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Diff amps spec at 500ohms plus, why?

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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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#489155

On Sat, 23 Dec 2017 08:21:52 -0800, Joerg <news@analogconsultants.com>
wrote:

>On 2017-12-22 20:33, John Larkin wrote:
>> On Fri, 22 Dec 2017 16:57:21 -0800, Joerg <news@analogconsultants.com>
>> wrote:
>>
>>> On 2017-12-22 16:30, John Larkin wrote:
>>>> On Fri, 22 Dec 2017 15:16:16 -0800, Joerg <news@analogconsultants.com>
>>>> wrote:
>>>>
>>>>> On 2017-12-22 14:40, John Larkin wrote:
>>>
>>> [...]
>>>
>>>>>
>>>>>> 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.
>>>>
>>>> I designed a couple things around the THS3062, which was claimed as
>>>> suitable as a VSDL line driver. What I didn't realize is that it's
>>>> *only* safe to use as a VSDL line driver. If you use it as a
>>>> general-purpose opamp, it tends to fry itself. The latest version of
>>>> the data sheet mentions the problem.
>>>>
>>>
>>> That one is a CFB amp. If used as an integrator or even with the
>>> slightest capacitive feedback it coan oscillate and unsolder itself.
>>> They also don't like capacitive loads but that goes for most high-speed
>>> VFB opamps as well.
>>>
>>>
>>>> So be careful!
>>>>
>>>
>>> I will. Sometimes I have the feeling that datasheets are written by
>>> marketing types. Why else would anyone spec a diff "driver" at 500, 800
>>> or in some cases even 1000 ohms? It's like specifying a pickup truck's
>>> performance with a load of two six-packs in the bed.
>>>
>>>
>>>> IC data sheets are not universally to be believed. Nor are their Spice
>>>> models. I usually breadboard a new part.
>>>>
>>>
>>> I might go with the ADA4950 for now and place 10ohms each in series so
>>> it won't go berserk when it sees a few pF of capacitive load.
>>
>> Why not 50 ohms in series with each output, to source terminate?
>>
>
>Then I don't get enough swing. The amplitude specs (for any decent 
>distortion performance) are just as paltry as the allowed load. Also, I 
>need +/-2.5V on each leg for some of the lines and with 5V a source 
>termination just isn't possible. If I have to use 24V DSL drivers I can 
>supply them with +/12V and then I'd use source termination. Have to, in 
>order to protect gear downstream that is on +/-5V if someone forgets the 
>end termination.

In that case, you'll probably need a couple of THS-series opamps.

If you need a good receiver for the other end, take a look at AD8130.
Really nice chip. 


-- 

John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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#489166

On 2017-12-23 10:20, John Larkin wrote:
> On Sat, 23 Dec 2017 08:21:52 -0800, Joerg <news@analogconsultants.com>
> wrote:
>
>> On 2017-12-22 20:33, John Larkin wrote:
>>> On Fri, 22 Dec 2017 16:57:21 -0800, Joerg <news@analogconsultants.com>
>>> wrote:
>>>
>>>> On 2017-12-22 16:30, John Larkin wrote:
>>>>> On Fri, 22 Dec 2017 15:16:16 -0800, Joerg <news@analogconsultants.com>
>>>>> wrote:
>>>>>
>>>>>> On 2017-12-22 14:40, John Larkin wrote:
>>>>
>>>> [...]
>>>>
>>>>>>
>>>>>>> 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.
>>>>>
>>>>> I designed a couple things around the THS3062, which was claimed as
>>>>> suitable as a VSDL line driver. What I didn't realize is that it's
>>>>> *only* safe to use as a VSDL line driver. If you use it as a
>>>>> general-purpose opamp, it tends to fry itself. The latest version of
>>>>> the data sheet mentions the problem.
>>>>>
>>>>
>>>> That one is a CFB amp. If used as an integrator or even with the
>>>> slightest capacitive feedback it coan oscillate and unsolder itself.
>>>> They also don't like capacitive loads but that goes for most high-speed
>>>> VFB opamps as well.
>>>>
>>>>
>>>>> So be careful!
>>>>>
>>>>
>>>> I will. Sometimes I have the feeling that datasheets are written by
>>>> marketing types. Why else would anyone spec a diff "driver" at 500, 800
>>>> or in some cases even 1000 ohms? It's like specifying a pickup truck's
>>>> performance with a load of two six-packs in the bed.
>>>>
>>>>
>>>>> IC data sheets are not universally to be believed. Nor are their Spice
>>>>> models. I usually breadboard a new part.
>>>>>
>>>>
>>>> I might go with the ADA4950 for now and place 10ohms each in series so
>>>> it won't go berserk when it sees a few pF of capacitive load.
>>>
>>> Why not 50 ohms in series with each output, to source terminate?
>>>
>>
>> Then I don't get enough swing. The amplitude specs (for any decent
>> distortion performance) are just as paltry as the allowed load. Also, I
>> need +/-2.5V on each leg for some of the lines and with 5V a source
>> termination just isn't possible. If I have to use 24V DSL drivers I can
>> supply them with +/12V and then I'd use source termination. Have to, in
>> order to protect gear downstream that is on +/-5V if someone forgets the
>> end termination.
>
> In that case, you'll probably need a couple of THS-series opamps.
>

Yes, that or just a DSL driver.


> If you need a good receiver for the other end, take a look at AD8130.
> Really nice chip.
>

That area isn't on my turf yet but it is a nice amp. Distortion isn't 
stated past 40MHz though and up there it doesn't look pretty.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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#489158

On 12/22/2017 06:16 PM, Joerg wrote:
> 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.
> 

A 100 MHz, 3600 V/us CFB _QUAD_ for two and a half bucks?  Where has 
this chip been all my life?

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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#489160

On Sat, 23 Dec 2017 13:56:35 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 12/22/2017 06:16 PM, Joerg wrote:
>> 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.
>> 
>
>A 100 MHz, 3600 V/us CFB _QUAD_ for two and a half bucks?  Where has 
>this chip been all my life?
>
>Cheers
>
>Phil Hobbs

Four times as much heat to get rid of.


-- 

John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[toc] | [prev] | [next] | [standalone]

#489161

On 12/23/2017 02:08 PM, John Larkin wrote:
> On Sat, 23 Dec 2017 13:56:35 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
>> On 12/22/2017 06:16 PM, Joerg wrote:
>>> 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.
>>>
>>
>> A 100 MHz, 3600 V/us CFB _QUAD_ for two and a half bucks?  Where has
>> this chip been all my life?
>>
>> Cheers
>>
>> Phil Hobbs
> 
> Four times as much heat to get rid of.

Yeah, but the rather nice 200-MHz THS3091 that I've been using costs 
five bucks in reels and ten bucks in onesies.

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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#489171

On 2017-12-23 11:11, Phil Hobbs wrote:
> On 12/23/2017 02:08 PM, John Larkin wrote:
>> On Sat, 23 Dec 2017 13:56:35 -0500, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> On 12/22/2017 06:16 PM, Joerg wrote:
>>>> On 2017-12-22 14:40, John Larkin wrote:

[...]


>>>>> 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.
>>>>
>>>
>>> A 100 MHz, 3600 V/us CFB _QUAD_ for two and a half bucks?  Where has
>>> this chip been all my life?


That one is old. Sometimes it is good to look at specialty markets since 
those chips are often not advertized in the regular analog marketplace. 
In the 80's we had similar problems where the only really fast opamps 
were from Harris but only came in the super-pricey mil-spec ceramic 
package, you had to call the utility before turning it one and they 
almost got hot enough to result in a blister after touching. Then I 
discovered the unsung heroes which were only marketed to engineers 
designing video recorders and hard drives. uA733 and such, those were a 
real bargain in all domains. Then some Japanese ICs that even our 
distributors didn't know about.

Same with discretes where PIN diodes were almost mil-pricing. Once I had 
to bypass our purchasing department because they wouldn't bypass "their" 
distributors which couldn't get that stuff. I ordered the diodes myself, 
in Malaysia, and that resulted in a VP office discussion where it got loud.


>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> Four times as much heat to get rid of.
>
> Yeah, but the rather nice 200-MHz THS3091 that I've been using costs
> five bucks in reels and ten bucks in onesies.
>

And sometimes you just need this much muscle. Just like a 2-liter engine 
is more efficient but can't tow the 5-ton trailer.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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#489168

On Thu, 21 Dec 2017 15:48:52 -0800, Joerg <news@analogconsultants.com>
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!
5V at 100 ohms is 0.25W. Have you checked some RF amplifiers.   Like
those in some antenna systems. They use 75R.

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#489181

On 2017-12-23 11:36, LM wrote:
> On Thu, 21 Dec 2017 15:48:52 -0800, Joerg <news@analogconsultants.com>
> 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!
> 5V at 100 ohms is 0.25W. Have you checked some RF amplifiers.   Like
> those in some antenna systems. They use 75R.
>

Unfortunately they have lousy to no DC performance. They also have poor 
linearity when the output swings +/-2.5V and most can't even do negative 
without some tricks.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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#489279

Add a transformer to get low output impedance and wrap the feedback loop around that?

Cheers

Klaus

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#489283

On Mon, 25 Dec 2017 00:56:23 -0800 (PST), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

>Add a transformer to get low output impedance and wrap the feedback loop around that?

He already stated that he needs to drive several volts, for some
strange reason.  A transformer just means he has to drive even higher
levels out of the amp.  Seems counterproductive.  I'd look at the
assumptions.  High line levels are the problem.  See if something can
be done about that.  If you don't like the answer, change the
question.  ;-)

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#489287

On 2017-12-25 05:51, krw@notreal.com wrote:
> On Mon, 25 Dec 2017 00:56:23 -0800 (PST), Klaus Kragelund
> <klauskvik@hotmail.com> wrote:
>
>> Add a transformer to get low output impedance and wrap the feedback loop around that?
>

We need this to work down to DC.


> He already stated that he needs to drive several volts, for some
> strange reason.  A transformer just means he has to drive even higher
> levels out of the amp.  Seems counterproductive.  I'd look at the
> assumptions.  High line levels are the problem.  See if something can
> be done about that.  If you don't like the answer, change the
> question.  ;-)
>

High line levels are customary in industrial environments. You also have 
those with DSL and such and there are nice chips for it. They are 
single-supply though (can be hacked if needed) and have huge power 
dissipation which would be a serious problem in this case. Those are 
meant to drive at >10Vpp.

Anyhow, it's the customer's wish and the customer is always king.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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#489288

On Mon, 25 Dec 2017 07:26:55 -0800, Joerg <news@analogconsultants.com>
wrote:

>On 2017-12-25 05:51, krw@notreal.com wrote:
>> On Mon, 25 Dec 2017 00:56:23 -0800 (PST), Klaus Kragelund
>> <klauskvik@hotmail.com> wrote:
>>
>>> Add a transformer to get low output impedance and wrap the feedback loop around that?
>>
>
>We need this to work down to DC.
>
>
>> He already stated that he needs to drive several volts, for some
>> strange reason.  A transformer just means he has to drive even higher
>> levels out of the amp.  Seems counterproductive.  I'd look at the
>> assumptions.  High line levels are the problem.  See if something can
>> be done about that.  If you don't like the answer, change the
>> question.  ;-)
>>
>
>High line levels are customary in industrial environments. You also have 
>those with DSL and such and there are nice chips for it. They are 
>single-supply though (can be hacked if needed) and have huge power 
>dissipation which would be a serious problem in this case. Those are 
>meant to drive at >10Vpp.

If it's so easy, what's your problem?

>Anyhow, it's the customer's wish and the customer is always king.

The customer is always the customer but you're the one he's hired to
be the expert.

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#489289

On 2017-12-25 07:46, krw@notreal.com wrote:
> On Mon, 25 Dec 2017 07:26:55 -0800, Joerg <news@analogconsultants.com>
> wrote:
>
>> On 2017-12-25 05:51, krw@notreal.com wrote:
>>> On Mon, 25 Dec 2017 00:56:23 -0800 (PST), Klaus Kragelund
>>> <klauskvik@hotmail.com> wrote:
>>>
>>>> Add a transformer to get low output impedance and wrap the feedback loop around that?
>>>
>>
>> We need this to work down to DC.
>>
>>
>>> He already stated that he needs to drive several volts, for some
>>> strange reason.  A transformer just means he has to drive even higher
>>> levels out of the amp.  Seems counterproductive.  I'd look at the
>>> assumptions.  High line levels are the problem.  See if something can
>>> be done about that.  If you don't like the answer, change the
>>> question.  ;-)
>>>
>>
>> High line levels are customary in industrial environments. You also have
>> those with DSL and such and there are nice chips for it. They are
>> single-supply though (can be hacked if needed) and have huge power
>> dissipation which would be a serious problem in this case. Those are
>> meant to drive at >10Vpp.
>
> If it's so easy, what's your problem?
>

As I have described, heat. Plus space. This thing also has to be very tiny.


>> Anyhow, it's the customer's wish and the customer is always king.
>
> The customer is always the customer but you're the one he's hired to
> be the expert.
>

If the customer wants something they usually have good reason why and I 
am the guy that needs to make it happen. If it was easy they wouldn't 
need me. Consultants tend to only get the difficult projects which is 
something I thoroughly enjoy.

In essence I have a solution which is brute force. If needed two regular 
diff-amps get paralleled. The main reason for this thread is my 
curiosity why most diff drivers are spec'd at unrealistically high Z.

-- 
Regards, Joerg

http://www.analogconsultants.com/

[toc] | [prev] | [next] | [standalone]

#489292

On Mon, 25 Dec 2017 07:51:38 -0800, Joerg <news@analogconsultants.com>
wrote:

>On 2017-12-25 07:46, krw@notreal.com wrote:
>> On Mon, 25 Dec 2017 07:26:55 -0800, Joerg <news@analogconsultants.com>
>> wrote:
>>
>>> On 2017-12-25 05:51, krw@notreal.com wrote:
>>>> On Mon, 25 Dec 2017 00:56:23 -0800 (PST), Klaus Kragelund
>>>> <klauskvik@hotmail.com> wrote:
>>>>
>>>>> Add a transformer to get low output impedance and wrap the feedback loop around that?
>>>>
>>>
>>> We need this to work down to DC.
>>>
>>>
>>>> He already stated that he needs to drive several volts, for some
>>>> strange reason.  A transformer just means he has to drive even higher
>>>> levels out of the amp.  Seems counterproductive.  I'd look at the
>>>> assumptions.  High line levels are the problem.  See if something can
>>>> be done about that.  If you don't like the answer, change the
>>>> question.  ;-)
>>>>
>>>
>>> High line levels are customary in industrial environments. You also have
>>> those with DSL and such and there are nice chips for it. They are
>>> single-supply though (can be hacked if needed) and have huge power
>>> dissipation which would be a serious problem in this case. Those are
>>> meant to drive at >10Vpp.
>>
>> If it's so easy, what's your problem?
>>
>
>As I have described, heat. Plus space. This thing also has to be very tiny.

So you want power but no heat.  That is an interesting problem.  Ya
think it's time to change the question, yet?

>>> Anyhow, it's the customer's wish and the customer is always king.
>>
>> The customer is always the customer but you're the one he's hired to
>> be the expert.
>>
>
>If the customer wants something they usually have good reason why and I 
>am the guy that needs to make it happen. If it was easy they wouldn't 
>need me. Consultants tend to only get the difficult projects which is 
>something I thoroughly enjoy.

Usually <> always.  Without understanding the complete problem, you
(and we) can't know.

>In essence I have a solution which is brute force. If needed two regular 
>diff-amps get paralleled. The main reason for this thread is my 
>curiosity why most diff drivers are spec'd at unrealistically high Z.

The answer to that is pretty obvious.

[toc] | [prev] | [next] | [standalone]

#489293

On Mon, 25 Dec 2017 12:53:01 -0500, krw@notreal.com wrote:

>On Mon, 25 Dec 2017 07:51:38 -0800, Joerg <news@analogconsultants.com>
>wrote:
>
>>On 2017-12-25 07:46, krw@notreal.com wrote:
>>> On Mon, 25 Dec 2017 07:26:55 -0800, Joerg <news@analogconsultants.com>
>>> wrote:
>>>
>>>> On 2017-12-25 05:51, krw@notreal.com wrote:
>>>>> On Mon, 25 Dec 2017 00:56:23 -0800 (PST), Klaus Kragelund
>>>>> <klauskvik@hotmail.com> wrote:
>>>>>
>>>>>> Add a transformer to get low output impedance and wrap the feedback loop around that?
>>>>>
>>>>
>>>> We need this to work down to DC.
>>>>
>>>>
>>>>> He already stated that he needs to drive several volts, for some
>>>>> strange reason.  A transformer just means he has to drive even higher
>>>>> levels out of the amp.  Seems counterproductive.  I'd look at the
>>>>> assumptions.  High line levels are the problem.  See if something can
>>>>> be done about that.  If you don't like the answer, change the
>>>>> question.  ;-)
>>>>>
>>>>
>>>> High line levels are customary in industrial environments. You also have
>>>> those with DSL and such and there are nice chips for it. They are
>>>> single-supply though (can be hacked if needed) and have huge power
>>>> dissipation which would be a serious problem in this case. Those are
>>>> meant to drive at >10Vpp.
>>>
>>> If it's so easy, what's your problem?
>>>
>>
>>As I have described, heat. Plus space. This thing also has to be very tiny.
>
>So you want power but no heat.  That is an interesting problem.  Ya
>think it's time to change the question, yet?

Run class D at maybe 500 MHz.


-- 

John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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#489295

On 2017-12-25 09:53, krw@notreal.com wrote:
> On Mon, 25 Dec 2017 07:51:38 -0800, Joerg <news@analogconsultants.com>
> wrote:
>
>> On 2017-12-25 07:46, krw@notreal.com wrote:
>>> On Mon, 25 Dec 2017 07:26:55 -0800, Joerg <news@analogconsultants.com>
>>> wrote:
>>>
>>>> On 2017-12-25 05:51, krw@notreal.com wrote:
>>>>> On Mon, 25 Dec 2017 00:56:23 -0800 (PST), Klaus Kragelund
>>>>> <klauskvik@hotmail.com> wrote:
>>>>>
>>>>>> Add a transformer to get low output impedance and wrap the feedback loop around that?
>>>>>
>>>>
>>>> We need this to work down to DC.
>>>>
>>>>
>>>>> He already stated that he needs to drive several volts, for some
>>>>> strange reason.  A transformer just means he has to drive even higher
>>>>> levels out of the amp.  Seems counterproductive.  I'd look at the
>>>>> assumptions.  High line levels are the problem.  See if something can
>>>>> be done about that.  If you don't like the answer, change the
>>>>> question.  ;-)
>>>>>
>>>>
>>>> High line levels are customary in industrial environments. You also have
>>>> those with DSL and such and there are nice chips for it. They are
>>>> single-supply though (can be hacked if needed) and have huge power
>>>> dissipation which would be a serious problem in this case. Those are
>>>> meant to drive at >10Vpp.
>>>
>>> If it's so easy, what's your problem?
>>>
>>
>> As I have described, heat. Plus space. This thing also has to be very tiny.
>
> So you want power but no heat.  That is an interesting problem.  Ya
> think it's time to change the question, yet?
>

No, I want linearity with a modest quiescent current. Power during 
signal peaks is not a problem because they will be short burst 
transmissions.


>>>> Anyhow, it's the customer's wish and the customer is always king.
>>>
>>> The customer is always the customer but you're the one he's hired to
>>> be the expert.
>>>
>>
>> If the customer wants something they usually have good reason why and I
>> am the guy that needs to make it happen. If it was easy they wouldn't
>> need me. Consultants tend to only get the difficult projects which is
>> something I thoroughly enjoy.
>
> Usually <> always.  Without understanding the complete problem, you
> (and we) can't know.
>

Well, I know :-)


>> In essence I have a solution which is brute force. If needed two regular
>> diff-amps get paralleled. The main reason for this thread is my
>> curiosity why most diff drivers are spec'd at unrealistically high Z.
>
> The answer to that is pretty obvious.
>

Looks like a marketing decision on the part of the mfgs to me. IMO there 
would be nothing wrong with stating "Here, this would be the max swing 
and distortion specs if you run it at 100ohms like almost anyone who 
wants to drive a line does".

-- 
Regards, Joerg

http://www.analogconsultants.com/

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#489305

On Monday, December 25, 2017 at 11:39:52 AM UTC-8, Joerg wrote:
> On 2017-12-25 09:53, krw@notreal.com wrote:

> > So you want power but no heat.  That is an interesting problem.  Ya
> > think it's time to change the question, yet?

> No, I want linearity with a modest quiescent current. Power during 
> signal peaks is not a problem because they will be short burst 
> transmissions.

Are there any solutions using class G amplifiers?  If you have dual-rail
plus ground, max heat is at 0.5 V+ and 0.5 V-; if you have six-rails plus
ground, max heat is at (V+-) * (2N+1)/6 , and the maxima are smaller.

But, the output circuit gets rather more complicated; does anyone
make an IC version?

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#489422

On 2017-12-25 17:16, whit3rd wrote:
> On Monday, December 25, 2017 at 11:39:52 AM UTC-8, Joerg wrote:
>> On 2017-12-25 09:53, krw@notreal.com wrote:
>
>>> So you want power but no heat.  That is an interesting problem.  Ya
>>> think it's time to change the question, yet?
>
>> No, I want linearity with a modest quiescent current. Power during
>> signal peaks is not a problem because they will be short burst
>> transmissions.
>
> Are there any solutions using class G amplifiers?  If you have dual-rail
> plus ground, max heat is at 0.5 V+ and 0.5 V-; if you have six-rails plus
> ground, max heat is at (V+-) * (2N+1)/6 , and the maxima are smaller.
>
> But, the output circuit gets rather more complicated; does anyone
> make an IC version?
>

I doubt it and a complicating issue is that this amp needs a GBW far 
above 1GHz.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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#489431

Den torsdag den 28. december 2017 kl. 01.17.34 UTC+1 skrev Joerg:
> On 2017-12-25 17:16, whit3rd wrote:
> > On Monday, December 25, 2017 at 11:39:52 AM UTC-8, Joerg wrote:
> >> On 2017-12-25 09:53, krw@notreal.com wrote:
> >
> >>> So you want power but no heat.  That is an interesting problem.  Ya
> >>> think it's time to change the question, yet?
> >
> >> No, I want linearity with a modest quiescent current. Power during
> >> signal peaks is not a problem because they will be short burst
> >> transmissions.
> >
> > Are there any solutions using class G amplifiers?  If you have dual-rail
> > plus ground, max heat is at 0.5 V+ and 0.5 V-; if you have six-rails plus
> > ground, max heat is at (V+-) * (2N+1)/6 , and the maxima are smaller.
> >
> > But, the output circuit gets rather more complicated; does anyone
> > make an IC version?
> >
> 
> I doubt it and a complicating issue is that this amp needs a GBW far 
> above 1GHz.

would this do? http://www.ti.com/product/LMH6881 

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#489446

On 2017-12-27 19:06, Lasse Langwadt Christensen wrote:
> Den torsdag den 28. december 2017 kl. 01.17.34 UTC+1 skrev Joerg:
>> On 2017-12-25 17:16, whit3rd wrote:
>>> On Monday, December 25, 2017 at 11:39:52 AM UTC-8, Joerg wrote:
>>>> On 2017-12-25 09:53, krw@notreal.com wrote:
>>>
>>>>> So you want power but no heat.  That is an interesting problem.  Ya
>>>>> think it's time to change the question, yet?
>>>
>>>> No, I want linearity with a modest quiescent current. Power during
>>>> signal peaks is not a problem because they will be short burst
>>>> transmissions.
>>>
>>> Are there any solutions using class G amplifiers?  If you have dual-rail
>>> plus ground, max heat is at 0.5 V+ and 0.5 V-; if you have six-rails plus
>>> ground, max heat is at (V+-) * (2N+1)/6 , and the maxima are smaller.
>>>
>>> But, the output circuit gets rather more complicated; does anyone
>>> make an IC version?
>>>
>>
>> I doubt it and a complicating issue is that this amp needs a GBW far
>> above 1GHz.
>
> would this do? http://www.ti.com/product/LMH6881
>
>

It has the same problem as the others. Inputs spec for 100ohms which is 
customary for diff lines such as ribbon. Output spec for 200ohms which 
is nonsensical in this day and age. Who writes datasheets these days? 
college kids? Marketing droids?

-- 
Regards, Joerg

http://www.analogconsultants.com/

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