An Eight-Lane 800-Gb/s Transceiver for PAM-4 Optical Direct-Detection Applications in 5-nm FinFET Process

In this article, we present an eight-lane 800-Gb/s transceiver, which enables the implementation of pluggable optical modules with pulse amplitude modulation (PAM)-4 modulation and direct detection. The transceiver features a host interface composed of eight TX and RX lanes compliant with the optical internetworking forum (OIF) common electrical I/O (CEI) 112G very short reach (VSR) and IEEE 802.3 chip to module (C2M) standards and integrates eight TX and RX lanes on the optical (line) side. Three fully integrated high-voltage optical TXs have been integrated with minimum area and power overhead by changing only few top metal masks: 3-Vpp silicon photonics (SiPho), 3-V open drain (OD), and 1.5-Vpp electro absorption modulated laser (EML) driver. External additional drivers suitable, e.g., for vertical cavity surface emitting laser (VCSEL) applications are supported by exploiting optical driver software reconfigurability into standard driver mode. The optical RXs, identical for all the applications, are digital signal processing (DSP) based, with the analog section consisting of a variable gain amplifier (VGA) and an analog-to-digital converter (ADC). The VGA can be dc coupled to an external trans-impedance amplifier (TIA) without the need for external components. The chip is implemented in 5-nm FinFET technology and it is designed to deliver the target performance both in package and bare die. Both versions meet the form factor and power requirements for quad small form factor pluggable double density (QSFP-DD) multi-source agreement (MSA) specifications and are suitable for optical interconnects covering most of the optical standards such as DR8/2xFR4/LR8/SR8.