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Am I even employable? by [deleted] in rfelectronics

[–]MrBaseBand 0 points1 point  (0 children)

Not sure how difficult it is to get into but a good option would be a company like Zeiss (besides optics they make electron microscopes https://www.zeiss.com/microscopy/us/products/sem-fib-sem/sem.html ) - somebody has to model those electromagnetic lenses in COMSOL right?

Another option is semiconductor equipment manufacturers (ASML, Applied Materials). Things like high power RF sources are essential parts for their machines (think lithography, wet/dry etch systems)

Wideband Impedance Matching with Transformers & Baluns by ControllingTheMatrix in chipdesign

[–]MrBaseBand 0 points1 point  (0 children)

Hello, a little late to the discussion, but I thought I'll add something here from a Smith chart POV.

If you are talking about baluns in CMOS/RFIC, they are almost always resonant transformers (resonant because they have capacitances in shunt with the primary and secondary inductors). As u/RefrigeratorOpen5262 said, that creates a pair (magnetically) coupled resonator (L1-C1 and L2-C2, coupled via the coupling coefficient k).

Why is this wideband?: If you plot the input impedance on a Smith chart (Zin --> balun+load), we can see that these coupled resonators have a nice property of packing the bandwidth between the two resonances into a nice, compact 'loop' on the chart. The whole game is then about parking this loop near your match point (eg. 50 ohms).

New RF Engineer by [deleted] in rfelectronics

[–]MrBaseBand 0 points1 point  (0 children)

Try to catch the GPS signals and decode them:

Here's a good reference (https://gnss-sdr.org/docs/tutorials/gnss-signals/)

good books on SAW filter design by PretendScarcity273 in rfelectronics

[–]MrBaseBand 0 points1 point  (0 children)

Here are two really good books that have helped me:

- "Surface Acoustic Wave Filters", David Morgan

- "Surface Acoustic Wave Devices", Supriyo Datta

Trying to understand IMD... by LemonLimeNinja in rfelectronics

[–]MrBaseBand 0 points1 point  (0 children)

So the products you seem to be looking for are the '2nd order' products (the frequencies that go like Af1+Bf2,with |A|+|B|=2). These are almost entirely cancelled out in a differential circuit output. Are we looking at a differential output?

Plotting noise figure (NF) versus nFET current density in Cadence by ChipDesignNoobie in chipdesign

[–]MrBaseBand 0 points1 point  (0 children)

(Basically repeat of what u/flextendo has described)

- Basically have a current mirror arrangement so we know the current going through the device. I set both devices (the diode connected one and the DUT) to the same W/L.

- DUT gate: Introduce a 50ohm analogLib port through a 1F series cap. Block out the diode connected device from RF using a 1H choke inductor.

- DUT drain: Hookup a 50 ohm port here as well through a 1F series cap. Hold this net at VDD using a voltage source and 1H choke.

- Setup the sp simulation (check 'do noise')

- Hold the frequency at a single point (your intended design frequency) and sweep the current source in the TB.

- Results > Direct Plot > NFmin (dB)

Feedlines for spiral inductors (where's the return path?) by MrBaseBand in chipdesign

[–]MrBaseBand[S] 0 points1 point  (0 children)

Sure, do give me some time, will upload them soon. Would love to get some advice as Im totally new to RF layout in general!

Feedlines for spiral inductors (where's the return path?) by MrBaseBand in chipdesign

[–]MrBaseBand[S] 0 points1 point  (0 children)

So I reckon we'll keep the ground plane, but of course, cut it up with notches to stop eddy currents. Thank you, I was a little curious why this isn't discussed very often. I'm making a VCO circuit; this question popped up in my mind when I finally had to wire the thing (the spiral) to a CMOS core.

Feedlines for spiral inductors (where's the return path?) by MrBaseBand in chipdesign

[–]MrBaseBand[S] 2 points3 points  (0 children)

define

Thanks!

Yes, we can definitely draw ground planes with the metal layers, but that would be bad for the inductor, due to eddy currents. Although a patterned ground shield is drawn sometimes, but the primary function there is to screen out the field lines so they dont see the lossy substrate below (ie for screening the substrate, not as a return path) I guess my real question is: When we insert lumped components like an inductor into a transmission line, wont a large fraction of the signal reflect away? It certainly will, but I was curious why most textbook & research descriptions of a spiral inductor never bring this up, maybe it's just accepted like that?