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Selecting the Sample Rate

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0dBc

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Hi guys,

What sample rate would you use if you were to digitize a 40MHz bandwidth signal centered at 70MHz? Availabe ADC supports rates upto 400MSPS. What sample rate makes the operations in the digital domain simpler?
Thanks in advance.
 

Hi,

70 MHz +/- 20MHz... so max is 90MHz.

If this is a purely sine signal, then according no nyquist you need more than 180 MHz sampling rate.
200 MHz is OK, but 400 MHz is better.

If the waveform is not sine, then you need to determine what max overtone frequency you need to detect. Then the sampling rate needs to be more then twice the overtone frequency.

400 MHz sampling rate is high, check if you can use "undersampling technique".

For digital signals I recommend to use comparators and a pure digital sampling.

Klaus
 

0dBc said:
Hi guys,

What sample rate would you use if you were to digitize a 40MHz bandwidth signal centered at 70MHz? Availabe ADC supports rates upto 400MSPS. What sample rate makes the operations in the digital domain simpler?
Thanks in advance.
Click to expand...

Answer depands what you want to do the signal after ADC.
Generally with Nyquist law (fs > 2B (B=40MHz)) u need at least 80 MSPS for undersampling application (choosing fs care should be taken to avoid fs mix fi unwanted aliasing).
U can read more about undersampling in this ti whitepaper
https://www.ti.com/lit/an/slaa594a/slaa594a.pdf
 

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