temperature compensation in pll design

[us1710]

i am designing a pll for 2.4 GHz . it is locking up to temperature of 37 degree, but beyond this , it is not working. can anyone help me , where would be the problem ? presently i am using ideal voltage and current sources( no bandgap reference ckt ). are they making a difference ? i could not sort out what is the problem .

 

[Sezi]

I suggest you to simulate your vco with a temperature sweep and check the oscillation frequency.. it may get out of capture range

 

[us1710]

i think problem is in vco gain. should i use temperature compensation technique or optimization would be sufficient if it can be done? if nybody have good paper in it then plz post it.

 

[Borber]

What Sezi said is truth. Your free running VCO frequency is too temperature sensitive. First find out how is free running frequency changing with temperature. Then you may change critical capacitors having different temperature coefficients.
Next method can be to use temperature dependent resistor (PTC, NTC) and varicap diode to compensate frequency change.
Finally you may place your VCO in an owen.

 

[us1710]

hi borber ,
i am using ring vco not LC one. so plz suggest me compensation for ring vco.