On Thursday, October 4, 2018 at 8:00:30 AM UTC-4, pcdh...@gmail.com wrote:> >>https://octopart.com/search?q=BFP650&oq=BFP650&start=0 > > >That would work, as a couple or few emitter followers to fan out my > >incoming signal. It has decent beta at, say, 50 mA or even 100 mA > >(driving something like 5 volts into 50 ohms). > > >The Vbe offset would be more predictable than the turn-on of a phemt. > > Their low drain impedances make pHEMTs very disappointing as followers, unless you bootstrap the drain. The late lamented ATF38148 could have a gain of 0.5 as a follower. > > >I'll be timing edges to picoseconds so I don't want unpredictable > offsets. > > You'll need a base resistor to keep it from oscillating. Don't let anybody hang a cable on it.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. Often the real problem with parasitics is they can occur at a frequency above your fastest scope, so you can't see them. Sometimes even touching part of a circuit can kill weak oscillations, making you believe the circuit is safe. Don't believe it. Add a base resistor to any circuit connected to the outside world, or any place where fast transistors are connected together. Often, a simple hand wave above a circuit can change the operating conditions, or a circuit may only go into oscillation at a certain point on the input waveform. Both issues are hit or miss. Add a base resistor. The value may range from 100 ohms for low frequency circuits, to perhaps 5 or 10 ohms for fast circuits. You can easily change the value as needed when you gain more experience with the circuit. But it is extremely difficult to add a base resistor to a smd transistor when you have forgotten to include it in the layout. Add a base resistor.> Cheers > > Phil Hobbs
really fast buffers
Started by ●October 3, 2018
Reply by ●October 4, 20182018-10-04
Reply by ●October 4, 20182018-10-04
torsdag den 4. oktober 2018 kl. 09.20.30 UTC+2 skrev Andy Bennet:> On 03/10/2018 23:23, Lasse Langwadt Christensen wrote: > > torsdag den 4. oktober 2018 kl. 00.03.49 UTC+2 skrev John Larkin: > >> I'm designing a test board for a laser controller. Incoming signals, > >> fast 5 volt pulses, will need to get routed to scopes, counters, and > >> some other stuff. It will be kind a maze of connectors and traces and > >> probably relays; it's hard to beat a relay as a test path switch. > >> > >> But life would be a lot better if I could fan out some of the signals > >> at their input connector. I want a zero-delay, zero-jitter buffer. > >> Under 1 ns delay might be a reasonable target, with very stable prop > >> delay. > >> > >> Just resistors could work, but that loses amplitude, and the ends of > >> the fanout traces would have to be always terminated to avoid > >> reflections. Something unilateral would be easier. > >> > >> Fast opamp? THS3201 maybe. I'll have to Spice the prop delay. > >> > >> Some sort of source follower, bipolar or phemt or something? > >> > >> ECL/Eclips gate? 10EP89 or something. > >> > >> One of the screaming Analog Devices comparators? > >> > >> > >> > >> CMOS parts are probably all too slow, and they have terrible delay > >> tempcos. > >> > > > > clock buffers ? > > > > All the low prop/zero prop clock buffers I know are PLL based and are no > good for random signal buffering.would they list a minimum frequency then? http://www.ti.com/lit/ds/symlink/cdc111.pdf
Reply by ●October 4, 20182018-10-04
On Thu, 4 Oct 2018 05:00:24 -0700 (PDT), pcdhobbs@gmail.com wrote:>>>https://octopart.com/search?q=BFP650&oq=BFP650&start=0 > >>That would work, as a couple or few emitter followers to fan out my >>incoming signal. It has decent beta at, say, 50 mA or even 100 mA >>(driving something like 5 volts into 50 ohms). > >>The Vbe offset would be more predictable than the turn-on of a phemt. > >Their low drain impedances make pHEMTs very disappointing as followers, unless you bootstrap the drain. The late lamented ATF38148 could have a gain of 0.5 as a follower. > >>I'll be timing edges to picoseconds so I don't want unpredictable >offsets. > >You'll need a base resistor to keep it from oscillating. Don't let anybody hang a cable on it. > >Cheers > >Phil HobbsLooks like the best, fastest, lowest delay, lowest delay TC, and lowest jitter digital logic buffer will be an opamp! -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●October 4, 20182018-10-04
On 10/4/18 11:39 AM, Steve Wilson wrote:> On Thursday, October 4, 2018 at 8:00:30 AM UTC-4, pcdh...@gmail.com > wrote: >>>> https://octopart.com/search?q=BFP650&oq=BFP650&start=0 >> >>> That would work, as a couple or few emitter followers to fan out >>> my incoming signal. It has decent beta at, say, 50 mA or even >>> 100 mA (driving something like 5 volts into 50 ohms). >> >>> The Vbe offset would be more predictable than the turn-on of a >>> phemt. >> >> Their low drain impedances make pHEMTs very disappointing as >> followers, unless you bootstrap the drain. The late lamented >> ATF38148 could have a gain of 0.5 as a follower. >> >>> I'll be timing edges to picoseconds so I don't want >>> unpredictable >> offsets. >> >> You'll need a base resistor to keep it from oscillating. Don't let >> anybody hang a cable on it. > > 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. > > Often the real problem with parasitics is they can occur at a > frequency above your fastest scope,Well, I have a couple of 40-50 GHz ones, so that probably won't be an issue. ;)> so you can't see them. Sometimes even touching part of a circuit can > kill weak oscillations, making you believe the circuit is safe.> > Don't believe it. Add a base resistor to any circuit connected to the > outside world, or any place where fast transistors are connected > together. > > Often, a simple hand wave above a circuit can change the operating > conditions,I've posted a few times about my "manual wavemeter". From July 2015, concerning a pHEMT bootstrapped with a SiGe:C BJT: "The first proto oscillated at around 12 GHz. I didn't have a microwave spectrum analyzer at the time, so I measured the frequency by an interesting manual wavemeter method: if I held my hand over the board at different heights, the oscillation amplitude varied periodically, with a period of a bit less than half an inch." "The actual board was fine, after a bit of Dremelling and adding a bunch of parallelled bypass caps. With 40-50 GHz transistors and lots of gain in a small space, half a nanohenry here and there can ruin your whole day."> or a circuit may only go into oscillation at a certain point on the > input waveform. Both issues are hit or miss.AKA a snivet.> Add a base resistor. > > The value may range from 100 ohms for low frequency circuits, to > perhaps 5 or 10 ohms for fast circuits. You can easily change the > value as needed when you gain more experience with the circuit. But > it is extremely difficult to add a base resistor to a smd transistor > when you have forgotten to include it in the layout. Add a base > resistor.That blanket rule doesn't cover all the bases, so to speak. ;) Base resistors trash the speed and noise performance, so a tight layout and close attention to minimum-inductance bypassing help a lot. Then I use a zero-ohm jumper as a placeholder for a possibly-needed resistor or bead. 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 4, 20182018-10-04
On 10/4/18 12:18 PM, John Larkin wrote:> On Thu, 4 Oct 2018 05:00:24 -0700 (PDT), pcdhobbs@gmail.com wrote: > >>>> https://octopart.com/search?q=BFP650&oq=BFP650&start=0 >> >>> That would work, as a couple or few emitter followers to fan out my >>> incoming signal. It has decent beta at, say, 50 mA or even 100 mA >>> (driving something like 5 volts into 50 ohms). >> >>> The Vbe offset would be more predictable than the turn-on of a phemt. >> >> Their low drain impedances make pHEMTs very disappointing as followers, unless you bootstrap the drain. The late lamented ATF38148 could have a gain of 0.5 as a follower. >> >>> I'll be timing edges to picoseconds so I don't want unpredictable >> offsets. >> >> You'll need a base resistor to keep it from oscillating. Don't let anybody hang a cable on it. >> >> Cheers >> >> Phil Hobbs > > Looks like the best, fastest, lowest delay, lowest delay TC, and > lowest jitter digital logic buffer will be an opamp! > >Lowest power and lowest cost too? ;) 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 4, 20182018-10-04
On Thu, 4 Oct 2018 08:39:11 -0700 (PDT), Steve Wilson <9fe142ac@gmail.com> wrote:>On Thursday, October 4, 2018 at 8:00:30 AM UTC-4, pcdh...@gmail.com wrote: >> >>https://octopart.com/search?q=BFP650&oq=BFP650&start=0 >> >> >That would work, as a couple or few emitter followers to fan out my >> >incoming signal. It has decent beta at, say, 50 mA or even 100 mA >> >(driving something like 5 volts into 50 ohms). >> >> >The Vbe offset would be more predictable than the turn-on of a phemt. >> >> Their low drain impedances make pHEMTs very disappointing as followers, unless you bootstrap the drain. The late lamented ATF38148 could have a gain of 0.5 as a follower. >> >> >I'll be timing edges to picoseconds so I don't want unpredictable >> offsets. >> >> You'll need a base resistor to keep it from oscillating. Don't let anybody hang a cable on it. > >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. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●October 4, 20182018-10-04
On Thu, 4 Oct 2018 12:39:29 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 10/4/18 12:18 PM, John Larkin wrote: >> On Thu, 4 Oct 2018 05:00:24 -0700 (PDT), pcdhobbs@gmail.com wrote: >> >>>>> https://octopart.com/search?q=BFP650&oq=BFP650&start=0 >>> >>>> That would work, as a couple or few emitter followers to fan out my >>>> incoming signal. It has decent beta at, say, 50 mA or even 100 mA >>>> (driving something like 5 volts into 50 ohms). >>> >>>> The Vbe offset would be more predictable than the turn-on of a phemt. >>> >>> Their low drain impedances make pHEMTs very disappointing as followers, unless you bootstrap the drain. The late lamented ATF38148 could have a gain of 0.5 as a follower. >>> >>>> I'll be timing edges to picoseconds so I don't want unpredictable >>> offsets. >>> >>> You'll need a base resistor to keep it from oscillating. Don't let anybody hang a cable on it. >>> >>> Cheers >>> >>> Phil Hobbs >> >> Looks like the best, fastest, lowest delay, lowest delay TC, and >> lowest jitter digital logic buffer will be an opamp! >> >> >Lowest power and lowest cost too? ;)I'm building a test set (for an astronomical heap of dollars) so that doesn't matter. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●October 4, 20182018-10-04
On Wednesday, October 3, 2018 at 3:03:49 PM UTC-7, John Larkin wrote:> I'm designing a test board for a laser controller. Incoming signals, > fast 5 volt pulses, will need to get routed... I could fan out some of the signals > at their input connector. I want a zero-delay, zero-jitter buffer. > Under 1 ns delay might be a reasonable target, with very stable prop > delay.How about SN65LVDS20? The 'enable' input can solve some of the switching issues. Differential gives you both polarities... ECL is good, too, because the slew rate of your input pulse will be high when passing the threshold (and any ECL gate has a bit of voltage gain anyhow, so output slew rate will be healthy). MC10H104 would be another candidate, and comes with a lovely opportunity to pay a Trump-era tariff, according to DigiKey.
Reply by ●October 4, 20182018-10-04
On Thursday, October 4, 2018 at 12:38:20 PM UTC-4, Phil Hobbs wrote:> On 10/4/18 11:39 AM, Steve Wilson wrote: > > On Thursday, October 4, 2018 at 8:00:30 AM UTC-4, pcdh...@gmail.com > > wrote: > >>>> https://octopart.com/search?q=BFP650&oq=BFP650&start=0 > >> > >>> That would work, as a couple or few emitter followers to fan out > >>> my incoming signal. It has decent beta at, say, 50 mA or even > >>> 100 mA (driving something like 5 volts into 50 ohms). > >> > >>> The Vbe offset would be more predictable than the turn-on of a > >>> phemt. > >> > >> Their low drain impedances make pHEMTs very disappointing as > >> followers, unless you bootstrap the drain. The late lamented > >> ATF38148 could have a gain of 0.5 as a follower. > >> > >>> I'll be timing edges to picoseconds so I don't want > >>> unpredictable > >> offsets. > >> > >> You'll need a base resistor to keep it from oscillating. Don't let > >> anybody hang a cable on it. > > > > 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. > > > > Often the real problem with parasitics is they can occur at a > > frequency above your fastest scope, > > Well, I have a couple of 40-50 GHz ones, so that probably won't be an > issue. ;) > > > so you can't see them. Sometimes even touching part of a circuit can > > kill weak oscillations, making you believe the circuit is safe.> > > Don't believe it. Add a base resistor to any circuit connected to the > > outside world, or any place where fast transistors are connected > > together. > > > > Often, a simple hand wave above a circuit can change the operating > > conditions, > > I've posted a few times about my "manual wavemeter". From July 2015, > concerning a pHEMT bootstrapped with a SiGe:C BJT: > > "The first proto oscillated at around 12 GHz. I didn't have a microwave > spectrum analyzer at the time, so I measured the frequency by an > interesting manual wavemeter method: if I held my hand over the board at > different heights, the oscillation amplitude varied periodically, with a > period of a bit less than half an inch." > > "The actual board was fine, after a bit of Dremelling and adding a bunch > of parallelled bypass caps. With 40-50 GHz transistors and lots of gain > in a small space, half a nanohenry here and there can ruin your whole day." > > > or a circuit may only go into oscillation at a certain point on the > > input waveform. Both issues are hit or miss. > > AKA a snivet. > > > Add a base resistor. > > > > The value may range from 100 ohms for low frequency circuits, to > > perhaps 5 or 10 ohms for fast circuits. You can easily change the > > value as needed when you gain more experience with the circuit. But > > it is extremely difficult to add a base resistor to a smd transistor > > when you have forgotten to include it in the layout. Add a base > > resistor. > > That blanket rule doesn't cover all the bases, so to speak. ;) Base > resistors trash the speed and noise performance, so a tight layout and > close attention to minimum-inductance bypassing help a lot. Then I use > a zero-ohm jumper as a placeholder for a possibly-needed resistor or bead. > > 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.comA zero ohm short may not be the best idea. You have to pay 1. to install the part. 2. to remove it when you find a problem. This can damage the pads. 3. to install a base resistor. This can also damage the pads. When you multiply the costs by the number of transistor involved, it can mean a substantial amount of money and time lost. If you install the resistor in the first place, you can eliminate these costs. After you gain some experience, you can pretty much tell how much resistance to use for each type of transistor and the kind of circuit used. I recommend using the highest value that won't degrade the performance of the circuit. Also remember you may have a slow transistor in this production run. The next batch may be on the hot side. Here's a problem you may not see often. This was in an audio amp. The top trace in blue is the input signal. The bottom trace in red is the parasitic oscillation. https://drive.google.com/open?id=1o0YZiXfmORF-yvekNMp3W7Ny6iS8nJQg Just because you are working in the audio range doesn't prevent a circuit from oscillating at VHF.
Reply by ●October 4, 20182018-10-04
On 03.10.18 11:03 PM, John Larkin wrote:> Just resistors could work, but that loses amplitude, and the ends of > the fanout traces would have to be always terminated to avoid > reflections. Something unilateral would be easier.This doesn't exactly fit the "single-ended, easy termination" bill, but I've recently had some fun (and success) with the ADCLK950: http://www.analog.com/media/en/technical-documentation/data-sheet/ADCLK950.pdf 2 inputs, 10 outputs, propagation delay ~210 ps, 75 fs rms jitter. How stable do you need the propagation delay to be? — David
