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Because diodes have threshold voltage, I suspect that there exists operating voltage range of frequency mixers using diodes without op-amps or transistors (anyway op-amps and transistors themselves have operating voltage range). Is this correct?

If so, can diodes' voltage range be pushed up or pushed down easily, without need to increase its size?

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I gave this picture in an answer yesterday and it seems appropriate today: -

enter image description here

The two graphs show the volt drop across a 1N4148 diode for different currents.

At 1 uA the diode voltage is about 275 mV.

At 10 uA it is about 380 mV.

At 100 uA it is about 500 mV.

To say a 1N4148 diode has a threshold voltage of about 0.62 is also to imply that this is at a current of 1 mA. We say this sort of thing a lot in EE and it's implied that we have in mind some sort of diode current, normally 1mA.

If you plotted these graphs on linear graph paper it would become more clear that a lot seems to be happening between 0.6 volts and 0.7 volts but, to be accurate there isn't really a threshold. Here's what I mean: -

enter image description here

This graph isn't related to diodes but some yearly events but, can you see that the linear graph "has a lot going on" at about 2008 to 2010.

Altogether this means that mixers using diodes can use quite small signals and not suffer excessive distortion.

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I'm not really sure what your question is.

What application are you thinking of? A normal receiver?

The threshold voltage of the diodes is not really an issue.

For most mixer applications there is a local oscillator signal that is supplied locally and it can be made as large as necessary - it is not dependent upon the strength of the received signal.

This local oscillator signal will be made large enough so that the diodes are fully conducting - there is then no threshold for the received signal to overcome.

Tutorial on Double Balanced Mixers

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