Hi Dave,

I guess you've looked at the chip based RF switches?
I'm not sure how well they meet your added disturbance requirement but they
have good bandwidth and isolation. Available in a number of pole and throw
configurations and not priced too bad unless you need exotic frequencies.

There are also USB switches that are basically analog switches but with
good high frequency capability. Again they may inject some charge when
switching.

RP

On 17 February 2017 at 06:52, Van Horn, David <
david.vanhorn@backcountryaccess.com> wrote:

> I'm comparing antennas, so I need to rapidly switch between receive
> antennas.
>
> TX/RX would be dead easy, and I wouldn't care about the transients at all=
..
>
>
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of alan.b.pearce@stfc.ac.uk
> Sent: Thursday, February 16, 2017 10:12 AM
> To: piclist@mit.edu
> Subject: RE: [EE] Gating microvolt level signals without transients
>
> > > I'm looking for a way, hopefully not too complicated, to gate
> > > signals on and off without inducing more than maybe 100nV of
> disturbance.
> > > The signals may be at ground, or may be riding on a volt or two.
> > > "off" means more than 30dB reduction.
> > >
> > > Any ideas?
> >
> > Some of the better commercial analog switches have a charge injection
> > of < 1pC.
> >
> > To get a 100nV of disturbance implies a load capacitance of 5-10uF.
> >
> > So if your source impedance is 1K you'd have a bandwidth of maybe
> > 30Hz, which might be limiting.
>
> I suspect that to get such a low injection voltage will require a shaped
> drive to the FETs to minimize any gate capacitance charge feedthrough. I
> would also be looking at series/shunt/series FETs to get the isolation.
>
> But from a previous post it sounds like the object is to do
> transmit/receive switching (Ham bands were mentioned), in which case I
> would have thought there could be a way of pulsing the AGC momentarily to
> desensitise the receiver. But if two series FETs are used with a shunt on=
e,
> and the series ones have their sources joined, the shunt one could be
> turned off microseconds after the series ones are turned on, thereby
> leaving a low impedance path for any feedthrough to be shunted to ground
> (I'm assuming the object of the question is to isolate the receiver from
> the transmitter power when transmitting).
>
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