Things you can do with diodes

Conspicuously absent are some of the analog circuit applications. Here are three of my favorites:

1. Frequency mixer, used for heterodyning, important in radio, so I hear. https://en.wikipedia.org/wiki/Frequency_mixer

2. Log converter, where the output voltage is proportional to the logarithm of the input voltage. https://electronics.stackexchange.com/questions/374440/log-c...

3. Diode ring, which provides variable gain, used in analog compressors like the Neve 33609 (I have a clone of the 33609, and I’m very fond of it)

Think about this: if you have a nonlinear device like a diode, then the dynamic resistance changes depending on the operating point. If you modulate the operating point, you’re modulating the dynamic resistance.

From my hobbying decades ago there is also the boring old rectifier to convert AC to a wavy DC.

4. Varactors! https://en.wikipedia.org/wiki/Varicap

Reverse biasing a diode at different levels changes the junction capacitance. Also used in radio, for things like variable filters.

edit: oh, it's topped pinned comment!

Zener diodes can be used as the basis for a quantum random number generator.

https://opg.optica.org/optcon/fulltext.cfm?uri=optcon-1-7-15...

Kinda interesting to hear about. I have a 500 chassis I’m slowly working on filling. I’m between the RND 535 or 543, and had never heard of a diode bridge comp before looking at the 535.

What kind of 33609 clone do you have?

4. Voltage controlled filter, (diode ladder VCF), as used in the Roland TB303

And a square law detector!

Temperature sensor.

You could also make a high speed signal sampler.

https://w140.com/tekwiki/wiki/Sampler

I have the Heritage HA-609A. I considered going 500-series. Maybe some day in the future. For now, I have two preamps and the HA-609A in a 4U rack, and most of my other gear is in storage. Keeping things light.

I did this once with a diode when I was a baby electrical engineer in college. But of course you need some kind of measurement circuit. So somehow(???) I figured out I could wire a diode into one axis of my analog Gravis joystick--hooked up to my soundcard--and get a fairly accurate and stable measurement of temperature by poking the monostable multivibrator (pretty sure that's what it was called) in the soundcard that would trigger the time it took to drain a set amount of charge through the joystick's x-axis/now-diode.

Novices who don't have a clue nor know any better come up with the weirdest solutions. I have no clue whatsoever now what inspired me to even try something like that.

Clipping diodes are common in distortion effects as well, especially guitar distortion pedals. Examples include silicon, germanium, LEDs, etc.

Those are covered in the article

PIN diode, a diode used as an AC on/off switch by passing current through it, very useful in RF circuits above 1GHz

Diodes are also used as a radiation detector in radiotherapy: https://oncologymedicalphysics.com/diode-detectors/

And particle accelerators ! They mostly detect gamma radiation, and they are used in conjunction with other detectors (ram chips, mosfets)

With some capacitors you can build a voltage multiplicator

https://en.wikipedia.org/wiki/Voltage_multiplier

Stereo decoder. You feed L+R and L-R to the corners of Full Bridge Rectifier and out comes Left and Right.

I heard his voice while reading this.

Two more from the world of analog music/guitar electronics:

1) Ring modulator: https://en.wikipedia.org/wiki/Ring_modulation

A device used to multiply two analog signals in time domain. Best known for the sound of the Daleks in the original 1960s Doctor Who series. Has some applications outside of music and sound effects. If you can find those old fashioned audio transformers, this effect does not require a power source.

2) Diode clipper: https://en.wikipedia.org/wiki/Clipper_(electronics)

Two diodes in parallel with opposite polarities. Clips the incoming AC signal to a +/- diode threshold voltage. Put a high voltage gain amplifier stage in front of it and you get the classic electric guitar distortion tone you know and love. Allegedly works best with germanium-unobtainium diodes. In their absence, using two different kinds of diodes can also have pleasant tonal qualities.

For log converters you should not use diodes, because their parasitic currents mask the current component that has an exponential dependence from the voltage.

For log converters, bipolar transistors are used, because their collector current depends only on the ideal diode current of the base-emitter diode, not also on its parasitic currents, so the base-emitter voltage has a logarithmic dependence on the collector current, for a relatively wide range of currents.

> 3. Diode ring, which provides variable gain, used in analog compressors like the Neve 33609 (I have a clone of the 33609, and I’m very fond of it)

I just had a quick look at the service manual, but isn't that more of a diode bridge than diode ring? A Ring Modulator has the diodes connected nose-to-tail in a ring, but the gain cell in the 33609 looks more like a rectifier :-)

You can see the same circuit in the VCF and (incorrectly drawn) in the VCA of the Korg MS50 synthesizer. In the former it acts as the "variable resistor" in a fairly straightforward Sallen-Key lowpass filter (there are two feedback capacitors, one to either side of the bridge, to attempt to prevent the input voltage also tuning the filter). On the VCA the diodes are drawn wrong but the pin numbers are correct.

> 2) Diode clipper: https://en.wikipedia.org/wiki/Clipper_(electronics)

I don't even know how many Boss DS-1 clones I've made, but the first one was probably when I was in high school about 35 years ago.

Diode ladder, but also in various Sallen-Key designs like the Steiner-Parker Synthacon which we all now know from the Arturia Minibrute (Yves Usson probably made more of these filters than Nyle Steiner ever did!) and as I've mentioned elsewhere the Korg MS50. I think the Yamaha GX1 filters used a diode bridge too, probably using discrete transistors similar to the Korg 700S filter.

> I have no clue whatsoever now what inspired me to even try something like that.

A combination of "what's the simplest thing that could possibly work?" and "well they didn't say you couldn't..."

So many distortion pedals use an op amp to run a signal into antiparallel diodes to create distortion. I’ve spent a few weeks trying to emulate it, and it’s a lot of fun.

Different flavors of diode make significant changes to the way it sounds. Even things like LEDs can be used (they are Light Emitting Diodes, after all).

Andy Simper of Cytomic is some kind of mad genius at this stuff. He’s created a painstakingly accurate emulation of the Ibanez Tube Screamer that allows you to change the values of basically every component in the circuit diagram. It’s jaw dropping: https://cytomic.com/product/scream/

He’s also shared a ton of incredible information about how he emulates circuits. The math can get really intense. If anyone is looking for a fun project, I strongly suggest experimenting with circuit modeling. It’s a great workout for the brain.

And you managed to reinvent the single-slope ADC :-)

https://www.cedarlakeinstruments.com/archives/841

https://www.monolithicpower.com/en/learning/mpscholar/analog...