EE版 - A question on USB physical layer |
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M**********e
发帖数: 44 | 1 Hi,
I am wondering why USB 2.0 can achieve 480bps rate.
I had a look on USB 2.0 spec, there isn't any modulation scheme. There is
only scrambling (every contineous "1", insert a "0" ) and NRZI coding. Does
it mean the 480Mbps signal is transmitted directly (i.e. 1 bit occupies 2.08
ns, and this signal can be sampled by local 480MHz clock directly )?
I know there are several other methods to improve speed in USB. Such as
transmitting signal by differential, and the cable is shielded, short
distance. But all of these methods are simple. If these methods are applied
on UART, can UART achieve 480Mbps?
For USB 3.0, I did't find the modulation scheme for 4.8Gbps data rate either
. Based on Spec, the TX procedure is: scrambler ==> 8b/10b encoding ==>
parallel to serial ==> transmitter differential driver ==> the differential
cable.
Is there any one can explain how the USB 2.0 and USB3.0 can achieve these
high speed without modulation?
(I saw there is SSC modulation in USB 3.0 Spec, but I don't know how it
works.)
Cheers, | M**********e
发帖数: 44 | 2 Several mistakes in my previous post:
"480bps" should be: "480Mbps";
"every contineous "1", insert a "0"" should be: every SIX contineous "1",
insert a "0" | k****y
发帖数: 781 | 3 Differential transmission line
Special connector
Special cable |
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