Analog Devices (and others) have nifty mixers that take in a local oscillator and generate its quadrature version internally over very wide frequency ranges -- several octaves. Example:
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... I'm used to the simple passive phasing networks that provide reasonably accurate quadrature over all of, say, 3kHz :-), so clearly they're using a different technique. Anyone know what it is? Perhaps a "polyphase" type network as described in, e.g., this patent:
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?
I'm sure Jim Thompson must have built a circuit like this at least by
Don't know how that got patented... the scheme is as old as Sidney Darlington.
Of course! Did it first in the first go-round of Garmin GPS chips. I don't think it was as early as 1970 though ;-)
But it sure pre-dated that patent.
...Jim Thompson
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| James E.Thompson, P.E. | 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 |
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"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
A broken patent system.
It's from, what... 2000... probably about the time a lot of companies jumped on the "let's try to patent each and every piece of IP we know about -- the courts can figure out which are 'non-obvious to those skilled in the art' or not!" bandwagon.
OK, thanks -- I'll dig through a few books.
Do you know any of the guys who started SiRFstar? Garmin (and many other GPS manufacturers) now seem to use them almost exclusively. I guess GPS just became a big enough market that you could create a company that did nothing but manufacture GPS chipsets...
--
| James E.Thompson, P.E. | 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 |
America: Land of the Free, Because of the Brave
The quadrature generation question was brought about from considering building wideband VCOs using some fixed oscillators mixed with a DDS. To avoid the need for pretty sharp filters (to avoid the imagine after mixing), just using the phasing method to generate SSB seems attractive... and I was happy to find that you can get a DDS that already has I and Q output DACs and those Analog mixers that contain a quadrature generator for the "fixed" oscillator and then two mixers, so... one DDS IC, one mixer IC, and a combiner and you've got the start of a pretty good wideband VCO.
I skimmed the manual for an HP 8648A function generator today... it's actually PLL-based, which surprised me (I had previously guessed DDS, although I once took a look at its output on a spectrum analyzer as was surprised at how low they were -- that should have clued me in then and there...). Their PLL runs the VCO at 500MHz-1GHz, and they then use a few mixers and a few fixed frequencies (generated off the same 10MHz reference clock their PLL uses) to go from (almost) DC to 1/2/3GHz (depending on the particular model).
500MHz-1GHz is a 4:1 varactor change -- apparently still well within the realm of reasonably low phase noise.
Yeah, I wouldn't consider their DDS ICs "boutiquey" anymore.
Who needs tight tolerance caps when you can just use a trim cap?
:-)
Actually, I fully realize that in large quantities trim caps are a Bad Idea, but for low-volume production they might still be the best option.
I bet there's a market for something similar to the 8648A with somewhat reduced specs for a greatly reduced price... one could use it to bootstrap the development of a spectrum analyzer.
Other than in very large RF power amps I have never used a single trim cap in a design during my whole career. And I am not planning to ;-)
Same for anything that could get banged around. Which is, uhm, pretty much any electronics product. Potmeters are similar, I do use them on the bench but not in designs.
Ok, laser trim, yes. Did it a lot but that results in a stable device.
Sadly, the lab equipment market for all things RF is miniscule. And from what I can see it's shrinking. People do buy analyzer gear for comms but that's fully automated stuff. Press a button -> report comes out.
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I have a trim cap on some receivers prototypes that are going out at the end of the month, but only because we changed cases on a crystal (it went from a small rectangular SMT case to one of those long/skinny HC49 styles... the PCB layout guy was protesting he just didn't have the room...) and it pulled the frequency off 300Hz (~7ppm)... so the trim cap just pulls the crystal back to where it "should" have been. :-( On the next batch we'll just get the crystal manufacturer to change the crystal itself, of course; it never occurred to me that changing a crystal's case would affect it that much. ! @$#%^
I don't think I've ever designed anything with the volumes to support laser trimming. Maybe some day...
Really? I'd think it'd be more popular than ever now, with cell phone, lots of various low power wireless systems, etc. There are people using the Chipcom/Nordic/etc. chipsets adding wireless data transfer to their boards who couldn't have begun to do so a decade ago, and it sure seems that as these people progress they'll eventually want at least spectrum analyzers and eventually function generators and network analyzers. And even some of the digital guys see the value of spectrum analyzers these days, although I suppose that market will be largely served by digital 'scopes with FFTs.
If it's just a fraction of a pF you might get away with an old trick: Two enameled wires, twirled up. Then snip, snip, snip until it's right on. Vernier can be achieved by twirling some more or untwirling. It drives non-RF guys crazy when they think it's a left-over probe connection, cut it off and then the whole thing doesn't work anymore. "What the heck was that?"
You'd be surprised when you see some of the design processes. Often the layout of an RF chip is verbatim lifted off the datasheet. Down to the last micrometer. That's the main reason they have it in there. Heck, people even do that with PWM chips for switchers. Then it's off to the EMC lab with shaking knees, hoping it'll be blessed.
WRT scopes and FFT I was quite amazed after I bought a modern DSO. I used it just like a scope for weeks. Then one day I pushed that FFT button just for kicks and it was rather impressive.
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Regards, Joerg
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Hopefully they remembered to specify the board material... at, say, 2.4GHz going from Rogers 4350 to run-of-the-mill FR-4 would definitely detune things a bit!
I expect they keep your (or some other consultant's) phone number handy in case that blessing doesn't come. :-)
That's where things can go seriously wrong. 2.4GHz is still ok though, most of the proposed matching networks are small enough. 5GHz is another matter although I did see products on FR4.
Here is a good example, starts at the bottom of page 19:
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And yes, I have seen 2.45GHz stuff on, gasp, phenolic. Never used that material above 1GHz myself but maybe I should try.
Yep :-)
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Yeah, if you're just trying to go from an RF output to an SMA jack or another
50 ohm termination in a tiny space... On boards I've done, even at 400MHz the matching networks have changed noticeably (one or two "standard 5% component" value increases or decreases) due to changes in layout where, say, one chip that was previously right next to another one is now 25mm away. (Although often you're talking matching from, say, 500 ohms to 50 ohms, so Q is pretty high and everything gets dicier -- a pF here and there rapidly adds up...)
Looks like you're on your own to build a PCB antenna -- understandably enough.
I'll bet there aren't a couple of dozen folks left in the world that know that gimmick capacitor trick. I'll bet there are even less that have made a single-tune "variable" capacitor out of a disk ceramic NPO and a dremel grinding wheel.
Yes, but I am often surprised how carelessly people do that. They lean over the board, the Dremel runs at a good clip, no safety goggles, and it takes only one minor twitch of the hand to send the shards of the fragile little disk right into an eye. There is a reason why these skinny disks come in packs of 50. I _always_ stop people when I see that, no matter whether it's at a client or elsewhere. It's more dangerous than riding a motorcycle with a T-shirt and slippers.
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