Overcome signal attenuation, noise and jitter interference challenges in USB 3.0 system design
The highly anticipated USB 3.0 is now seeing widespread adoption across notebook, docking, PC, server and upcoming tablet, handheld and portable media devices. USB 3.0 delivers an unprecedented bandwidth, 10x that of USB 2.0, and supports full-duplex communication, or the ability to send and receive data simultaneously. It also improves Quality of Service (QoS) and overall bus power consumption thanks to advanced data error checking coupled with smart power savings from USB 3.0 link power management. More importantly, USB 3.0 is 100% backward compatible to USB 2.0 devices.
However, with all of its added benefits and features, the high-speed differential signal of USB 3.0 also introduces uncontrollable noise and jitter due to signal attenuation, causing USB 3.0 signal voltage swing to overshoot or undershoot the optimal eye opening. This distorts the quality of USB 3.0 signal eye during high-speed signal switching. USB 3.0 signal quality is gravely impacted when random or deterministic noise degrades the signal quality with crosstalk during transmitting and receiving of packet transfers between USB 3.0 hosts and peripheral devices.
To offset the signal quality degradation, a broad array of USB 3.0 redrivers are now available for maintaining a high level of signal integrity during Tx and Rx of USB 3.0 high-speed signals. A USB 3.0 ReDriver enables USB 3.0 system designers to overcome USB 3.0 signal layout constraints, routing high-speed signals through multi-layer PCBs, extensive VIAs and connectors, or across extensive cable lengths. It also allows designers to achieve an overall cost saving in PCB and trace materials with standard micro-strip or strip-line trace on FR4 PCB materials. The programmable emphasis and equalization settings of the USB 3.0 redriver devices compensate for the incurred Insertion loss of USB 3.0 signal while maintaining optimal opening of USB 3.0 signal eye with a sizable margin to spare.
The eye pattern scopes below show the captured Insertion loss at 6? and 48? USB 3.0 signal trace. Using a Pericom USB 3.0 ReDriver in between USB 3.0 host and devices can effectively neutralize the signal insertion loss due to USB 3.0 signal attenuation and noise occurrence.
Faced with complex PCB layout challenges, USB 3.0 system designers experience significant benefits from redrivers in transmitting and receiving reliable USB 3.0 signals with adequate output swing, effective jitter removal, flexible transmit emphasis, and receiver equalization. System designers don╒t always have full control in how USB 3.0 end-point devices such as external HDDs, digital cameras, handhelds, or tablets, are connected between host and end-point devices. When the signal travels thru extensive traces, multi-layer vias, and connectors before exiting to USB 3.0 ports or cables, the transmit eye of USB 3.0 host or device may show significant degradation from high occurrences of noise, jitter, signal attenuation or insertion loss. As result, the USB 3.0 Link may likely suffer significant bit error rate (BER) and link recovery issues during USB 3.0 cable plug and unplug processes. Faced with USB 3.0 signal degradation, USB 3.0 system designers should consider taking careful measures to ensure strong SI during USB 3.0 Tx and Rx signal transmission. USB 3.0 ReDriver devices offer just this sort of control: the USB 3.0 eye is fully optimized to maintain consistent level of SI when routing extended USB3.0 traces across connectors and vias.
System designers are given greater flexibility to design and route High-Speed USB 3.0 traces in a constrained layout environment while maintaining consistent level of signal quality. USB 3.0 redriver devices feature programmable equalization (EQ) and de-emphasis (DE) settings to optimize signal Tx and Rx performance over a variety of physical mediums.
Redrivers keep signals clear from host to end point.
Redrivers provide adjustable EQ and de-emphasis (DE) settings to optimize USB 3.0 signal Tx and Rx performance over a variety of physical signal mediums on PCB or across cable.
Adjustable DE and EQ settings of Pericom USB3.0 ReDriver:
Pre-configured to specific DE and EQ settings, Pericom USB 3.0 ReDriver effectively minimizes the risk of Inter-symbol Interference (ISI) and maintains optimal eye opening during high-speed signal transmission. To identify best EQ and DE settings on a real-time environment, Pericom offers a USB 3.0 ReDriver Reference Design Kit to conduct real-time inter-op testing against Intel, NEC and Fresco USB 3.0 host controllers. These kits are useful in real-time USB 3.0 system inter-op testing and allow system designers to verify and fine-tune DE and EQ settings with respect to the USB3.0 trace layout architecture.
The following reference USB 3.0 applications and platforms that would greatly benefit from a USB 3.0 ReDriver for maintaining consistent level of SI standard.
Notebook / Docking:
Peripheral Interconnect to USB3.0 Devices:
Front Panel USB3.0 Ports of Server/Workstation MBs
About the Author
Joseph Juan is the Product Marketing Manager, Connect Products (PCIe3.0, USB3.0 I/O Interconnect Products), Pericom Semiconductor Corp., responsible for general product and feature definition, whole product launch, and merchandising of USB 3.0 and PCIe3.0 I/O interface products. He holds a BS in Computer Science & Math and MS in Computer Engineering, University of British Columbia. He can be reached at jjuan@pericom.com.
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