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Groups > sci.electronics.design > #489051
| From | Joerg <news@analogconsultants.com> |
|---|---|
| Newsgroups | sci.electronics.design |
| Subject | Re: Diff amps spec at 500ohms plus, why? |
| Date | 2017-12-22 09:34 -0800 |
| Message-ID | <fa4u0hFnb05U2@mid.individual.net> (permalink) |
| References | <fa2visF9pgmU1@mid.individual.net> <p1hvb302qa0@drn.newsguy.com> |
On 2017-12-21 19:48, Winfield Hill wrote: > 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! > > In Aoe III, Table 5.10, page 375, covers full differential > amplifiers, with diff IN+OUT, listing about 45 parts. Many > are intended to drive ADCs, etc., rather than low-Z cables. > > Two differential outputs at +2 and -2 volts, driving a back- > terminated 100-ohm differential load, will experience a > load current of 4V/200 ohms = 20mA, which isn't too bad. > > 2 volts amplitude at 100mHz requires an wA = 1260 V/us > slew rate. That's within the range of the THS4503 specs. > I tabulated the Vpp-out max and the slew rates, and many > parts are dramatically faster then the THS4503. I'm > sorry I didn't tabulate the maximum output currents. > Most have drivers that are in the single-digit ohms and can easily drive 100ohms. However, the distortion performance drops dramatically under such load and in many of my cases that really matters. Sometime they end the distortion plots in the datasheet below 200ohm, probably because that wouldn't look good. -- 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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