Executive Summary

This project was completed during my final year of electrical engineering. The aim of this capstone project is to: (1) evaluate the suitability of the TSMC 65nm CMOS technology for millimeter wave applications, particularly wireless transmission, (2) model a wireless link for a next generation use case and determine suitable specifications for a power amplifier, (3) create a circuit level implementation and study the results. The 140 GHz band was chosen due to an industry consensus that moving to higher carrier frequencies will enable greater bandwidth which will be necessary to serve greater wireless throughput. Typically, such high power, high frequency applications are implemented in niche, RF-centric technologies which are expensive and have low integration complexity. CMOS on the other hand may have worse RF performance but offers extremely high integration with digital circuits and low cost when manufactured at scale. A single chip solution with digital and analog/RF circuits lowers costs and eliminates complexity caused by interfaces between disparate dies. This project successfully demonstrates a power amplifier in 65nm CMOS from 136 to 142 GHz (6 GHz bandwidth with 1dB gain flatness) which delivers up to 12 dBm to a 50 Ω load while consuming 240 mW of DC power from a 1.2 V supply with an area of only 0.3 by 0.3 mm^2. Such a power amplifier can enable wireless links with a range of up to 29 meters with a data rate of 7 Gbps.

This is our booth poster for our capstone project at the final year engineering design fair - 6GCMOS.pdf

Full project report - Report

Project Motivation and Objectives

Major technological trends are driving wireless networks towards sixth generation (6G) communications, including the internet of things (IoT), artificial intelligence (AI) as wireless users, and pervasive digital presence. These trends will push the total number of wireless devices in the world to over 500 billion in the next decade, demanding an order of magnitude increase in data throughput while decreasing network latency. While human user experiences have defined the previous five generations of wireless networks, AI will soon have a presence as a legitimate user that far exceeds the perceptions requirements of human users. For example, AI systems could generate or demand machine vision data many times greater than the spatial or time resolution requirements for human-to-human video conferencing. Emerging applications in “XR,” which is a combination of virtual reality (VR), augmented reality (AR), and mixed reality (MR) will rely on much higher data rates than what is capable with 5G to provide truly immersive user experiences. Initial estimates put the minimum data rate for immersive 16K VR at approximately 1 Gbit/s for a single user, which is already the current experienced user data rate.

Currently, 5G will only serve as a stop gap on our way to exponentially increasing data capacity. To enable the growth of 6G, new hardware systems will have to be designed to support high frequencies and new ways of transmitting and receiving wireless signals. According to the Shannon capacity limit (1), to increase the maximum capacity of a wireless channel (C), the bandwidth (B) and/or the signal to noise ratio (SNR) must be increased. Increasing SNR usually involves increasing the power of the transmitted signal which becomes impractical as the improvement in C from SNR increases at a log rate. Not to mention limits on transmitted power and depending on the carrier frequency, fundamental limits of the transmitter technology compound its impracticality.

C = B * log₂(1 + SNR)

On the other hand, increasing bandwidth yields a linear increase to channel capacity. Due to a combination of physics and frequency allocations, shifting to higher carrier frequencies can provide orders of magnitude increase in bandwidth. Firstly, (2) illustrates that the bandwidth of a resonator is linearly proportional to the resonant frequency of the system. So simply by virtue of increasing the operating frequency in a conventionally tuned circuit, more absolute bandwidth is available.

B = f_c / Q

Recent regulation changes have also opened up vast amounts of the radio spectrum above 100 GHz. Compared to sub-6GHz 5G networks and wireless LAN, the THz range (100 GHz to 10 THz) could enable a 50 to 100 fold increase in carrier frequencies and an associated 5 to 20 fold increase in available bandwidth. Going such high frequencies will require extensive design investigation for current integrated circuit (IC) technology, as common process technologies such as a complementary metal oxide semiconductor (CMOS) struggle to operate in this frequency range. Therefore the key enabling engineering solution that will enable 6G communication will be power amplifiers that can operate in the THz range with reasonable efficiency, reliability, and cost. The objective of this capstone project is twofold. Firstly, the efficacy of wireless communications above 100 GHz will be examined and a series of technical specifications will be developed. Secondly, a circuit will be designed that satisfies these requirements and acts as a proof of concept technology for 6G on a physical level. By designing a low cost chip that can communicate in the THz range will support the exponential rise of data rate required, beyond what 5G can provide and enabling a whole host of exciting applications from enhanced autonomous vehicles to extending the presence of AI to everyday life.