Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.electronics.design > #489079

Re: Diff amps spec at 500ohms plus, why?

Show all headers | View raw

On 2017-12-22 14:40, John Larkin wrote:
> On Fri, 22 Dec 2017 14:19:12 -0800, Joerg <news@analogconsultants.com>
> wrote:
>
>> 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".
>
> Some of the semi people have support folks that prowl the forums and
> really answer questions; quality varies. I think the idea is that if
> support is done inn public, more people get to see it all.
>

That has gradually become a business driver for me. Years ago larger 
companies could still get someone from the semi mfg who almost lived 
there for a week and helped them with a tricky design. Not anymore, now 
they are on their own.


> But it's impressive how often nobody has the answer. A recent question
> invoked the response "That's an old Burr-Brown part. Nobody knows
> anything about it." (dual 14-bit TXDAC.)
>

Or they might say "You have to go to Golden Sunset Senior Center and ask 
for resident Joe Smith".

Just came across the THS6214 which looks more capabable than the others 
but +/-5V would be at the very bottom supply range for this chip:

http://www.ti.com/lit/ds/symlink/ths6214.pdf

It's also long in the tooth. 2009 is almost ancient for telco chips.

-- 
Regards, Joerg

http://www.analogconsultants.com/

Back to sci.electronics.design | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

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

csiph-web