Right.. I am constantly annoyed at the same name for very different functio= ns.=20 This is somewhat similar to using multiple resistors coming into the summin= g junction of an opamp. (minus the opamp) Offset: It won't matter, the whole thing is AC coupled. Ham 600 meter band. 475kHz -----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 When all four signals are ON, what does the mixing? I assume by mixing you = mean addition (like audio mixing) and not multiplication (like RF mixing). Do they just mix because multiple sources are fed to one load? That wouldn'= t be very accurate since the load impedance seen by the ON channels would c= hange when one of them goes OFF. Also, if the inputs can each have differen= t offsets, what do you want the offset of the output to be? What is the fre= quency range (lower and upper limits) of the 300nV signal? On Wed, Feb 15, 2017 at 2:40 PM, Van Horn, David < david.vanhorn@backcountr= yaccess.com> wrote: > 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. > > I can AC couple in and out of the switching section. > > 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. > > 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. > > > -----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 > > 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? > > On Wed, Feb 15, 2017 at 11:53 AM, Van Horn, David < david.vanhorn@=20 > backcountryaccess.com> wrote: > > > > > 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? > > > > > > > > > > -- > > David VanHorn > > Lead Hardware Engineer > > > > Backcountry Access, Inc. > > 2820 Wilderness Pl, Unit H > > Boulder, CO 80301 USA > > phone: 303-417-1345 x110 > > email: david.vanhorn@backcountryaccess.com > backcountryaccess.com> > > > > -- > > 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 > > > -- > 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 > > -- > 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 > -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclis= t --=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 .