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Temperature dependencies of electronic components
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Temperature dependencies of electronic components
Grumble
I am asked by a colleague to say something about temperature dependencies of electronics.
Is there a pdf or something like that floating around with some basic knowledge about this subject?
Googling gives me a lot of hits but no "textbook" type of article.

Can somebody point me in the right direction plzz?
guest
was anything more specific asked for? if i had to give a short presentation on temperature dependency, i would probably look at a just a few fundamental components: resistors, capacitors, transistors. you can pull up some datasheets for these, and present the graphs inside that show how key parameters vary with temperature. i would show data for 3 different types of capacitors: plasitc film, ceramic, and electrolytic. for resistors, the cost has come down so much that there is almost no need to use anything other than metal film resistors (at least for SMT), which are quite good. and for transistors, there are a number of parameters that vary, but current increases for increasing temperatures, which can lead to thermal runaway. the temperature effects of ICs are then just a result of the temperature effects of the transistors they are made out of.

i wish i had a single reference, but most of this is from a few paragraphs in random textbooks.
Grumble
Thank you for your input, but reading datasheets would work for me, but not in this case.
The colleague is a phd doing research with a device designed for measuring the circumference of the torso.She discovered that there was a drift in the output signal of the device and she thought (correctly) that the drift was temperature dependent.
But now she has to explain why she thought it was drift caused by temperature change and not by some other phenomenon while to me it is quite obvious.
It’s like that there is a difference between a man and a woman obvious to everyone, but explain that scientifically is a problem.
guest
well, you could collect data with a temperature probe and show that its related, although that wont give insight on how to fix it.

do you believe the drift is due to the circuitry or the sensor? if its in the circuitry, you can add up the drifts of all the components (from datasheets) and then give an overall drift of the circuit. the sensor would be more difficult if its a custom device.
Grumble
both the sensor and the measuring device (which is a black box to me) are new in methode and design.
in my lab there is a temperature controlled oven, and she already discovered that there is a temp. dependancy in the drift when the measuring device is in the oven when there is a temp. change while the output stays the same with no drift if just the sensor is in the oven with a changing temp.
So that is not realy the issue, I was more looking for a pdf or something like that with some examples of temp. dependence in electronics.
guest
the "precision circuit techniques" chapter of horowitz and hill is pretty good at covering basic opamp circuits, and where temperature drift comes from. if you learn anything more about the "black box" i might be able to point you toward more specific resources. also, if its an offset drift, its typically the powersupply or opamps, if its a scale drift its typically the resistors.
ixtern
It's not so easy. Particular parts may be temperature dependent but whole circuit may be or may be not.
Example: if you take two resistors of the same type - both are temperature dependent but in classic voltage divider scheme absolute values are not so important as relative ones. If both resistors have the same temp coefficients, circuit may be temperature independent.
Another one: capacitors. Good mica capacitor may have positive (e.g.+70 ppm/deg) and styroflex capacitor negative (e.g.-160 ppm/deg) coefficients. Combining two of them with proper capacitance relation may result in zero temperature coefficient.

Transistors and diodes have exponential temp relation but there are methods to compensate it (we all know transistor pairs and tempco or oven in VCOs).

What I am trying to say is that all depends on circuit design, not on components only.
Grumble
Thanks,
@guest: I have found a free pdf version of that book and sent it to my colleague.
Since we do not have the schematics of the measuring device she has to stay with common behavior of electronic components.
Thanks for thinking about this!
jorg
Your colleague should be using an instrumentation-grade amplifier. These are commonly used in medical equipment.
chuckg
I would think that proving that the measurement device is temperature-dependent is good enough for the work, without need to explain why.

More important is to take steps to reduce the dependency, or account for it in some way.
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