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  • Signal Conditioners for Reliable and Robust Industrial High Speed Links

    • SNLA388 June   2021 DS160PR410

       

  • CONTENTS
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  • Signal Conditioners for Reliable and Robust Industrial High Speed Links
  1.   Trademarks
  2. 1Introduction
  3. 2Signal Conditioners
    1. 2.1 USB Interface
    2. 2.2 HDMI and DisplayPort Interface
    3. 2.3 PCIe Interface
    4. 2.4 Ethernet Interface
  4. 3Summary
  5. 4References
  6. IMPORTANT NOTICE
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TECHNICAL WHITE PAPER

Signal Conditioners for Reliable and Robust Industrial High Speed Links

Trademarks

All trademarks are the property of their respective owners.

1 Introduction

Industrial automation has become much more sophisticated with integrated image processing, video analytics and sensor networks. High bandwidth data communication has imposed significant challenges on preserving signal integrity to avoid data loss across high speed industrial communication links. Ensuring reliable and low latency communication from one machine to another is critical to achieve the precision of the industrial operation.

Various high-speed communication protocols such as USB, PCIe, HDMI, Display Port and Ethernet are being used in industrial interface links. These interfaces have been increased to multi-gigabit speed level to facilitate the increasing bandwidth needs of the data processing. The high-speed signals face significant challenges to maintain signal integrity (SI) when transmitting over long printed circuit board (PCB) traces or cables. To combat signal integrity challenges and provide a reliable and error free link signal conditioning components such as redrivers, retimers or active multiplexers are often required. The signal conditioners help compensate for and overcome signal impairments and losses of a high speed link. A signal conditioning element in a link can help pass standard compliance and provide margin in a cost effective way.

2 Signal Conditioners

High speed data and video links in industrial application must be reliable and robust for efficient operation with seamless and consistent data throughput. The links often suffer from too much loss, low margin, susceptibility to environmental condition such as supply voltage and temperature variation, internal and external noise. High speed signal conditioners when used in a data or video link improve overall signal integrity by eliminating loss and jitter.

A signal conditioning element such as a redriver or retimer in a high speed industrial link provides equalization to eliminate inter symbol interference (ISI) effectively, increasing overall link reach and SI margin. Additionally a retimer component has clock and data recovery circuits (CDR) that can eliminate SI impairments such as random jitter, cross-talk and reflection. For addional differences between a redriver and retimer see TI Precision lab video. Figure 2-1 shows what redrivers, retimers and active muxs can provide in a link.

Redriver Retimer Active Mux
GUID-20210517-CA0I-LV6R-3638-NKKKXL5Q0GWB-low.png GUID-20210517-CA0I-X07X-P7BN-4MPSLNG8XLT6-low.png GUID-20210517-CA0I-0RXP-Q7DC-NNGFQ8JQTSS5-low.png
  • Cost effective signal conditioner
  • Solves signal intergrity degradation casued by ISI
  • Compensates for channel loss
  • Best performing signal conditioner
  • Eliminates input jitter
  • Compensate for both channel loss and jitter
  • Facilitates signal routing options while compensating for channel loss
  • Active mux can be with integrated redriver or retimer

Figure 2-1 Functions of Redriver, Retimer, and Muxes

Industrial PCs likely use the most diverse set of high speed interface links in industrial applications. These systems can be considered as the brain of industrial automation. They process and analyze vast amount of data to implement critical functions, interface with human operators, and display the results in to industrial monitors. Mutliple CPUs are often connected together to form a powerful compute cluster in an industrial PC. Multiple systems are also connected together over a back plane or network to implement a complex function. Figure 2-2 shows the most commonly used interfaces inside a industrial PC system. In this article, industrial PC system is used an example to discuss different high speed interfaces. However this can be extended into other relevant industrial applications also.

GUID-20210518-CA0I-Z3C5-HHS7-DZJGLQDN6HHX-low.gif Figure 2-2 High speed interfaces inside an industrial PC system

User interfaces include USB, Display Port, HDMI and Ethernet which are external interfaces that provide access for operators and allow connectivity to additional functional end equipment such as display monitors, Ethernet networks, USB disks etc. Board to board interfaces illustrate system connectivity between different boards through a back plane. LVDS are typically used for lower speed data, while PCIe and Ethernet are used for high bandwidth data connections in back plane application.

A user interface port typically needs to meet industry compliance so that it can inter-operate and communicate with any device connecting to it. Compliance tests require a signal to meet certain eye-opening margin and jitter performance criteria which can be challenging since signal degradation can occur for high speed data after traversing along PCB traces and connectors. The same signal integrity challenge can also be imposed for signals traveling through a back plane for board to board communications. Long PCB traces and connectors can degrade signal quality causing compliance issues, downgrade of data throughput and even resulting in communication failure. By adding signal conditioners, such as redrivers, retimers and active muxes, in a CPU system, the designer can ensure compliance at the connectors per standard specifications, while also improving the signal quality at the receiver side to enable a more robust communication system.

Now let’s look at more detailed examples on how to use signal conditioners to solve signal impairment problems for USB, PCIe, Display Port, HDMI, and Ethernet interfaces.

2.1 USB Interface

USB is a ubiquitous interface that is found in almost all electronic gadgets. To provide easy user interface options for operators in industrial applications, USB is widely used. The interface is also used for expanding the functionality of the equipment through connecting external devices into the system. Depending on the data bandwidth needs of the intended function, either USB2, USB3 or USB Type-C can be used for industrial communications.

USB2 interface has widespread use for user interface and is typically used for management or control interface in industrial applications. The USB2 can support up to 480Mbps speed. Even though when compared with other Gigabit interfaces, USB2 is considered a relatively low speed interface, USB2 has a very stringent compliance standard that is difficult to meet without violating the eye mask at the connector. Adding a redriver to a USB2 data path design can easily solve these challenges.

Figure 2-3 demonstrates the signal integrity of a USB2 data path both with and without a USB2 redriver. Without a redriver, the USB2 signal can only pass compliance with a 1-meter cable. Adding a USB2 redriver such as TUSB216 to the system, it is able to pass compliance with up to 5-meters of cable in this specific link example.

GUID-20210518-CA0I-FRPW-0P6Z-DLXNXSPRKSLK-low.gif Figure 2-3 Using USB2 Redriver to Pass Compliance

USB3 and USB Type-C can support 5Gbps, 10Gbps and even 20Gbps data rates. These high speed interfaces are typically used when video or other high bandwidth data need to be sent across USB interface. In an industrial PC system, the distance between the USB host and the USB connector is fixed, the channel loss profile can be predetermined, and a redriver with a fixed equalization (FEQ) can work to compensate for the egress data path loss of the link. However, on the host ingress path, since the signal loss from the connector is dependent on what device and cable the remote side is connected to, it is beneficial to have adaptive equalization (AEQ) to compensate variety of channel loss profile as illustrated in Figure 2-4. Adaptive EQ offers the capability to adjust a receiver’s EQ setting based on the quality of the incoming signal. For example, if a USB device is plugged directly into a USB receptacle without a cable, the redriver’s AEQ algorithm will select a lower EQ setting than it would if the USB device was plugged into receptacle through a cable. Adaptive EQ enables the redriver to be more intelligent and provide best signal quality at its output while saving design effort on device tuning.

GUID-20210518-CA0I-Q2JJ-DHFB-LCLWLFCJKFSB-low.gif Figure 2-4 USB3 and Type-C Redriver with Adaptive EQ

 

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