1. Home
  2. Field-Programmable Gate Arrays
  3. cmos delay vs temperature

cmos delay vs temperature

I found one old Fairchild appnote that has some numbers

formatting link

which averages to around +3000 ppm/degC, or about +3 ps per ns of prop delay per degree C. That's with 50 pF loading, sorta high.

This is HC, pretty old technology.

I have a vague impression that the innards of a typical FPGA may be better. Here's a ring oscillator inside an Altera FPGA, which looks close to +1000 PPM/degC delay tempco. But that's deep inside, probably CLB and not interconnect limited, and i/o cells may be different.

ECL is much better, generally way under 1000 PPM.

Do any semiconductor jocks have any comments on cmos tempco?

Do any of the FPGA design tools report timing tempcos? I don't drive those tools myself.

I suppose one could tweak Vcc vs temp to null out a native tempco.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin
Loading thread data ...

I've seen timing analysis tools that will evaluate the design at high temp, low temp or typical, but I've never seen them offer tempcos. If you analyze your design at high and low temps it would be easy enough to calculate of course. Analyze it at typ temp just to make sure it's linear. But this may not be what you want. These are not real numbers. They are worst case production run numbers. I have no idea how they will compare to real world numbers.

I know the timing analysis tools are not always accurate. 15 years ago Altera had moved on to Quartus for new work and MAX+II was only used for existing designs on previous generation chips. Their delay calculations for heavily loaded routes was not accurate and our designs would fail when the part warmed up. Quartus didn't support the chips then, so we had to shotgun it by routing some 10 to 20 runs a night and then testing them the next day with a chip heater.

The delay isn't all silicon, so I don't know how it would be calculated over temp. What happens to the R and the C of metal runs on a chip with temperature? Is that significant? The actual delay is. Or that may be the Si switches used to interconnect the routes. Don't know. That's kinda the point of digital techniques. Deal with the pesky analog effects to get them out of the picture so we can focus on the complicated stuff.

--

Rick C
Reply to
rickman

Until some time ago, most FPGA timing analysis tools used the worst-case parameters from the datasheets, that should have been characterized pretty well. In fact, it was completely normal that a real design in a lab environment performed a lot better than the timing simulation would suggest.

However I'm not aware of the "last" (5-10 years) evolutions of the design tools.

--
Fletto i muscoli e sono nel vuoto.
Reply to
dalai lamah

I am not an expert in this field either, but to my knowledge, things got mu ch more complex with the smaller process geometries.

Generally things will still become faster at higher supply voltage and lowe r temperature, but I had also designs which (according to the timing analyz

Regards,

Thomas

formatting link
- Home of EEBlaster and JPEG CODEC

Reply to
thomas.entner99

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.