >> >>>>> 1. 50 MHz sine wave arrives at board mounted SMA in 50-ohm system > >> >>>>> 2. Converted to 100 ohms differential using Mini-Circuits ADT2-1T > >> >>>>> transformer > >> >>>>> 3. Carried 10mm along pair of closely-spaced traces to 100-ohm 0402 > >> >>>>> resistor > >> >>>>> adjacent to differential input of LMH7324 high-speed comparator. > > >> >>>>> I think some 1 GHz from my VCO (3 inches away) is getting into the (3.84 > >> >>>>> Gbps rated) LMH7324 comparator input and modulating the zero-crossings. > >> >>>>> Result: integer boundary spurs when the VCO frequency is set very close to > >> >>>>> an integer multiple of the reference. > > >> >>>>> Reducing reference drive level increases integer boundary spurs. > >> >>>>> Increasing reference drive level reduces integer boundary spurs (quite > >> >>>>> encouraging reduction is possible). > >> >>>>> Touching one side of the transformer secondary with the metal blade of a > >> >>>>> plastic-handled scalpel increases integer boundary spurs. > > >> >>>>> Presumably, the 1 GHz enters the comparator as a common-mode signal. I > >> >>>>> would like to try two small caps from the comparator inputs to ground. > >> >>>>> Unfortunately, there are no convenient grounds to be had in that area. > >> >>>>> The > >> >>>>> transformer secondary centre-tap is grounded and I could easily put small > >> >>>>> (10pF?) caps across the secondary windings; but that's 10mm away. I will > >> >>>>> just have to try a few different things and maybe drill some holes through > >> >>>>> to the continuous copper ground plane on the bottom. Annoyingly, there > >> >>>>> are > >> >>>>> some decouplers on the bottom just under the 0402 100-ohm. > > >> >>>>> How/why is the 1 GHz leaking all over the board like this? > > >> >>>>> Should I have split my ground plane between reference frequency and VCO > >> >>>>> frequency areas of the board? > > >> >>>>> Any other suggestions? > > >> >>>>> TIA > > >> >>>> 1. The transformer may be doing more harm than good. Its leakage > >> >>>> inductance could be increasing the impedance downstream, and the > >> >>>> transformer is likely not perfectly balanced. > > >> >>>> 2. A tuned circuit right at the comparator input is nice. That would > >> >>>> improve 1 GHz rejection, and could give an amplitude boost, too. It > >> >>>> would improve all sorts of rejection... radio stations, cell phones, > >> >>>> whatever. > > >> >>>> 3. A slower comparator might paradoxically result in less phase noise. > > >> >>>> 4. Caps from the transformer outputs to ground will probably help.. > >> >>>> Make them big enough to contribute some decent lowpass filtering, and > >> >>>> maybe seesaw their values to trim CMRR. Better yet, replace the > >> >>>> wideband transformer with something that resonates. > > >> >>>> 1 GHz does get around. Splitting the planes may not help and could > >> >>>> make things worse. > > >> >>>> What's your target voltage range for the 50 MHz input? > > >> >>>> John > > >> >>> Thanks for the suggestions. Using a tuned circuit sounds good. I was > >> >>> planning to support 10 or 50 MHz reference inputs; but I could drop that > >> >>> requirement and stick to one frequency. > > >> >> How about a 10 MHz tuned circuit driving one input of the comparator, > >> >> and a 50 MHz network driving the other? You could do all that with 5 > >> >> or 6 parts and get some voltage gain too. > > >> >Or build a filter with two peaks, one at 10MHz and the other at 50MHz.. > >> >They are far enough apart, should work. > > >> I suppose I could design a network that would have two peaks and some > >> voltage gain at both, but it would hurt my head. > > >> John- Hide quoted text - > > >> - Show quoted text - > > >Hmm wouldn't a Q = ~5 high pass filter at 10 MHz followed by a Q = ~5 > >Low pass filter at 50 MHz do it? Of course it would be relativly flat > >in between. > > >(Or is that too simple?) > > >George H. > > That might work. Post a schematic! > > The ideal clock-input-reference filters have narrowband responses > around the input frequency, as narrow as parts tolerances allow, to > reject as much non-ref crud as possible. You want to be operating on > the flat part of the frequency response curve, so's not to convert any > amplitude or temperature effects into phase shift... so too much Q is > bad too. That suggests higher-order filters in extreme cases. > > At 10 MHz, we usually use a simple R-L-C with a Q around 5. That also > allows ugly inputs, like square waves that ring and whatever. > > John- Hide quoted text - > > - Show quoted text - That might work. Post a schematic! Ouch, sorry John, I was speaking theoretically. I never designed any RF filters. Ive only been mucking about at audio frequencies where with opamps it would be dead easy. George H.
From: Fred Bartoli on 26 Feb 2010 05:34
Jim Thompson a �crit : > On Thu, 25 Feb 2010 15:24:11 -0500, Phil Hobbs > <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >> On 2/25/2010 3:20 PM, Jim Thompson wrote: >>> On Thu, 25 Feb 2010 15:18:31 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>> >>>> On 2/25/2010 2:22 PM, Jim Thompson wrote: >>>>> On Thu, 25 Feb 2010 11:09:57 -0800 (PST), osr(a)uakron.edu wrote: >>>>> >>>>>> On Feb 25, 2:00 pm, o...(a)uakron.edu wrote: >>>>>>>> You want real fun? Try to align a 'Tubular Filter' without a network >>>>>>>> analyzer. >>>>>>>> -- >>>>>>>> Greed is the root of all eBa >>>>>>> That DOES NOT need to be the five hours it usually takes... >>>>>>> >>>>>>> On odd element microwave ones, short the Inner element. Adjust the >>>>>>> outer ones for SWR as desired, open up the inner one. >>>>>>> >>>>>>> Dishal's method.... The guy wrote a brilliant paper on it.. >>>>>>> >>>>>>> Steve >>>>>> Ah found it: >>>>>> >>>>>> Dishal, M., � Alignment and Adjustment of Synchronously Tuned Multiple- >>>>>> Resonant- >>>>>> Circuit Filters,� Elec. Commun., pp. 154-164, June, 1952. >>>>>> >>>>>> Also see Hayward, >>>>>> � Introduction to Radio Frequency Design,� ARRL, 1994, pp95-101. >>>>>> >>>>>> Steve >>>>>> >>>>> Steve, Many of us have no access to either of those articles (I have >>>>> only 1981 and 1999 ARRL Handbooks). >>>>> >>>>> Can you post, or provide a link where IEEE rears their ugly head ?:-) >>>>> >>>>> Thanks! >>>>> >>>>> ...Jim Thompson >>>> Dishal works best with high-Q filters--it relies on the fact that >>>> detuned series sections look like open circuits and detuned parallel >>>> sections like shorts. You use a return-loss test setup, start from the >>>> end you're measuring, and get all the bumps in the calculated spots. >>>> >>>> Also it doesn't matter what you put in parallel with a series >>>> section--in the limit of high Q, you can't move its resonance. >>>> >>>> Works well for Q>~ 20 IME, but not as well at lower Q since the >>>> approximations don't hold as accurately. >>>> >>>> The thing to watch out for is the temptation to make the filter look >>>> nice but with a slightly too-narrow bandwidth: "There's no way to get >>>> there from here." >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> I was thinking of using it for simulation tools ;-) >>> >>> ...Jim Thompson >> If you already know where the section resonances should go, that'll work >> fine, although I'm not sure what problem you're trying to solve.... >> Generally what makes filter tuning hard is that you're adjusting L and >> C, whereas you really want to adjust f_0 and Q, and simulators don't >> have that problem. >> >> Cheers >> >> Phil Hobbs > > Every once in a while I have to demonstrate a filter made from RLC's > (but in PSpice) that meets the clients needs. > > _Possibly_ this method will allow me to "fake" some real filters ;-) > You could have a look at spice opus. It's free and has quite a rich optimization algorithms set. http://www.spiceopus.si/optimize.html It's been a while since I used it and I don't know whether they've included a GUI or not, so it might bring you back to the good editor/netlist old days, but for a few RLCs filters this is pb OK. (my spice being a 3F5-Xspice based one I could use it straight with some hand written added commands for the spice opus unsupported specific commands) -- Thanks, Fred. |