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Groups > sci.electronics.design > #489073
| From | Joerg <news@analogconsultants.com> |
|---|---|
| Newsgroups | sci.electronics.design |
| Subject | Re: Diff amps spec at 500ohms plus, why? |
| Date | 2017-12-22 14:19 -0800 |
| Message-ID | <fa5emlFr5vtU1@mid.individual.net> (permalink) |
| References | <fa2visF9pgmU1@mid.individual.net> <fa56v6Fpdu5U1@mid.individual.net> <rprq3dl3p9odq38gkvbs0tn96u9q5dd137@4ax.com> <fa5bq5Fqhk7U1@mid.individual.net> <880r3dtahda6d21rkiq22ovf363vekh98s@4ax.com> |
On 2017-12-22 14:06, John Larkin wrote: > On Fri, 22 Dec 2017 13:29:52 -0800, Joerg <news@analogconsultants.com> > wrote: > >> On 2017-12-22 12:54, John Larkin wrote: >>> On Fri, 22 Dec 2017 12:07:12 -0800, Joerg <news@analogconsultants.com> >>> wrote: >>> >>>> On 2017-12-21 15:48, Joerg wrote: >>>>> On a design I am working right now I need to drive differential cables >>>>> at up to 100MHz and with gusto, several volts swing. I'd use coax >>>>> instead but the customer is king. Looking at the various diff amps du >>>>> jour I consistently find specs like this: >>>>> >>>>> http://www.ti.com/lit/ds/symlink/ths4503.pdf >>>>> >>>>> That example has all the performance data at an even higher load >>>>> resistance of 800ohms. Considering that regular ribbon is around 100ohms >>>>> diff and even grandpa's old TV cable was 300ohms, what good does that do? >>>>> >>>>> I guess now I have to not just find a diff amp but also add an analog >>>>> diff buffer IC (if they still exist) or roll my own transistor stuff. >>>>> Which will double as a space heater where I really can't use heat. Grumble! >>>>> >>>> >>>> Looking a the modem at my Internet connection, one option might be to >>>> use DSL or PLC drivers like this: >>>> >>>> http://www.analog.com/media/en/technical-documentation/data-sheets/ADA4311-1.pdf >>>> >>>> Gets iffy though, the GND thermal pad would need to be connected to a >>>> VCC- plane. They are also not intended to work well down to DC but >>>> probably will be ok there. >>>> >>>> Has anyone used DSL or PLC drivers as differential amps? >>> >>> I've used the ADA4950-1 as a differential ADC driver, but it should be >>> able to drive a cable. Seems well behaved. >>> >> >> Thanks, that one looks nice though the data for 2Vpp and 200ohms is >> marginal. I need 5Vpp into 100ohms. Maybe the dual version ADA450-2 >> could be run in parallel. Possibly that requires 10ohms or so in series >> with each output, meaning four more resistors. >> >> http://www.analog.com/media/en/technical-documentation/data-sheets/ADA4950-1_4950-2.pdf >> >> Figure 22 seems to contradict figure 23. >> >> >>> Actually, I designed my gadget with an LT6402, but it was nasty so I >>> had to redesign with the ADI part. >>> >> >> The distortion specs don't look good. > > THD increases even more when a part breaks into oscillation. > Oh yeah. Sometimes oscillation goes unnoticed until a neighbor bangs on the door. > >> High speed or RF isn't really >> LTC's turf, they are more a switch-mode controller company. Well, now >> it's all AD anyhow. > > Some of the LTC stuff is good, but it's all too expensive. > > ADI often gets the digital parts of mixed-signal stuff wrong. LTC > seems OK about that. > > TI does good work. > I am sloshing through DSL drivers now. This was seriously better in the olden days where National had their "fast drivers" and "damn fast drivers". No kidding, that's what they wrote in the databook for the LH0063. I guess nobody sends stuff over cable anymore. It's now all Bluetooth and apps and virtual-whatever. One of the problems with AD, TI and some other companies is that they have done away with real support at least for smaller companies and consultants (even though this project is for a really big client). They think that a user forum comprises "support". -- Regards, Joerg http://www.analogconsultants.com/
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Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-21 15:48 -0800
Re: Diff amps spec at 500ohms plus, why? George Herold <gherold@teachspin.com> - 2017-12-21 18:53 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 09:31 -0800
Re: Diff amps spec at 500ohms plus, why? Winfield Hill <hill@rowland.harvard.edu> - 2017-12-21 19:48 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 09:34 -0800
Re: Diff amps spec at 500ohms plus, why? bloggs.fredbloggs.fred@gmail.com - 2017-12-24 09:37 -0800
Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-21 19:55 -0800
Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-21 19:59 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 09:39 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 12:07 -0800
Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highland_snip_technology.com> - 2017-12-22 12:54 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 13:29 -0800
Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highland_snip_technology.com> - 2017-12-22 14:06 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 14:19 -0800
Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highland_snip_technology.com> - 2017-12-22 14:40 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 15:16 -0800
Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-22 16:30 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 16:57 -0800
Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-22 20:33 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-23 08:21 -0800
Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-23 10:20 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-23 11:33 -0800
Re: Diff amps spec at 500ohms plus, why? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-12-23 13:56 -0500
Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-23 11:08 -0800
Re: Diff amps spec at 500ohms plus, why? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-12-23 14:11 -0500
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-23 11:42 -0800
Re: Diff amps spec at 500ohms plus, why? LM <sala.nimi@mail.com> - 2017-12-23 21:36 +0200
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-23 12:18 -0800
Diff amps spec at 500ohms plus, why? Klaus Kragelund <klauskvik@hotmail.com> - 2017-12-25 00:56 -0800
Re: Diff amps spec at 500ohms plus, why? krw@notreal.com - 2017-12-25 08:51 -0500
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-25 07:26 -0800
Re: Diff amps spec at 500ohms plus, why? krw@notreal.com - 2017-12-25 10:46 -0500
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-25 07:51 -0800
Re: Diff amps spec at 500ohms plus, why? krw@notreal.com - 2017-12-25 12:53 -0500
Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-25 09:58 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-25 11:39 -0800
Re: Diff amps spec at 500ohms plus, why? whit3rd <whit3rd@gmail.com> - 2017-12-25 17:16 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-27 16:17 -0800
Re: Diff amps spec at 500ohms plus, why? Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-12-27 19:06 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-28 00:47 -0800
Re: Diff amps spec at 500ohms plus, why? Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-12-27 16:38 -0800
Re: Diff amps spec at 500ohms plus, why? George Herold <gherold@teachspin.com> - 2017-12-27 18:03 -0800
Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-28 00:50 -0800
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