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Groups > sci.electronics.design > #518255 > unrolled thread
| Started by | John Larkin <jjlarkin@highland_snip_technology.com> |
|---|---|
| First post | 2018-10-03 15:03 -0700 |
| Last post | 2018-10-05 10:44 -0400 |
| Articles | 20 on this page of 96 — 26 participants |
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really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-03 15:03 -0700
Re: really fast buffers Lasse Langwadt Christensen <langwadt@fonz.dk> - 2018-10-03 15:23 -0700
Re: really fast buffers Andy Bennet <andyb@andy.com> - 2018-10-04 08:20 +0100
Re: really fast buffers Lasse Langwadt Christensen <langwadt@fonz.dk> - 2018-10-04 08:45 -0700
Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-03 15:52 -0700
Re: really fast buffers George Herold <gherold@teachspin.com> - 2018-10-03 18:08 -0700
Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-03 20:02 -0700
Re: really fast buffers bitrex <user@example.net> - 2018-10-03 21:54 -0400
Re: really fast buffers Steve Wilson <9fe142ac@gmail.com> - 2018-10-03 20:10 -0700
Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-03 20:40 -0700
Re: really fast buffers pcdhobbs@gmail.com - 2018-10-04 05:00 -0700
Re: really fast buffers Steve Wilson <9fe142ac@gmail.com> - 2018-10-04 08:39 -0700
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-04 12:38 -0400
Re: really fast buffers Steve Wilson <9fe142ac@gmail.com> - 2018-10-04 14:35 -0700
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-04 18:27 -0400
Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-05 03:21 +0000
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-05 10:38 -0400
Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-04 11:50 -0700
Re: really fast buffers Clifford Heath <no.spam@please.net> - 2018-10-05 09:26 +1000
Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-04 17:09 -0700
Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-05 03:12 +0000
Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-05 14:18 -0700
Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-05 23:42 +0000
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-06 14:41 -0400
Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-05 03:09 +0000
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-05 10:40 -0400
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-05 11:06 -0400
Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-05 19:16 -0700
Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-05 14:26 -0700
Re: really fast buffers George Herold <gherold@teachspin.com> - 2018-10-05 18:36 -0700
Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-05 19:22 -0700
Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-06 02:28 +0000
Re: really fast buffers <698839253X6D445TD@nospam.org> - 2018-10-06 06:03 +0000
Re: really fast buffers Steve Wilson <9fe142ac@gmail.com> - 2018-10-05 23:41 -0700
Re: really fast buffers <698839253X6D445TD@nospam.org> - 2018-10-06 08:12 +0000
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-06 14:46 -0400
Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-06 19:03 +0000
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-06 15:32 -0400
Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-06 20:08 +0000
Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-06 22:19 +0200
Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-06 21:02 +0000
Re: really fast buffers tabbypurr@gmail.com - 2018-10-06 16:57 -0700
Re: really fast buffers krw@notreal.com - 2018-10-06 22:30 -0400
Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-07 04:30 +0200
Re: really fast buffers <698839253X6D445TD@nospam.org> - 2018-10-07 07:15 +0000
Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-07 08:24 -0700
Re: really fast buffers bill.sloman@ieee.org - 2018-10-07 18:51 -0700
Re: really fast buffers tabbypurr@gmail.com - 2018-10-08 08:16 -0700
Re: really fast buffers Winfield Hill <hill@rowland.harvard.edu> - 2018-10-07 07:19 -0700
Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-10 00:38 -0700
Re: really fast buffers tabbypurr@gmail.com - 2018-10-10 03:02 -0700
Re: really fast buffers bill.sloman@ieee.org - 2018-10-10 04:07 -0700
Re: really fast buffers DecadentLinuxUserNumeroUno@decadence.org - 2018-10-10 11:28 +0000
Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-11 22:06 -0700
Re: really fast buffers bill.sloman@ieee.org - 2018-10-12 00:08 -0700
Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-13 22:29 -0700
Re: really fast buffers bill.sloman@ieee.org - 2018-10-14 00:30 -0700
Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-15 19:38 -0700
Re: really fast buffers bill.sloman@ieee.org - 2018-10-15 20:55 -0700
Re: really fast buffers tabbypurr@gmail.com - 2018-10-14 04:31 -0700
Re: really fast buffers bill.sloman@ieee.org - 2018-10-14 07:29 -0700
Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-15 19:42 -0700
Re: really fast buffers bill.sloman@ieee.org - 2018-10-15 20:57 -0700
Re: really fast buffers tabbypurr@gmail.com - 2018-10-16 08:41 -0700
Re: really fast buffers krw@notreal.com - 2018-10-16 17:38 -0400
Re: really fast buffers bill.sloman@ieee.org - 2018-10-16 19:37 -0700
Re: really fast buffers bill.sloman@ieee.org - 2018-10-16 19:40 -0700
Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-15 19:40 -0700
Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-11 22:04 -0700
Re: really fast buffers tabbypurr@gmail.com - 2018-10-12 08:02 -0700
Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-10 14:06 +0200
Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-10 08:31 -0700
Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-11 01:49 +0200
Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-10 17:41 -0700
Re: really fast buffers "John Miles, KE5FX" <jmiles@gmail.com> - 2018-10-10 20:53 -0700
Re: really fast buffers Jasen Betts <jasen@xnet.co.nz> - 2018-10-11 05:47 +0000
Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-11 12:35 +0200
Re: really fast buffers George Herold <gherold@teachspin.com> - 2018-10-06 12:39 -0700
Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-06 20:11 +0000
Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-08 20:26 -0700
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-06 14:45 -0400
Re: really fast buffers George Herold <gherold@teachspin.com> - 2018-10-06 12:46 -0700
Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-08 21:00 -0700
Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-09 07:11 +0200
Re: really fast buffers Chris Jones <lugnut808@spam.yahoo.com> - 2018-10-09 23:20 +1100
Re: really fast buffers Jeroen Belleman <jeroen@nospam.please> - 2018-10-09 15:17 +0200
Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-04 09:18 -0700
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-04 12:39 -0400
Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-04 11:51 -0700
Re: really fast buffers Piotr Wyderski <peter.pan@neverland.mil> - 2018-10-08 13:19 +0200
Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-08 08:52 -0700
Re: really fast buffers whit3rd <whit3rd@gmail.com> - 2018-10-04 11:57 -0700
Re: really fast buffers David Nadlinger <david@klickverbot.at> - 2018-10-04 23:05 +0100
Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-04 17:23 -0700
Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-05 11:26 +0200
Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-05 10:44 -0400
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| From | John Larkin <jjlarkin@highland_snip_technology.com> |
|---|---|
| Date | 2018-10-03 15:03 -0700 |
| Subject | really fast buffers |
| Message-ID | <gnaardpdk6o2lvfm2fd10d0b15mj8lpkgv@4ax.com> |
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. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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| From | Lasse Langwadt Christensen <langwadt@fonz.dk> |
|---|---|
| Date | 2018-10-03 15:23 -0700 |
| Message-ID | <5c855309-15a9-448a-b48d-3cdf3c066cde@googlegroups.com> |
| In reply to | #518255 |
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 ?
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| From | Andy Bennet <andyb@andy.com> |
|---|---|
| Date | 2018-10-04 08:20 +0100 |
| Message-ID | <C-ednYzQ5oqkIijGnZ2dnUU78eOdnZ2d@brightview.co.uk> |
| In reply to | #518259 |
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.
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| From | Lasse Langwadt Christensen <langwadt@fonz.dk> |
|---|---|
| Date | 2018-10-04 08:45 -0700 |
| Message-ID | <5dd78f95-c26e-4787-a4b6-921ed4fe6bdd@googlegroups.com> |
| In reply to | #518308 |
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
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| From | John Larkin <jjlarkin@highland_snip_technology.com> |
|---|---|
| Date | 2018-10-03 15:52 -0700 |
| Message-ID | <elhardpeogu58b9e1se34b13jufriqhub0@4ax.com> |
| In reply to | #518255 |
On Wed, 03 Oct 2018 15:03:38 -0700, John Larkin <jjlarkin@highland_snip_technology.com> wrote: >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. TI's BUF602 looks pretty good for this. It's designed to be a gain-of-one buffer. Weird pinout, not like an opamp. GBW is 1 GHZ, pretty good, but the slew rate is 8 v/ns. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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| From | George Herold <gherold@teachspin.com> |
|---|---|
| Date | 2018-10-03 18:08 -0700 |
| Message-ID | <b741cdb2-b7a8-4f2c-8ae1-b1cb1801e169@googlegroups.com> |
| In reply to | #518262 |
On Wednesday, October 3, 2018 at 6:52:28 PM UTC-4, John Larkin wrote: > On Wed, 03 Oct 2018 15:03:38 -0700, John Larkin > <jjlarkin@highland_snip_technology.com> wrote: > > >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. > > TI's BUF602 looks pretty good for this. It's designed to be a > gain-of-one buffer. Weird pinout, not like an opamp. > > GBW is 1 GHZ, pretty good, but the slew rate is 8 v/ns. 8 v/ns is too slow? how much voltage do you need? (sorry I mostly live in 'audio' land, ~10 v/us.) George H. > > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
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| From | John Larkin <jjlarkin@highlandtechnology.com> |
|---|---|
| Date | 2018-10-03 20:02 -0700 |
| Message-ID | <g70brddun7h6vonn4idmk79ks5pnq6isi9@4ax.com> |
| In reply to | #518285 |
On Wed, 3 Oct 2018 18:08:33 -0700 (PDT), George Herold <gherold@teachspin.com> wrote: >On Wednesday, October 3, 2018 at 6:52:28 PM UTC-4, John Larkin wrote: >> On Wed, 03 Oct 2018 15:03:38 -0700, John Larkin >> <jjlarkin@highland_snip_technology.com> wrote: >> >> >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. >> >> TI's BUF602 looks pretty good for this. It's designed to be a >> gain-of-one buffer. Weird pinout, not like an opamp. >> >> GBW is 1 GHZ, pretty good, but the slew rate is 8 v/ns. >8 v/ns is too slow? how much voltage do you need? No, the 1 GHz is mediocre. The 8v/ns is great. I'll be following about a 4 volt logic swing from the DUT. This is a real analog buffer, so if I route the buffered signal to a scope I'll see pretty much what's there, not a digitally cleaned-up or attenuated version. I'm guessing it won't add much jitter. >(sorry I mostly live in 'audio' land, ~10 v/us.) How do you tolerate waiting around? -- John Larkin Highland Technology, Inc lunatic fringe electronics
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| From | bitrex <user@example.net> |
|---|---|
| Date | 2018-10-03 21:54 -0400 |
| Message-ID | <GpetD.55761$6y.30486@fx09.iad> |
| In reply to | #518255 |
On 10/03/2018 06:03 PM, John Larkin wrote: > 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. > > My intuition thinks to skip the op amp and CMOS gates and go directly for the source follower, maybe using like a phemt and fast bipolar or phemt and mosfet in a compound arrangement, will get there.
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| From | Steve Wilson <9fe142ac@gmail.com> |
|---|---|
| Date | 2018-10-03 20:10 -0700 |
| Message-ID | <389c8897-eca4-4dcd-843a-f3406f3d23d7@googlegroups.com> |
| In reply to | #518289 |
On Wednesday, October 3, 2018 at 9:54:51 PM UTC-4, bitrex wrote: > My intuition thinks to skip the op amp and CMOS gates and go directly > for the source follower, maybe using like a phemt and fast bipolar or > phemt and mosfet in a compound arrangement, will get there. I'm with you on the follower, perhaps a 42GHz BFP650, $0.285CAD @QTY100 at Arrow: https://octopart.com/search?q=BFP650&oq=BFP650&start=0 How would you use these in a compound arrangement? (LTspice ASC wellcome for the schematic. I wouldn't expect it to run.)
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| From | John Larkin <jjlarkin@highlandtechnology.com> |
|---|---|
| Date | 2018-10-03 20:40 -0700 |
| Message-ID | <3j2brdlncd0dsn48vkv3e8cfu96el9k9at@4ax.com> |
| In reply to | #518296 |
On Wed, 3 Oct 2018 20:10:43 -0700 (PDT), Steve Wilson <9fe142ac@gmail.com> wrote: >On Wednesday, October 3, 2018 at 9:54:51 PM UTC-4, bitrex wrote: > >> My intuition thinks to skip the op amp and CMOS gates and go directly >> for the source follower, maybe using like a phemt and fast bipolar or >> phemt and mosfet in a compound arrangement, will get there. > >I'm with you on the follower, perhaps a 42GHz BFP650, $0.285CAD @QTY100 at Arrow: > >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. I'll be timing edges to picoseconds so I don't want unpredictable offsets. > >How would you use these in a compound arrangement? (LTspice ASC wellcome for the schematic. I wouldn't expect it to run.) You could servo out the Vbe offset with an opamp, but that would be a hassle to do lots of times on my board. -- John Larkin Highland Technology, Inc lunatic fringe electronics
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| From | pcdhobbs@gmail.com |
|---|---|
| Date | 2018-10-04 05:00 -0700 |
| Message-ID | <2ac37dbb-2c85-4351-94de-8d8bb2e4e7a7@googlegroups.com> |
| In reply to | #518299 |
>>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
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| From | Steve Wilson <9fe142ac@gmail.com> |
|---|---|
| Date | 2018-10-04 08:39 -0700 |
| Message-ID | <41a5fdec-97e2-495c-95a3-2ba9d316fd09@googlegroups.com> |
| In reply to | #518319 |
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
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| From | Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> |
|---|---|
| Date | 2018-10-04 12:38 -0400 |
| Message-ID | <gZSdndBi0eBs3CvGnZ2dnUU7-SnNnZ2d@supernews.com> |
| In reply to | #518327 |
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
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| From | Steve Wilson <9fe142ac@gmail.com> |
|---|---|
| Date | 2018-10-04 14:35 -0700 |
| Message-ID | <69ab9041-df1e-4d9a-a574-6120aaa3b93e@googlegroups.com> |
| In reply to | #518340 |
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.com A 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.
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| From | Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> |
|---|---|
| Date | 2018-10-04 18:27 -0400 |
| Message-ID | <noWdnW-q4aF1DivGnZ2dnUU7-f3NnZ2d@supernews.com> |
| In reply to | #518365 |
On 10/4/18 5:35 PM, Steve Wilson wrote: > 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. > A 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. You only have to do it on the first article. Then you change the BOM and birds chirp. > > 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. And wind up with crap performance needlessly. > > 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. Right, which is my zero-ohm jumper. ;) > > 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 Sure. Transistors get faster (up to a point) at higher I_C. > > Just because you are working in the audio range doesn't prevent a circuit from oscillating at VHF. The slowest scope I use regularly is 1 GHz, 4 GS/s, so those don't get by me. 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
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| From | Steve Wilson <no@spam.com> |
|---|---|
| Date | 2018-10-05 03:21 +0000 |
| Message-ID | <XnsA971ED88C3F9Eidtokenpost@69.16.179.22> |
| In reply to | #518372 |
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > On 10/4/18 5:35 PM, Steve Wilson wrote: >> A 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. > You only have to do it on the first article. Then you change the BOM > and birds chirp. Then you find you have a problem in the field. You have to rework all the units you have shipped. Why not add a suitable base suppression resistor to critical circuits in the first place. >> 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. > And wind up with crap performance needlessly. I specified a value that does not degrade performance. There is absolutely no value in having a wider bandwith than you really need. >> 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. > Right, which is my zero-ohm jumper. ;) >> Also remember you may have a slow transistor in this production run. >> The next batch may be on the hot side. > Cheers > > Phil Hobbs > >
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| From | Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> |
|---|---|
| Date | 2018-10-05 10:38 -0400 |
| Message-ID | <rYSdnc50g5jD6irGnZ2dnUU7-TXNnZ2d@supernews.com> |
| In reply to | #518402 |
On 10/4/18 11:21 PM, Steve Wilson wrote: > Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 10/4/18 5:35 PM, Steve Wilson wrote: >>> A 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. > >> You only have to do it on the first article. Then you change the BOM >> and birds chirp. > > Then you find you have a problem in the field. You have to rework all the > units you have shipped. Why not add a suitable base suppression resistor to > critical circuits in the first place. > >>> 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. > >> And wind up with crap performance needlessly. > > I specified a value that does not degrade performance. In your circuits, maybe. I often care very much about fractional nanovolts of noise. > > There is absolutely no value in having a wider bandwith than you really > need. In an audio amp, very true. In instruments, not so much. One of my main support headaches is people using the log output of the laser noise canceller, and adjusting the feedback bandwidth to set their measurement bandwidth. Causes all sorts of mayhem when the beam power ratios vary by order unity at frequencies near the feedback bandwidth. Running it fast fixes that, and it's easy to put an RC on the output if you like. It's usually best to have lots of bandwidth and then put in a good quality filter near the end. For instance, several of my gizmos use THS3091 CFAs as the output stage, configured as a two-pole Sallen-Key lowpass, and with a 50-ohm resistor in series with the output. The amp is 100 times faster than some of those circuits need, but it's super beefy (and hence student-resistant), and the extra speed keeps the S-K rolloff well controlled. > >>> 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. > >> Right, which is my zero-ohm jumper. ;) > >>> Also remember you may have a slow transistor in this production run. >>> The next batch may be on the hot side. Or it might have lower beta, in which case your procedure has the same problem. I generally go for about a factor of 1.5x to 2x more resistance than needed to cure the oscillation, and have never had an oscillation problem in the field. 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
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| From | John Larkin <jjlarkin@highland_snip_technology.com> |
|---|---|
| Date | 2018-10-04 11:50 -0700 |
| Message-ID | <04ocrddpiae33n4nl4pnd4llspimlg180o@4ax.com> |
| In reply to | #518327 |
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
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| From | Clifford Heath <no.spam@please.net> |
|---|---|
| Date | 2018-10-05 09:26 +1000 |
| Message-ID | <wkxtD.55207$LL1.25705@fx23.iad> |
| In reply to | #518357 |
On 05/10/18 04:50, John Larkin wrote: > 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. How does an emitter follower do anything useful if the base is tied to ground?
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| From | John Larkin <jjlarkin@highland_snip_technology.com> |
|---|---|
| Date | 2018-10-04 17:09 -0700 |
| Message-ID | <6radrdlhndgq53euojt6jpr8dqjbq4tcrp@4ax.com> |
| In reply to | #518378 |
On Fri, 5 Oct 2018 09:26:17 +1000, Clifford Heath <no.spam@please.net> wrote: >On 05/10/18 04:50, John Larkin wrote: >> 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. > >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. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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