All digital FPGA-implementable time-average-frequency direct period

All Digital FPGA-implementable Time-AverageFrequency Direct Period Synthesis For IoT Applications Liming Xiu BOE Technology Group CO., LTD. Beijing, 100176, China Abstract—Time-Average-Frequency Direct Period Synthesis (TAF-DPS) is an emerging frequency synthesis technique. It is built upon the concept of Time-Average-Frequency (TAF). Its distinguishing characteristics are small frequency granularity and fast frequency switching. These features make TAF-DPS an ideal on-chip frequency generator. In this paper, a TAF-DPS circuit is constructed using digital approach of HDL coding and synthesis. It is then mapped to FPGA. Using this full digital TAFDPS as a tool, several innovative examples in application level are demonstrated. The aim of this work is to demonstrate that this low design effort and compact frequency synthesizer is a handy and powerful tool for engineers to “play with frequency” and subsequently innovate in their high level IoT applications. Keywords—Time-Average-Frequency, Flying-Adder, FPGA, Clock, Frequency Synthesis.

I.

INTRODUCTION

Traditionally, Phase Locked Loop (PLL) has been used as mainstream on-chip clock generator. Viewed from a level higher than PLL, clock technology could be regarded as the 4 th major IC design technology alongside processor, memory/storage and analog/RF technologies. Looking inside clock technology, there are three subject-of-study: clock usage (e.g. setup/hold check and spectral purity), clock distribution and clock generation. For clock generation, there are four challenges: good frequency stability (low phase noise/jitter), high frequency, small frequency granularity (resolution) and fast frequency switching. In the past several decades, for a given specific application, clock is mostly used in the form of fixed-frequency with high frequency stability. For this reason, majority of clock-related research and engineering effort was focused on the first two issues (stability and high frequency). Internet of Things (IoT) is the third wave in the development of the Internet, following the development of network connectivity for desktops and then for mobile devices. IoT makes everyday objects connected and smarter. Due to IoT’s capability to collect and report real-time data in healthcare, education, entertainment, utility, insurance, business, and industrial environments, it is projected that it will revolutionize the way we live. For IoT oriented electronic system, however, clock signal of fixed-frequency is no longer sufficient because the usage environment is not expected to be stationary but dynamic. This fact has recently forced researchers to shift their attention to the latter two challenges: small frequency granularity and fast frequency switching. Further, in the case of IoT, most tasks have to be accomplished under the condition of low cost, low power and miniaturization. For those reasons, IoT presents new challenges to the construction of frequency/clock source.

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Fig. 1. The working principle of TAF-DPS. 1/fTAF = TTAF = F∙∆

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Time-Average-Frequency Direct Period Synthesis (TAFDPS) is an emerging frequency synthesis architecture which is based on the novel TAF concept [1]. Its uniqueness lies in the features of small frequency granularity and fast frequency switching, achieved simultaneously for a given design. Moreover, its frequency switching speed is quantifiable. These features make TAF-DPS an ideal tool for frequency generation in IoT applications. Fig. 1 shows the working principle of TAF-DPS. Starting from a base time unit ∆ and a control word F = I + r where I is an integer and r is a fraction of 0 ӌ r