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Maximum channel temperature - RF Cafe Forums
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shireesha
Post subject: Maximum channel temperature Posted: Tue
Oct 20, 2009 12:58 am
Captain
Joined: Wed Jun 04, 2008
3:23 am
Posts: 11
My question is on the maximum channel temperature
specified in the power amplifier data sheets. How is this value determined?
What does it signify?
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nubbage
Post subject:
Re: Maximum channel temperaturePosted: Wed Oct 21, 2009 4:16 am
General
Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Hi shireesha
This is a basic parameter for
the channel and substrate, above which the device performance will degrade,
and much above it the device will suffer thermal runaway and be irreversibly
damaged.
It is used to input the value into thermal design software
in order to arrive at the design of heatsink needed to keep the device
within the stated performance parameters.
_________________
At bottom, life is all about
Sucking in and blowing out.
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shireesha
Post subject: Re: Maximum channel temperaturePosted:
Wed Oct 21, 2009 6:24 am
Captain
Joined: Wed Jun 04,
2008 3:23 am
Posts: 11
Sir,
Thanks for your reply. Could you
explain how this value (of maximum channel temperature) is arrived at?
Is it generally provided by the foundry or is there a way of determining
it ourselves?
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nubbage
Post subject: Re: Maximum
channel temperaturePosted: Fri Oct 23, 2009 4:04 am
General
Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location:
London UK
Hi shireesha
This is most accurately measured by the
manufacturer of the device, because they have access to the open die
of a test sample during pre-production. With the device in a test fixture
they are able to measure device performance parameters and measure the
channel temperature by a non-contact method such as a calibrated infra-red
scanner.
None of these facilities are normally available to the end
user.
_________________
At bottom, life is all about
Sucking
in and blowing out.
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biff44
Post subject:
Re: Maximum channel temperaturePosted: Tue Nov 10, 2009 5:47 am
Colonel
Joined: Wed Apr 08, 2009 11:07 am
Posts: 33
A semiconductor device is made a little like how you bake a chocolate
chip cookie. Once it is made, it is delicious to eat. However, if you
leave it on the dashboard of your car in the summer, the chocolate chips
melt and run all over the place--making a big mess. The same happens
with your semiconductor. If you keep it nice and cool after it is made,
all the various dopants and metals stay where they are supposed to,
and you can enjoy a good semiconductor operating life. Let it get too
hot, and those dopants and metals start to diffuse around. If they move
around too much, then a catastrophic failure can occur. Some devices
are more prone to this (such as silicon junction devices), while others
are less prone to this (GaAs mesfets), so there are different allowable
operating temperatures.
If you wanted to determine the allowable
operating temperature, you would do an "acelerated Life" test, where
you take 100 or so devices (set up as amplifiers, for example), and
measure an important parameter (like gain or output power). You put
them in an oven at some very high temperature, and take them out every
once in a while and mesure the electrical parameter. Once it is seriously
degraded, you extrapolate when the average device would fail. From that
you can determine the maximum operating temperature for a given "mean"
failure time. A complicated test--so usually only the device manufacturer
does it.
_________________
Rich
Maguffin Microwave Consulting
www.MaguffinMicrowave.com
Posted
11/12/2012
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