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.

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!

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.

Step recovery diode!

Abuse minority carrier lifetime to very suddenly turn from resistive to capacitive just after switching from forward current to reverse bias; use the fact that the current wants to keep flowing to force it to concentrate into another step recovery diode that's about to cut out, in turn making the cut off spike even sharper, and on.

Surprisingly capable for e.g. blasting a FET gate off while tanking the Miller effect gate current needs through sheer power of SRD-based-pulse-shaping. Because for e.g. GaN and SiC if you have to choose between ZVS and ZCS, you can take ZVS and just furnish a gate pulse that _makes_ the channel remain off as the current drops and the voltage soars. At least if you pull some tricks and make the current commutation loop sufficiently low inductance to keep your transistors from blowing out in self-inflicted overvoltage due to a current that needed to pass too high an inductance in too short a time. (Total drain charge is sadly fundamental to the channel's existence, and non-ZVS turn-on is unavoidably lossy. A majority carrier device is theoretically capable of just switching off though if you can arrange the structure for extremely low inductance.)

> 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.

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.

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...

You could also make a high speed signal sampler.

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

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

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

With some capacitors you can build a voltage multiplicator

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

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

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

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

In synthesizers, diodes are used in oscillators to shape triangle waves into sine waves.

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

Temperature sensor.

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?

And a square law detector!