temperature compensation.

[Paul Maddox]

Dear all,

  Ive been toying with tempature compensation of VCO's.. for most circuits 
we need a NTC 3300 PPM resistor..

  If you look at the ASM one we have this

  OPAMP> -----VVVV----+------ base of transistor
                      >
                      < NTC resistor
                      >
                      |
                      0v

  Why couldnt you simply swap the two around and use a PTC, these seem to be 
more common, ie....

  OPAMP> -----VVVV-----+---- Base of transistor
             PTC res   |
                       >
                       <  Fixed value res
                       >
                       |
                       0v

  Am I missing something obvious as to why this couldnt be done?

  Paul




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