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Issue with AD8339

Question asked by AnoobEC on Apr 9, 2015
Latest reply on Apr 9, 2015 by jstaley

Hello to everyone,

Wish to post an issue with AD8339.

 

I am using AD8339 I/Q demodulator in one of the projects. I found that  I/Q demodulator output is not as expected. Please find the below mentioned details:


I am using DDS AD9954 to generate sine wave with frequencies ranging  from 32kHz to 50kHz. This sine wave is connected to a QTF. The output of the QTF is to AD8339 demodulator inputs RF1N and RF1P via AD8331 LNA. Using one more DDS AD9954 to generate a square wave with 4 times the frequency of the sine wave. This square wave is connected to the demodulator inputs 4LON and 4LOP.

Observed that the sine wave and square wave generated by the DDS are proper. Also the signal coming out from the QTF is proper. QTF is reaching the resonance at the frequency of 42kHz. When I sweep the frequency from  32kHz to 50kHz, near 40kHz amplitude of the QTF signal starts increasing and  reaches maximum at 42kHz. After 42kHz amplitude starts decreasing and settles after 44kHz. Observed that the signals generated by the DDS and QTF are proper for every run of frequency sweeping from 32kHz to 50kHz. But the output of the AD8339 I/Q demodulator varies for each run.

 

Why I/Q demodulator is not giving steady voltage?

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