4pcs relays are packaged in a 24-lead, 5 mm × 4 mm × 1.0 mm

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#5
Look at the applications: probe cards, ATE, RF test equipment. Its cheap in those applications. One Teledyne relay can be lots more. However 2 Ohms on resistance is not very good in many applications. I would not hesitate if I needed an 18 GHz relay. Not for audio. However if they get the volume up is should be $2. Look at the price of MEMs mikes.
 
#6
As I understand, this is an electro-mechanical switch i.e. tiny metal2metal contact-resistance area, presumably a golden one. At nearly zero voltage across such contacts, I believe should be very high current linearity. A higher voltage with such a tiny resistor will strongly affect VCR and H3, that's what we can see in the paper.
 
#8
IVX said:
As I understand, this is an electro-mechanical switch i.e. tiny metal2metal contact-resistance area, presumably a golden one. At nearly zero voltage across such contacts, I believe should be very high current linearity. A higher voltage with such a tiny resistor will strongly affect VCR and H3, that's what we can see in the paper.
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Exactly. You can measure this or simulate it easily enough in Spice of some kind.

There's some really good FET switches now that have low Rds-on and Rds is flat with varying applied voltages. The distortion thus is really, really low. Yeah, the parasitic capacitance across the FETs is not zero, so for audio applications the isolation degrades at higher audio frequencies. But, if you use two switches in series with a shunt switch to ground in between, the isolation becomes suitable even for test gear.

Again, you can simulate this in Spice. The exact distortion numbers may not be 100% accurate, but you can certainly see the trends and the results are probably within an order of magnitude.

The MEMs switches have been around for at least two decades now. The manufacturing volume probably has increased over that time, but not to the level of microphones...
 
#10
IVX said:
As I understand, this is an electro-mechanical switch i.e. tiny metal2metal contact-resistance area, presumably a golden one.
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There is some information on special alloy developed by GE for such MEMS relays:
One of the most difficult technical challenges, says Giovanniello, was finding an electrically conductive alloy that could withstand billions of bending-unbending cycles. “The real issue was the actuator,” he says. “That’s really where GE put the bulk of its effort, coming up with alloys. We’ve developed some proprietary alloys that are highly conductive, that make them really good for relays. But they’re extremely strong mechanically, almost like polysilicons.

“GE had, for decades, done a lot of work in alloys for jet engines and it was really some of those people that helped us to solve some of these fundamental reliability issues,” he added. Menlo has not revealed the composition of its alloys, but a research paper written by GE and Menlo engineers about five years ago indicates that they were then working with separate alloys of nickel and of gold.
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https://spectrum.ieee.org/how-rf-mems-tech-finally-delivered-the-ideal-switch
and whole paper for IEEE subscribers:
https://ieeexplore.ieee.org/document/7777586/metrics#metrics
 
#11
IVX said:
CG, I did simulate that and tried practically as well, it works as expected. THD@1k<130db at 680ohm feedback impedance, hence, THD+N is also -130db or close.
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Yeah, for that application with those impedances, I'm sure you're right. I guess you could parallel a dozen and maybe be ok.

For source switching at an audio preamp input, the load impedance is usually much higher, so the problem is accordingly less.
 
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