What is Chord Signaling?

2019-12-12  |  4 min read 

Driven by 5G technology, data-intensive applications such as virtual reality (VR), artificial intelligence (AI), machine learning (ML), Internet of Things (IoT), and the roll-out of autonomous vehicles will create a surge in computing, storage, and performance demands on data centers. As a result, data centers need to evolve from 100 gigabit Ethernet (100GE) data speeds to 400GE and beyond. 400GE speeds require moving from non-return-to-zero (NRZ) to new modulation technologies such as four-level pulse amplitude modulation (PAM4), or the use of ChordTM signaling, patented by Kandou.

Kandou is an interface technology company that specializes in the invention, design, license, and implementation of industry-leading chip-to-chip link solutions. According to Kandou, this new category of signaling can provide two to four times the bandwidth of conventional serializer/deserializer (SerDes) technologies at half or less the total power consumption. New system architectures for products ranging from mobile devices to hyperscale data centers, can benefit from the use of Chord signaling.

The Chord signaling architecture is a generalization of differential signaling. While differential signaling delivers one bit on two correlated wires, Chord signaling delivers n bits on n+1 correlated wires. An associated “code” is the combination of the signaling on the wires and the comparators used to identify the bits.

Chord signaling types include, amongst many others:

  • ENRZ: Ensemble NRZ transmits three bits on four correlated wires
  • CNRZ-5: Chord NRZ transmits five bits on six correlated wires

ENRZ and CNRZ-5 enable significant power savings depending on the application. For example, with CNRZ-5 enabled Ultra Short Reach (USR) SerDes, it is possible to save from three to ten times the power in some applications versus other traditional signaling methods.

As data rates increase, channel loss between the transmitter and the receiver becomes more important, as well as minimizing power consumption. Printed circuit board traces, connectors, and cables all contribute to loss in the signal path. This channel loss results in intersymbol interference (ISI) that depends on the channel material and dimensions, the data rate, and the bit pattern. High-speed digital receivers tolerate a certain amount of total jitter, which typically includes some ISI caused by channel loss. According to Kandou, its SerDes technology provides high-system bandwidth, much lower vulnerability to ISI and to the reflection form of ISI than PAM4, and low power consumption via a much lower need for equalization through the use of Chord signaling.

Chord signaling provides an alternative to PAM4 modulation to reach the hundreds of gigabits per second to terabits per second speeds required to support these new applications. Chord signaling is a multi-wire signaling approach that generalizes differential signaling. According to Kandou, Chord signaling delivers faster, denser, simpler, more robust, and lower power interconnects compared to PAM4 and NRZ technologies.

Read the case study ‘Chord Signaling for High-Speed Chip-to-Chip Applications’ to learn more Kandou’s Chord signaling technology. Find out how Keysight’s first-to-market solutions enabled Kandou to validate their Chord signaling algorithms, and how Kandou’s customers use Chord signaling to validate their 400GE and beyond designs.