Entities such as telecommunications enterprises, online retailers, and social media generate huge amounts of data, and most of these entities use cloud computing to process and store the data in data centers having communication speeds of 200 Gbps or higher. Although advanced communication equipment for 200 GbE can produce a greater data rate with smaller size and lower cost and power, the size reduction can cause reliability issues in data centers, as electromagnetic interference (EMI) can become a significant problem in these highly dense facilities.

Optical transceivers supporting four-level pulse amplitude modulation (PAM-4) signaling are widely used in high-speed communication links in data centers, and while it is true that the optical communication channel is immune to EM radiati...[ Read more ]

Entities such as telecommunications enterprises, online retailers, and social media generate huge amounts of data, and most of these entities use cloud computing to process and store the data in data centers having communication speeds of 200 Gbps or higher. Although advanced communication equipment for 200 GbE can produce a greater data rate with smaller size and lower cost and power, the size reduction can cause reliability issues in data centers, as electromagnetic interference (EMI) can become a significant problem in these highly dense facilities.

Optical transceivers supporting four-level pulse amplitude modulation (PAM-4) signaling are widely used in high-speed communication links in data centers, and while it is true that the optical communication channel is immune to EM radiation, the transmitter in the transceiver package consists of electronic components which can generate and radiate EMI. Additionally, to compensate for the bandwidth (BW) limitation of the laser and channel, different types of equalization are utilized. It is intuitive to believe that a fractional-spaced asymmetric feed forward equalizer (FSA-FFE) circuit could further increase the EM emission from the transmitters. Also, advanced technology nodes like 14 nm FinFETs are extensively used for implementation of high-speed communication systems, and the technology scaling can significantly affect the EM emission from the transmitter. However, a systematic study of how asymmetric equalization and technology scaling affect the EM emission is still lacking. To fill this gap, this thesis analyzes the effect of technology scaling and the sources of EMI-related CM noise in PAM-4 transmitters, and then proposes an on-chip active technique to mitigate EMI-related CM noise.

In the first part of the thesis, the effects of the PAM-4 current-mode logic (CML) driver, different FFE configurations and technology scaling on EMI-related CM noise are analyzed mathematically, and then further evaluated by behavioral and transistor-level simulations in 40 nm CMOS and 14 nm FinFET technologies. It is observed that the CM current in differential circuits generates CM noise which radiates in the environment and causes EMI with electronic devices in proximity. This noise is generated due to the rising and falling time mismatch created by the driver circuit and asymmetric equalization. It is demonstrated that the intrinsic impedance variations of the CML driver circuit, amplitude of the equalization current, and offset in the FSA-FFE circuit are the main sources of EMI-related CM noise in transmitters. Additionally, the technology scaling is used to achieve higher data rates, which results in increase of the CM noise in advanced technology nodes.

In the second part of the thesis, we present a novel on-chip active circuit technique to mitigate EMI-related CM noise in high-speed PAM-4 transmitters. An automatic CM noise cancellation (CMNC) system architecture in 40 nm technology is designed for a 56 Gbps PAM-4 optical transmitter. This solution provides the benefits of small size and low cost by eliminating the need for discrete components to suppress EMI. It is demonstrated that the CM noise cancellation system efficiently mitigates EMI by suppressing the CM noise up to 90% while consuming 5 mW, with a core area of 17 μm × 9 μm.