TE zQSFP+ (QSFP28) Interconnects: Get the Speed You Need From Q to Z

Get the Speed You Need From Q to Z As dependence on mobile devices increases, datacenters have become a key focus of the tech industry with emphasis on improved accessibility to data with reduced latency. This dependence created a unique challenge for engineers as larger amounts of data need to be transferred at faster rates.

In response to the significant market demand for technology in data center applications, TE Connectivity (TE) offers a comprehensive zQSFP+ interconnect product portfolio providing customers with one of the widest product selections in the market. 

Previous interconnect solutions supported speeds of 10Gbps, but as data transfer requirements increase, these solutions will no longer support the elevated demands. Providing four channels with data rates up to 28Gbps, the zQSFP+ interconnect supports 100Gbps Ethernet, 128G Fiber Channel, 50/100G consortium and 100 Gbps InfiniBand Enhanced Data Rate (EDR) requirements for high speed designs. 

TE’s new 28Gbps solution is backward compatible with existing QSFP/QSFP+ 10Gbps cables and transceivers, increasing design flexibility and enabling a seamless migration path while meeting industry interconnect standards.  For systems where increased data rates are not required, but an upgrade in interconnect hardware is necessary for improved margin, the new zQSFP+ solution enables an improved loss budget for optics and copper cables designed for 10Gbps. This behind and through bezel caged solution meets different configuration types with various heat sink and light pipe options. 

TE’s zQSFP+ interconnects help optical modules and cable assemblies increase data transfer rates by 2.5 times over existing solutions. Since increased data rates can make EMI (electromagnetic interference) protection more challenging due to increased frequency generated by short rise times, the zQSFP+ interconnect product portfolio is designed to enable improved EMI protection through 28 Gbps, reducing the possibility of FCC non-compliance due to the interconnect. The improved thermal performance can be attributed to the cage design which provides an improved heat sink, yielding better thermal performance and heat dissipation during peak demands of operation. 

The performance of high-speed interconnects are primarily characterized by the return loss and insertion loss of the interconnect as well as differential to common mode conversion. The return loss is the magnitude of the reflection coefficient, expressed in terms of dB vs. frequency. The return loss explains how well a reference impedance matches a particular system impedance. A low value of return loss is desirable for optimal performance, as this implies a well-matched system. For high-speed differential interconnects, 100 ohms and 85 ohms are common differential impedance targets. Figure 1 below, plots the differential return loss of the connector. Most interconnect or signal integrity engineers recognize the difficulty associated with getting connector geometries to provide uniform impedance when using a connector in a high-speed interconnect. Due to the difficult geometries often encountered, the connector can be a primary contributor to impedance discontinuities in the interconnect.

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Figure 1.  Differential Return Loss for SMT connector

Figure 1. demonstrates the connector has quite impressive -- <= -10dB -- differential return loss results up to 14 GHz, which is just beyond the Nyquist frequency for 25Gbps. It is important to note that much of the frequency content of a Pseudo Random Bit Sequence (PRBS) pattern will have a sinx/x spectrum, with the lion share of its energy found at 0.5/rise time of the signal. Referencing the return loss plot above, it can be determined that the majority of the energy generated by a 25Gbps signal will not have most of its energy reflected, due to the connector.  Given that most of the energy contained in the signal will be at 12.5 GHz and below, some of the 3rd and higher odd harmonics will be at higher frequencies, but with less and less energy content. 

An additional challenge of working with high-speed interconnects is the amount of loss incurred in the channel. The insertion loss reveals how much energy is transmitted through the interconnect compared to how much energy was injected into the interconnect over a broad band of frequencies.

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Figure 2 illustrates the amount of loss versus frequency the SMT connector contributes to the interconnect. There is less than 1.3dB of loss, clear out to 14 GHz. The return loss (Fig. 1) and insertion loss (Fig.2) data indicate the connector design for this interconnect performs well.  Historically, connectors are poor performers when used with high-speed interconnects. This SMT solution demonstrates these connectors have excellent performance for the data rates and rise times of interest.

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Figure 3 illustrates the Power Sum FEN performance of the TE zQSFP SMT connector. This connector exhibits excellent FEN performance with less than -40dB of noise up to & exceeding the 14 GHz Nyquist frequency. Also note that no significant resonant structures are seen in the frequency band of interest.

TE’s comprehensive zQSFP+ interconnect portfolio, provides a scalable interface to easily move from 10Gbps to 28Gbps data rates, giving engineers the design flexibility to meet the growing demands expected of datacenters. 

TE Connectivity, TE and TE connectivity (logo) are trademarks of the TE Connectivity Ltd. family of companies. 
zQSFP+ is part of the ZXP® family of connectors and uses ZXP technology. ZXP is a trademark of Molex, LLC.

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