PORTS Forum

Ports and Interfaces => USB => Topic started by: Chris on April 28, 2011, 08:18:06 am

Title: How to detect LFPS signals in USB3.0phy。
Post by: Chris on April 28, 2011, 08:18:06 am

hi,
I'm confused of which part should be responsible for LFPS's send in PHY, digital circuit or analogous circuit ?
The LFPS signals is the low frequency periodic signal.which have a period of 20ns--120ns,and it's duty cycle is 40%-50%.LFPS signals is used in U1,U2,U3 and loopback.
Thanks!

Regards
!

Title: Re: How to detect LFPS signals in USB3.0phy。
Post by: Jan Axelson on April 28, 2011, 09:45:32 am

Why do you ask? Are you designing USB 3.0 hardware?

Jan

Title: Re: How to detect LFPS signals in USB3.0phy。
Post by: Chris on April 28, 2011, 09:06:58 pm

Quote from: Jan Axelson on April 28, 2011, 09:45:32 am

Why do you ask? Are you designing USB 3.0 hardware?

Jan

Actually,I'm not a hardware designer.But I'm studying USB3.0 lately.There's so many differents with USB2.0. And i want make clear the new USB SPEC's change.For example,there is no LFPS in USB2.0,but it used in state change in 3.0.So,what's the sense of make use of LFPS.
As we know,low power is importat to the PHY,if used analogous circuits ,it can used low power in detect LFPS.But it needed a new pll which worked on the central frequency of 10-50MHZ. I think it is impossible. when used digital circuits to detect LFPS,it must use high frequency to detect the low frequency ,to detect its tperiod of 20ns--100ns and duty cycle's 40%--60%, so it cant holding a low power state in U1-U3. I was so confued --

Title: Re: How to detect LFPS signals in USB3.0phy。
Post by: Jan Axelson on April 29, 2011, 09:59:21 am

The low-level USB 3.0 protocols are a whole different animal, that's for sure. My notes say that the interface designers selected the LFPS signaling method because it was easy to generate and uses little power.

Jan

Title: Re: How to detect LFPS signals in USB3.0phy。
Post by: Chris on May 03, 2011, 07:04:18 am

Asyou say:LFPS signaling method because it was easy to generate and uses little powerd. How does LFPS signals can save power? If used analogous circuit,it may used a ring oscillator,i think it's complex. And if used digital circuit,it may waste much power.That what am i confused.

Title: Re: How to detect LFPS signals in USB3.0phy。
Post by: Jan Axelson on May 03, 2011, 04:04:07 pm

This isn't an answer to your question, but this article talks a little about USB 3.0 power and other issues:

http://www.edn.com/article/458585-USB_3_0_A_simple_idea_full_of_challenges.php

Jan

Title: Re: How to detect LFPS signals in USB3.0phy。
Post by: Chris on May 03, 2011, 08:36:46 pm

Thanks Jan,God Bless You!!
Regads!
Chris.