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Re: analog failures

From Joerg <news@analogconsultants.com>
Newsgroups sci.electronics.design
Subject Re: analog failures
Date 2017-02-19 08:32 -0800
Message-ID <egtvlfFba1lU1@mid.individual.net> (permalink)
References (10 earlier) <egpfp7Fel2lU1@mid.individual.net> <o8826j$6fq$1@dont-email.me> <fi8faclfpk5tpnvt44abh2n351dn99nq44@4ax.com> <tj9fac5pkfmi8cr3tousj1rdmo1er6dtd5@4ax.com> <o8bb9t$nu2$1@dont-email.me>

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On 2017-02-18 21:45, rickman wrote:
> On 2/17/2017 8:56 PM, John Larkin wrote:
>> On Fri, 17 Feb 2017 20:27:45 -0500, krw@notreal.com wrote:
>>
>>> On Fri, 17 Feb 2017 18:51:29 -0500, rickman <gnuarm@gmail.com> wrote:
>>>
>>>> On 2/17/2017 6:37 PM, Joerg wrote:
>>>>> On 2017-02-17 14:58, rickman wrote:
>>>>>> On 2/17/2017 5:38 PM, Joerg wrote:
>>>>>>> On 2017-02-17 14:16, rickman wrote:
>>>>>>>> On 2/17/2017 5:05 PM, Joerg wrote:
>>>>>>>>> On 2017-02-17 12:30, rickman wrote:
>>>>>>>>>> On 2/15/2017 11:30 AM, John Larkin wrote:
>>>>>>>>>>> On Wed, 15 Feb 2017 07:53:18 -0800, Joerg
>>>>>>>>>>> <news@analogconsultants.com>
>>>>>>>>>>> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> On 2017-02-14 19:55, Reinhardt Behm wrote:
>>>>>>>>>>>>> AT Wednesday 15 February 2017 11:00, bill.sloman@ieee.org
>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Wednesday, February 15, 2017 at 1:52:23 PM UTC+11,
>>>>>>>>>>>>>> Reinhardt
>>>>>>>>>>>>>> Behm
>>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>>> AT Wednesday 15 February 2017 07:05, Lasse Langwadt
>>>>>>>>>>>>>>> Christensen
>>>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Den tirsdag den 14. februar 2017 kl. 23.47.11 UTC+1
>>>>>>>>>>>>>>>> skrev John
>>>>>>>>>>>>>>>> Larkin:
>>>>>>>>>>>>>>>>> http://semiengineering.com/devices-threatened-by-analog-content/
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> IME most analog failures are caused by ESD and that is often
>>>>>>>>>>>> squarely in
>>>>>>>>>>>> the court of the board level designer.
>>>>>>>>>>>>
>>>>>>>>>>>> Upsets without subsequent chip damage are also considered a
>>>>>>>>>>>> fault
>>>>>>>>>>>> where
>>>>>>>>>>>> the function is mission-critical. That is very often due to
>>>>>>>>>>>> EMI.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> My experience is that we find a lot of bugs and
>>>>>>>>>>>>>>>>> documentation
>>>>>>>>>>>>>>>>> problems
>>>>>>>>>>>>>>>>> with the digital parts of mixed-signal chips.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> It does seem like when analog designers get to design the
>>>>>>>>>>>>>>>> digital
>>>>>>>>>>>>>>>> parts
>>>>>>>>>>>>>>>> of a chip it often ends up with a hairball of hazards
>>>>>>>>>>>>>>>> and weird
>>>>>>>>>>>>>>>> quirks
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> That was always my experience with part from NatSemi. Pure
>>>>>>>>>>>>>>> analog
>>>>>>>>>>>>>>> was
>>>>>>>>>>>>>>> good, pure digital was good, mixed mostly was a mess.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Mixed signal design is difficult, and doing it on a chip,
>>>>>>>>>>>>>> where
>>>>>>>>>>>>>> it is
>>>>>>>>>>>>>> harder to keep the noisy digital bits away from the sensitive
>>>>>>>>>>>>>> analog bits,
>>>>>>>>>>>>>> wouldn't have made it any easier.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Sadly, mixed signal design can do a lot more than pure
>>>>>>>>>>>>>> analog or
>>>>>>>>>>>>>> pure
>>>>>>>>>>>>>> digital, so if you have got something complicated to do, that
>>>>>>>>>>>>>> tends
>>>>>>>>>>>>>> to be
>>>>>>>>>>>>>> what you end up doing.
>>>>>>>>>>>>>
>>>>>>>>>>>>> It was never the problem of digital noise coupling into the
>>>>>>>>>>>>> analog
>>>>>>>>>>>>> portions
>>>>>>>>>>>>> but the digital totally mixed up, like the LM75 going into
>>>>>>>>>>>>> a state
>>>>>>>>>>>>> where
>>>>>>>>>>>>> only a power cycle helps to get it working again. This can be
>>>>>>>>>>>>> caused by
>>>>>>>>>>>>> noise on the I2C signals.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> I2C is a bus I try not to use if it can be avoided because of
>>>>>>>>>>>> various
>>>>>>>>>>>> hang-ups. SPI is much more robust IME and, therefore, that is
>>>>>>>>>>>> what I
>>>>>>>>>>>> prefer.
>>>>>>>>>>>
>>>>>>>>>>> I prefer SPI too, and it's faster, but lots of people design
>>>>>>>>>>> terrible
>>>>>>>>>>> SPI interfaces, bad logic design and bad clock/data circuits.
>>>>>>>>>>> Every
>>>>>>>>>>> SPI should have schmitt inputs and safe timing margins. Maybe
>>>>>>>>>>> cooking
>>>>>>>>>>> a digital design into an analog process causes compromises,
>>>>>>>>>>> but I
>>>>>>>>>>> suspect it's just sloppy engineering.
>>>>>>>>>>
>>>>>>>>>> Not trying to be snarky, but most digital engineers work to
>>>>>>>>>> eliminate
>>>>>>>>>> noise and to have proper clocks without noise on the
>>>>>>>>>> transition edge.
>>>>>>>>>> Schmitt is only needed on the clock inputs, but even there proper
>>>>>>>>>> design
>>>>>>>>>> at the board level eliminates the need.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Schmitt is needed everywhere a signal connect to the outside
>>>>>>>>> world. A
>>>>>>>>> lot of uC design engineers do not understand this.
>>>>>>>>
>>>>>>>> Define "outside world".  Do you mean off board?
>>>>>>>>
>>>>>>>
>>>>>>> Yes, or via a noisy area on the board. Also if slow on-board
>>>>>>> sensors are
>>>>>>> involved.
>>>>>>
>>>>>> That's why I said...
>>>>>>
>>>>>> "most digital engineers work to eliminate
>>>>>> noise and to have proper clocks without noise on the transition
>>>>>> edge. "
>>>>>>
>>>>>
>>>>> .... and then overlook that there can be external influences into
>>>>> boards
>>>>> and system. Such as EMI, magnetic fields or even weird stuff like that
>>>>> inexplicable double-pulse whenever somebody uses the freight elevator.
>>>>> But who am I to complain, this stuff brought me plenty of assignments.
>>>>
>>>> I'm not overlooking anything.  All that is part of the engineer's job.
>>>> A Schmitt trigger would be a panacea for none of the above.  A Schmitt
>>>> trigger is useful when appropriate, but the original post was about
>>>> "every SPI" having Schmitt inputs.  First, its only useful on edges and
>>>> so only the clock.  Secondly it is not something you can't add
>>>> externally.  I don't know why a chip designer wouldn't include a
>>>> Schmitt
>>>> trigger on clock inputs, but I'm not going to second guess them on
>>>> something as unimportant as this.  I'd much prefer they got the circuit
>>>> design right.
>>>
>>> I can't imagine why a Schmitt trigger should be on every clock, SPI in
>>> particular.  The designer should be able to design the board so there
>>> isn't crap on the clock edges.  I don't see the big deal with SPI.
>>> I've had a lot more trouble with I2C than I have with SPI but I've
>>> abused it more, too.
>>
>> If you come out of a wimpy ARM pin, and run the SPI clock all over a
>> multilayer board, to multiple targets, the edges will get slow. Slow
>> edges splayed all around a board are very noise sensitive. Schmitts
>> fix that, and let you run the SPI clock at a frequency that's
>> compatible with all that capacitive loading, traces and chips
>> combined.
>
> Schmitt trigger inputs don't "fix" noise.


Sure they do.


>                                    ... They may mask the problem if
> it is not so severe.  I don't recall ever seeing an edge so degraded by
> loading that it started having noise problems.  Your problem isn't the
> lack of Schmitt trigger inputs, your problem is excessive loading on a
> clock line.  Add some clock buffers.
>
>> Noise on \CS is well avoided, too.
>
> Only if CS is an edge triggered signal.  Fix your noise problem and you
> don't need to worry about the lack of built in Schmitt trigger inputs.
>

It's often got nothing to do with how it is triggered. I had cases where 
fast logic input stages did a little tarantella dance every time a 
signal change logic level. Just for a few hundred nsec. That did not 
upset the functionality of the system but was enough to fail EMC. The 
initial reaction of the guys was like yours in this thread: "You've got 
to be kidding!". Except I wasn't kidding. This is one of the reasons why 
I never travel to an EMC problem case without the near-field probe kit. 
With that you can narrow it down to the offending chip, sometimes even 
to the trace.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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Thread

analog failures John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-14 14:47 -0800
  Re: analog failures Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-14 15:05 -0800
    Re: analog failures Reinhardt Behm <rbehm@hushmail.com> - 2017-02-15 10:52 +0800
      Re: analog failures bill.sloman@ieee.org - 2017-02-14 19:00 -0800
        Re: analog failures Reinhardt Behm <rbehm@hushmail.com> - 2017-02-15 11:55 +0800
          Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-15 07:53 -0800
            Re: analog failures John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-15 08:30 -0800
              Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-15 10:19 -0800
                Re: analog failures John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-15 10:53 -0800
                Re: analog failures Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-15 10:58 -0800
                Re: analog failures "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-15 21:25 -0600
                Re: analog failures John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-15 20:18 -0800
                Re: analog failures rickman <gnuarm@gmail.com> - 2017-02-17 15:44 -0500
              Re: analog failures rickman <gnuarm@gmail.com> - 2017-02-17 15:30 -0500
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-17 14:05 -0800
                Re: analog failures rickman <gnuarm@gmail.com> - 2017-02-17 17:16 -0500
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-17 14:38 -0800
                Re: analog failures rickman <gnuarm@gmail.com> - 2017-02-17 17:58 -0500
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-17 15:37 -0800
                Re: analog failures rickman <gnuarm@gmail.com> - 2017-02-17 18:51 -0500
                Re: analog failures krw@notreal.com - 2017-02-17 20:27 -0500
                Re: analog failures John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-17 17:56 -0800
                Re: analog failures "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-17 21:03 -0600
                Re: analog failures krw@notreal.com - 2017-02-17 22:36 -0500
                Re: analog failures rickman <gnuarm@gmail.com> - 2017-02-19 00:45 -0500
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-19 08:32 -0800
                Re: analog failures John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-21 12:31 -0800
                Re: analog failures rickman <gnuarm@gmail.com> - 2017-02-23 14:57 -0500
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-23 12:02 -0800
                Re: analog failures John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-17 17:27 -0800
                Re: analog failures rickman <gnuarm@gmail.com> - 2017-02-17 20:39 -0500
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-18 07:41 -0800
                Re: analog failures John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-18 08:04 -0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-18 08:16 -0800
            Re: analog failures Reinhardt Behm <rbehm@hushmail.com> - 2017-02-16 06:49 +0800
              Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-16 07:14 -0800
                Re: analog failures John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-16 07:24 -0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-16 07:41 -0800
                Re: analog failures Reinhardt Behm <rbehm@hushmail.com> - 2017-02-17 13:22 +0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-17 06:58 -0800
                Re: analog failures John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-17 12:26 -0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-17 14:03 -0800
                Re: analog failures "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-17 21:05 -0600
                Re: analog failures John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-18 08:07 -0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-18 08:20 -0800
                Re: analog failures John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-18 09:20 -0800
                Re: analog failures rickman <gnuarm@gmail.com> - 2017-02-19 00:48 -0500
                Re: analog failures John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-21 12:39 -0800
                Re: analog failures "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-21 22:54 -0600
                Re: analog failures krw@notreal.com - 2017-02-17 20:33 -0500
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-18 07:37 -0800
                Re: analog failures dagmargoodboat@yahoo.com - 2017-02-22 15:45 -0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-23 10:43 -0800
                Re: analog failures krw@notreal.com - 2017-02-23 20:42 -0500
                Re: analog failures "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-24 03:31 -0600
                Re: analog failures grahamholloway@graham65.plus.com - 2017-02-24 06:39 -0800
                Re: analog failures Don Kuenz <g@crcomp.net> - 2017-02-24 14:58 +0000
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-25 12:48 -0800
                Re: analog failures pcdhobbs@gmail.com - 2017-02-26 04:39 -0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-26 07:52 -0800
                Re: analog failures dagmargoodboat@yahoo.com - 2017-02-24 09:02 -0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-25 12:44 -0800
                Re: analog failures dagmargoodboat@yahoo.com - 2017-02-26 08:29 -0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-26 09:46 -0800
                Re: analog failures John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-26 10:11 -0800
                Re: analog failures krw@notreal.com - 2017-02-26 17:55 -0500
                Re: analog failures John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-26 15:09 -0800
                Re: analog failures krw@notreal.com - 2017-02-26 19:30 -0500
                Re: analog failures John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-27 10:37 -0800
                Re: analog failures Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-24 09:14 -0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-25 12:46 -0800
                Re: analog failures Klaus Kragelund <klauskvik@hotmail.com> - 2017-02-26 17:44 -0800
                Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-27 07:51 -0800
                Re: analog failures Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-02-23 21:36 +0200
                Re: analog failures dagmargoodboat@yahoo.com - 2017-02-24 08:38 -0800
                Re: analog failures krw@notreal.com - 2017-02-24 20:20 -0500
                Re: analog failures kevin93 <kevin@whitedigs.com> - 2017-02-24 17:36 -0800
      Re: analog failures Ralph Barone <ralph@invalid.com> - 2017-02-15 03:25 +0000
    Re: analog failures John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-14 19:20 -0800
  Re: analog failures Tim Wescott <seemywebsite@myfooter.really> - 2017-02-14 17:46 -0600
    Re: analog failures Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-14 17:50 -0700
      Re: analog failures Tim Wescott <tim@seemywebsite.com> - 2017-02-14 23:49 -0600
        Re: analog failures Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-15 07:03 -0700
        Re: analog failures John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-15 10:18 -0800
          Re: analog failures Tim Wescott <seemywebsite@myfooter.really> - 2017-02-15 15:06 -0600
  Re: analog failures legg <legg@nospam.magma.ca> - 2017-02-16 23:06 -0500
    Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-17 07:00 -0800
      Re: analog failures legg <legg@nospam.magma.ca> - 2017-02-17 13:22 -0500
        Re: analog failures Joerg <news@analogconsultants.com> - 2017-02-17 11:06 -0800

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