Diodes Tackles Signal Integrity with Latest ReDrivers for HDMI to PCIe 4.0
Recently, Diodes Inc. has pushed out new ReDriver technologies, which aim to improve signal integrity. What are these new releases and how do ReDrivers stack up to ReTimers?
Signal margin is a critical performance benchmark for stable communication channels. Electrical losses, including resistive drops, intersymbol interference (ISI), and crosstalk, reduce the margin. This reduction is where ReDrivers come into play.
The main method for determining the viability of a communication channel is through an eye diagram and a mask, where a “closed” eye indicates a channel is out of spec with a given standard, USB Type-C. With this in mind, ReDrivers can amplify an in-channel signal, reduce bit error rates (BER), and ultimately bring the system into spec.
Diodes Incorporated builds upon its existing product line, bringing new ReDrivers into its portfolio of integrated circuits. These new ReDrivers are said to offer speeds up to 20 Gbps (device dependent).
The new 8-channel ReDriver for UPI2.0/PCIe 4.0. Image used courtesy of Diodes Incorporated
This article will overview these three announcements from Diodes Inc:
- Tunable Linear ReDrivers
- 8-Channel ReDriver with Internal Coupling Capacitors
- 1.8 V 10 Gbps USB Type-C & DisplayPort Linear ReDrivers
However, before breaking down the electrical specifications and applications for these new components, let's go over a brief redux of the ReDriver and its competition, the ReTimer.
What Is A ReDriver?
When it comes to ReDrivers, there are two technologies associated with the concept of an electrical repeater, both of which improve the signal integrity (SI) of a signal in transit from source to destination. ReDrivers, as opposed to ReTimers, are less complex and operate through amplification.
An example of a block diagram for a ReDriver circuit. Image used courtesy of Maxim Integrated
Tuning a linear ReDriver involves selecting the appropriate equalization and flat gain needed to ensure the “eye” meets the required specification, all while avoiding the output compression of the driver.
Equalization allows for analog amplification at all frequencies. Image used courtesy of ON Semiconductor
The process of equalization ensures a closely matched amplitude between low frequency and high-frequency signals by varying the gain concerning frequency.
Amplification is one potential method for improving signal integrity, but there is another technology as well, ReTimers.
Where Do ReTimers Fit In?
The second technology, ReTimers, actually terminates the signal and retransmits a clean copy.
Below, a signal integrity improvement with a ReDriver can be seen, then a clean restoration of the original signal with a ReTimer. So, which technology is “better”?
An eye is attenuated by a channel (left), after a ReDriver (middle), and after a ReTimer (right). Image used courtesy of PCI-SIG
At first glance, ReTimers appear to be the more appropriate technology for optimal signal integrity, especially for the newest specification of PCI Express.
However, as seen through Diodes Inc.'s continued R&D, ReDrivers can play an important role in other interconnect channels, including HDMI, DisplayPort, and USB.
Diodes Incorporated Goes The Distance with ReDrivers
Engineers can get a sense of where a ReDriver is appropriate by looking at the selection of devices recently released by Diodes Incorporated.
ReDrivers for Applications in Workstation Productivity
Application example of the 1:2 demux ReDriver. Screenshot used courtesy of Diodes Incorporated
These chips are intended for mobile workstations, docking, and KVM (keyboard, video, mouse) and display monitors. The ReDrivers utilize continuous-time linear equalization (CTLE) to optimize the DisplayPort/HDMI channels. The non-blocking design allows for pre-shoot and de-emphasis from transmitter to receiver with decision feedback equalization (DFE).
An adjustable pin-strap controls their control and settings, and the equalization is variable [with 8-levels]. Additionally, there are four settings for flat gain output.
ReDrivers For USB Type-C, PCIe 4.0 & UPI 2.0
ReDrivers for Intel’s Ultra Path Interconnect. Image used courtesy of Diodes Incorporated
The PI3UPI1608 has eight differential channels and integrated coupling capacitors and is intended to be used in applications such as CPU-to-CPU interconnect.
Finally, wrapping up the interconnect ReDriver technology roundup is a series of 1.8 V components designed for 10 Gbps throughput for USB-C and DisplayPort. The PI2DPX1066 (and PI2DPX1217) support multiple modes, which are configurable via an I2C interface.
The ReDrivers from Diodes Incorporated allows for flexible tuning of extended interconnects. The user can adjust the gain and equalization for a specific application using I2C or pin-strap, thereby improving channel signal integrity.
Have you used a ReDriver or a ReTimer in your designs? What design considerations did you have to contend with? Let us know in the comments below.