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The Relationship Between Amplifier Gain and Temperature - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


boon
Post subject: The relationship between amplifier gain and temperature
Unread postPosted: Tue May 24, 2005 10:00 pm

What is the relationship between amplifier gain and temperature?

Thanks.


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Jeanalmira
Post subject:
Unread postPosted: Thu May 26, 2005 3:40 am
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Joined: Tue Mar 15, 2005 11:43 pm
Posts: 65
Location: Singapore
Hi :

At typical case, amplifier gain will be decreased as temperature increased. It's related to transistor parameters changes over temperature. Therefore, at large difference gain over temperature, the thermistor design is necessary at DC bias line to compensate the changes caused by temperature difference.

hope it helps.

Cheers,
Jean :-)


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Guest
Post subject:
Unread postPosted: Thu May 26, 2005 1:57 pm

Hello,

I agree with Jean. Another point you have to consider is that as the temperature increases the amplifier's output power capability (P1dB) degrades as well as its linearity. The exact opposite happens in lower temperatures.


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Guest
Post subject:
Unread postPosted: Fri May 27, 2005 10:35 am

Cant remeber which it is, but BJTs and FETS behave differently over temperature. I think ( not sure) the BJT gain will increase at higher temperature since the number of electrons injected in to the base will increase. FETs will decrease at higher temperature since it is a voltage controlled device and the channel resistance goes up at high temperatures.


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Guest
Post subject:
Unread postPosted: Fri May 27, 2005 3:57 pm

Don't mix between DC Gain and RF Gain. for example in BJT's the beta will increase with temperature, where the S21 will decrease with temperature.


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Guest
Post subject:
Unread postPosted: Sat May 28, 2005 8:07 am

Your probably right, I may be thinking of the current and not S21.



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