high temperature affects gain. Why?

[yuvalkesi]

Hi,
Can someone please explain how does high temperature affects RF gain (of a PA, for example)?
I know gain is reduced as temp goes high, but I want to know more thoroughly.
I also know thermal noise is increased as temp goes high (does it affect gain?)
Thx!
Tom

 

[vfone]

The transistor transconductance (gm) is affected by temperature, and this would affect the gain.

 

[yuvalkesi]

Affected how?
and why?

 

[BigBoss]

Affected how?
and why?

Vt has approx. -2mV/C slope and gm=Ic/Vt
So, gm is dependent to temp.

 

[jiripolivka]

All semiconductor devices (and to some extent, vacuum tubes, too) are temperature dependent. Their gain and in principle junction parameters depend exponentially upon temperature. For example, operation point of a transistor amplifier stage must be designed to achieve a stable operation over a specified temperature range.
Another problem is power dissipation; all unused power is released as heat. If not treated, the excessive heat can damage or destroy a semiconductor component.

Read a basic textbook on semiconductor devices used in electrical circuits.

---------- Post added at 21:23 ---------- Previous post was at 21:21 ----------

And there is more to add: not only a"high" temperature but any temperature changes do affect amplifier gain.