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Cursed circuits #5: capacitance multiplier

lcamtuf.substack.com

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Re: Cursed circuits #5: capacitance multiplier

#11

Post by Animats »

femto wrote: post #4
inigyou wrote: post #3

The last circuit, in steady state, behaves exactly as R2, but when the signal changes, the current through the capacitor is the derivative of the signal, reducing the amount by which the circuit is just R2. I speculate it acts like an inductor because that would be a logically silly thing for it to do but I'm not doing the math at 1am on my phone. I've always admired lcamtuf.

Yep. That topology is called a gyrator. Often used in IC's where it is hard to make an inductor.

Similarly, this capacitance multiplier is more likely to be seen on a chip than outside one. Capacitance inside an IC takes up a lot of chip area, while transistors are small.

Re: Cursed circuits #5: capacitance multiplier

#12

Post by readingnews »

"I keep coming back to this topic for two reasons. First, I think these components are usually explained poorly, making them a major stumbling block for folks trying to learn the craft. Second, op-amps have gotten really good, inexpensive, and small, so I think they should be used more."

No offense, but these are words typically spoken by someone who has never taken any electrical engineering courses or read any of Walter Jungs books, after having some electronics background.

"gotten really good"? Really, like in the 1970s?? (the 741, still widely used today was released in 1968). I recall in the 1980s in the electronics that were once completely discrete, they were _everywhere_ and still are today.

Re: Cursed circuits #5: capacitance multiplier

#13

Post by rcxdude »

readingnews wrote: post #12

"I keep coming back to this topic for two reasons. First, I think these components are usually explained poorly, making them a major stumbling block for folks trying to learn the craft. Second, op-amps have gotten really good, inexpensive, and small, so I think they should be used more." No offense, but these are words typically spoken by someone who has never taken any electrical engineering courses or read any of W…

to be fair, the 741 is not a particularly good op-amp nowadays. It's used mainly through sheer inertia.

Re: Cursed circuits #5: capacitance multiplier

#14

Post by viraptor »

readingnews wrote: post #12

"I keep coming back to this topic for two reasons. First, I think these components are usually explained poorly, making them a major stumbling block for folks trying to learn the craft. Second, op-amps have gotten really good, inexpensive, and small, so I think they should be used more." No offense, but these are words typically spoken by someone who has never taken any electrical engineering courses or read any of W…

I think you're doing a https://xkcd.com/2501/

I've done a few EE courses across two countries on the path to masters. The opamps were used at most for small signal processing in those. No more creative uses like frequency/capacitance multipliers. Comparing notes with friends in other unis, it wasn't that different there. You'd have to go into degrees much more focused on electonics to go to that level.

Re: Cursed circuits #5: capacitance multiplier

#15

Post by laughing_man »

readingnews wrote: post #12

"I keep coming back to this topic for two reasons. First, I think these components are usually explained poorly, making them a major stumbling block for folks trying to learn the craft. Second, op-amps have gotten really good, inexpensive, and small, so I think they should be used more." No offense, but these are words typically spoken by someone who has never taken any electrical engineering courses or read any of W…

Everybody uses the 741's pin-outs, but nobody should be using the actual 741 for new designs. And that's been true for many decades.

Re: Cursed circuits #5: capacitance multiplier

#16

Post by kilobaud »

laughing_man wrote: post #15
readingnews wrote: post #12

"I keep coming back to this topic for two reasons. First, I think these components are usually explained poorly, making them a major stumbling block for folks trying to learn the craft. Second, op-amps have gotten really good, inexpensive, and small, so I think they should be used more." No offense, but these are words typically spoken by someone who has never taken any electrical engineering courses or read any of W…

Everybody uses the 741's pin-outs , but nobody should be using the actual 741 for new designs. And that's been true for many decades.

Eh there are also decades worth of audio electronics designs which use the 741 and the decision of which actual part to use is often an aesthetic one. (i.e., assuming all other parameters are compatible then just use your ears). There are always new (hobbyist) designs being drafted around specific parts that are otherwise obsolete simply due to the musical character of certain parts

Re: Cursed circuits #5: capacitance multiplier

#17

Post by bombela »

kazinator wrote: post #6

These multiplication effects are unsurprising to hobbyists who studied electronics from the basics using a textbook. Amplifier circuits multiply impedances. For instance in a common emitter amplifier stage around a BJT (bipolar junction transistor), the input impedance is much larger than what is implied by the emitter resistor. In effect, the transistor multiplies the apparent resistance of that component. If a capa…

I have always found the term "capacitance multiplier" misleading. I see it as a voltage regulator with a filtered input.

Re: Cursed circuits #5: capacitance multiplier

#18

Post by jdontillman »

Capacitance multipliers are how wah-wah pedals work.

The classic Vox / Dunlop/ Cry Baby wah-wah pedal used by Hendrix, Gilmour, Clapton, Harrison, and so many others, is built from a resonant LC filter.

How do you change the resonant frequency of an LC filter with a pedal mechanism? The pedal turns a pot, and that controls a capacitance multiplier circuit.

Simple and elegant.

Re: Cursed circuits #5: capacitance multiplier

#19

Post by HappMacDonald »

userbinator wrote: post #8
kazinator wrote: post #6

These multiplication effects are unsurprising to hobbyists who studied electronics from the basics using a textbook. Amplifier circuits multiply impedances. For instance in a common emitter amplifier stage around a BJT (bipolar junction transistor), the input impedance is much larger than what is implied by the emitter resistor. In effect, the transistor multiplies the apparent resistance of that component. If a capa…

Analog electronics is a topic that was widely covered in mid-century textbooks, but it's definitely become more of a specialist niche today.

It fascinates me how many utterly critical foundational technologies have become specialist niches (while only ever growing more foundational and critical) over the past century. 8I
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