unexpected frequency doubler or rectifier

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Yann Guidon / YGDESYann Guidon / YGDES 05/20/2020 at 03:100 Comments

So I was Falstad'ing some ECL/differential amplifier topologies and playing with the resistor values ratios...

I found some strange behaviours with this single-ended circuit when the collector and emitter resistors are equal.

At 5V the turning point is at 3.1V, so I created a sine wave centered around 3V with +/- 1V peaks. The output looks like a rectified version...

The effect disappears when the ratio of the resistors is modified. This might be a desired effect or an unwanted behaviour, and since I'm playing with ECL topologies, I want to avoid this so I need to understand what is going on.

This is important because I would like to save a transistor at the common emitter node so the resistor value must be well chosen. It's good to know that a 1/1 ratio is BAD, and changing it affects the kink point...

But OTOH it opens up potential for fun, such as sound effects :-P