displaying sigals up to 100Mhz in PC

[STU_KNTU]

displaying siganls up to 100Mhz in PC

hi all.
I'm wondering how PC based Oscilloscope can display signals up to 100 Mhz or higher While USB's band width is below 50 Mbyte.
for example with 8 bit ADC and 50Mbyte USB speed we can sample in range of 0 to 50M sample per second and we can display 25Mhz signal.
Do you how an idea?

 

[KlausST]

Hi,

it simply is not "real time": (non continous sampling)
* It waits for the trigger event
* takes a lot of samples and buffers them
* transmits them to the PC


***
some USB slave ICs have built in hardware FIFO buffer (on USB slave side).
For example if FIFO buffer size is 1024 bytes then the DAC could be as fast as the FIFO buffer.
But USB_slave to USB_host doesn´t need to be that fast.

With a 100MSamples/s ADC and 1024 bytes buffer it is able to take a snapshot of about 10us in time.
But usually it´s no problem if the transmission takes 10ms.

Klaus

 

[ftsolutions]

Alot of buffering, and non real time as KlausST points out, but also there can be data compression, especially useful in periodic waveforms or in cases like PC-based logic analyzers where there may be long intervals of little/no change in the input signals being monitored.