Phase locking a Yig tuned oscillator - Page 1
Forum section: electronics / rf-microwave

author: ThomasDK
author_rank: Regular Contributor
timestamp: February 06, 2016, 02:39:18 am
content: So, I bought a Microlambda YTO on ebay, advertised as 2-8 GHz.Dragged it to the microwave lab at the university, and tested it on a spectrum analyzer:Works fine, although it doesn't go lower than 2.13Ghz, no big deal, my target operation area is 4.5-8 Ghz.I have absolutely no data on it other than the pinout and operating voltage, which the seller was kind enough to include.It must be a custom part, as it doesn't match anything on the Microlambda website... Some weird hybrid of these two:http://www.microlambdawireless.com/pdfs/MLMY%20VXI%20VME%20Data%20Sheet.pdfhttp://www.microlambdawireless.com/pdfs/MLMH%20Data%20Sheet1.pdfIt looks like a MLMH, as it has wires coming out of the back.Also, the supply voltages given by the seller matches the MLMH series (+15/-5V), but the main coil resistance and inductance doesn't.My unit is 10R/10mH, doesn't match any of their datasheets.Tuning curve is 20MHz/mA, which matches the MLMY series:I can't measure the FM coil, as the inductance is too low for my LCR meter. I have tested it, and deviation is 15MHz/50mA... Matches well with the 310kHz/mA in the datasheets.AnywayI want to make a synth from it, which will later be part of another project of mine (building a 3.5Ghz spectrum analyzer).The main coil will be powered by a simple opamp+mosfet current source + 16 bit dac.The FM coil will be connected to a PLL. I have never done a PLL before, so this is the tricky bit (for me anyway).I plan on using an ADF4169:http://www.analog.com/en/products/rf-microwave/pll-synth/fractional-n-plls/adf4169.htmlTo start with, the reference will be a 245MHz OCXO (another ebay score), divided by two, giving me a PFD frequency of 122.5MHz.Later I might change the reference for a second PLL, to fight integer boundary spurs.Anyway, I need to calculate a loop filter for the thing. I have been playing around with ADI's PLL tool, and it seems the sweet spot loop bandwidth is 50kHz.The YTO datasheets tells me that the -3dB bandwidth of the FM coil is 400 kHz.To drive the coil, I will be using a slightly modified version of the shematic provided by simPLL:I have basically told simPLL to that R2 must be 18R (as that translates to +/-180mA in the coil).After that, I have moved the pole created by C1 and R1, until simPLL calculated the pole created by R2 and C3 to be at 400kHz. I then plan to remove C3, and let the bandwidth of the coil replace the last pole.Long text, but I wanted to describe what I have, what I'm doing, and what Ithinkshould be done, rather than just ask "how do I do XYZ?"Am I on the right track, or am I doing this completely wrong?Thomas

author: uncle_bob
author_rank: Unknown
timestamp: February 07, 2016, 02:10:37 am
content: HiThe more important part:How are you going to sample the output of the YIG and isolate it from your load?The ADF4169 can / will /may back feed spurs and noise into the YIG. Your your external load will pull the YIG every bit as much as the FM coil. I would focus on your amplifier architecture before the PLL. The PLL is mostly DC stuff and (except for the input) fairly non critical layout wise. The higher frequency stuff is more critical. Get the hard part done and then fit the easy stuff in around it.All that said, your approach isn't to bad. You will need a quiet supply on the main coil. Some of the values you show look a bit odd. Without all the relevant data and a day to chug through it, that may not mean anything at all. Your OP-27 is not going to directly drive that coil without some sort of major buffer. I would size R2 so that the buffer is saturated at the limits. That way the resistor (rather than the chip) soaks up more power.Bob

author: ThomasDK
author_rank: Regular Contributor
timestamp: February 08, 2016, 02:39:20 am
content: Thanks for the commentsQuote from: uncle_bob on February 07, 2016, 02:10:37 amI have put some thought into this, and I plan to do it like this:The average output power of the YIG is 13dBm in my frequency span of interest.First a 3dB attenuator, just to make the rest look more like 50R. Output power: ~10dBmAfter this a 20dB directional coupler (can be bought for peanuts on ebay.)PLL Path:Output from coupled port: ~ -10dBmThis is then amplified to 0 dBm, which is again attenuated to -10dbmFinally another amplification to 0 dBm, which will be fed to the PLL.The other way around, a signal from the PLL will be attenuated by 73dB before getting back to the YIG.Output path:Direct path from coupler: ~ 9.5 dBmThis goes into a 0 deg splitter, output ~6.5 dBm3dB attenuator, to be nice to the output amps, output ~3.5dBmThis is then amplified, letting the amplifiers clip to get flat power output vs frequency. I'm thinking of using LEE39+ for all amplifiers:http://194.75.38.69/pdfs/LEE-39+.pdfThis should give a flat-ish output of 10dBm, which is then attenuated by 3dBm, to be fed into a mixer.Quote from: uncle_bob on February 07, 2016, 02:10:37 amHow quiet does this need to be? I figured the PLL would take care of most of the noise. I'm planning on regulating it with something simple like a 7812/7815.The OP27 is buffered by a BUF634:http://www.ti.com/lit/ds/symlink/buf634.pdfNot the most efficient part in the world, but it is fast, so it won't mess with my loop bandwidth.I will power it with +/- 9V, which will make it clip at +/- 4V, hence the low value of the resistor.Thomas

author: uncle_bob
author_rank: Unknown
timestamp: February 08, 2016, 02:58:12 am
content: HiThere are a lot of different ways to do the RF section. It looks like the isolation for PLL back feed is plenty. You also get the directivity of the coupler. The other way to do the main line is with a ferrite isolator. Cost of that depends a lot on what shows up on eBay. Often you see them spec'd for much narrower bandwidths than what they really do. Not at all clear if your amps are cheaper.If the amps are the typical low level amps, be very careful about finding some that will handle > 0 dbm outputs without messing up badly. I've run into that problem a couple of times. (20 db increase in noise figure / mucked up phase noise). It's often tough to sort out what's what unless you test them.The gotcha on the supply is that you are feeding it (via the DAC) into the coarse tune port. You have a *much* higher modulation capability there. As you go past the PLL bandwidth it's a shame to see the phase noise rise just due to a supply issue. It is not hard to take care of as long as you realize it can happen.Bob

author: ThomasDK
author_rank: Regular Contributor
timestamp: February 08, 2016, 04:33:52 am
content: Quote from: uncle_bob on February 08, 2016, 02:58:12 amThe amps are 1.25 EUR in qty 20, so quite cheap. Will take a look at isolators.Quote from: uncle_bob on February 08, 2016, 02:58:12 amQuite a gotcha, these are indeed low level amps. Any suggestions on amps that will saturate gracefully?Quote from: uncle_bob on February 08, 2016, 02:58:12 amOh okay, I see what you mean. 2mA noise will move the frequency out of the range of the PLL. Will use a good low noise reference for the DAC, with plenty of filtering. The opamp controlling the FET should handle the rest. After all, the 10mH inductance of the coil works as a pretty good LPF.Thomas

author: uncle_bob
author_rank: Unknown
timestamp: February 08, 2016, 05:55:34 pm
content: Quote from: ThomasDK on February 08, 2016, 04:33:52 amHiAbout the only way to be *sure* is to find amps that have a saturation level that is (gulp) 20 db above your operating point. If you are trying to run -10 dbm, that might not be to bad. At normal signal generator type levels that gets pretty crazy pretty fast. Indeed I have some >1W amps around here that I use for 10 to 20 dbm signals.The other approach is the good old try it and see. Hook up a phase noise analyzer and measure the effects. While you have it set up, check it with a network analyzer to see what the S parameters look like at high levels.Bob

author: ThomasDK
author_rank: Regular Contributor
timestamp: February 08, 2016, 07:06:35 pm
content: Quote from: uncle_bob on February 08, 2016, 05:55:34 pmOuch! There goes my plan of purposely running the amps into saturation to get flat output power... No free lunch I guessIs this really necessary? All I need is to drive two mixers with 7dBm each, one for upconversion of 0-3.5 Ghz to 4.5Ghz, and one for a tracking generator.The isolators are starting to look friendly...I'll dig up some old HP/Tek service manuals and see how they do it.Quote from: uncle_bob on February 08, 2016, 05:55:34 pmThis might be the way to go, could order some samples through the university and start sorting the good from the ugly.Thomas

author: max-bit
author_rank: Frequent Contributor
timestamp: February 08, 2016, 07:51:24 pm
content: I am experimenting with YIG synthesizer stellex.http://www.thegleam.com/ke5fx/stellex.htmIt is a complete synthesizer, along with TUNE and FM coil driver.Include directional coupler, amplifier, divider (by4) PLL synthesis and described the coil driver.I'm trying to force cooperation with the oscillator yig Avantek.My YIG oscillator working 3,4 - 12,3 GHzCurrent ver freqPower ver freqUnfortunately, I have problems with the stability of operation of the current driver (base TCA0372) of the TUNE coil.On the coil appear oscillations and is currently working on a solution to this problem. Presumably, high currents and try to control trigger oscillations.The original YIG oscillator (Endwave) was controlled by a small current in the range of approximately 200mA.Another problem which is encountered in this synthesizer is that of an directional coupler and system cascaded amplifier and high frequency divider.The synthesizer used were two types divider HMMC Agilent and CND UMS.First divider operation to about 12 GHz (HMMC) CND unfortunately only up to about 10 GHz.Pinout two divisors is not compatible.What makes the full range of retuning of the oscillator is a problem (in this embodiment)I have a question if anyone experimented with synthesizer stellex and using different oscillators yig?below are some photosbelow are some photos:

author: ThomasDK
author_rank: Regular Contributor
timestamp: February 08, 2016, 08:26:52 pm
content: Quote from: max-bit on February 08, 2016, 07:51:24 pmYou are trying to pull 3x the rated current through the driver?Thomas

author: max-bit
author_rank: Frequent Contributor
timestamp: February 08, 2016, 08:41:59 pm
content: YesIn theory, it should work TCA0372 work up to 1 AAnd it works, but there are oscillations.

author: uncle_bob
author_rank: Unknown
timestamp: February 08, 2016, 11:29:28 pm
content: Quote from: ThomasDK on February 08, 2016, 07:06:35 pmHiIf you want a low noise signal source, yes indeed it is. If a "20 db worse that could have been" answer is ok, then no. Exactly what the "will get" and "could have been" are unknown unless you take some phase noise data.Bob

author: KE5FX
author_rank: Super Contributor
timestamp: February 09, 2016, 12:47:02 am
content: Couple of thoughts --1) Watch out for phase reversal behavior in the opamp; some of them don't recover properly if their output voltage hits the rail during lockup. This can be very confusing in a PLL.Not sure if that applies to the OP27, but one good alternative that definitely doesn't suffer from phase reversal is the LT1677.2) Saturation of the output MMIC is likely to be OK at the levels of phase noise involved here, because the YIG's output noise will likely still dominate. If your intention is to drive a mixer, the signal level isn't very critical as long as the LO port itself is driven into saturation.3) The main coil/pretune driver really needs to be quiet. Study those old HP schematics for sweeper plugins and SAs. Clean supplies are a BIG deal. Remember that most PSRR ratings on DACs and opamps apply at low audio frequencies, not 100 kHz+.4) If the FM coil bandwidth is 400 kHz, that'sprobablyOK for a 50 kHz loop bandwidth, but personally I prefer not to have any other poles within 10x of the loop BW.5) Just FYI in case it's useful, here's another ADISimPLL implementation I put together several years ago to drive a 10 GHz Gunn source:http://www.ke5fx.com/gunnpll.html. I used this same setup to drive a YIG oscillator.6) Watch out for cases where the 13 GHz PLL chip tries to lock to the second or even third harmonic of your YTO output. Consider adding a lowpass filter to discourage this tendency, even if it's just a trace that's a bit wider than necessary. You'll have plenty of available RF power going into the PLL, so don't be afraid to roll it off at higher frequencies.7) YTOs are a massive pain in the neck in general. Make sure you really need one in your project. Consider something like the ADF5355 as an alternative, maybe?

author: uncle_bob
author_rank: Unknown
timestamp: February 09, 2016, 01:04:35 am
content: HiA few plusses with the ADF5355:They do indeed work as described. You simply need to be careful about the board layout.They cover a monstrous output range, but not all from one output pin.There is enough power do do what you need to do, with the amps you have sketched in for the YIG.You get all the neat phase noise and harmonic data ahead of time so you can make rational decisions without a lot of testing.They work better than the National Semiconductor equivalent parts.A few minuses:You probably need some filtering to get a harmonic free output (same with the YIG plus saturated amps).You DO need a pc board.Getting everything in the right registers and doing the right things can be time consumingSo now, for a really cool design:Use the ADF as the signal source and put a YIG tracking filter after it ... very neat.Bob

author: dkozel
author_rank: Regular Contributor
timestamp: February 09, 2016, 06:04:55 am
content: The ADF5355 also has driver code available here:https://github.com/mathworks/xilinx-linux/blob/master/drivers/iio/frequency/adf5355.chttps://github.com/mathworks/xilinx-linux/blob/master/include/linux/iio/frequency/adf5355.hhttps://github.com/mathworks/xilinx-linux/blob/master/Documentation/devicetree/bindings/iio/frequency/adf5355.txtI've used it and it's pretty reasonable. The datasheet is decent and there's an example (Windows) program which shows register values for given configurations.

author: ThomasDK
author_rank: Regular Contributor
timestamp: February 09, 2016, 06:23:33 am
content: Quote from: KE5FX on February 09, 2016, 12:47:02 amThanks!Quote from: KE5FX on February 09, 2016, 12:47:02 amNoted, I think I have a few LT1677's laying around somewhereQuote from: KE5FX on February 09, 2016, 12:47:02 amThe mixers will be Minicircuits SIM83+ :http://194.75.38.69/pdfs/SIM-83+.pdfThey are specified for both 7 and 10dBm, so I guess I can just shoot for the middle, instead of saturating the amps.Quote from: KE5FX on February 09, 2016, 12:47:02 amGot it, I've been looking at the schematic for a TEK 2715, they seem to be keeping it simple:(The 8.5V is connected directly to one terminal of the main coil)The -5V supply comes from a TL431.Will need to dig deeper to see where the +10V comes from, but it seems straight forward.Quote from: KE5FX on February 09, 2016, 12:47:02 amThat is a good rule of thumb, however according to my professors, it should be "nothing within 10x the highest frequency pole in the system".This limits things a lot in a 3rd order filter, therefore I placed the poles, so the coil bandwidth can replace one of them... As in, I'm using the 400kHz bandwidth as a pole in my loop filterFor belt and braces, it is designed for 60 deg phase margin, to avoid nasty surprises.Quote from: KE5FX on February 09, 2016, 12:47:02 amInteresting setup, how did you power the coil?Quote from: KE5FX on February 09, 2016, 12:47:02 amWill do. A small stepped impedance filter is practically free. The board will be FR4, so the third harmonic should be attenuated a lot from that alone.Quote from: KE5FX on February 09, 2016, 12:47:02 amSo it seems, I actually choose a YIG as I thought it would be easierThe ADF5355 is nice, I did have a look at it before choosing the YIG.The frequency range is nice, but the sub harmonics are awful. Tuning it to 8 GHz would give a subharmonic at 4, which is only 500MHz from my lower working area.Using it would require some sort of switchable filter bank, so I figured using a YIG would be less work.Thomas

author: ThomasDK
author_rank: Regular Contributor
timestamp: February 09, 2016, 06:33:37 am
content: Quote from: dkozel on February 09, 2016, 06:04:55 amHow bad is the reference leak-through? This this one of my main objections against an integrated VCO/PLL. Might be easy enough to filter though?Quote from: uncle_bob on February 09, 2016, 01:04:35 amNow that's an interesting ideaYig filters in my frequency range are abundant on ebay, might be worth looking intoThomas

author: max-bit
author_rank: Frequent Contributor
timestamp: February 09, 2016, 07:30:30 am
content: To experiment with the ADF5355 can use EV-ADF5355SD1Z EVAL BOARD cost ~400 $ (+50$ USB contr)As a synthesizer to yig can alternatively use: ADF4169 (59) ADF41020 etc ....The problem is the correct design of the current driver coil FM and TUNE.And under the concept of modification of PCB (RF in) stellex (see picture).

author: dkozel
author_rank: Regular Contributor
timestamp: February 09, 2016, 05:18:34 pm
content: I have the evaluation board. If you let me know what measurements you'd like I can take some for you.

author: max-bit
author_rank: Frequent Contributor
timestamp: February 09, 2016, 05:32:23 pm
content: Which do you have? ADF5355?

author: uncle_bob
author_rank: Unknown
timestamp: February 09, 2016, 05:41:14 pm
content: Quote from: ThomasDK on February 09, 2016, 06:33:37 amHiThe tracking filter takes care of a whole enormous range of odd problems. You mention a concern about reference feed thru, it will take care of that.Even with the YIG, when you hit the output amps with a "saturation level" sort of input power, you may see more harmonic energy (-10 dbc) than you would like. It's hard to get a system to tune an octave or more and keep things like that from popping up. Switched or tuned filters of some sort generally creep into the design.Bob

author: dkozel
author_rank: Regular Contributor
timestamp: February 11, 2016, 11:47:36 am
content: The ADF5355 and ADF4350 eval boards.

author: ThomasDK
author_rank: Regular Contributor
timestamp: February 12, 2016, 10:31:54 pm
content: So, I have looked at my options, and considered the pros and cons of the different approaches:Phased locked YIG:Pros:High output power (+13-ish dBm)Better phase noise performance (unless I mess it up)Cheapest (as I already have it, including the PLL chip)Simple RF layoutBoard can be FR4Cons:Power hungryNeeds multiple very clean supply rails, both positive and negativeSlow tuning speedADF5355 + Filter bank:Pros:Internal VCO, no messing around with getting the signal fed into the PLLLow power consumption3.3 and 1.8V suppliesWider frequency rangeSimple passive loop filterCons:Higher phase noiseLower output power (-4 ish dBm)Lots of microwave circuit design needed for filter bankExpensive, the chip itself is EUR 58, and then comes all the switchesRogers-like board needed for implementation of the filtersADF5355 + YIG filter:Pros:Same as above + FR4 board possibleCons:Phase noise, especially with the doubler activatedPower hungry YIGPriceWill still need at least one switch, to cover my frequency range of interestI've decided to stick to the YIG oscillator, as I already have most of the parts.I have just scored a 4-8GHz 20db coupler from ebay, $30 including shipping.The final goal is to build a 3.5 GHz spectrum analyzer with tracking generator and VNA. I have done some preliminary planning on how the whole thing should work, and identified requirement for the major building blocks. Doing it as several small projects, one thing at a time, has a larger chance of actually being completed, than one big overwhelming thing.To begin with, I will focus on getting the signal from the coupled port into the PLL, and getting the thing to lock. The signal distribution from the main output to the mixers can be dealt with later.Thomas

author: KE5FX
author_rank: Super Contributor
timestamp: February 13, 2016, 01:13:24 am
content: Quote from: ThomasDK on February 09, 2016, 06:23:33 amThe main coil was pretuned by a 16-bit DAC from Maxim, I believe, driving a quiet opamp feeding a Darlington (2N3904 + 2SC1847 if I remember correctly). The main area of concern with the main coil driver, besides noise, is tempco. The power resistor used as a reference for voltage-to-current conversionmustbe a high-quality power resistor like one of the metal-finned Dale parts. If you try to use a random resistor from the junk box here, the drift will be too much for the pretuning mechanism to deal with.Ideally the resistor should be Kelvin-connected, with a separate voltage-sense line going back to the opamp. Keep the current in one path and the voltage in another, if that makes any sense.

author: aseok
author_rank: Contributor
timestamp: December 03, 2020, 07:44:12 pm
content: Hidoes yig oscillator fail with no load connected at its output?