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Do I need to bias up the didoes in a double balanced ring mixer?

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Some diodes have turn on voltage at 0.3V, and some turn on at 1.2V. If LO power is about 5dBm (~0.6V peak voltage), I would need extra bias if the diodes I choose has turn-on voltage of 1.2V. Am I correct?

If so, where should I add the bias, I am confused now.

Thanks.

Missfresstyle
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  • They don't really have a much of a "turn on" value, but they have an IV graph and you most likely want to locate the point of interest on there. – PlasmaHH Feb 13 '18 at 16:39
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    No they don't need biasing. Get hold of a free simulator and try it and see but use diodes that are the same type. – Andy aka Feb 13 '18 at 16:40
  • Notice T1 is drawn with more turns on the mixer side than on the LO side. That's probably intentional. – The Photon Feb 13 '18 at 16:43
  • @Andyaka If no need biasing, how could the diodes be turned on? – Missfresstyle Feb 13 '18 at 18:01
  • Diodes conduct at very low voltages. For instance we all tend to say that about 0.7 volts a diode (a 1N4148 for instance) might be conducting about 10 mA but at 0.5 volts it will be conducting 0.1 mA. It tends to fall by 10x for each reduction of 100 mV. There is no on-off point for a diode. So, at 0.4 volts the current might be 10 uA and at 0.3 volts it might be 1 uA. [Picture](https://forum.allaboutcircuits.com/proxy.php?image=http%3A%2F%2Fforum.allaboutcircuits.com%2Fpicture.php%3Falbumid%3D247%26pictureid%3D2165&hash=606ccd31658bb0663be827f26e415953) – Andy aka Feb 13 '18 at 18:07
  • See my answer here: https://electronics.stackexchange.com/questions/260801/circuit-with-adjustable-source-and-a-diode – Andy aka Feb 13 '18 at 18:12
  • Thanks @Andyaka !I I think I know what you are saying now. In this ring mixer shown about, two diodes are needed to be on and the other two to be off at the same time. With your explanation, I guess i could consider uA scale current as a off state. So far we have been considering forward current, what about reverse current? Base on the I-V curve, diode should drives nearly 0 current also, so the diodes are "off"... right? I have been seeing wired results in my studying and posted as new question. Please check it out and see if you have any thoughts. – Missfresstyle Feb 13 '18 at 22:36
  • https://electronics.stackexchange.com/questions/355987/why-current-appears-at-reverse-bias – Missfresstyle Feb 13 '18 at 22:38
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    I never consider a forward biased to be on or off no matter how small the current. If you've ever designed an ion beam amplifier you'd realize that a full scale deflection of 1 nA is nowhere near "off". – Andy aka Feb 13 '18 at 23:38

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