Why 4*LO has problems in AD8333

Really thank you for your help.

I am struggling with the application of AD8333.

I am confused that when I input 4*LO sine wave to Din of DS90C401, its output (Dout-, Dout+) was not a sine wave. Even though I adjust the amplitude of the input. It still could not work.

I don't how to solve this issue. 

The purple trace with a sine wave is the input to Din of DS90C401,but the other two traces were Dout(+, -). I don't know why they were not sinewave.

Thanks for your kind help

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    •  Analog Employees 
    on Dec 12, 2019 12:55 AM

    Hi,

    Can you provide a schematic of your circuit? Do you have the transimpedance amplifiers on the outputs of the AD8333? See Figure 64 in the AD8333 datasheet as a reference.

  • I am very grateful for your kind reply. I actually followed the reference design of the AD8333 datasheet. I firstly simulated this circuit in Multism, but it seemed to have problems that are shown below.

    As the figure above, I input a reference signal with 4MHz(sinewave) to 4LO directly, and I set  Reset to a high level. RFIP and RFIN were a pair of differential signals which were converted by the previous VGA circuit. The output was as follows. In fact, It did not accomplish I/Q demodulation when I set Reset to High.

    However, when I put Reset to a Low level. It seemed to work with 2Lo signal plus DC component, but its signal was definitely weird, like below.

Reply
  • I am very grateful for your kind reply. I actually followed the reference design of the AD8333 datasheet. I firstly simulated this circuit in Multism, but it seemed to have problems that are shown below.

    As the figure above, I input a reference signal with 4MHz(sinewave) to 4LO directly, and I set  Reset to a high level. RFIP and RFIN were a pair of differential signals which were converted by the previous VGA circuit. The output was as follows. In fact, It did not accomplish I/Q demodulation when I set Reset to High.

    However, when I put Reset to a Low level. It seemed to work with 2Lo signal plus DC component, but its signal was definitely weird, like below.

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