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diff --git a/docs/umich/img/w24_wrapup/311_bad_apple.jpg b/docs/umich/img/w24_wrapup/311_bad_apple.jpg Binary files differnew file mode 100644 index 0000000..e0cb06f --- /dev/null +++ b/docs/umich/img/w24_wrapup/311_bad_apple.jpg diff --git a/docs/umich/img/w24_wrapup/311_hp_4155b.jpg b/docs/umich/img/w24_wrapup/311_hp_4155b.jpg Binary files differnew file mode 100644 index 0000000..d998519 --- /dev/null +++ b/docs/umich/img/w24_wrapup/311_hp_4155b.jpg diff --git a/docs/umich/img/w24_wrapup/311_latex.png b/docs/umich/img/w24_wrapup/311_latex.png Binary files differnew file mode 100644 index 0000000..d5d4561 --- /dev/null +++ b/docs/umich/img/w24_wrapup/311_latex.png diff --git a/docs/umich/img/w24_wrapup/gummy_worm_cake.jpg b/docs/umich/img/w24_wrapup/gummy_worm_cake.jpg Binary files differnew file mode 100644 index 0000000..50ee4cb --- /dev/null +++ b/docs/umich/img/w24_wrapup/gummy_worm_cake.jpg diff --git a/docs/umich/index.md b/docs/umich/index.md index 9174997..ee428cb 100644 --- a/docs/umich/index.md +++ b/docs/umich/index.md @@ -6,3 +6,6 @@ so basically i live in ann arbor now - [Fall 2023 Wrapup](f23_wrapup.md) - [Fall 2023 winter break wrapup](f23_winter_break.md) - [Winter 2024 Wrapup](w24_wrapup.md) + - [EECS 482, Intro to OS](w24_482.md) + - [EECS 373, Intro to Embedded System Design](w24_373.md) + - [EECS 311, Analog Circuits](w24_311.md) diff --git a/docs/umich/w24_311.md b/docs/umich/w24_311.md new file mode 100644 index 0000000..7080ee4 --- /dev/null +++ b/docs/umich/w24_311.md @@ -0,0 +1,238 @@ +# Winter 2024 Course Review: EECS 311 + +2024-05-03 + +Course Title: Analog Circuits + +Rating: 3/5 + +## Instructor (David Garmire) + +On the first lecture I had a feeling I've seen him before. I checked the +"courses offered" spreadsheet at SJTU last semester, and he taught 281. + +He's all nice and stuff, and he never judges you. But the vibes are not +the best I could imagine. He's pretty reserved, and often seems in doubt +of himself, as if he's teaching it for the first time. Contrary to two +other EECS professors I had this semester, he had the least "authority +figure" vibes. (Robert Dick sometimes has too much; Brian Noble has it +just right.) Sometimes we can't tell if we're wrong or he's wrong. If we +point out he _might_ be wrong, he stops right away, which is good, but his +first assumption is always he _is_ wrong, which hurts credibility if he's +not. + +One thing I like about David Garmire is his analogies. The best one is how +the NPN BJT is like a leaky tub of water. + +## Course topics + +- Introduction & review (e.g. Laplace transform, Bode plots) +- Opamps + - Inverting & non-inverting amplifiers + - Nonidealities +- Sallen & Key filters +- Diodes +- BJTs + - CE, CC and CB configurations + - High frequency + - Degeneration +- MOSFETs + - CS, CG and CD configurations + - High frequency + - Degeneration + +### Personal reflections + +Compared to EE majors in the room, I was all chill about this course. +I enrolled because I was interested, not because I was required to. It's +not like my degree or life depended on it. But my life does depend on +music, and it's part analog circuitry. + +Personally, I think Sallen & Key (S&K) just came out of nowhere. There was +no motivation. It's just a table of equations that we use to solve for +like six unknowns. It's not fun. + +BJTs are the most complex topic. You've got three currents coming in or +out of the BJT, one of which can _sometimes_ be ignored. You have three +modes: cutoff, active and saturation. To make a useful amplifier, you have +to juggle the voltage correctly to bias it in the right range; then you +get a transconductance, then you convert it to a linear circuit with +a dependent current source, then you either do a bunch of nodal analysis +or just apply formulas. In most cases formulas Just Work™. + +I remember taking 215 (the OG circuits course) and scoffing at the notion +of a "voltage-dependent current source". Like who would use that in real +life? I bet you ten bucks you can't even build one. However, it turns out +if you apply superposition principle to a non-linear circuit, and +constrain your input to a narrow range to pretend it was linear, an +"X-dependent Y source" appears, and it helps you apply linear formulas to +an otherwise unholy "e to the power of v over something" pasta. + +MOSFETs are just BJTs but with different names for everything (the "active +region" of the BJT is analogous to "saturation mode" of MOSFETs). Also one +of the three currents is gone (except in high frequency) and you juggle +the voltages in a different way. + +Overall, this course was more inspiring and extensive than I thought. +However, it was also pretty elementary. I enrolled because two of my +hobbies (ham radio and music) are closely relevant to analog circuits, and +I had hoped to build an amp after this course. Although half of the course +_is_ building amps, it's pretty theoretical. + +### Building amps + +The majority of our discussion toward the second half of the course was +transistor-based amplifiers. Interest was mostly on NPN common-emitter or +NFET common-source, but there are other configurations to fit niches. We +had these parameters to optimize for: + +- Gain (open-circuit, loaded, or overall) +- Output voltage swing (how many Vpp can you output before clipping) +- Bandwidth (low & high 3dB cutoff) +- Output impedance (affects loaded gain) +- Input impedance (affects overall gain) +- Power dissipation (how much DC power does it draw) + +Desiging amps, especially multi-stage ones such as what I did in lab 5, is +an ardous chain of trial and error. My observations are + +- Build first stage with around 10x the signal impedance +- Think about gain first +- 1 mA is usually a good DC current to start with +- If it doesn't work, try 1.5 or 2 +- DC current determines gain, output impedance, and power +- Too little and too much current both lead to bad overall gain +- Decouple all stages by chucking in a 1 µF to 47 µF cap +- If load impedance is small, add a buffer at the last stage +- Bandwidth is the last thing to worry about +- If you need to squash highs, add a cap from a signal to ground +- If you need more lows to pass, use larger decoupling caps + +Those tradeoffs are an inevitable part of an electronic engineer's life. +Besides, some transistor parameters (such as beta) depend on temperature +and fab variations, so we had to add feedback to make our circuit less +susceptable. I now appreciate the amount of work that analog engineers go +through just to create a usable amp. + +### Sine wave breakdown & shoutout to Samuel + +Another way to look at amp-building in the scope of 311 is to break down +a sine wave: + +x(t) = A * sin(ωt + ɸ) + b + +- A: amplitude, or in our case, gain. We talk _a lot_ about gain. Arguably + the _point_ of amps is gain. +- ω: frequency. We spent two lectures on high frequency response, one for + BJTs and one for MOSFETs, which discuss internal capacitances within the + transistors. The effect of external capacitors is discussed in the first + half of the course, in analog filters. +- ɸ: phase. We hardly ever talked about phase, and phase Bode plots were + not required. However we were required to tell apart inverting and + non-inverting amps. +- b: DC offset. In general not a thing to worry too much about. If you + need to get rid of it, just add a cap. If you need it back, bias your + base/gate/whatever. It's just a stepping stone for the AC signal. + +The frequency discussion is very interesting. We used a duo of methods +called OCTC and SCTC (open/short circuit time constant) to estimate the +lower and upper 3dB cutoff frequencies. They work like magic. Two separate +occasions, the estimate I got with them is within 1% of SPICE simulations. +Huge kudos to Samuel Nolan, our IA, for explaining the methods in the lab. +He is the GOAT IA this semester. + +### Analog vs. digital + +On the first 311 lecture, David Garmire talked about the quote unquote +"superiority" of analog circuits over digital ones, such as energy +efficiency. Somewhat ironically, exams two and three had one design +problem on each, and the premises are both to design an amplifier for an +ADC, presumably into a chain of DSP algorithms. + +Many systems now use DSP, which often is cheaper and/or more noise-proof, +so unless you're an retro-audiophile or still live in the 1900's, very few +things actually have analog circuitry from top to bottom. They usually +have at least one piece of integrated circuit somewhere. But even if it is +the case — he argues — analog circuits are essential. + +There was a 373 lecture dedicated to ADC/DAC, and later there were a few +slides that discuss analog filters. It was one of the few occasions this +semester that 311 was useful for another course. I am more than sure it'll +be useful for 473 next semester as well. + +Robert Dick acknowledges that sometimes there are problems 1's and 0's +cannot solve. One such example is high frequency noises in the ADC input, +which cause aliasing, and are a pain to distinguish from actual signal in +software. So the solution is to add a lowpass filter to the input. + +I am unsure whether my preference is analog or digital. On one hand, +analog is cool because my bass is an analog system. But the DAW is digital +(it literally stands for digital audio workstation). Let's leave it this +way. + +## Labs + +Labs are the heaviest workload of 311. There are five labs in total, each +spanning over two or three weeks. + +- Lab 1A/B: opamps +- Lab 2A/B: S&K filters with opamps +- Lab 3A/B: voltage boosting & power harvesting with diodes +- Lab 4A/B: single-stage BJT amp, measuring beta and capacitances of BJT +- Lab 5: designing a 3-stage amp + +The typical roadmap of a lab: + +- Prelab: Do calculations, simulate in SPICE +- In-lab: Build circuit, measure with ADALM and Scopy + +Note: + +- The ADALM is a virtual lab kit USB device by Analog Devices +- Scopy is the software to interface with the ADALM. It's got an + oscilloscope, a voltage supply, a multimeter, and a network analyzer + (which you use to get Bode plots). Thankfully it is open source and runs + on Linux (was a pain to install though because it's not in any pacman + repo or AUR. Had to manually build it because I didn't want flatpak. + Somehow it wanted a patched version of Qt and many other deps so I had + to build like six libraries and manually change CMakeLists so one of + them compiles) +- SPICE is a circuit simulator. The lab docs mention LTSpice, which does + not run on Linux, so I used ngspice integrated in KiCad. Halfway through + the semester, KiCad upgraded to 8.0 which includes a major overhaul of + the ngspice frontend — huge improvement. + +In lab 3B, I built a circuit that harvests power from a 3.5mm jack to +light up an LED. Naturally, I made it play Bad Apple: + + + +In lab 4B, I hooked an NPN BJT to a giant beast of a machine, the HP 4155B +semiconductor parameter analyzer that thought it was 1997. + + + +Despite not having an A/B, lab 5 took three weeks. After designing and +simulating (but not building) a circuit, I needed to write a report for +the design of my three-stage amp. It "must be written with a word +processor", but did not mention which one. + + + +I used up like 10 pages of scratch paper (single sided) just for the +calculations. Glad I did meet the specs. + +## Verdict + +It's just a gateway drug to EE. Don't expect too much — you won't be an +expert when you walk out, but do expect mind-bending moments, like how +I discovered that I've been misunderstanding BJTs for like five years. + +If your job involves interfacing with "weird" analog signals, like signal +impedances in the megaohms, then this course is essential. + +Would be better if the lab was larger though. It's like a can of sardines. diff --git a/docs/umich/w24_wrapup.md b/docs/umich/w24_wrapup.md index 3956133..714083b 100644 --- a/docs/umich/w24_wrapup.md +++ b/docs/umich/w24_wrapup.md @@ -14,6 +14,7 @@ them up into individual articles, listed below. - [EECS 482, Intro to OS](w24_482.md) - [EECS 373, Intro to Embedded System Design](w24_373.md) +- [EECS 311, Analog Circuits](w24_311.md) - Other courses WIP ## Notable material gains |
