Is it better to use bandswitching diodes (not PIN diodes) in (DBM) HF...VHF mixers?
RDmax=0.7 ohm @ 3 mA
Have somebody measured how fast they switch?
E.g. BA591:
Main page:
Another question:
How about using SiC diodes in (DBM) HF...EHF mixers?
Unfortunately only power diodes are manufactured?:
/Glenn
I would say no, neither. Bandswitch diodes are optimised for low Rd at lowish forward current not for switch speed and I have seen some with Trr times of micro-seconds.
Your best bet are regular silicon or even GaS schottky diodes intended for RF use. SiC are schottky but for high temp high voltage power switching and will have too much capacitance for VHF use. Unless you want your mixer to run at kilo-watt level SiC would be unsuitable choice.
piglet
Wouldn't think SiC diodes would have any advantage... Rs is much higher and you don't get any advantage from Vrm. Unless you somehow arranged it so you could deliver 500V into the LO port without it being shorted away by two Vfs, which would give pretty ridiculous dynamic range I suppose. But given the sizes commercially available, it would only work up to HF or so.
A diode-strapped BJT might be of interest. Relatively low capacitance and quite fast switching (much faster than a single junction alone -- effectively, self Baker clamped). 2N3904 is supposed to be nanoseconds fast, though Cbe isn't going to help much relative to, say, 1N914. A particularly small type might fare better (but beware of the low Vebo of RF types).
Tim
-- Seven Transistor Labs Electrical Engineering Consultation Website:
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