ADC sampling to USB speed conversion

Thread Starter

Gpand

Joined Dec 11, 2023
105
Supposed an amplifier has 16 analog inputs with 24 Bit and 38.400 Hz sampling frequency per channel (Each analog to digital converter is operating with 2.4576 MHz and performs a 64 times oversampling resulting in a sampling rate of 38.400 Hz for each channel).

How do you compute the USB speed required to transmit the data to the PC? 480Mbps? 12Mbps? How do you convert Hz to Mbps?
 

crutschow

Joined Mar 14, 2008
34,844
Then it would appear the data rate from the ADC is 16 * 24 * 38,400 = 14.75 Mbps, which would be the minimum USB data rate.
 

Thread Starter

Gpand

Joined Dec 11, 2023
105
USB 2.0 Full Speed is 12Mbps
USB 2.0 High Speed is 480Mbps.

So it will always run at USB HS? What if you only use one channel. Will 14.75 Mbps be engaged?
 

MisterBill2

Joined Jan 23, 2018
19,459
Considering that the USB protocol and hardware were created to provide convenience in connection as the primary goal, with all other things secondary, it is good to understand that the USB data transfer rate also depends on the software involved.
So it is quite probable that USB will not perform as required for the stated application.
 

MrChips

Joined Oct 2, 2009
31,088
Supposed an amplifier has 16 analog inputs with 24 Bit and 38.400 Hz sampling frequency per channel (Each analog to digital converter is operating with 2.4576 MHz and performs a 64 times oversampling resulting in a sampling rate of 38.400 Hz for each channel).

How do you compute the USB speed required to transmit the data to the PC? 480Mbps? 12Mbps? How do you convert Hz to Mbps?
You are combing and confusing two different rates.
There is the ADC sampling rate and there is the USB transfer rate.
USB has different data transfer mechanisms. For transferring large amounts of data you need to use bulk transfer.

Thus, depending on the application, the ADC is allowed to sample data at its required rate which would be independent of the USB transfer rate. Thereafter, the application would transfer the data in bulk at whatever rate is available.

I am doing this right now with my Android oscilloscope. The ADC samples at a maximum rate at 50Msps. The data is transferred to the Android tablet via bluetooth at whatever rate this happens.
 
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