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ramu
07-20-2008, 12:29 AM
hey ppl

i have a USB web cam. so it it has data+ and data- connections for USB communication

when i tried to give the data+ connection through a buffer (opamp- voltage follower), the computer says "device error". without any buffer, its working fine.

the thing is when i connect through the voltage follower, the voltage output at Data+ terminal of the webcam gets altered !!

why is it so ? voltage follower should suppose to give the same voltage right ??[/img]

avinash_g
07-20-2008, 08:47 AM
Hi
usb is very fast simple op-amps can't keep up.

Ulhas
07-20-2008, 01:16 PM
Depending upon device speed either D+,D- line gets pull up by pheripheral. This is the way by which Host (PC) understand that some USB is connected to it.

Check eventhough you are using very high speed opamp that you are not playing with your pc as what i wrote above

ramu
07-20-2008, 03:23 PM
so what exactly i should do to work with my USB camera signal outputs ?

see, the thing which i wanted to do is to modulate the camera data, then demodulate and then give the demodulated signal to the usb of a computer .. but when i connect the camera output to a load (buffer), the signal gets altered ... so how should i suppose to proceed ?

MohitM
07-20-2008, 08:18 PM
the thing which i wanted to do is to modulate the camera data, then demodulate and then give the demodulated signal to the usb of a computer
Huh?!

ramu
07-20-2008, 09:13 PM
what ?

docel
07-21-2008, 06:02 AM
what ?

........is exactly WHAT we would all like to know!

Please be specific about your intent or idea.

Before that, a little reading about USB, signals, modulations etc., would be proper and necessary.

debu
07-21-2008, 03:29 PM
@ramu: Three points here.

1) Your buffer has to be able to work with 96 MHz signals. The USB specifications say that high speed upstream devices create SYNC packets that fast. Also try to ensure that the propogation delay in the buffer is >1ms.
(See section 5.12.2 of the USB specs Rev2.0).

2) Your buffer should work with 3.3v signals. The USB Specifications 2.0 says that the signals from the USB peripheral to the host must always be 3.3v. (See section 7.1, page 119/120 of the USB specs Rev 2.0).

3) Make sure the buffer is bi-directional. Both D+ and D- are bi-directional.

Apart from these three points, there should be no problem if a buffer is amplifying your signal between a host and a peripheral.

Regards,

Debu :)

Ulhas
07-21-2008, 08:59 PM
hey ppl

i have a USB web cam. so it it has data+ and data- connections for USB communication

when i tried to give the data+ connection through a buffer (opamp- voltage follower), the computer says "device error". without any buffer, its working fine.

the thing is when i connect through the voltage follower, the voltage output at Data+ terminal of the webcam gets altered !!

why is it so ? voltage follower should suppose to give the same voltage right ??[/img]

Why you need buffer???????

ramu
07-29-2008, 06:20 PM
i am actually trying to modulate the digital data output of my usb camera, send it wirelessly to another point, demodulate the signal and the feed it to the computer ..

debu
07-30-2008, 10:46 AM
@ramu: What kind of wireless module are you using?

Remember the three points I mentioned earlier? These apply for your wireless module too.

The signals should be 3.3v and it should support bi-directional differential signals (this means that Rx, Tx modules wont work. Both lines need to be differential AND bi-directional), and for a high speed USB device, it should support 480MBps throughput.

If you were just using a buffer, to amplify your signal, a 100LVEL11 or equivalent would work fine.

Regards,

Debu :)

ramu
07-30-2008, 05:10 PM
hey debu, i read the 100LVEL11 datasheet .. but couldn't clearly understand about that .. what exactly is it ?