CPU construction

[P0pinjay]

I am intimately familiar with standard thermocouples....how they look, operate, different types, etc. However, I'm at a loss as to how they integrate them into CPU's. The smallest thermocouples I've seen look too big to appropriately "embed" them somewhere on the CPU so how do they do it?

 

[redbox]

I belief they are on the motherboard but I could be wrong.

 

[TuxDave]

The voltage/current behavior of transistors are sensitive to temperature. Using them you can create a PTAT (proportional to absolute temperature) reference circuit which will output a voltage or a current that will be linearly proportional to temperature. The simpliest configuration can be done using 2-3 transistors so they can be fairly small.

Doh.. gotta plane to catch, I hope this helps. Google PTAT reference and hopefully you can find some papers. I haven't tried but good luck.

 

[dkozloski]

Intel uses a thermal diode that is part of the chip which means it must be pretty darn small. At least as small as any other element on the chip.

 

[Goi]

Different CPU manufacturers place them at different locations on the core, based on thermal simulations. Some CPUs even have multiple thermal sensors. These are placed in the "hotspots" of the CPU, i.e. the locations that get the hottest, such as the issue unit and the execution units for example. The sensors are obviously not off the shelf thermocouples, but actually thermal diodes built with transistors into the die itself, AFAIK.

 

[f95toli]

Thermocoples are generally not very accurate. They are usefull because they are cheap and can be used at high temperatures but at moderate (or low) temperatures other types of sensors are often better. Standard silicon diodes are often used as temperature sensors. However, usually you need to calibrate them somehow. But there are also diodes that are made specifically to be used as temperatures sensors which follow a "standard curve".
In CPU they use silicon transitors instead of diodes (a transitor is just two diodes back to back) but the principle is the same.

 

[PsYcHoCoW]

http://www.national.com/images/pf/LM86/10130303.pdf
this picture demonstrates how to use one of National Semiconductor's temperature IC to monitor a remote transistor..

http://www.thermengr.com/TB/TB-02.pdf
the first paragraph explains (shortly) why/how it works

I've seen an application note that used a really common transistor (2n3904) to measure temperature, and apparently it is quite reliable and precise.

 

[f95toli]

I have actually used Schottkydiods as temperature sensors (I think I used BAT25) and they work very well. But obviously they need to be calibrated.

 

[bdww00]

they put it in the third row in the transistor order