400 V  Square wave oscillator - Page 1
Forum section: electronics / projects

author: sdouble
author_rank: Frequent Contributor
timestamp: July 22, 2017, 09:35:00 pm
content: hi guys,I need to build a very fast switcher. I do need to switch a capacitor (actually parallel plates used to deflect ions).Only 400 V, so not that much but I do need to switch from 0 to 400 V in 20 ns.I was thinking about using a GAN FET in cascode configuration. I have the impression that the Transphorm product could fit my needs.Does someone have some experience with those products ?thanks in advance.

author: sdouble
author_rank: Frequent Contributor
timestamp: July 22, 2017, 09:59:50 pm
content: forgot to mention that the oscillator needs to operate at 2.5 MHz

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 22, 2017, 10:03:29 pm
content: Maybe use a RF amplifier tube?

author: calexanian
author_rank: Super Contributor
timestamp: July 23, 2017, 03:46:12 am
content: What kind of current and what kind of load are you driving. Gonna be really hard to get a sharp square wave at those frequencies at any appreciable power level.

author: daqq
author_rank: Super Contributor
timestamp: July 23, 2017, 04:35:59 am
content: Behlke has some modules that might help you in this.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: July 23, 2017, 04:45:30 am
content: Wolfspeed makes 900 V SiC MOSFET's that should be fast enough. You need to think about ringing.

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 07:32:21 am
content: Quote from: daqq on July 23, 2017, 04:35:59 amthanks, i also saw the Behlke modules. They look pretty interesting. They are more "high voltage" oriented (ie 2+ kV) as far as I could see

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 07:40:16 am
content: Quote from: calexanian on July 23, 2017, 03:46:12 amI have essentially a capacitive load (35pF, 25 nH). I agree that they are issues like ringing, EMC, current handling. The good thing is that I don't have to deal with significantly high voltage.The neat thing is that I can cope with moderate ringing.

author: daqq
author_rank: Super Contributor
timestamp: July 23, 2017, 07:48:21 am
content: That's true about the Behlke modules, though there are some low-ish voltage devices. Down to 500V if I remember correctly.

author: kridri
author_rank: Contributor
timestamp: July 23, 2017, 08:14:59 am
content: You can het inspired by looking to some older crt schematics. Especially the high speeds scopes have a broadband 'high voltage' (around 300-400V) x and y deflection drivers.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 23, 2017, 11:22:41 am
content: Nothing special. Any modern MOSFET will do, no need for GaN, SiC or exotica.If it's a capacitive load (just an electrode deflecting ions?), you don't need DC gate drive. The transistors can be driven from a transformer. Very easy at 2MHz!If you need adjustable duty cycle, then you need a DC restorer circuit as well, no big deal.Tim

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 12:29:23 pm
content: any modern MOSFET will switch (on and off) 400 V in 20 ns ?not really sure

author: ganzuul
author_rank: Contributor
timestamp: July 23, 2017, 12:58:10 pm
content: The on/off time here is 2000V/us. A higher-voltage transistor should be faster when it operates closer to its linear range, signified by its gain -3db point.* However, that means you need a HV PSU and snubber diodes for when something goes wrong.Is 2.5MHz cycle repetition rate or the highest harmonic of the square wave? If you need very little ringing at 2.5 MHz you might want those snubbers, but depending on the resistance that could mean your 170MHz load oscillation frequency is breathing down your neck due to the high voltage, necessitating a filter.Is this a chopper for an ion beam, a cyclic device, or a single-shot kind of deal?* This might not be clear. This is what I mean:

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 01:41:19 pm
content: Quote from: ganzuul on July 23, 2017, 12:58:10 pmOf course, I have both devices in stock.Quote from: ganzuul on July 23, 2017, 12:58:10 pmSorry , it seems that I was not very clear. The 2.5 MHz is the repetition rate. It's actually a chopper for an ion accelerator.

author: capt bullshot
author_rank: Super Contributor
timestamp: July 23, 2017, 01:46:08 pm
content: Quote from: sdouble on July 23, 2017, 12:29:23 pmYes, they do, even faster:http://cmosedu.com/jbaker/papers/1992/MST31992.pdfJust for fun, I had build a version for 900V / 6.5ns fall time:http://wunderkis.de/pulser/pulser.pdfhttp://wunderkis.de/pulser/Somewhen later I tried this circuit with a modern SIC MOSFET instead of the IRFBG30, yielding a much slower fall time (don't remember the number right now, maybe 20...30ns)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 23, 2017, 03:14:38 pm
content: I did an industrial inverter, 5kW 400kHz, with middle-aged MOSFETs (VDMOS, 900-1200V, not SuperJunction -- so their performance sucked!). 650V edges in 50ns. Good thing I didn't go with optoisolators, that's more dV/dt than any I've seen can handle.Win Hill (of AoE fame; he posts on sci.electronics.design) has been working on a higher voltage pulser, using SiC MOSFETs. I think that was 10ns for the whole edge (a few kV). SiC aren't really much faster than regular Si, they're just higher voltage (so, higher gate and drain voltages).Tim

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 03:26:58 pm
content: did you estimate the power efficiency of your circuit ?I need mine to be quite efficient. It will operate in vacuum "slightly" hampering the natural convection. I foresaw a water cooling for the power transistors, but still, I'd prefer the circuit to be as efficient as possible.Quote from: capt bullshot on July 23, 2017, 01:46:08 pm

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 03:34:12 pm
content: Quote from: T3sl4co1l on July 23, 2017, 03:14:38 pmI was more thinking about a GAN FET . Those are actually faster with very low RDSon.Another point that I didn't raise is that the board will be in a harsh environment (SF6 gaz around and some radiation). THerefore, I'm after a solution which would be as robust s possible. That's one of the reason for which I looked at integrated modules, with, possibly, integrated cooling.There will be no chance to open the tank to change easily a burned MOSFET. Will take days before being allowed to have access to the board.

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2017, 03:43:24 pm
content: This one is a little pricey, but it has the low and high side driver built in with protection & it slightly exceeded your requirements:http://www.ti.com/product/LMG3410?keyMatch=lmg3410&tisearch=Search-EN-EverythingIf price is an issue, don't bother as it is a fancy slick component.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 23, 2017, 03:49:20 pm
content: Hmm, radiation might be more of a concern for modules? SiC or GaN might be better than Si, too, with suitable arrangements to have the driver at a distance, or shielded properly.SF6 is rather inert stuff IIRC, unless you mean it's particularly nasty from the radiation (radicals), which I can see being a possibility.At worst, use mil spec hermetically sealed parts (SiC FETs are available in gold-lid TO-220-lookalike packages for about $100 each), or seal up the circuit (with something nice like N2 or Ar) inside a tin.Tim

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 04:04:01 pm
content: Quote from: BrianHG on July 23, 2017, 03:43:24 pmReliability is muuuch more important than price. Shuting down the accelerator cost ten grants.... opening the tanks ten more....thanks for the datasheet. THis is a part that I did not know.

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 04:24:07 pm
content: No idea whether the module would be more prone to failure than individual components. I would guess that this depends more on the transistor technology than the integration of the circuit.a Moderate shiedling is foreseen. It won't be 100% efficient though.I was again a bit fast (bad habit, my wife said it too last night). The board will operate in vacuum. The SF6 will be close by. To have access to the board, we have to evacuate the SF6 into dedicated reservoirs fill the tank with air and only then open the tank. Strangly, Gold is not so good for me. Gold loves neutrons... inducing gamma ray emission.Quote from: T3sl4co1l on July 23, 2017, 03:49:20 pm

author: ahbushnell
author_rank: Frequent Contributor
timestamp: July 23, 2017, 04:29:55 pm
content: This one is 8 ns switching speed.http://www.wolfspeed.com/media/downloads/949/C3M0120100J.pdfNote you can control oscillations by adjusting the gate resistor. It does increase switching losses. The energy stored in the output capacitance of the switch will be dissipated in the device. At 400 V and 2.5 MHz I get 8 watts.There is a 900 V device that's a little faster in similar package.Andy

author: ahbushnell
author_rank: Frequent Contributor
timestamp: July 23, 2017, 04:42:20 pm
content: Quote from: sdouble on July 23, 2017, 04:24:07 pmVacuum could be a problem at 400 V. This will depend on how hard the vacuum is. This is driven by Paschen curve. It's a function of the gap x pressure. The minimum is around 1 to 5 torr-cm. The minimum is around 300 volts. If you can get down to under 0.1 torr-cm then it looks like you would be ok. I'm not sure what low pressure would do to electronic packaging.https://en.wikipedia.org/wiki/Paschen%27s_law

author: capt bullshot
author_rank: Super Contributor
timestamp: July 23, 2017, 04:45:50 pm
content: Quote from: sdouble on July 23, 2017, 03:26:58 pmNo, this circuit isn't suitable for you purpose, since it switches the whole 900 Volts into a 50 Ohm resistor. It's usable for short pulses and low duty cycle. My circuit operates with 1us wide pulses at 100Hz repetition rate.To generate a square wave, I'd suggest a half or full brigde architecture. Should work with standard MOSFETs like the IRF840 used in the original paper. As Teslacoil said, gate driving should work with a simple transformer driven by a beefy driver like the IX4427 I've used.Power dissipation will then be rather low, mostly dissipating your loads charge as abushnell pointed out. Plus the MOSFETs parasitic capacitance, which would be higher.You might also consider building a full bridge running at low voltage and stepping up the output to your desired voltage using a custom build transformer. 2.5MHz shouldn't be too difficult for a pulse transformer. This saves you a lot of parasitic capacitance switching at 400V.BTW, @Teslacoil: 650V in 50ns is just 13kV/us - nothing a modern gate driver optocoupler can't handle, they're usually spec'd for at least 25kV/us

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 05:53:43 pm
content: Quote from: ahbushnell on July 23, 2017, 04:42:20 pmThis is handled with no issue.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 23, 2017, 06:00:25 pm
content: Quote from: ahbushnell on July 23, 2017, 04:42:20 pmPeople who work on particle accelerators generally don't consider 0.1 torr a vacuum

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 06:27:36 pm
content: Quote from: ejeffrey on July 23, 2017, 06:00:25 pmthat's correct.. by several orders of magnitude.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: July 23, 2017, 08:19:13 pm
content: Quote from: ejeffrey on July 23, 2017, 06:00:25 pmA nit. It's torr-cm. If it is a hard vacuum, is out gasing going to be a problem from plastic in the circuit?Sent from my SM-G930V using Tapatalk

author: jbb
author_rank: Super Contributor
timestamp: July 23, 2017, 08:45:28 pm
content: Quote from: sdouble on July 23, 2017, 01:41:19 pmThe presence of radiation near the beam line suggests you probably don't want to use the TI fully-integrated GaN FET. It's a whole IC, with manyradiation detectorstransistors in it. Also, important question: what happens if a switching event fails? Would a ... frisky ... particle beam go somewhere it shouldn't?Quote from: sdouble on July 23, 2017, 04:04:01 pmYeah, I did wonder about that when seeing pictures of accelerators. So... much... stuff.Absent the radiation, I would suggest putting the electronics as close to the output as possible so you don't get transmission line effects. However, with radiation and high service costs, it might be time to look at a remote electronics solution. I'm frankly guessing here, but might 500mm of transmission line be enough to get your electronics out of the beam line and behind a few mm of shielding? I'm thinking a carefully designed 'RF' feedthrough would be fairly reliable over the major maintenance period of the accelerator...What's the plate capacitance expected to be?Considering a transmission line in frequency domain:Propagation velocity v = 2e8 m/sFrequency of interest f = 15 * 2.5e6 Hz = 37.5e6 (going up to 15th harmonic gives a pretty good square wave)Expected wavelength = 5.33mA transmission line exhibits fairly lumped behaviour for up to 1/10th of a wave length, i.e. 0.533mLooks OKConsidering a transmission line in time domain:Propagation velocity v = 2e8 m/sLength = 0.5mHence electrical length = 2.5 nsTricky...Traditionally, an electrical engineer would say that we could get lumped-parameter behaviour with 10 periods i.e. 25ns rise time, but it would probably work with 20s rise time.Extra trick: make the transmission line a bit resistive to damp reflections (subject to thermal considerations!)

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2017, 08:51:13 pm
content: Quote from: sdouble on July 23, 2017, 04:04:01 pmCheck out their Half bridge evaluation module and driver board on the web page at the top left. TI did your design work for you. In fact, you can just purchase TI power modules and drive with you own logic driver.The eval module's .pdf has a scope shot of a 100khz 480v switched signal with rise and fall well under 20ns...

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 08:58:48 pm
content: Quote from: BrianHG on July 23, 2017, 08:51:13 pmI did look at their design of half bridge circuit and that sounds really interesting.However, I do think that I'll have to redesign the PCB since the connectors mounted on the evalution boards clearly does not fit my needs.Now, my main concern is the capability of the circuit to sustain an operation at 2.5MHz. The datasheet mentions 1 MHz...

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 09:09:32 pm
content: Quote from: jbb on July 23, 2017, 08:45:28 pmNo problem, we have rad resistant operators.more seriously, no big deal.... if it does not happen too often. If so, thos missed events will lead to some activation of the area, which is not something you want.Quote from: jbb on July 23, 2017, 08:45:28 pm35 pF. The latter includes 20 pF coming from 25 cm of 50 ohms coax cable.

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2017, 09:12:18 pm
content: The total propagation turn off delay + fall time of 50ns vs turn on delay + rise time of 36ns, switching the device at 2.5MHz will be a tricky pulse width drive source a little too close for comfort in my book, but not impossible.You would be better off driving the gates yourself of discrete GaN devices shrinking those delays, giving you wider clearance, but, on off / rise fall times will still be un-matched and you will still need to generate a custom-shaped gate drive if you want to optimize minimum heat, ring, striving for that optimum long-term fault free stable operation.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: July 23, 2017, 09:23:20 pm
content: This is similar to a pockel cell that is used for Q switching lasers. You might want to look that up.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: July 23, 2017, 09:27:07 pm
content: Quoteshouldn't that be at least 75 Ohm coax? less pF/m for next to no cost diffRG-62, 63 even higher Z, lower C but different connectors as you go up in Z

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2017, 09:38:48 pm
content: @sdouble, how do you intend to synthesize your 2.5Mhz gate signals?

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 09:44:02 pm
content: Quote from: f5r5e5d on July 23, 2017, 09:27:07 pmdoes not really make sense to try to save 5pF thereThe power handling of 50 ohm coax is much higher.

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 09:47:31 pm
content: Quote from: BrianHG on July 23, 2017, 09:38:48 pmThe accelerator ions source provides me with the 2.5MHz low power signal.

author: ganzuul
author_rank: Contributor
timestamp: July 23, 2017, 10:08:06 pm
content: Quote from: sdouble on July 23, 2017, 01:41:19 pmDoes it need to be on-target both half-cycles? Could it work with a half-bridge rectifier?To wit, semiconductors fail in radiation because rad creates activation products which act as dopants. Some U.S. spacecraft monger found out that they are better off using big components instead of many small ones. Presumably this means that more voltage margin in the component is more better, and the capacitance of the component is also lower. High current on the other hand ought to mean a wider junction and so more space in which failure can occur, so the transformer route albeit cool might not be the correct one. Fewer junctions also means fewer points of failure, and a diode is the minimum.SiC is being evaluated for its good rad-hardness. It could make for some interesting nuclear betavoltaics one day.Quote from: sdouble on July 23, 2017, 04:04:01 pmIs there room for two in there?Quote from: jbb on July 23, 2017, 08:45:28 pmThey should add an air lock while they're at it.

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 10:12:10 pm
content: Quote from: ganzuul on July 23, 2017, 10:08:06 pmyes, there is room for 2 in there !

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2017, 10:25:27 pm
content: Quote from: sdouble on July 23, 2017, 09:47:31 pmYes, ok, I assume this signal is sinusoidal, Am I correct?How will you be shaping it to optimize your gate drive, regardless of which type of transistors you use, to a nice square pulse, with corrective t-on and t-off to achieve a 2.5MHz square wave output where the high and low transistors don't burn each other out?

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: July 23, 2017, 10:37:19 pm
content: do you have a waveform envelope/template - the absolute widest range/minimal requrements on rise/fall/overshoot, ringing, 'flatness'?'cable power handling' only applies in matched Z terminated source/loadyou have to eval the I, V ( <1 Apk, >400 Vpk) for your higly reflective termination situation, I'm pretty sure the higher characteristic Z is a win15 pf plate load Z ~ 4j kOhm @ 2.5 MHz, so even the 20th harmonic Z is still higher than the 128 Ohm coaxnot that you need transmission line modeling for 25 cm, 2.5 MHz square waves whereQuoteQuote from: sdouble on July 23, 2017, 09:44:02 pm

author: sdouble
author_rank: Frequent Contributor
timestamp: July 23, 2017, 11:13:13 pm
content: Quote from: BrianHG on July 23, 2017, 10:25:27 pmnope, you're not correct.I get a so-called NIM signal from the accelerator.

author: sdouble
author_rank: Frequent Contributor
timestamp: July 24, 2017, 05:58:37 am
content: Quote from: f5r5e5d on July 23, 2017, 10:37:19 pmFrequency is fixed. There is no margin there. Moreover, it must be extremely stable. But i don't see a problem there.Rise and fall time should be from 18 to 22 ns 10-90%.I'm much more flexible on the other parameter : overshoot , ringing or flatness. I have a 20% margin there

author: Marco
author_rank: Super Contributor
timestamp: July 24, 2017, 12:05:41 pm
content: Ixys has 65MHz single package 500V push pull MOSFETs which switch under 10ns including delay, that might be fast enought to just put 2 100 Ohm resistors from the MOSFETs to the load and driving them with GDTs with a shared wire for the primary. Without having to worry too much about shoot through.

author: floobydust
author_rank: Super Contributor
timestamp: July 24, 2017, 07:01:17 pm
content: How far off from OP's requirements is the deflection circuitry for analog CRT oscilloscopes?Looking at an old TEK434 from 1980, 25MHZ vertical deflection is common-base amplifier for ~110VDC, 20nsec/div horizontal deflection ~225V cascode.

author: jbb
author_rank: Super Contributor
timestamp: July 24, 2017, 08:26:44 pm
content: Quote from: sdouble on July 23, 2017, 09:09:32 pmOK, so 35pF * 20 V/ns = 35 e-12 * 20 e9 = 700 e-3 = 0.7A, which is very reasonable.So how much coax would you need to get the electronics to the outside of the vacuum & SF6 systems?Quote from: sdouble on July 24, 2017, 05:58:37 amAaaah -stable- will the accelerator operations crew be annoyed if it drifts all over the place (with temperature, ageing etc.)?In that case I would recommend building a few candidates and experimentally testing them with mock-up transmission line and plates. Your true goalmaybe stable response rather than speed, in which case I suggest you design forcontrolleddV/dt. (Normally dV/dt will be implicitly controlled by gate drive and device parasitics and drifts around a bit). Then again, if you don't have particle bunches going through the beam line at the time it won't really matter much, will it?If some ringing / non-flat behaviour is allowed, a transformer-fed design might be possible. You might be able to use a 1:8 transformer near the deflection plates to adjust the plate impedance down to around j50 Ohms and then use a longer, terminated transmission line with series termination at source. Then the drive electronics could be driven from a 50V DC bus (but output 8A peak). But you would get at least some ringing.Quote from: f5r5e5d on July 23, 2017, 10:37:19 pmYouneedone of these. It should be a proper drawing with labeled axes and references to documents/design studies etc. You could ask the technical person responsible to try to come up with a 'we want' and 'weneed' envelope. You should ask questions like 'when do the bunches go through the deflector exactly? Are there periods where you don't care about the voltage?' because the accelerator designers may be trying to make your requirements 'simpler' by not telling you everything.If you can't get one, flag this to the project manager immediately but politely, because it would be evidence of communication problems.As you can see from all the questions here, there are alotof possibilities. Ultimately you're going to be spending a significant amount of time evaluating options and doing simulations.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 24, 2017, 09:48:11 pm
content: Quote from: jbb on July 24, 2017, 08:26:44 pmI would recommend making the driver stable and somewhat faster than needed, then tuning the output network to get the desired response.The most important part will be reducing the dependency between rise time and semiconductor properties. Gate drive is a bad way to get this -- then again, if you add external Miller compensation capacitance (that is linear), you can swamp the transistor's capacitance, giving a more stable relation between gate drive current and output dV/dt.And if efficiency is not required, it's not like there's anything wrong with brute-forcing this thing with a matched 50 ohm transmission line. Sure, it'll burn about a kilowatt, but it'll work, damn it!A lot of responses are hinting at linear (class A or AB) amplifiers, as well, which may be more control than is needed here, and will definitely get hot -- but will absolutely do the job. (You also use a smaller fraction of the full operating range of the transistors, so the nonlinear capacitance is less significant.)QuoteNot so. At this bandwidth, a very clean transformer can be designed and built, and the circuit matched to eliminate ringing (\$\xi \ge 1\$). Or peaked (2nd or 3rd order, or even higher) to get a better step response (i.e., a Bessel response, most likely).Example design:Assume 50 ohm system.Assume 2MHz +/- (low) dB, so that -3dB falls at 0.2MHz, say.That sets Lp = (50 ohm) / (2*pi*(0.2MHz)) = 39.8uH minimum.A half dozen turns on a large #43 ferrite bead will do the job there, so that's easy.If t_r ~ 10ns, then Fmax ~ 100MHz (actually a bit under 50MHz). Let's say 200MHz or more to keep the response independent of the transformer (i.e., not relying on the transformer too much as a reactive component*).*Which can be done, when using suitable designs (transmission line transformers). Or, in effect: the maximum bandwidth is simply made very, very high, so that the properties at modest frequencies are well controlled (i.e., it behaves as a transmission line).200MHz at 0.67c velocity is a 1m winding length. "A half dozen turns" then needs to be under 160mm per turn, which is fine. (We don't even have to employ TLT design to implement this transformer, at least for the primary winding!)Taking the load as a lumped capacitance (it's not, it has 250mm of coax and 15pF of plate; but for the above reason, we probably don't need to worry about the TL being too reactive), to achieve 200MHz frequency response it needs to be driven by a maximum resistance of 22.7 ohms. Or for the minimum response (tuning everything as a filter, for t_r ~ 10ns), 90.9 ohms.Well, that's not very much ratio against 50 ohms, so that's kind of a downer.Regardless, even a 1:1 transformer has leakage inductance*, so even if this ratio isn't as large as 1:8, the analysis can continue.*Which is actually transmission line length. The asymptotic low frequency equivalent of a TL is stray inductance, or in a transformer, leakage inductance. But when working with RF, one must always keep in mind the assumptions they are using: in this case, the lumped LF model uses LL and Cp that arise from the TL characteristics of the winding(s). A conventionally wound transformer has poorly controlled TL characteristics, usually giving exaggerated LF parameters; but with only a little effort, we can control those characteristics, cleaning up the LF model (making it a better approximation to the real device) and making a simple TL model suitable above there.To get a matched 90 ohm impedance, we need LL = 290nH (secondary referred). Then the equivalent circuit is:(source) --- 50 ohms --- (transformer) --- (capacitor)The source is 50 ohms matched. After the transformer, it's 90 ohms (secondary referred). The transformer has 290nH LL (which manifests as series inductance). The capacitor has 35pF (plus some TL, but we should be okay to ignore that here). This is a series RLC circuit, with Zo = sqrt(L/C) = 91 ohms, R = 90 ohms, and so Fo = 50MHz and Q = 1.0.The step response will be critically damped, i.e., no overshoot. (Actually, it can be slightly underdamped, and still have no overshoot.)If we add some CLC around the transformer, we can use the transformer as a series inductor, and the load as the final capacitor, of a ladder type filter network, with a suitable filter type (such as Bessel, Gaussian, or equiripple group delay). The filter will also be a source-terminated type, because the load resistance is ~infinite. (It's not well known that filters can be singly terminated, but yes, it works, and there are tables for them!)The transformer spec, 290nH, suggests a winding length around 0.6m, nicely in the ballpark of reasonable transformers. You'd want to use enameled magnet wire, winding one layer for the primary, then an extension winding on top of it (as an autoformer) for the 90 ohm secondary. The stray inductance of two adjacent cylindrical layers isn't too bad, and will probably come out close. (Ideally, you'd design it with less than necessary, then add inductance to bring it up.)QuoteI'm also very concerned that the OP is posting on the internet like a valid answer is expected here.I mean, really. If you're not academic, then... you must be a professional with enough qualifications to figure this out yourself?If you are academic, then it sounds like you're in a study position (grad or undergrad, perhaps?), and should have this kind of support from the curriculum and faculty. And if you don't -- that you've been burdened with this task, without the necessary knowledge and tools to create the solution -- it seems you've been set up to fail, and need to bring it to the department head, or registrar.And if there's $10k's worth of downtime associated with failure of this device, one would hope it's at least reviewed by some or all of the above, especially if the designer has to resort to soliciting the internet for ideas.Tim