Reply by John Larkin September 18, 20132013-09-18
On Wed, 18 Sep 2013 07:14:25 -0700 (PDT), George Herold <gherold@teachspin.com>
wrote:

>On Tuesday, September 17, 2013 1:44:29 PM UTC-4, Spehro Pefhany wrote: >> On Tue, 17 Sep 2013 07:10:09 -0700 (PDT), George Herold >> ><snap> > >> >> >If it's >2pF then you have to buy me a beer if I'm every in SF. >> >> >(I get buy yours at the same time.) >> >> >> >> >George H. >> >> Bud Light? >> >> >Sure, you probably don't have Genesee out there. >> >> >http://beeradvocate.com/beer/profile/302/865 >> >George (there's no such thing as bad beer) Herold >> >> Gennie cream ale is a bit of an acquired taste, IMHO. > >Grin, beer seems to be an acquired taste.
Like oysters. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by George Herold September 18, 20132013-09-18
On Tuesday, September 17, 2013 1:44:29 PM UTC-4, Spehro Pefhany wrote:
> On Tue, 17 Sep 2013 07:10:09 -0700 (PDT), George Herold >
<snap>
> >> >If it's >2pF then you have to buy me a beer if I'm every in SF. > >> >(I get buy yours at the same time.) > >> > >> >George H. > >> Bud Light? > > >Sure, you probably don't have Genesee out there. > > >http://beeradvocate.com/beer/profile/302/865 > >George (there's no such thing as bad beer) Herold > > Gennie cream ale is a bit of an acquired taste, IMHO.
Grin, beer seems to be an acquired taste. As a youth growing up in Western NY it was almost a requirement that the first beer you had was Genny Cream. I'm not sure why... I guess it's a bit sweeter than 'normal' beer, and still very cheap. I haven't had a Genny Cream in ages. George H.
Reply by miso September 18, 20132013-09-18
On 9/17/2013 1:26 PM, Fred Bartoli wrote:
> Le Tue, 17 Sep 2013 10:12:03 -0700, miso a &eacute;crit: > >> For simulation purposes, they lump the common mode capacitance to >> ground. But in real life, the common mode capacitance could be to any AC >> ground. > > I was just telling what the Ccm value was. > >> I can't see this being significant unless the device was driven >> with a very high impedance source. If the source was very high >> impedance, there could be power supply coupling issues. >> Again it depends on the circuit, but common mode capacitance in real >> life is more likely to be to one of the power supply rails, or even more >> than one rail. If you visualize the input stage, the common mode >> capacitance is really a combination of parasitics. > > > Yup, but not necessary so high impedance. I was once working on a sub ppm > 50kHz LPF (MFB so as to avoid CM distorsion) and found THD to be > unexpectedly high. It was just the output stage class B action that > modulated the supply rails which in turn sneaked into the opamp virtual > ground node through the supply to input parasitics. > >
I understood you were just giving the ccm from the spice file. Your example shows the pitfalls of a model just lumping the common mode capacitance to ground. Some CMOS op amps put the long tail pair in a well. I can see that kind of parasitic screwing up some designs if they just lumped it to ground.
Reply by Spehro Pefhany September 17, 20132013-09-17
On Tue, 17 Sep 2013 07:55:04 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

>On Tue, 17 Sep 2013 07:10:09 -0700 (PDT), George Herold <gherold@teachspin.com> >wrote: > >>On Monday, September 16, 2013 9:41:12 PM UTC-4, John Larkin wrote: >>> On Mon, 16 Sep 2013 17:36:21 -0700 (PDT), George Herold >> >><snap> >>> >> I do. I'd better measure it, I guess. Grumble. >>> >>> > >>> >>> >Great, I hope it is 0.75pF! >>> >>> >If it's >2pF then you have to buy me a beer if I'm every in SF. >>> >>> >(I get buy yours at the same time.) >>> >>> >George H. >> >>> Bud Light? >>Sure, you probably don't have Genesee out there. >>http://beeradvocate.com/beer/profile/302/865 >> >>George (there's no such thing as bad beer) Herold >> > >I've had Genesee. It's made from Genesee river water, one of the more polluted >waterways on the planet. Pretty tasty beer. > >I could take you to Zeitgeist a few blocks away. Al fresco dining (actually, >picnic tables under a freeway ramp) and 44 beers on tap. Biker bar, but >bicycles. Joerg likes it. > >Or The Monk's Kettle, with beers ranging from $6 a glass up to $80.
Don't go on Monday, though. ;-)
Reply by Fred Bartoli September 17, 20132013-09-17
Le Tue, 17 Sep 2013 10:12:03 -0700, miso a &eacute;crit:

> For simulation purposes, they lump the common mode capacitance to > ground. But in real life, the common mode capacitance could be to any AC > ground.
I was just telling what the Ccm value was.
> I can't see this being significant unless the device was driven > with a very high impedance source. If the source was very high > impedance, there could be power supply coupling issues. > Again it depends on the circuit, but common mode capacitance in real > life is more likely to be to one of the power supply rails, or even more > than one rail. If you visualize the input stage, the common mode > capacitance is really a combination of parasitics.
Yup, but not necessary so high impedance. I was once working on a sub ppm 50kHz LPF (MFB so as to avoid CM distorsion) and found THD to be unexpectedly high. It was just the output stage class B action that modulated the supply rails which in turn sneaked into the opamp virtual ground node through the supply to input parasitics. -- Thanks, Fred.
Reply by John Larkin September 17, 20132013-09-17
On Tue, 17 Sep 2013 13:44:29 -0400, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

>On Tue, 17 Sep 2013 07:10:09 -0700 (PDT), George Herold ><gherold@teachspin.com> wrote: > >>On Monday, September 16, 2013 9:41:12 PM UTC-4, John Larkin wrote: >>> On Mon, 16 Sep 2013 17:36:21 -0700 (PDT), George Herold >> >><snap> >>> >> I do. I'd better measure it, I guess. Grumble. >>> >>> > >>> >>> >Great, I hope it is 0.75pF! >>> >>> >If it's >2pF then you have to buy me a beer if I'm every in SF. >>> >>> >(I get buy yours at the same time.) >>> >>> >George H. >> >>> Bud Light? >>Sure, you probably don't have Genesee out there. >>http://beeradvocate.com/beer/profile/302/865 >> >>George (there's no such thing as bad beer) Herold > >Gennie cream ale is a bit of an acquired taste, IMHO.
Tried Wexford? It's delish. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by Spehro Pefhany September 17, 20132013-09-17
On Tue, 17 Sep 2013 07:10:09 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Monday, September 16, 2013 9:41:12 PM UTC-4, John Larkin wrote: >> On Mon, 16 Sep 2013 17:36:21 -0700 (PDT), George Herold > ><snap> >> >> I do. I'd better measure it, I guess. Grumble. >> >> > >> >> >Great, I hope it is 0.75pF! >> >> >If it's >2pF then you have to buy me a beer if I'm every in SF. >> >> >(I get buy yours at the same time.) >> >> >George H. > >> Bud Light? >Sure, you probably don't have Genesee out there. >http://beeradvocate.com/beer/profile/302/865 > >George (there's no such thing as bad beer) Herold
Gennie cream ale is a bit of an acquired taste, IMHO.
Reply by miso September 17, 20132013-09-17
For simulation purposes, they lump the common mode capacitance to 
ground. But in real life, the common mode capacitance could be to any AC 
ground. I can't see this being significant unless the device was driven 
with a very high impedance source. If the source was very high 
impedance, there could be power supply coupling issues.

Again it depends on the circuit, but common mode capacitance in real 
life is more likely to be to one of the power supply rails, or even more 
than one rail. If you visualize the input stage, the common mode 
capacitance is really a combination of parasitics.


Reply by George Herold September 17, 20132013-09-17
On Tuesday, September 17, 2013 11:30:33 AM UTC-4, Jim Thompson wrote:
> On Tue, 17 Sep 2013 08:23:09 -0700 (PDT), George Herold > > <gherold@teachspin.com> wrote: > >On Tuesday, September 17, 2013 10:55:04 AM UTC-4, John Larkin wrote:
> > The Monongahela (watershed in West Virginia) joins the Allegheny River > to form the Ohio River at Pittsburgh, PA. >
Grin, they don't call it "Three River Stadium" for nothing. I really love watershed maps. George H.
> > (The Ohio River forming the western boundary of West Virginia, between > > WV and Ohio. I grew up in Huntington, WV :-) > > > > ...Jim Thompson > > -- > > | James E.Thompson | mens | > > | Analog Innovations | et | > > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > > | San Tan Valley, AZ 85142 Skype: Contacts Only | | > > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > > | E-mail Icon at http://www.analog-innovations.com | 1962 | > > > > I love to cook with wine. Sometimes I even put it in the food.
Reply by Jim Thompson September 17, 20132013-09-17
On Tue, 17 Sep 2013 08:23:09 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Tuesday, September 17, 2013 10:55:04 AM UTC-4, John Larkin wrote: >> On Tue, 17 Sep 2013 07:10:09 -0700 (PDT), George Herold <gherold@teachspin.com> >> wrote: >> >On Monday, September 16, 2013 9:41:12 PM UTC-4, John Larkin wrote: >> >> On Mon, 16 Sep 2013 17:36:21 -0700 (PDT), George Herold >> >> Bud Light? >> >> >Sure, you probably don't have Genesee out there. >> >> >http://beeradvocate.com/beer/profile/302/865 >> >George (there's no such thing as bad beer) Herold > >> I've had Genesee. It's made from Genesee river water, one of the more polluted >> >> waterways on the planet. Pretty tasty beer. > >I'm not sure how polluted it can be, (the genesee river) it mostly runs though agricultural land. It 'makes' Letchworth state park (A must see when 'dressed' in the Autumn foliage.) It ehn goes through Rochester NY where I guess there would be some industrial pollution, more so in the past. >http://en.wikipedia.org/wiki/Genesee_River > >Hey.. (well this is getting way OT.) looking at the map reminded me that there's a spot in Pennsylvania where three watersheds meet, the Genesee runs up and dumps into the great lakes, the Allegheny goes across and down to the Mississippi and the Susquehanna which flows into Chesapeake Bay. > >George H.
The Monongahela (watershed in West Virginia) joins the Allegheny River to form the Ohio River at Pittsburgh, PA. (The Ohio River forming the western boundary of West Virginia, between WV and Ohio. I grew up in Huntington, WV :-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.