74LVT transition times: How low can you go?

On Tue, 06 Mar 2007 13:38:32 -0500, CBFalconer <cbfalconer@yahoo.com>
wrote:

>Jim Granville wrote:
>> CBFalconer wrote:
>>> Jim Granville wrote:
>>>> CBFalconer wrote:
>>>>> Jim Granville wrote:
>>>>>
>>>>>... snip ...
>>>>>
>>>>>> The other issue that can bite, is transistion oscillation.
>>>>>> Without a Schmitt, if you scoped the output at the 4mA peak,
>>>>>> you will see what I mean.  That can cause real problems with
>>>>>> downstream devices - I've seen even unrelated pin drive have
>>>>>> edge-oscillation effects that needed external remedies.
>>>>>
>>>>> Actually a Schmidt trigger input can make things worse.  Without
>>>>> it, a single CMOS inverter using a Vcc that allows a linear input
>>>>> bias can stabilize using just a large resistor from output to
>>>>> input.  With it, the input voltage must be some sort of sawtooth,
>>>>> depending on the innate input capacitance.  The half period will
>>>>> be the time needed for the input to rise (or fall) the hysteresis
>>>>> voltage.
>>>>
>>>> You've lost me here.  I'm talking about unwanted transistion
>>>> oscillation, which can be in the 100's of MHz region in modern
>>>> devices. There is no feedback resistor, and a Schmitt IP does not
>>>> make transistion oscillation worse, it removes it.
>>>>
>>>> I think you are thinking of RC oscillators, or even Crystal
>>>> oscillators ( using unbuffered gates, HCU04 type) which are about
>>>> oscillators you'd try and do linear feedback, without real care.
>>>
>>> There is always feedback, possibly only via the capacitance between
>>> input and output.  It is possible that the leakage current into the
>>> input pin is so small that the system becomes quiescent, but not
>>> too likely.  That is why one normally ties unused inputs to ground
>>> (or Vcc).  With, say 12V CMOS it is possible to bias the input pin
>>> so that both transistors are entirely off, and the system is
>>> stable.  This is one of the curses of low Vcc CMOS logic - there is
>>> no real stable point where both input transistors are firmly off.
>> 
>> You've moved even further from my transistion oscillation instance,
>> but I'm lost as to what "both transistors are entirely off" can
>> mean.
>
>I've been delaying a response, because I beieve somebody has their
>head up, and I have come to the conclusion that it is me.  I was
>thinking of old fashioned 4000 series CMOS, where the transistors
>are enhancement mode, with thresholds of something like 8V.  At a
>Vcc of 12 V no input voltage can turn both units on, but as you
>reduce Vcc you come to the condition where both are on at some
>input level.  I really am not familiar with the characteristics of
>the devices forming modern chips, so my opinion becomes relatively
>worthless.

I am not sure what you mean by old fashioned 4000 series CMOS, but at
least the "McMos Handbook" second edition (1974) from Motorola at page
3-15 display the Idd for MC14011AL NAND gate for Vdd 10 and 15 volts.

At Vdd = 10 V, the drain current starts to rise at 1.5 V input voltage
reaching a peak of about 2 mA at 4,5 V and falling back to zero at 8
V.

At Vdd=15 V, the drain current starts to rise at 2 V reaching a peak
of 5-6.5 mA at 6,5 V and falling back to zero at 13 V.

Clearly both transistors are on even with Vdd=10 V for a long period
of time.

About the question could the device self destruct due to too much
heat, taking the peak current of 6.5 mA and the 15 V supply voltage,
this is only 100 mW and with 4-6 elements in a package, we are talking
about 400-600 mW, which is quite a lot for a 14-16 pin DIP package,
but at least not destroy the package immediately.

Paul
 

Joerg wrote:
> 
> And the lower it goes the more leakage has to be dealt with. Probably
> Jim has pulled his hair at times about that. I couldn't because my hair
> is already gone :-(


   Damn deserters! ;-)  OTOH, I was completely gray by my 22nd birthday.
A jerk that I used to work with loved to tease about it, but I kindly
pointed out that he would never have to worry, because he was already
half bald, and my age. His favorite line was, "Your hair dye can't
handle the job", so I bought one of those temporary kits and used it. It
was an almost perfect match for my hair when I was in high school.  The
shocked looks when i walked into work? ;-)  Three days later it had
washed out, without a comment. I caught them all together and told them
I know i am 100% gray, but I don't care.  You've seen how I used to
look, but you'll never see it again.  I'm on the inside, can't see my
hair without looking into a mirror, and really don't care what color it
is so laugh all you want.

-- 
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

On Wed, 07 Mar 2007 03:41:16 GMT, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

>Joerg wrote:
>> 
>> And the lower it goes the more leakage has to be dealt with. Probably
>> Jim has pulled his hair at times about that. I couldn't because my hair
>> is already gone :-(
>
>
>   Damn deserters! ;-)  OTOH, I was completely gray by my 22nd birthday.
>A jerk that I used to work with loved to tease about it, but I kindly
>pointed out that he would never have to worry, because he was already
>half bald, and my age. His favorite line was, "Your hair dye can't
>handle the job", so I bought one of those temporary kits and used it. It
>was an almost perfect match for my hair when I was in high school.  The
>shocked looks when i walked into work? ;-)  Three days later it had
>washed out, without a comment. I caught them all together and told them
>I know i am 100% gray, but I don't care.  You've seen how I used to
>look, but you'll never see it again.  I'm on the inside, can't see my
>hair without looking into a mirror, and really don't care what color it
>is so laugh all you want.

I have the same amount of hair now as I did as a teenager.

It's just that it's moved down to my nose, ears and eyebrows ;-)

                                        ...Jim Thompson
-- 
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Jim Thompson wrote:
> 
> On Wed, 07 Mar 2007 03:41:16 GMT, "Michael A. Terrell"
> <mike.terrell@earthlink.net> wrote:
> >
> >   Damn deserters! ;-)  OTOH, I was completely gray by my 22nd birthday.
> >A jerk that I used to work with loved to tease about it, but I kindly
> >pointed out that he would never have to worry, because he was already
> >half bald, and my age. His favorite line was, "Your hair dye can't
> >handle the job", so I bought one of those temporary kits and used it. It
> >was an almost perfect match for my hair when I was in high school.  The
> >shocked looks when i walked into work? ;-)  Three days later it had
> >washed out, without a comment. I caught them all together and told them
> >I know i am 100% gray, but I don't care.  You've seen how I used to
> >look, but you'll never see it again.  I'm on the inside, can't see my
> >hair without looking into a mirror, and really don't care what color it
> >is so laugh all you want.
> 
> I have the same amount of hair now as I did as a teenager.
> 
> It's just that it's moved down to my nose, ears and eyebrows ;-)


   When I stop coughing up chunks of phlegm and shaking, (over 10 days
now) I'm going to try to get a decent picture of myself.  A new Fuji
Finepix S5200 digital camera was donated to my Veteran's website
project, in trade for help launching a small business website.  The
woman wanted some pictures of her shop for her site.  I told her that my
camera wasn't very good.  She asked what camera I wanted to use, then
she bought the camera so I could take her photos. Then told me to use it
for the Veterans project. :-)


-- 
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Michael A. Terrell wrote:

> Joerg wrote:
>> 
>> And the lower it goes the more leakage has to be dealt with. Probably
>> Jim has pulled his hair at times about that. I couldn't because my hair
>> is already gone :-(
> 
> 
>    Damn deserters! ;-)  OTOH, I was completely gray by my 22nd birthday.
> A jerk that I used to work with loved to tease about it, but I kindly
> pointed out that he would never have to worry, because he was already
> half bald, and my age. His favorite line was, "Your hair dye can't
> handle the job", so I bought one of those temporary kits and used it. It
> was an almost perfect match for my hair when I was in high school.  The
> shocked looks when i walked into work? ;-)  Three days later it had
> washed out, without a comment. I caught them all together and told them
> I know i am 100% gray, but I don't care.  You've seen how I used to
> look, but you'll never see it again.  I'm on the inside, can't see my
> hair without looking into a mirror, and really don't care what color it
> is so laugh all you want.
> 

My first white hairs were noticed at age 14, i was thouroghly salt and
pepper by 17.  I have thinned on top but it is still somewhat salt and
pepper decades later.  (way heavy on the salt though)

-- 
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller