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 change when one of them goes OFF. Also, if the inputs can each have different offsets, what do you want the offset of the output to be? What is the frequency range (lower and upper limits) of the 300nV signal? On Wed, Feb 15, 2017 at 2:40 PM, Van Horn, David < david.vanhorn@backcountryaccess.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 introducin= g > 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 > ground, and then a series resistor so that I don't pull down the amplitud= e > of the other signals too much. > The gate charge ends up on the signal line before and during the fet > switchoff, and is huge relative to the signals. > I tried gate resistors, but that lowers the amplitude but prolongs the > agony. > > I thought about amplifying and then switching, but that would add a lot o= f > complexity, and even at that, I am only going to be working with a few > hundred microvolts or less. > > > -----Original Message----- > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On 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 gated > ON at the same time? In other words, is this a MUX or something more like= a > sample and hold? What are the source and load impedances? When you gate t= he > signal OFF does that mean you want to continue to pass the DC offset but > not the AC component? > > On Wed, Feb 15, 2017 at 11:53 AM, Van Horn, David < david.vanhorn@ > backcountryaccess.com> wrote: > > > > > 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? > > > > > > > > > > -- > > 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 > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at http://mailman.mit.edu/ > mailman/listinfo/piclist > > -- > 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 .