Bob Schematic - Usb Filtering

[jokeman]

i've a question about the USB Host BoB Schematic.
i've already finished my BoB and it's working fine, but i also want to know, what i have done

what is this USB filtering for?
and what is filtert?

i looked into the USB 1.1 Spec and there are similar schematics (figure 7-8)
but i don't know, what they are for

 

[Squidge]

art said he couldn't get anything to work without the filtering because the signal was too noisy.

That's all I know...

 

[donny662]

It is a "low-pass" filter, which means that it allows low-frequency signals to go to the output and blocks high-frequency signals.

If you know a little about circuits, you probably know that a capacitor in a DC circuit will act like an open circuit. In other words, it blocks low-frequency voltages (DC can be thought of as a 0 Hz signal). But, to high-frequency signals, the capacitor acts like a short.

In the USB filter circuit, noise from ambiant sources will generally be relatively high-frequency, so they will be dissipated to ground through the capacitor. On the other hand, the low-frequency pulses of the USB signal will see the capacitor as an open circuit and will be read by the GP2X.

 

[jokeman]

hmm... ok... this make things clear
thanks

so has this something to do with the "USB termination" scope picture in the USB Host Wiki?

and is this low-pass filter the same thing described in the USB 1.1 Spec chapter "7.1.2 Data Signal Rise and Fall"?
or is this something different?