Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

high frequency solid-state relay

Status
Not open for further replies.

zoulzubazz

Member level 5
Joined
Apr 26, 2012
Messages
87
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,288
Activity points
2,034
Hey guys,

I need to switch a 10MHz signal through an array of 8 air-core coils. the maximum peak to peak amplitude of the signal is +-20V and the current i am looking to switch is a maximum of 400mA. The figure attached shows what i am looking to do. I was looking at solid state relays but am not sure if they cant handle signals of 10MHz through them. The switching on/off time required is a few ms. What switch would you recommend for this application? Thanks.

IMG_20150721_231926.jpg
 

betwixt

Super Moderator
Staff member
Joined
Jul 4, 2009
Messages
15,516
Helped
5,026
Reputation
10,076
Reaction score
4,861
Trophy points
1,393
Location
Aberdyfi, West Wales, UK
Activity points
131,509
I don't think an 8-way multiplexer exists that can handle that voltage and current, even at low frequency. As the switching speed is low, you could try using miniature relays but I think the approach I would be to use the 10MHz to drive 8 individual power driver stages and do the switching by controlling the DC to each driver.

Brian.
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
50,020
Helped
14,496
Reputation
29,262
Reaction score
13,426
Trophy points
1,393
Location
Bochum, Germany
Activity points
287,099
If a solid state relays is suitable for 10 MHz depends on if you can accept the switch capacitance in your application.

Low voltage solid state relays in the 0.5 to 2A range are availaible on the market, if you don't find a suitable type, you make your own one using a MOSFET pair and a photovoltaic coupler.
 

zoulzubazz

Member level 5
Joined
Apr 26, 2012
Messages
87
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,288
Activity points
2,034
thanks, the SSR with the lowest out capacitance i could find was about 25pF which means about 45mA of current through the switch in off state, which is not acceptable in this case unfortunately. is there a way to circumvent this problem?
 
  • Like
Reactions: FvM

    FvM

    Points: 2
    Helpful Answer Positive Rating

betwixt

Super Moderator
Staff member
Joined
Jul 4, 2009
Messages
15,516
Helped
5,026
Reputation
10,076
Reaction score
4,861
Trophy points
1,393
Location
Aberdyfi, West Wales, UK
Activity points
131,509
Just a thought, given the DC path to ground, I wonder if PIN diodes might be an option. I suspect the losses may be too great. At only 10MHz it might just be possible to use a normal Shottky diode if it could be forward and reverse biased enough and the signal leakage could be tolerated. Some expermentation would be needed but it could be a cost effective solution.

Brian.
 

Dan Mills

Advanced Member level 2
Joined
Nov 10, 2013
Messages
510
Helped
239
Reputation
478
Reaction score
230
Trophy points
43
Activity points
4,558
Pin diode switches are the obvious approach, and at 10MHz there are common power rectifier diodes that will work perfectly well for this.

You need to hold off with a DC reverse bias greater then the RF peak voltage (ideally quite a bit greater, 100 - 200V is typical), and for on state you need to forward bias with a reasonably significant current (but the voltage drop is tiny).

Hell, you can do it with 1N4007s at that frequency and power level.

Here is a TR switch for ham radio done with 4007s, aparently good for a KW. https://sites.google.com/site/k7fjdiodeqskswitchbyw5uxh/home/k7fj-original-schematic

Regards, Dan.
 

crutschow

Advanced Member level 5
Joined
Feb 22, 2012
Messages
4,096
Helped
952
Reputation
1,902
Reaction score
986
Trophy points
1,393
Location
Colorado USA Zulu -7
Activity points
23,180
thanks, the SSR with the lowest out capacitance i could find was about 25pF which means about 45mA of current through the switch in off state, which is not acceptable in this case unfortunately. is there a way to circumvent this problem?
Is the concern about the current itself or that it will be going through the load?
If the latter, then you can use a additional switch at the output to ground, as FvM suggested, to short the leakage current to ground.
 

zoulzubazz

Member level 5
Joined
Apr 26, 2012
Messages
87
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,288
Activity points
2,034
hey guys, thanks very much for the replies. FvM's ideal to use additional switch is very good but the system would be bleeding too much current unnecessarily.

Pin diodes seem to be a good option, is it possible to use Mosfet drivers to turn the diode on/off quickly?

Keeping the non-linear distortion to the minimum is desired, the signal being switched is AC coupled into the 8 coils.

Thanks very much.
 

betwixt

Super Moderator
Staff member
Joined
Jul 4, 2009
Messages
15,516
Helped
5,026
Reputation
10,076
Reaction score
4,861
Trophy points
1,393
Location
Aberdyfi, West Wales, UK
Activity points
131,509
Here is a TR switch for ham radio done with 4007s, aparently good for a KW. https://sites.google.com/site/k7fjdi...inal-schematic

There is your example of using MOSFETS. You don't need to replicate all the circuit 8 times, just follow the basic principles of using the diode in series with the RF but ensuring it doesn't work as a rectifier (or conductor) by driving it hard into continuous conduction to 'switch on' and apply a high reverse voltage to 'switch off'.

I think I would have some concerns about using more than one diode in series, I think I would have wired resistors (1M maybe) across each diode so the reverse voltage was shared equally.

Brian.
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
21,980
Helped
4,591
Reputation
9,196
Reaction score
4,808
Trophy points
1,393
Activity points
145,109
Hi,

you could use an OPAMP for each channel independently. There are OPAMPS with enable pin. So you select just the channels with logic levels.

Like this one from LT: LT1210 (but this doesn´t meet your voltage and current requirements)

Maybe you find a suitable one...

Klaus
 

dick_freebird

Advanced Member level 5
Joined
Mar 4, 2008
Messages
7,802
Helped
2,221
Reputation
4,448
Reaction score
2,158
Trophy points
1,393
Location
USA
Activity points
62,420
400mA is not huge for a high power RF CMOS switch. But
these all want DC-blocked, ground-symmetric signals.

What's wrong with a plurality of latching relays, if you
need to keep coil power minimal? Or for that matter, a
plain old reed relay? We used to use Coto relays of
DIP-16 or sub-DIP size on ATE load boards at much
higher frequency and at least the same current, a lot.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top