On 10/5/18 5:26 AM, Gerhard Hoffmann wrote:> Am 05.10.2018 um 02:23 schrieb John Larkin: >> On Thu, 4 Oct 2018 23:05:20 +0100, David Nadlinger > >> Nice, but it's all low-voltage differential. I need 5 volt swings in >> and out. > > A real pain. And the receiver inputs after that will probably switch at > 1.6V. > >> >>> >>> How stable do you need the propagation delay to be? >> >> My DUT will be spec'd to 1 ns accuracy (well, the customer wants 200 >> ps, but that's silly) and maybe 30 ps RMS jitter. We'll have to >> occasionally characterize all the component and traces and cable >> delays in the test set, and fudge them out of the tests. Gigantic >> pain. After that, we'd like things to be stable to maybe 100 ps. > > A customer of mine measured their cables in the temp chamber. > That was real "fun". > It is well-known that PTFE has a crystallization change at 23°C, > where it hurts most, esp. when most quality cables are PTFE.Yup. TC of epsilon is about 2000 ppm/K in the glass transition region iirc. Polyethylene is much better.> > If you want stable delays, it's probably best to try to be as > fast as possible and then limit the BW with film R and NP0 C > to sane values. Excess BW brings excess noise, brings excess jitter. > > Distributing a sine wave + a qualifier for the zero crossings > takes cable dispersion out of the equation. One gains precisely > located points in time but loses arbitrary edge position.Interesting idea. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
really fast buffers
Started by ●October 3, 2018
Reply by ●October 5, 20182018-10-05
Reply by ●October 5, 20182018-10-05
On 10/5/18 10:40 AM, Phil Hobbs wrote:> On 10/4/18 11:09 PM, Steve Wilson wrote: >> John Larkin <jjlarkin@highland_snip_technology.com> wrote: >> >>> On Thu, 4 Oct 2018 08:39:11 -0700 (PDT), Steve Wilson >>> <9fe142ac@gmail.com> wrote: >>>> I hope that anyone playing with 42GHz GBW would automatically >>>> add a base resistor to kill parasitic oscillations. Even a >>>> lowly 2N3904 can go into parasitics with a long base lead. >>> Or as an emitter follower with the base well bypassed to ground. >>> The wire bonds inside are nice high-Q inductors. >> How do you make an emitter follower when the base is bypassed to >> ground? Where do you put the signal? >> > > The classical example is the one-transistor !RESET generator, which > is a slow RC with an emitter follower.Oh, and the cap multiplier, of course. They can oscillate if you use too fast a transistor.> > Cascading PNP and NPN followers to compensate V_BE is also a good way > of making an oscillator. >Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●October 5, 20182018-10-05
On Fri, 05 Oct 2018 03:12:42 GMT, Steve Wilson <no@spam.com> wrote:>John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >> On Fri, 5 Oct 2018 09:26:17 +1000, Clifford Heath <no.spam@please.net> >> wrote: > >>>How does an emitter follower do anything useful if the base is tied to >>>ground? > >> I said "bypassed to ground." But an emitter follower can certainly >> work, and oscillate, if its base is really grounded. > >How? There's no signal on the base.Just pull the emitter negative with a resistor or a current sink. That can make a nice UHF oscillator. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●October 5, 20182018-10-05
On Fri, 5 Oct 2018 10:40:12 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 10/4/18 11:09 PM, Steve Wilson wrote: >> John Larkin <jjlarkin@highland_snip_technology.com> wrote: >> >>> On Thu, 4 Oct 2018 08:39:11 -0700 (PDT), Steve Wilson >>> <9fe142ac@gmail.com> wrote: >>>> I hope that anyone playing with 42GHz GBW would automatically add a base >>>> resistor to kill parasitic oscillations. Even a lowly 2N3904 can go into >>>> parasitics with a long base lead. >> >>> Or as an emitter follower with the base well bypassed to ground. The >>> wire bonds inside are nice high-Q inductors. >> >> How do you make an emitter follower when the base is bypassed to ground? >> Where do you put the signal? >> > >The classical example is the one-transistor !RESET generator, which is a >slow RC with an emitter follower.Exactly. That's the first time I saw an emitter follower oscillate, an RC+emitter follower+74xx schmitt. The base hung and never charged up enough to trip the schmitt; the RF used too much base current or something. That confused me for a while. 2N2219 loved to oscillate.> >Cascading PNP and NPN followers to compensate V_BE is also a good way of >making an oscillator.Never seen that; good to know. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●October 5, 20182018-10-05
John Larkin <jjlarkin@highland_snip_technology.com> wrote:> On Fri, 05 Oct 2018 03:12:42 GMT, Steve Wilson <no@spam.com> wrote:>>John Larkin <jjlarkin@highland_snip_technology.com> wrote:>>> On Fri, 5 Oct 2018 09:26:17 +1000, Clifford Heath <no.spam@please.net> >>> wrote:>>>>How does an emitter follower do anything useful if the base is tied to >>>>ground?>>> I said "bypassed to ground." But an emitter follower can certainly >>> work, and oscillate, if its base is really grounded.>>How? There's no signal on the base.> Just pull the emitter negative with a resistor or a current sink. That > can make a nice UHF oscillator.Might as well just ground the base. But that's not an emitter follower, as you stated in your first post. There's no place to put a signal. Just put a proper value resistor in series with the base. It won't oscillate. But it's still not an emitter follower.
Reply by ●October 5, 20182018-10-05
On Friday, October 5, 2018 at 5:26:37 PM UTC-4, John Larkin wrote:> On Fri, 5 Oct 2018 10:40:12 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >On 10/4/18 11:09 PM, Steve Wilson wrote: > >> John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >> > >>> On Thu, 4 Oct 2018 08:39:11 -0700 (PDT), Steve Wilson > >>> <9fe142ac@gmail.com> wrote: > >>>> I hope that anyone playing with 42GHz GBW would automatically add a base > >>>> resistor to kill parasitic oscillations. Even a lowly 2N3904 can go into > >>>> parasitics with a long base lead. > >> > >>> Or as an emitter follower with the base well bypassed to ground. The > >>> wire bonds inside are nice high-Q inductors. > >> > >> How do you make an emitter follower when the base is bypassed to ground? > >> Where do you put the signal? > >> > > > >The classical example is the one-transistor !RESET generator, which is a > >slow RC with an emitter follower. >It oscillates because of a slow edge and no hysteresis? Is it similar to cap. multiplier oscillations? (do all single transistor circuits map onto each other?) George H.> Exactly. That's the first time I saw an emitter follower oscillate, an > RC+emitter follower+74xx schmitt. The base hung and never charged up > enough to trip the schmitt; the RF used too much base current or > something. That confused me for a while. 2N2219 loved to oscillate. > > > > >Cascading PNP and NPN followers to compensate V_BE is also a good way of > >making an oscillator. > > Never seen that; good to know. > > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●October 5, 20182018-10-05
On Fri, 5 Oct 2018 11:06:22 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 10/5/18 10:40 AM, Phil Hobbs wrote: >> On 10/4/18 11:09 PM, Steve Wilson wrote: >>> John Larkin <jjlarkin@highland_snip_technology.com> wrote: >>> >>>> On Thu, 4 Oct 2018 08:39:11 -0700 (PDT), Steve Wilson >>>> <9fe142ac@gmail.com> wrote: >>>>> I hope that anyone playing with 42GHz GBW would automatically >>>>> add a base resistor to kill parasitic oscillations. Even a >>>>> lowly 2N3904 can go into parasitics with a long base lead. >>>> Or as an emitter follower with the base well bypassed to ground. >>>> The wire bonds inside are nice high-Q inductors. >>> How do you make an emitter follower when the base is bypassed to >>> ground? Where do you put the signal? >>> >> >> The classical example is the one-transistor !RESET generator, which >> is a slow RC with an emitter follower. > >Oh, and the cap multiplier, of course. They can oscillate if you use >too fast a transistor.Or a Sallen-Key filter. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●October 5, 20182018-10-05
On Fri, 5 Oct 2018 18:36:33 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Friday, October 5, 2018 at 5:26:37 PM UTC-4, John Larkin wrote: >> On Fri, 5 Oct 2018 10:40:12 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >> >On 10/4/18 11:09 PM, Steve Wilson wrote: >> >> John Larkin <jjlarkin@highland_snip_technology.com> wrote: >> >> >> >>> On Thu, 4 Oct 2018 08:39:11 -0700 (PDT), Steve Wilson >> >>> <9fe142ac@gmail.com> wrote: >> >>>> I hope that anyone playing with 42GHz GBW would automatically add a base >> >>>> resistor to kill parasitic oscillations. Even a lowly 2N3904 can go into >> >>>> parasitics with a long base lead. >> >> >> >>> Or as an emitter follower with the base well bypassed to ground. The >> >>> wire bonds inside are nice high-Q inductors. >> >> >> >> How do you make an emitter follower when the base is bypassed to ground? >> >> Where do you put the signal? >> >> >> > >> >The classical example is the one-transistor !RESET generator, which is a >> >slow RC with an emitter follower. >> >It oscillates because of a slow edge and no hysteresis?The transistor itself can oscillate, typically around 100 MHz, in the emitter follower config, if the base is RF bypassed to ground. A bit of resistance in series with the base, 33 or 50 ohms or something, kills it. That adds some noise, Johnson noise and Ib shot noise current into the resistor. I don't use bipolar transistors much any more. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●October 5, 20182018-10-05
George Herold <gherold@teachspin.com> wrote:> It oscillates because of a slow edge and no hysteresis?It oscillates because of inductance in the base lead. Along with the base- emitter capacitance and capacitance from the emitter to ground, this forms a Colpitts oscillator, which is one of the most vigorous oscillators known. It can accept an extremely wide range of parameters and still oscillate. The purpose of the resistor in the base lead is to dampen the Q of the tank so oscillations are no longer possible.> Is it similar to cap. multiplier oscillations?Could be. Any place where you have some inductance in the base and capacitance from the emitter to ground could form a Colpitts, especially where you have some inductance in the emitter lead. Other configurations where fast transistors are connected together could become an oscillator. Some examples are: Cascode Darlington Sziklai pair etc> (do all single transistor circuits map onto each other?)The various configurations of the Colpitts are basically the same. It's just where you put the ground that makes them look different. The difficulty with the Colpitts is it loves to oscillate. The conditions are layout-dependent and dependent on the gain and bandwidth of the transistor. The oscillations can completely destroy the desired performance of the circuit. My approach is to assume the circuit will oscillate under the right conditions, and to include a resistor in the base in all critical circuits that could be susceptible to parasitics. After a while, you get to know what value would be appropriate, usually from 5 to 50 ohms. But check carefully. This creates a problem. Often the oscillation frequency is far above the frequency range of the best equipment available in your lab. To compensate, you need some way to perturb the circuit and look for any change in the operating parameters. One method is to use a dental pick which is available at most pharmacies. This is a small stainless hook imbedded in plastic, with a cover to fit over the top. You can touch various points in the circuit an see if you can detect any change in the operataion. The best by far is a wideband spectrum analyzer. You can make a small loop feeding a coax cable to the analyzer. Bring the loop near the circuit. any oscillation should become visible in the display. Of course, with modern transistors, especially SiGe, you need a very high frequecy specctrum analyzer. These are not cheap.> George H.
Reply by ●October 6, 20182018-10-06
Steve Wilson wrote:>The best by far is a wideband spectrum analyzer. You can make a small loop >feeding a coax cable to the analyzer. Bring the loop near the circuit. any >oscillation should become visible in the display.Yep, for a bit lower Ft transistors my FM radio warns me:-) I have, and this is REAL fun, a bug detector from ebay, it will beep if any RF in the GHz range is detected, very similar to this one: https://www.ebay.com/itm//372193315564 < 8$ free shipping! Wideband spectrum analyzer my foot! You can test your microwave's leakage with it too. I build some simple detectors uses microwave diodes too.
