I am now working on a project, which needs a cheap analog acquisition device with a sampling rate of no less than 5MHz. Before, I only used Arduino, and rarely operated the registers on Arduino. I hope to use Arduino due to complete it. I spent a lot of time researching and querying solutions, but it didn't succeed. I hope someone can help me.
I haven't used the Due, but I understand its ADC is rated for 1 MHz sampling. If that's its absolute limit then you can't expect 5 MHz. However, judging by the Unos which I have used, you may be able to push things by limiting the number of bits. This gives a speed boost two ways, by shortening the time the ADC uses to acquire the data, and if you limit to 8 bits you have half as many bytes to move into memory.
Do not try to use more than one channel, since then you have multiplexer delays as well.
Also, you may want to skip interrupts and just sample in a tight loop. Using this loop trick doubles the useful ADC rate of the Uno, from 50 kHz to over 100 kHz. (You'll need to figure out the actual sample rate by reading the timer before and after the loop, then divide by the loop size and take the reciprocal.)