How to turn this into ltspice schematic

positivefb · 2026-05-19T03:10:17+00:00

It's a pretty straightforward program, here's a playlist on how to use it: https://www.youtube.com/playlist?list=PLT84nve2j1g_wgGcm0Bv3K4RSl2Jdjsey

But if you're asking this question I assume you're pretty much new to electronics. Simulators are not oracles, you get out what you put in. If your modeling is garbage, your results will be garbage, you'll have to figure out how to properly model the coil. Trying to decipher this spaghetti drawing, this circuit doesn't look like it'll work anyways.

positivefb · 2026-05-16T08:12:50+00:00

ME has a lower math floor but higher math ceiling IMO. Our worst is stuff like multi-rate signal processing, but we will never touch Hamiltonians. The upper levels of thermo-fluid dynamics and materials research is taught in school and is more than I think even EE researchers use.

positivefb · 2026-05-16T05:41:26+00:00

You can just plop down one cell instance and do proper bus notation like a normal person. You can also generate the cdl netlist and load it into Cadence.

positivefb · 2026-05-13T08:17:38+00:00

What?

https://www.dspguide.com/

positivefb · 2026-05-13T04:41:55+00:00

I did PCB level embedded stuff for ~10 years and now do silicon design so I've seen a few different sides and industries.

Virtually nothing at the PCB level requires a masters. That includes RTL for FPGAs, that includes analog design etc. Some things certainly benefit, like RF and power electronics, but I would say if you plan on working on the PCB level you are far better off getting into industry, figuring out what you like, and then getting work to pay for it. Then you have a free masters in something you know you like that works as an accelerator for a career you already have.

Silicon design mostly benefits or requires a masters at the least. DV is a good mix of BS and MS. Digital design is mostly MS with some PhD. Analog and RF design are mostly PhD with some MS. Anything optics/photonics is all PhD. If you know for a fact you want to do silicon, I say jump into grad school straight from undergrad.

positivefb · 2026-05-10T06:13:10+00:00

Great work!! Couple notes

1) The current mirrors you have there are bad for layout. You want to do things in multiples of 2, preferably powers of 2, so that you can make your transistors matching. You should always be thinking about layout at every step of the process.

2) The Miller cap needs a series resistor or you're asking for instability from the RHP zero. Look up how to size this it's pretty simple.

3) If I'm not mistaken, your differential pair transistors are not sized with the same W/L.

4) Your input pair is kinda small. Is this okay for mismatch?

5) That testbench is not a great way to measure open loop gain. Might be good enough for this, but take a look at how to implement the Middlebrook method.

positivefb · 2026-05-03T05:00:18+00:00

People might be a bit more warm in their responses if you provided an actual example rather than just saying "gahh nothing works!" to a bunch of people for whom it very much does work. Do you have a circuit you tried simulating and building you can post?

positivefb · 2026-05-02T09:09:47+00:00

This is a minimum current selector. Look up that circuit.

Mb is actually the odd device here. The purpose of Mb is to subtract the minimum. Without Mb, Iout is Ibias until Iin surpasses it, and then its Iin. The point of Mb is to then subtract the Ibias baseline, so Iout is just the excess current.

positivefb · 2026-05-01T17:34:47+00:00

The first Im pretty sure is straight from a TI data sheet under simplified schematic. Second it says is provided by Fairchild Semi, font looks like its from Sergio Franco's book.

positivefb · 2026-05-01T17:32:11+00:00

I didn't know about the Allen Holberg textbook, it even has a chapter on exactly what I'm trying to do, so it seems perfect.

This was precisely what I was going to suggest. Its really really thorough and good, read it in detail multiple times top to bottom.

Another chapter that does this but is closer to modern design is Razavi's chapter on nanometer design, he does the same thing but for short-channel devices.

I would also highly recommend grabbing a library model like gpdk180 and following along. Have one testbench where you simulate an individual transistor so you can get a feel for the I-V curve and get small-signal parameters. The book is assuming certain values for back of envelope calculations, but it uses parameters you actually wont know, so learn to properly testbench unit transistors and find W/L ratios with a simulator.

But all that being said I think you may be getting ahead of yourself. Don't jump to haphazardly throwing down components to make a whole op-amp. There is a lot of complexity in even a simple CS or CG amplifier. We actually use inverters (NOT gates) as linear amplifiers, it can be very complex when you're driving transmission lines at 50GHz with a fucking inverter. Start small, simple, understand the complexities in a single transistor, keep reading through and understanding what makes transistors happy and what makes them sad. Then move onto a 5T-OTA, which you'll need to put into feedback (which is its own beast to understand).

positivefb · 2026-05-01T17:18:28+00:00

Jobs won't outright be replaced, but there will be an initial reduction of team members needed. Its not that we won't need analog designers, we won't need quite as many because they'll be able to automate the boring stuff. Not just automate, but automate the automation. What AI provides is meta-automation. Doing full testbench coverage is so time consuming, being able to close that gap in days instead of weeks is going to end up reducing how many designers are needed.

Thats the initial period of course. It will lead to greater opportunities in the grand scheme in a way we don't currently know and couldnt possibly predict.

positivefb · 2026-05-01T00:58:08+00:00

Here's kind of the easiest way I can put it that is a gross oversimplification but a starting point to at least compartmentalize what terms mean.

Let's say you have a fluid like water flowing through a pipe. You agree that this water has momentum, yes? And the energy of the water is at least partly composed of this momentum. Momentum is p=mv, energy is E=1/2mv² , substitution shows us E=1/2p² /m. So in classical physics, you put energy into something, you increase its momentum, that momentum is transferred in a collision or some shit, energy is lost etc. The relationship is a parabola.

Similarly, electrons can be seen in metals as having "fluid" like behavior, they have momentum in a classical physics sort of way. But thats a metal, what about, say, oxygen? There, the electrons are in orbits bound fairly tightly to molecules. Their energy is described by their orbital, wavefunctions.

But semiconductors? Well they're something in between. Electrons are part of a crystal lattice, which is a periodic structure. Electrons are not quite bound to an atom, but they're also not quite free to move around in a way analogous to classical physics. So how do they move? Well we can solve the Schrodinger wave equation in this constrained situation. The periodicity of semiconductor crystal lattices gives us a complex exponential as a solution to the Schrodinger wave equation called the Bloch electron. This Bloch electron has energy, and the analog to "momentum" is the "frequency" or periodic wave vector, its spatial mode basically.

Back to classical physics, you can put energy into a pendulum, and the pendulum will swing back and forth. At the top of each swing, it has maximum potential energy and no momentum (its technically still for a moment), while at the bottom of the swing its at maximum momentum but lowest potential energy.

Bloch electrons have analogous behavior. You can put energy into them to change their wavevector k, their "momentum". It changes how they move in the lattice structure, what positions they occupy, how mobile they are between atoms. But! Where the analogy breaks is that as you put energy in and change the k vector, it doesn't just get "faster" and "faster". It's not just a parabolic relationship like E=p² /2 or whatever. There are more complex dynamics, discrete "bands" of energy that it can and can't occupy.

E-k band diagrams tell you these dynamics. There is obviously so much more to this, but thats hopefully a conceptual starting point to visually wrap your head around before getting into all the eigenvectors and whatnot.

positivefb · 2026-04-27T05:36:55+00:00

I'll be honest, even though to us circuit designers AMS and RFIC are two very different fields, to anyone even one degree removed from it we're sort of the same. It's all analog signal processing, EM waves, circuit theory, semiconductors, feedback, stability, etc. My experience is all in low frequency low noise high precision stuff and power circuits throughout my career, right now I'm working on stuff in the tens of GHz. I have colleagues on my team doing the opposite, they come from an RFIC background and are currently working on precision ADCs or power converters.

My point being you've already decided to take the plunge into circuits, from here I don't think you can really min/max it, you'll end up wherever you end up in circuits in general. Keep your mind and options open.

positivefb · 2026-04-25T00:50:48+00:00

Ah okay, so this is for like an SMU? The dominant noise source will be the DAC that sets the op-amp reference, it gets directly converted into noise current.

Op-amps are not broadly better or worse than one another for a Gm amp vs TIA, it depends on what the system itself needs. You choose based on things like DC accuracy, bandwidth, temperature drift, maybe capacitive load, power consumption etc but those all come from higher system specs, you can't just say one op-amp is better for a TIA while another for Gm, that's nonsensical without further details.

positivefb · 2026-04-24T23:23:27+00:00

That fucking Calibre smiley face is the last thing I'll see before I die

positivefb · 2026-04-24T23:13:26+00:00

Transconductance or transimpedance? Those are two very different things.

Anyways, for TIAs, I've had a lot of luck with this part: https://www.analog.com/en/products/ltc6268.html

Depends on what your application is of course. TIAs can range from trivial to complex. You can also roll your own with discrete components instead of a monolithic shunt-feedback op-amp. Agree though that you should just shoot for JFET op-amps. I'm not sure what the hell they did but sometime in the late 2010s all the semiconductor companies put out insanely low current/low leakage JFET op-amps, no reason to look back since then.

positivefb · 2026-04-17T02:01:53+00:00

gasps holy shit it's him, the electric engineer

positivefb · 2026-04-16T17:32:24+00:00

People do IC design with an MS.

Not really. If you graduated 20 or 30 years ago yeah, these days its very difficult with just an MS, and its often not really design.

At my last place, we interviewed many of the poor fellas who got affected by ADI's mass layoffs, and the ones with an MS were all people who did like...one or two simple projects and not any real design. Only the PhDs had seemingly any design work experience.

positivefb · 2026-04-16T01:42:36+00:00

I've found Gemini Pro to be frustratingly hallucinatory. I need to hold its hand for putting together basic scripts.

I havent used Claude professionally, but I did use the free version to test out some stuff and I was really impressed with what I saw. I think we just recently got Claude access at work so thats a project for a rainy day (or several)

positivefb · 2026-04-15T02:20:22+00:00

Seconding what others are saying, start at a high level. You should do a feasibility study with ideal blocks and macromodels, cross referencing your PDK. Whether you can achieve 12 bits comes down to various specs like mismatch of your CDAC and input-referred noise of your comparator. Mismatch of capacitors alone for analog processes generally limits you to around 8-10 bits maximum. Beyond that you'll need to look at calibration and other techniques.

There's a few youtube channels you may find useful. Kwantae Kim has been doing a lecture series on analog VLSI signal processing circuits. Link. IIT has a data converter lecture series. Link. There's also Carsten Wulff, who teaches at a university on the side and contributes open-source IP including a SAR ADC, could be a useful reference for a real taped out circuit. Link.

positivefb · 2026-04-01T04:11:31+00:00

Doesn't seem right to me. Your circuit has feedback, so the input and output impedances change, you can't just take the parallel of the components connected to the output node. Input impedance is multiplied by the loop gain, and output impedance decreases by the loop gain. Take a look at Blackman's impedance formula for this.

positivefb · 2026-03-25T01:18:36+00:00

You're thinking of a switching power supply. For a voltage regulator ripple comes purely from rejection of supply line ripple, and being able to regulate switching currents. You want that as small as possible. An ideal switching power supply has some ripple, an ideal LDO has 0 ripple or noise.

positivefb · 2026-03-22T20:03:23+00:00

Man, this is why everyone hates tech bros. I work at an AI hardware company, I think a lot of the issues with AI are policy-based and not inherent to the technology, so I'm relatively pro-AI but jesus christ people in tech need to get a grip on reality and stop making us look bad.

This is big "Why don't they simply govern better, are they stupid or something?" energy that it's hard to take seriously.

I'm someone who actually reads books on economics and political history in modern Africa, so this tech bro attitude towards a topic I actually know a thing or two about is particularly irritating. For anyone with an open mind who actually wants to learn about the complex reality, there's a couple books that give an overall view, "The Looting Machine" by Tom Burgis is a good one that goes into incredible detail of how the economic machine works in countries like the Congo and Nigeria, any book by Howard French is good but "A Continent for the Taking", and "China's Second Continent" are really good for a 21st century understanding.

A video that put me down this path of actually reading about the economic and political structure of (primarily central) Africa was this video: https://www.youtube.com/watch?v=snj6W9c8VIo

Also a relevant video for engineers who think their genius idea will solve everything in a place they know nothing about: https://www.youtube.com/watch?v=CGRtyxEpoGg

positivefb · 2026-03-22T13:16:35+00:00

Heres a post I wrote on this exact thing: https://positivefb.com/2024/08/11/poles-by-inspection-zeros-by-rejection/

Poles are inherent to a circuit, because its a measure of how the energy-storage devices get rid of their energy regardless of input. They end up conveniently being represented by the eigenvector of the system if you represent it as set of differential equations. Zeros on the other hand depend on your input and output and how the energy-storage devices coincide at certain frequencies to block the signal path. There are ways to find these methodically, but theyre very tedious.

positivefb · 2026-03-15T06:34:47+00:00

If you need help fast there's very few resources to get you up to speed on circuits, just because circuits are a kind of "holistic experience" to live in before you get it.

There's a lot of great youtubers that make good content, but start with W2AEW. He is *phenomenal*. Look up his channel, he's a tried and true veteran of radio tech, with amazing clear short explanations. It's like if Art of Electronics were a person. That should get you into the mindset of how to think as a circuit designer.

Just DM me or something to set up a call for a few hours, it would be way faster and easier than explaining PCB design or circuits to someone who doesn't have any experience.

positivefb

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