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AD8302 500 kHz oscillation in phase output

Question asked by k3ko on Aug 4, 2011
Latest reply on Aug 24, 2011 by k3ko

Trying to use at 10 MHz to calibrate a Rb oscillator vs GPS DO.

 

Changed components as follows

C1,4,5,6 =,1 uf

C8,C2 = 1 nf

 

Inputs are ~10 MHz sine waves of 100 and 50 mv peak to peak.  Phase output seems to follow the frequency difference.  That is the phase output peaks get twice as close as the frequency of one oscillator is changed from 1KHz higher to 2KHz higher.   However the output phase is contaminated with a 500 KHz sine wave.  It never drops below 0.8 V but peaks approach the correct value.  The VMAG output does follow oscillator level changes qualitatively but is also contaminated.

 

This unit was built on a 14 pin DIP sized breakout board.  The cost of the Evaluation board precluded its use.

 

Other information.  Current draw =20 ma, reference voltage at VREF =1.8 V.  Ohmmeter checks from the IC to the breakout board show continuity and no pin to pin shorts.  VPOS is bypassed to ground with 0.1 and 100 pf caps.  A nearly single point ground is used for all inputs, caps and output.

 

Is it possible that I have killed the IC?  Alternatively what steps can I take to kill the oscillation?

 

Regards,

Brian

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