I'm comparing antennas, so I need to rapidly switch between receive antenna=
s.

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=20
> > signals on and off without inducing more than maybe 100nV of disturbanc=
e.
> > The signals may be at ground, or may be riding on a volt or two.
> > "off" means more than 30dB reduction.
> >
> > Any ideas?
>=20
> Some of the better commercial analog switches have a charge injection=20
> of < 1pC.
>=20
> To get a 100nV of disturbance implies a load capacitance of 5-10uF.
>=20
> So if your source impedance is 1K you'd have a bandwidth of maybe=20
> 30Hz, which might be limiting.

I suspect that to get such a low injection voltage will require a shaped dr=
ive to the FETs to minimize any gate capacitance charge feedthrough. I woul=
d 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/receiv=
e 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 rece=
iver. But if two series FETs are used with a shunt one, 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 f=
or 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 transmi=
tting).

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