Some Problems about the ADC Module LTC2183

Hello!

I'm Chen Hongqiang, a student of Zhejiang University of technology. I encountered some problems when using the ADC module LTC2183 of analog company. I want to consult.

I'm on the company website www.analog.com/.../218543f.pdf In the bottom right corner of page 14, I see such a picture. The picture is placed below. The input signal of this picture is 140MHz, and the sampling frequency is 80Msps. In my personal understanding, in this case, the signal sampled by AD has multiple frequencies, 140-80 = 60MHz; 80*2-140=20MHz; 80 * 3-140 = 100MHz... Indicates that the frequency components after sampling are 20MHz, 60MHz, 100MHz... While the picture shows only 20MHz spectrum. Is this because there is a low-pass filter in LTC2183?

The above is my personal understanding. If there is no problem with my understanding, I would like to know the cut-off frequency of the low-pass filter in LTC2183 and LTC2185, or where I can see the information of this low-pass filter. If my understanding is wrong, please give me guidance. Thank you very much!

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