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Things you can do with diodes

(lcamtuf.substack.com)
325 points zdw | 1 comments | 03 Nov 25 23:49 UTC | HN request time: 0s | source
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dietrichepp ◴[04 Nov 25 00:27 UTC] No.45806185[source]▶
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.

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1. adrian_b ◴[04 Nov 25 11:16 UTC] No.45809691[source]▶
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.