Hi Steve it seems There is some confusion...

Shown below is the output from the precision full wave rectifier which is going to the analog input of ADC PCF8591.



When the lower portion of the wave is zoomed it shows..



This indicates an distortion of the output wave with negative going tiny spike. If this is directly fed to the PCF8591 which is not meant for -ve measurements I am affraid the inputs of ADC may blow up due to this -ve input. Thus I want to use clamp diode which can eat up this tiny spike and can protect the ADC by not letting it enter the input of my ADC.

Thanks & Regards,
Prahlad Purohit.