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Class D with LC filter works
I had a class-D amplifier working at the beginning of January, but I’ve changed the specs a bit since then (adding the LC filter) , and the students have a different comparator chip than I used then...
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Twentieth day of circuits class
We started today with a do-now problem, asking what the following circuit does: After 5 minutes, no one had any idea, so I asked questions until we got that In had a voltage of 0V, that the interesting...
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Twenty-fifth day of circuits class
I started class today with a do-now problem: What is the gain at 0Hz? ∞Hz?At what frequencies does the behavior change? Only a couple of students had any clue how to do this problem, though they’ve had...
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Twenty-sixth day of circuits class
I started today with feedback on the writing. The students have been getting much better about the content and organization of their reports, and the writing is pretty good from at least half the...
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Tried EKG design on protoboard
I built and tested an EKG circuit today using the protoboard that the students will use on Thursday, to make sure that there are no probems. I decided to try out a circuit that uses active feedback for...
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Action potential lecture and EKG lab
I did not lecture on Wednesday, but had a guest lecturer from the biology department, who gave a lecture on action potentials, based on a similar lecture she gives in a neuropsychology course. The...
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Twenty-eighth day of circuits class
Yesterday’s lecture was a mish-mash of odds and ends that we hadn’t covered well previously, and questions that had come up. I started with talking about where the EKG signal comes from. The guest...
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Supplemental sheets, draft 3
This post updates and replaces the Supplemental sheets, draft 2. It reflects the redesign of the course based on running a prototype version of the course in as a group tutorial in Winter 2013. Lecture...
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2-op-amp instrumentation amp
Last summer, I tried building an instrumentation amp using the MCP6002 op amps and external discrete resistors, and ended up with an amplifier that had terrible common-mode rejection, which is why I...
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3-op-amp instrumentation amp
Yesterday in 2-op-amp instrumentation amp, I worked through the analysis of the differential gain and common-mode gain for an instrumentation amp made from two op amps. There is a classic design of an...
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Common-mode noise in EKG
In 2-op-amp instrumentation amp, I said I’ll have to make some measurements later this week to see how large the common-mode noise on the EKG signals really is. Of course, it is likely to be highly...
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Some failed designs
For the past couple of days I’ve been exploring variations on the Blinky EKG project, looking at alternative approaches. For example, I looked at the possibility of eliminating the most expensive part...
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Logarithmic amplifier
My son wanted to design a circuit to convert microphone inputs to loudness measurements usable by an Arduino (or other ATMega processor). We discussed the idea together, coming up with a few different...
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Logarithmic amplifier again
Yesterday, in Logarithmic amplifier, I ended with the following plot: (click plot to see larger version) The cloud of points is broad enough to be consistent with slightly different parameter values. I...
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Still more on log amplifiers
Yesterday, I spent the day testing different transistors in the log amplifier, to see whether it made much difference which transistor I used. I wanted to test all 11 transistors in the iteadstudio...
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Precision rectifier
The log amplifier that I’ve spent the last several days understanding (posts a, b, c) is not the only non-linear circuit needed for a loudness detector. We also need to convert the audio input signal...
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Improved rectifier
In the Precision rectifier post, I gave the simplest circuit for making a precision rectifier: This circuit is both a log amplifier and a precision rectifier. If Vb is set to a constant voltage, then...
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Improved rectifier with Schottky diodes
In the Improved rectifier post, I gave the following circuit for an inverting rectifier and showed traces of its performance using diode-connected S9018 NPN transistors as diodes: Only one of D1 and D2...
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Virtual ground circuits
To use single-supply op amps properly, one usually needs to create a “virtual ground” or “bias voltage” between the two power-supply rails. I have used 3 different circuits for these virtual grounds:...
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Wire loop vs. twisted pair try 1
I was thinking about things we might do in the first lab day for the Applied Circuits course next quarter, now that I have 2 lab sessions a week. The first, obvious thing is to unpack the lab kits and...
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More on loudness circuits
My son got interested in a loudness circuit again, and we tried coming up with one that that would take few components. We decided on having a 3-stage system: a preamp to get voltage up, a peak (or...
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First op amp lecture
Today’s lecture was the first introduction of op amps to the students. I managed to present The basic notion of a differential amplifier: . Generic negative feedback amplifier. Generic...
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Block diagrams and audio amps
In today’s lecture, I introduced the notion of block diagrams as having two types of objects: functional blocks and connections between them. I emphasized that both parts were equally important, though...
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Audio amp lab
As I expected, no one came to lab today with their prelab homework done. There was a lot this week, as they needed to figure out the sensitivity of the microphone, decide how to bias it, figure out the...
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Low-power audio amp lab completed
Everyone finished their audio amps yesterday and got them working, and most finished on time, though one group took a bit longer than the rest, so I was in the lab for 5 hours instead of 3. They did...
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Second op amp lecture
Today’s lecture was the second one on op amps, after their audio amp lab. I had 3 topics I wanted to cover: virtual grounds, transimpedance amplifiers, and gain-bandwidth product. The gain-bandwidth...
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Phototransistor lab
Once again, no one came to lab today with their prelab homework done. There was a lot to do again this week, as they needed to figure out how much light was emitted by an LED, how much of that would...
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Mixed topics in lecture
Today’s lecture was a mish-mash of different topics. Pre-lab assignments not getting done. I asked the students for advice on how to get them (or next year’s class) to do the pre-lab assignments before...
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Instrumentation amp from op amps still fails
I’ve been trying to decide whether to have students build an instrumentation amp out of op amps in the circuits course. Currently the INA126P instrumentation amp chip that I have them use is a black...
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Instrumentation amp from op amps fine for EKG
As I mentioned in Instrumentation amp from op amps still fails, I’ve been trying to decide whether to have students build an instrumentation amp out of op amps in the circuits course. I decided that...
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Soldered EKG from op amps
Today I decided to solder the EKG design from Instrumentation amp from op amps fine for EKG onto one of my instrumentation amp protoboards, leaving out the instrumentation amp chip—I wanted to see how...
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Freshman design projects moderately successful
I just finished grading this year’s freshman design projects. I think that the projects were more successful this year than last year, in part because I kept the students focussed on electronics and...
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Ag/AgCl electrode lab went ok
Like on Tuesday, on Thursday I spent a long time in the lab, from about 9 a.m. to after 6 p.m., because it takes a fair amount of time to set up and clean up when we are dealing with liquids (in this...
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First op-amp lab was quick
On Monday I provided a little feedback on the design reports for the electrode lab. The big issues were Students not reporting the models they were fitting to the data. Students not reporting the...
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Lecture in middle of first op-amp lab
The lecture between the halves of the first op-amp lab did not cover much material. A big chunk of the first part was a discussion with the class about whether we should have a midterm quiz. After...
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First instrumentation-amp lecture
I started today’s lecture by returning a parts-and-tools kit to a student who had left it in lab yesterday—but admonished students not to tease him, since I had left my laptop in the classroom on...
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Testing nFET body diode with function generator
Continuing yesterday’s post on the i-vs-v characteristics of the PSMN022-30PL nFETs, I decided to look at the body diode characteristics. I changed the circuit only slightly from Circuit for measuring...
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Gain-bandwidth product
I spent yesterday afternoon collecting data for two figures for my book illustrating the limitation on gain caused by the gain-bandwidth product: This graph shows the measured gain of non-inverting...
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Screaming op amp
Santa Cruz’s Museum of Art and History is having a “drawing activity” online while the museum is closed, based on their 2017 Screaming Hand Exhibit. I’d like to see a screaming banana slug, but I can’t...
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Controlling current
In the electrode lab this year, students had even more trouble than usual in understanding that the the goal was to provide a constant current to the silver-wire electrodes for a measured time period,...
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