AD974 output fluctuates

[zaknwfp]

I am using AD974 to convert analog voltage from an instrumentation amplifier and send the result to PIC microcontroller. The output from AD974 fluctuates as much as 100mV. I am providing clock from the PIC by just toggling a pin on a port. My clock does not have 50% duty cycle. I have also tied the WR1 and WR2 to ground to have the latch transparent since I want to use all four channels and don't want to toggle WR1 and WR2 all the time. Any idea why the ouput fluctuates?

 

[felixc]

Are your inputs connected to anything when you measure this, or have you put locally generated dummy input voltages to eliminate any external influence?

 

[zaknwfp]

I tried it even with a fixed voltage and also monitored the voltage with the multimeter. It still fluctuates.

 

[ScottyUK]

Does you circuit have adequate power supply decoupling? You should have, as a minimum a local decoupling cap on each IC of about 10 - 100nF, and bulk decoupling at the origin of the supply. If your PIC has large current pulses, add a 10uF electrolytic local to the IC.





----------------------------------

If we learn from our mistakes,
I'm getting a great education!