Re: mmic switch with dc-transmission

From: John Larkin (jjlarkin_at_highSNIPlandTHIStechPLEASEnology.com)
Date: 07/01/04 

Date: Thu, 01 Jul 2004 10:04:02 -0700

On 1 Jul 2004 04:09:29 -0700, kopfschuss.osv@web.de (Vau) wrote:

>hi everybody!
>
>I´m a student in electrotechniques and working on a thesis.
>
>In this I need to switch up to 100 RF signals (up to 200 Mhz). I found
>a lot of different mmic switches, which would be applicable because
>off small smd packages and limited space on pcb.
>
>My problem is that all found switches need dc-cut capacitors, but I
>need dc transmission because of measuring logic levels.
>
>Does anybody know mmic switches which transfer dc or any other
>suggestion to solve this problem?
>
>thanks in advance
>
>Vau

Most of the integrated RF switches do pass DC, because capacitors are
hard to fabricate in-chip. But they tend to work best at weird DC
offsets; you can get around that be figuring out what their inherent
offset is, and shifting your power supplies to translate that to
ground. Of course, your control logic levels have to move, too.

Depending on your isolation requirements, the little Fairchild cmos
logic switch/mux things might work... they're just analog transmission
gates.

The Hittite HMC253 is a nice 8:1 mux, very fast, and the price just
dropped from $22 to $5. It conducts DC in its transmission path but,
interestingly, has series caps on its terminations!

Don't overdrive any of these things or very strange stuff will happen.

A 100:1 tree will be interesting in any technology.

John

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