Hi,
I wanted to know why a certain component might require some minimum clock frequency in order to operate.
For example, I read somewhere that
when the USB interface is used in an application, the clock input must be at least 18 MHz in
order to support internal operations of the USB block...
Are you talking about a certain USB interface chip or a microcontroller?
If microcontroller:
The processing speed of microcontrollers depend on clock frequency.
The microcontroller needs to answer the incoming USB request within a limited time.
If it´s clock speed is too low it can´t react within the time and communication fails.
But the USB block here is an on-chip peripheral of the microcontroller (LPC23xx), so shouldn't the clock to the USB block be same as the CPU clock and therefore the said situation shouldn't arise.