David, Have you tried pin diode switches? Just my $0.02, Jean-Paul N1JPL > On Feb 15, 2017, at 5:51 PM, Van Horn, David wrote: >=20 > Right.. I am constantly annoyed at the same name for very different funct= ions.=20 > This is somewhat similar to using multiple resistors coming into the summ= ing junction of an opamp. (minus the opamp) >=20 > Offset: It won't matter, the whole thing is AC coupled. >=20 > Ham 600 meter band. 475kHz >=20 >=20 > -----Original Message----- > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf = Of Sean Breheny > Sent: Wednesday, February 15, 2017 2:20 PM > To: Microcontroller discussion list - Public. > Subject: Re: [EE] Gating microvolt level signals without transients >=20 > When all four signals are ON, what does the mixing? I assume by mixing yo= u mean addition (like audio mixing) and not multiplication (like RF mixing)= .. > Do they just mix because multiple sources are fed to one load? That would= n't be very accurate since the load impedance seen by the ON channels would= change when one of them goes OFF. Also, if the inputs can each have differ= ent offsets, what do you want the offset of the output to be? What is the f= requency range (lower and upper limits) of the 300nV signal? >=20 >=20 >=20 > On Wed, Feb 15, 2017 at 2:40 PM, Van Horn, David < david.vanhorn@backcoun= tryaccess.com> wrote: >=20 >> Picture a four input mixer, where all four channels are normally on. >> I need to shut off various combinations of the signals without=20 >> introducing huge transients. >> Unfortunately the signals here are about 300nV. >> Source and load about 2k ohms. >>=20 >> I can AC couple in and out of the switching section. >>=20 >> I tried bringing each source in through a DC block cap, then a fet to=20 >> ground, and then a series resistor so that I don't pull down the=20 >> amplitude of the other signals too much. >> The gate charge ends up on the signal line before and during the fet=20 >> switchoff, and is huge relative to the signals. >> I tried gate resistors, but that lowers the amplitude but prolongs the=20 >> agony. >>=20 >> I thought about amplifying and then switching, but that would add a=20 >> lot of complexity, and even at that, I am only going to be working=20 >> with a few hundred microvolts or less. >>=20 >>=20 >> -----Original Message----- >> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On=20 >> Behalf Of Sean Breheny >> Sent: Wednesday, February 15, 2017 11:49 AM >> To: Microcontroller discussion list - Public. >> Subject: Re: [EE] Gating microvolt level signals without transients >>=20 >> I am having trouble getting a clear picture of what you are trying to do= .. >> When you gate a signal OFF is there another signal which should be=20 >> gated ON at the same time? In other words, is this a MUX or something=20 >> more like a sample and hold? What are the source and load impedances?=20 >> When you gate the signal OFF does that mean you want to continue to=20 >> pass the DC offset but not the AC component? >>=20 >> On Wed, Feb 15, 2017 at 11:53 AM, Van Horn, David < david.vanhorn@=20 >> backcountryaccess.com> wrote: >>=20 >>>=20 >>> 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. >>>=20 >>> Any ideas? >>>=20 >>>=20 >>>=20 >>>=20 >>> -- >>> David VanHorn >>> Lead Hardware Engineer >>>=20 >>> Backcountry Access, Inc. >>> 2820 Wilderness Pl, Unit H >>> Boulder, CO 80301 USA >>> phone: 303-417-1345 x110 >>> email: david.vanhorn@backcountryaccess.com>> backcountryaccess.com> >>>=20 >>> -- >>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 >>> View/change your membership options at=20 >>> http://mailman.mit.edu/mailman/listinfo/piclist >>>=20 >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 >> View/change your membership options at http://mailman.mit.edu/=20 >> mailman/listinfo/piclist >>=20 >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 >> View/change your membership options at=20 >> http://mailman.mit.edu/mailman/listinfo/piclist >>=20 > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/cha= nge your membership options at http://mailman.mit.edu/mailman/listinfo/picl= ist >=20 > --=20 > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .