[sdiy] Temperature compensation with a MOSFET

[Jim Patchell]

That is a really tough one to call.

The idea is sound...but I am not too sure how practical it would be.  My 
experience with mosfets has not been good.  They can do a lot of 
marvelous things, but in linear circuits the problem they have is no two 
are the same.  That is one advantage that BJTs have over mosfets is that 
they are very predictable unit to unit.

Somebody would have to set up an experiment to see just how practical 
this may be.  It may turn out to be pretty easy.

This is sort of a similar idea to Ian's dial a tempco, except you use a 
mosfet, instead of a tempco resistor.

If I had the spare time...I would do the experiments... because this 
does have the potential to be a big money saver....(mosfets cost pennys, 
while a tempco, even a cheap one, is pretty costly).

-Jim


rjelliffe at allette.com.au wrote:
> Interesting Nokia patent: they find PTATs expensive too!
> 
> http://www.wipo.int/pctdb/en/wo.jsp?IA=FI1998000736&DISPLAY=DOCS
> 
>  "The invention relates to a method for temperature compensation in an
> electric circuit. In order to get rid of costly manufacturing processes
> and external components, a PTAT resistor is replaced by a series
> connection of two resistive elements (Rx, 31), the first of said elements
> (Rx) having essentially constant resistance regardless of the
> temperature, and the second element (31) having a resistance which is
> non-linearly dependent on the temperature. The resistance value of the
> first element is selected so that an approximation of the resistance of
> said series connection is directly proportional to the temperature"
> 
> The patent suggests a MOSFET with a 1V gate source and suitable resistor
> can do the job. I wonder whether it is good enough for synths?
> 
> Cheers
> Rick Jelliffe
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