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Verifying datasheet LTC2165 evaluation board

Question asked by binupandians on Mar 27, 2018

Hi,

We are using LTC2165 in one of our designs.

We have DC1762A (Eval board) and DC890B(USB data capture) boards with us and looking to verify the datasheet characteristics(SNR, SFDR,...) using pscope.

However, we are stuck at the very first step(checking SNR).

 

As per datasheet, we expect SNR to be 75dB minimum. However, we are able to acheive only 70dB.

Following is our setup.

Analog input is 140MHz.

Sampling clock is 125MHz, 0dBm.

 

Also,

we have tested with one more setup to find the noise floor in the board.

Analog input is 50ohm terminated.

Sampling clock is 125MHz, 0dBm.

As shown in the diagram, the noise floor is -115dBFS with 64K-FFT.  Integrating the noise floor for 64K/2 bins, we get,

= -115+10log(64K/2)

which gives me  -70dBFS.

 

This makes the maximum SNR possible 70dB.

 

To get SNR  >=75dB, we think noise floor to be atleast -120dBFS.  From the graphs on page11 of LTC2165 datasheet, it looks like the noise floor is greater than -120dBFS.

 

Is our understanding right?

Kinldy let us know how to achieve datasheet level values.

 

Thanks and Regards,

Binupandian S.

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