# Review of CMOS Integrated Circuit Technologies for High-Speed Photo-Detection
## 7 Summary and Outlook  
This paper presents the history and review of the CMOS IC technology for high-speed photo-detection without relying on complex expressions or formulas, in order to provide an insight on the technology even for the readers who are not professional circuit designers. Recent high-speed photo-detecting sensor technology provides one of the most powerful forces which drive the evolution of optical links into the short-reach applications. On the other hand, another remarkable breakthrough has come from the CMOS IC technologies which convert the current-mode signal from the PD into the VLSI-compatible voltage-mode signal, because the CMOS platform provides low-power consumption, low cost, and compatibility with high-density CMOS logic blocks, which are highly required for the short-reach optical links. Because the CMOS IC for photo-detection bridges the two historic technologies of the fiber optics and the silicon VLSI systems, there is a high demand for a guidebook which introduces the technology to non-experts on IC, including optical device engineers. However, to the best of the authors' knowledge, there has been no publication which offers good overview and summary of the CMOS IC technologies for high-speed photo-detection. The technology becomes more and more complex as the history deepens, and therefore it becomes more difficult for beginners to catch up with, as there is no publication that provides an overview of the technology evolution. For that purpose, in this paper, tens of technical papers which present high-speed photo-detecting circuits with strict verifications of theory based on IC fabrication results are thoroughly selected, reviewed, and categorized. In addition, several papers which provide a technical background of such IC design are introduced as well.  
Looking ahead, the present electrical link will be 'eventually' replaced by the optical link, because of inherent bandwidth limit of electrical channel. The matters are when and which speed, but the ending will not change, although there are many impressive efforts to extend the limit of electrical link. The authors also believe that the platform of the optical link will be CMOS technology and thus CMOS interface circuit will play an important role. Based on the trend of last 20 years, which is described in this paper, the future optical receiver is expected to include the following features:  
1. Circuit and system topologies which utilize the advantages of highly-scaled CMOS technology, such as the inverter-based TIA and all-digital CDR. It is because advanced CMOS technology focuses on optimizing digital circuits.
2. Circuit techniques to overcome the noise-bandwidth tradeoff in front-end circuit, such as the inductive peaking techniques, the equalization scheme, and the integration-based circuit. Since it  
Figure 45: All-digital CDR presented in [74].  
is obvious that the front-end circuit has been and will be the bottleneck, both in terms of speed and SNR, it is highly required to break the tradeoff.  
[PERSON]-[PERSON] and [PERSON] collected data, organized, wrote, revised the manuscript; [PERSON]-[PERSON] edited and approved the final manuscript.  
The authors declare no conflict of interest.