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The output of AD9954 using frequency sweep

Question asked by KYO on Dec 20, 2012
Latest reply on Dec 22, 2012 by sitti

MCU:SILICON LABS  C8051FX20-TB    晶片:C8051F120

http://www.silabs.com/Support%20Documents/TechnicalDocs/C8051F12x-13x.pdf

evaluation board:ANALOG DEVICES AD9954

http://www.analog.com/static/imported-files/data_sheets/AD9954.pdf

 

AD9954 evaluation board:

   only use DUT1

   power:VDD_I/O=VCC=3.3V   DVDD=AVDD=1.8V

   U13:PS10、SK、I/O SYNC、PD、CLKMODESEL are ground

       RB_ENABLE don't connect anything

       SCLK、SDIO、PS0、FUD、RESET、CS  connect with Port4 of 8051

   REF_CLK_DUT1  connect to signal generator(5MHz Square wave  500mVpp  offset:250mV)

   because no Oscillator on board.

 

Why the amplitude of output is changing with frequency?

1.jpg

The horizontal axis  is frequency.        log(1MHz)=6

The vertical axis is amplitude(V)

 

100K_10M.JPG

The sweeping frequency is from 100KHz  to 10MHz.

The difference of amplitude is about 1.76V.

How can I solve this problem?  Let the amplitude is fixed.    Example:  It is always fixed in 3V.

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