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AD9951 Amplitude

Thread Summary

The user inquired about the expected amplitude of 290mVpp on a 50Ω pullup and 550mVpp single-ended through a transformer with AD9951 settings at 10mA full scale and 12.88MHz. The support engineer confirmed the amplitude is expected based on bench tests, and suggested that the 500mVpp output is on the cusp of violating the DAC compliance voltage. Using a lower load resistor or a buffer amplifier could help, but the transformer is recommended for impedance matching.
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Dear Technical Support Team,

Hi,

My circuit shows 290mVpp on 50Ω pullup and 550mVpp Single-End through transformer.

Settings of AD9951 are 10mA(FullScale with ASF=0x3FFF) and 12.88MHz 

Is it expected amplitude?

Here is schematic and waveform.

PDF

It seems that there is a resistance of about 50Ω in parallel on the secondary side of the transformer.
When the impedance on the secondary side reaches about 38Ω,

Primary side: 275 mVpp
Secondary side: 550 mVpp

It will be about.
If there is about 50Ω in parallel on the secondary side

50Ω // (51Ω + 49.9Ω + α) = 38Ω
α is the impedance of the LC filter (at 12.88MHz)

Best Regards,

ttd

Parents Reply
  • Hi,

    I also find this somehow mysterious. Will have to setup a bench test next week for us to verify this one. We're still waiting for some components to arrive. 

    Also can you verify the new output given on your latest comment? It seems like the one you sent is just the same as the first one. 

    Regards,

    Jules

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