Technology Transfer

Signal Integrity

Titelbild.jpgWith further development of system interconnect technologies from parallel bus systems to serial methods, transmitting speeds on the electrical level increased rapidly beyond the gigahertz threshold. Despite differential transmission and current source transmitters, the traces on FR4 base materials via connectors, solder points or even cable lines resulted in significant distortions and attenuation, in particular where extended transmission distances had to be bridged.

So-called signal integrity products, i.e. signal conditioners, are designed to remedy this problem, as they are able to filter the original signals from background noise. IDT offers these amazing SIP components for all established transmission standards.

Retimers and Repeaters

I1.jpgOn their path across the circuit board, high speed signals of current serial standards are easily affected by damping, reflection and distortion. This becomes apparent when looking at the so-called “eye diagram”, which provides a fairly clear measure for the quality of such signals. As shown in fig. 1, the “eye” of a signal can all but close due to these effects, which means technical measures are required for reconditioning.

I4EN.jpgOne way of achieving this is to optimize the transmission path, i.e. by coherently implementing microstrip technology on circuit boards and minimizing the number of connectors. However, this strategy is very difficult to consistently apply in practice, which means that electronic signal re­conditioning often remains the only realistic alter­native.

The semiconductor manufacturer IDT has developed a range of repeater & retimer components for this purpose, offering solutions for the most common transmission standards.

I3.jpgRepeaters and retimers differ in their complexity and the resulting conditioning options: while repeaters generally consist of an input equalizer and an output booster, thus reducing random jitter, retimers dispose of resources for interpreting signals and are thus able to eliminate deterministic jitter as well.

Retimers are therefore protocol specific and also add noticeable latency to the transmission range, in the case of IDT’s PCIe retimers, for instance, in the range of 30ns.

IDT Repeaters

Repeater components of the IDT SIP portfolio are available for 5 Gbps PCI Express® (PCIe) Gen2, USB 3.0, 6 Gbps SAS/SATA; 6.25Gbps Serial RapidIO® 2.1 and other standards for computing, storage & communication applications.

I2_0.jpgSIP components comprise powerful receiver equa­lizers and transmit-de-emphasis amplifiers as well as diagnostic functions, allowing simple designs and fast development cycles.

They are able to drive long circuit paths on PCBs (e.g. on backplanes) and to secure cable lines to external devices, guaranteeing optimal system performance. They are also able to recognize signal interruptions (LOS - loss of signal) and provide individual loopback diagnostics for each channel and 2:1 multiplexing & de-multiplexing functions.

I5.jpgThese components are available for 2, 4 or 8 differential channels and can be configured via I2C,  control pins or EEPROMs. They also offer power saving operation modes in order to reduce power consumption.

IDT Retimers

IDT retimers were developed with the goal to improve signal integrity while at the same time doubling the transmission range. They minimize random & deterministic jitter of input signals and are thus perfectly suited for blade servers, enter­prise storage or communication systems which require longer cable lines or backplane traces.

I10.jpgThe most recent additions to the extensive product range are the 89HT0808P and 89HT0816P retimers. They are the first of their kind to fully support the new PCIe automatic link equalization process, simplifying system design and improving reliability of PCIe compliant adapter cards or host bus adapters. The 8 channel 89HT0808P retimer and the 16 channel 89HT0816P retimer are able to provide data communication rates of 8 Gbps per channel across twice the range as standard PCIe 3.0 devices and via typical system back­planes, at the same time improving sys­tem perfor­mance and reliability and reducing ma­terial costs, since the overall design complexity is reduced.

I8EN.jpgBoth retimers comprise a very powerful analogue frontend and are linked to a continuous time linear equalizer (CTLE), a five-level decision feedback equalizer (DFE) and a clock & data recovery unit.

The very sensitive input offers dynamic optimization options and is able to restore low quality signals and to eliminate randomized and deterministic jitter, exceeding the thresholds of the PCIe 3.0 specification.

I6.jpgIn order to enable rapid in-system testing, an extensive suite of diagnostic loopback characteristics was integrated in IDT’s retimer monitoring functions. An evaluation board is available for IDT’s 89HT0808P and 89HT0816P retimers, to­gether with a software utility with a graphic user interface.

I7.jpgIDT’s extensive signal integrity product range comprises so­lutions for industry stan­dard interfaces such as PCIe Gen 2 and Gen 3, USB 3, XAUI, SATA, SAS and Serial RapidIO® and is available in a variety of channel numbers and casing sizes.