John Larkin <jjlarkin@highland_snip_technology.com> wrote:> On Tue, 16 May 2017 01:22:14 GMT, Steve Wilson <no@spam.com> wrote:>>There are cases where an extra resistor is actually needed, such as a >>base parasitic resistor or in the gate of a fast MOSFET. These can >>remind you to include the resistor in the pcb layout, and help >>determine the value needed in the circuit.> I'm not likely to forget, but Spice is useless in determining the > value that will kill oscillations. It can establish that some value > won't slow down normal operation too much. I tend to use 33 ohms.But you have already forgotten. Remember the tiny pcb you made where you didn't have enough room to add parasitic suppression resistors? As far as helping determine the value needed, finding a value that won't slow down normal operation too much is exactly what I meant. We agree.
Fast buffer idea
Started by ●May 14, 2017
Reply by ●May 16, 20172017-05-16
Reply by ●May 16, 20172017-05-16
"Jan Panteltje" wrote in message news:ofcvan$1ak0$1@gioia.aioe.org... On a sunny day (Mon, 15 May 2017 19:50:40 +0100) it happened "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> wrote in <Ca6dnRH1w-4cZYTEnZ2dnUU7-dfNnZ2d@giganews.com>:>"bitrex" wrote in message news:EEiSA.74451$bl5.68044@fx25.iad... > >On 05/15/2017 10:01 AM, John Larkin wrote: > >> BW is 230 MHz as a unity-gain buffer. Each half of the dual will >> source and sink 88 mA. And there are lots of faster THS-series parts. >> >>> >>> But indeed you can do that with a few NPNs of the old days, >>> >> >> Post it. > >>With discretes you can have: > >>1) wide bandwidth > >>2) low parts count > >>3) low quiescent current draw > >Actually, you missed accuracy. > >The key technical limit is the triple of speed, accuracy, and power. You >can't chose them independently. > >>Typical example, to get lower distortion in a feedback system, gain might >>be >>increased. This means you have to slow it down with compensation to make >>it >>stable. You can increase he BW back up by increasing the current. >>Increasing >>current reduces collector output resistance by Va/Ic, but the gain stays >>the >>same because gm has gone up. The lower ro.Cl increases the BW of the >>stage.>Hi Kevin, just wanted to ask, >I was following some public lectures by several professors last week, >and the last one was about the Higgs boson. >In that space is not empty and filled with the Higgs field. >Today I have been studying that stuff.. >and found some interesting mass related problems. >Did you have thoughts about that?Higgs stuff is way, way to complicated for us engineers. However, empty space, most certainly, isn't empty. Things are popping in and out of existence all the time. Lots of mass related problems. What causes inertia? Is it mass sending out gravitons that boomerang back to oppose motion, or a sea of of vacuum stuff. I don't buy the Mach principle bit. Its all mystery darkness...>Ever met the man?I have not met Pete, however, I did get a signed letter from him around 2,000. I was thinking about applying to do a Ph.D at Edinburgh Uni. The idea faded though. -- Kevin Aylward http://www.anasoft.co.uk - SuperSpice http://www.kevinaylward.co.uk/ee/index.html
Reply by ●May 16, 20172017-05-16
On Tue, 16 May 2017 18:55:54 GMT, Steve Wilson <no@spam.com> wrote:>John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >> On Tue, 16 May 2017 01:22:14 GMT, Steve Wilson <no@spam.com> wrote: > >>>There are cases where an extra resistor is actually needed, such as a >>>base parasitic resistor or in the gate of a fast MOSFET. These can >>>remind you to include the resistor in the pcb layout, and help >>>determine the value needed in the circuit. > >> I'm not likely to forget, but Spice is useless in determining the >> value that will kill oscillations. It can establish that some value >> won't slow down normal operation too much. I tend to use 33 ohms. > >But you have already forgotten. Remember the tiny pcb you made where you >didn't have enough room to add parasitic suppression resistors?When you're doing fast stuff, and every picosecond is worth money, adding any resistor in the signal path, or wasting any space, is a defeat.> >As far as helping determine the value needed, finding a value that won't >slow down normal operation too much is exactly what I meant. > >We agree.-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●May 16, 20172017-05-16
Am 16.05.2017 um 20:16 schrieb John Larkin:>> There are cases where an extra resistor is actually needed, such as a >> base parasitic resistor or in the gate of a fast MOSFET. These can remind >> you to include the resistor in the pcb layout, and help determine the >> value needed in the circuit. > > > I'm not likely to forget, but Spice is useless in determining the > value that will kill oscillations. It can establish that some value > won't slow down normal operation too much. I tend to use 33 ohms. > >Yes. I second that. In simulation, my 4*IF3601 preamp is definitely stable, but in real live: < https://www.flickr.com/photos/137684711@N07/34701106245/in/album-72157662535945536/ > For most frequencies outside of the Smith diagram, if you look into the input. Any L on the input with small enough resistance will oscillate, including ferrite beads. The usual gate stopper is not possible for obvious noise reasons. :-( Gerhard (Sorry for the choice of colours.)
Reply by ●May 16, 20172017-05-16
"Steve Wilson" wrote in message news:XnsA776AA98AC34Eidtokenpost@69.16.179.22... John Larkin <jjlarkin@highland_snip_technology.com> wrote:> The current probe is twitchy. I like to add visible current-shunt > resistors to make it easier to probe.In SS. its place testpoint on pin. Done.>Nothing wrong with that, except you have to add separate node names to >either side of the resistor.> Then instead of plotting Ib(Q2) you will plot >I(R12). The polarity will depend on the orientation of the resistor.Yeah, I haven't gotten round to auto sign inversion on two terminal devices. However, press m (mirror) of f (flip vert) and run again !> This >is not so bad, except you will have to turn it around to get the flow in >>the direction you want. Or you could simply add a minus sign to the plot >>to >get it to the direction you want.>These are simple things, but are part of the huge learning curve in spice.SS automatically puts in zero volts source in .subckts, so again, its place testpoint on pin. Done. However, I don't really agree that the is a huge learning curve in spice. Its all GUI for the most part. The bulk of spice is all hidden. If one can't figure out that running 10,000 cycles at small time steps is going to take a long time, I doubt if one should be using spice at all. -- Kevin Aylward http://www.anasoft.co.uk - SuperSpice http://www.kevinaylward.co.uk/ee/index.html
Reply by ●May 16, 20172017-05-16
John Larkin <jjlarkin@highland_snip_technology.com> wrote:> On Tue, 16 May 2017 18:55:54 GMT, Steve Wilson <no@spam.com> wrote:>>But you have already forgotten. Remember the tiny pcb you made where you >>didn't have enough room to add parasitic suppression resistors? > > When you're doing fast stuff, and every picosecond is worth money, > adding any resistor in the signal path, or wasting any space, is a > defeat.Nice marketing, poor engineering. When you are trying to ship fast stuff, and it oscillates, that is a defeat. You have to fix it, and you had no room. You should have expected it and solved it before making lots of pcbs. Coupled high speed transistors or facing long leads is a potential disaster. I'll bet you check now.
Reply by ●May 16, 20172017-05-16
On Tue, 16 May 2017 20:33:54 GMT, Steve Wilson <no@spam.com> wrote:>John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >> On Tue, 16 May 2017 18:55:54 GMT, Steve Wilson <no@spam.com> wrote: > >>>But you have already forgotten. Remember the tiny pcb you made where you >>>didn't have enough room to add parasitic suppression resistors? >> >> When you're doing fast stuff, and every picosecond is worth money, >> adding any resistor in the signal path, or wasting any space, is a >> defeat. > >Nice marketing, poor engineering.Design some picosecond stuff yourself. And show us. And don't be an asshole.> >When you are trying to ship fast stuff, and it oscillates, that is a >defeat.It got fixed and we got paid.> >You have to fix it, and you had no room. > >You should have expected it and solved it before making lots of pcbs. >Coupled high speed transistors or facing long leads is a potential >disaster. > >I'll bet you check now.I've been doing picosecond electronics for decades, and sold a ton of it... more as time goes on. Sometimes things happen on the first PCB rev of a difficult design. We fix it. No big deal. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●May 16, 20172017-05-16
John Larkin <jjlarkin@highland_snip_technology.com> wrote:> On Tue, 16 May 2017 20:33:54 GMT, Steve Wilson <no@spam.com> wrote: > >>John Larkin <jjlarkin@highland_snip_technology.com> wrote: >> >>> On Tue, 16 May 2017 18:55:54 GMT, Steve Wilson <no@spam.com> wrote: >> >>>>But you have already forgotten. Remember the tiny pcb you made where >>>>you didn't have enough room to add parasitic suppression resistors? >>> >>> When you're doing fast stuff, and every picosecond is worth money, >>> adding any resistor in the signal path, or wasting any space, is a >>> defeat. >> >>Nice marketing, poor engineering.> Design some picosecond stuff yourself. And show us. And don't be an > asshole.I was doing femtosecond stuff in 1970. Your insult about being an asshole has no effect. Stop being a jerk.>>When you are trying to ship fast stuff, and it oscillates, that is a >>defeat. > > It got fixed and we got paid.So what heppened to your picoseconds?>>You have to fix it, and you had no room. >> >>You should have expected it and solved it before making lots of pcbs. >>Coupled high speed transistors or facing long leads is a potential >>disaster. >> >>I'll bet you check now.> I've been doing picosecond electronics for decades, and sold a ton of > it... more as time goes on. Sometimes things happen on the first PCB > rev of a difficult design. We fix it. No big deal.As I said, you should have expected it, and you did not. So much for your claims of picosecond electronics. In fact, nothing you do is in picoseconds. Perhaps tenths of a nanosecond, but not much more. False claims, but they can make a lot of money.
Reply by ●May 16, 20172017-05-16
On 16/05/17 06:17, John Larkin wrote:> On Mon, 15 May 2017 19:51:11 +0100, "Kevin Aylward" > <kevinRemovAT@kevinaylward.co.uk> wrote: > >>> "bitrex" wrote in message news:xW2SA.99882$jo6.643@fx33.iad... >> >> it... >>> >>>> Is your object to drive a length of coax? If it's terminated, you can >>>> just ignore the cable entirely. Or poke in a Spice transmission line >>>> to explore mismatch consequences. >>> >> >>> Ya, exploring the "mismatch" consequences I'd like to do. How do I do that? >>> I haven't used Spice transmission line models before... >> >> Well... in SS, you just place a transmission line symbol from the lib, and >> double-click on it to pop up its setup box. :-) > > LT has a transmission line. It's fully symmetric, like an unshielded > twisted pair. And it acts as if it has an ideal transformer inside; it > tolerates any common-mode difference between ends. In fact, it makes a > handy ideal transformer. > > To simulate an actual twisted pair, I use three of the LT Spice TXLINE > things. > > https://dl.dropboxusercontent.com/u/53724080/Circuits/TxLines/Twist_1.jpg > > Probably the middle one should have a different prop delay.Is that to handle the shield? How would you model UTP?
Reply by ●May 16, 20172017-05-16
On Tue, 16 May 2017 21:21:49 GMT, Steve Wilson <no@spam.com> wrote:>John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >> On Tue, 16 May 2017 20:33:54 GMT, Steve Wilson <no@spam.com> wrote: >> >>>John Larkin <jjlarkin@highland_snip_technology.com> wrote: >>> >>>> On Tue, 16 May 2017 18:55:54 GMT, Steve Wilson <no@spam.com> wrote: >>> >>>>>But you have already forgotten. Remember the tiny pcb you made where >>>>>you didn't have enough room to add parasitic suppression resistors? >>>> >>>> When you're doing fast stuff, and every picosecond is worth money, >>>> adding any resistor in the signal path, or wasting any space, is a >>>> defeat. >>> >>>Nice marketing, poor engineering. > >> Design some picosecond stuff yourself. And show us. And don't be an >> asshole. > >I was doing femtosecond stuff in 1970. Your insult about being an asshole >has no effect. Stop being a jerk. > >>>When you are trying to ship fast stuff, and it oscillates, that is a >>>defeat. >> >> It got fixed and we got paid. > >So what heppened to your picoseconds? > >>>You have to fix it, and you had no room. >>> >>>You should have expected it and solved it before making lots of pcbs. >>>Coupled high speed transistors or facing long leads is a potential >>>disaster. >>> >>>I'll bet you check now. > >> I've been doing picosecond electronics for decades, and sold a ton of >> it... more as time goes on. Sometimes things happen on the first PCB >> rev of a difficult design. We fix it. No big deal. > >As I said, you should have expected it, and you did not. So much for your >claims of picosecond electronics. > >In fact, nothing you do is in picoseconds. Perhaps tenths of a >nanosecond, but not much more. False claims, but they can make a lot of >money.https://dl.dropboxusercontent.com/u/53724080/Optos/95_ps_optical_pulse.jpg https://dl.dropboxusercontent.com/u/53724080/Circuits/Fast_Stuff/100_ps_steps.jpg https://dl.dropboxusercontent.com/u/53724080/Circuits/Fast_Stuff/NB7_Steps.jpg https://dl.dropboxusercontent.com/u/53724080/Circuits/Fast_Stuff/DSRD_neg-2KV.JPG -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
