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CD4066B as an HF switch?

时间:04-04 整理:3721RD 点击:
Hi, I want to build this circuit ../imgqa/eboard/Antenna/rf-vk5bcm0pjxv.gif and I need a way to switch different crystals in it, so that I can convert more than one SW bands into a CB (let's ignore the input filtering for now).

Instead of using a mechanical switch I was thinking of a cd4066b.
If it was a relay It could be done by switching in and out one of the crystals pins, but with the 4066, I do not know if it allows that high frequency (max 28MHz) to pass through it without introducing weird oscillations, because it is not an ideal wire switch.

Can you please help me on this?

CD4066 (as well as other analog switches) has considerable capacitance and also series resistance. I feel that it won't work as crystal mux above a few MHz.

In any case, the oscillator circuit gain and impedance must be considered in analysis.

Can you think of any other way I can do it without using mechanical DIP switches or slide switches?

Many options, e.g. discrete diodes, RF BJT or small MOSFET. Suitable DC bias needs to be designed.

I do not know if a simple diode switch can do it. You see the configuration in this crystal oscillator is weird to me. It reminds me something like a crystal multivibrator. See the attachment of how he connects the crystal.
This is different than the SA612AN. In the Sa612AN, the separate colpitts oscillator would require capacitors switching as well for multi-band operation, but the s042p does not. That is why I have chosen this design. But I do not know if diode switching would be adequate.

GaAs switches are an excellent low capacitance option, but biasing of the NJFETs is a bit tricky, thus I hesitate to suggest it. I have e.g. used Skyworks AS169-73 as high frequency analog switch.

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