kopia lustrzana https://github.com/bristol-seds/pico-tracker
124 wiersze
3.1 KiB
TeX
124 wiersze
3.1 KiB
TeX
\documentclass[12pt]{article}
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\usepackage{graphicx}
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\usepackage{color}
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\usepackage{fixltx2e}
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\usepackage{datatool}
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\usepackage{float}
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%\usepackage[showframe=true]{geometry}
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\addtolength{\textwidth}{1in}
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\addtolength{\textheight}{1in}
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\addtolength{\evensidemargin}{0.5in}
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\addtolength{\oddsidemargin}{-0.5in}
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\addtolength{\topmargin}{-0.5in}
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\setlength{\parindent}{0cm}
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\begin{document}
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\section{Hardware}
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The hardware exists in two versions: a minaturised version intended
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for flight and a development version intended for firmware
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developement and debugging etc. The two verisons share the same
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circuit diagram, and hence firmware should be generally interoperable
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between the two.
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However to allow detection of the hardware version PA02 is shorted to
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ground on the development version while is will be pulled high
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internally on the flight version.
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\subsection{Dimensions}
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The flight hardware has a total size of 50 x 12 mm.
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Components are positioned on a 1/16 (0.0625) mm grid, with major
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components on a 1/4 mm grid.
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\subsection{Routing}
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The board is routed with 6 mil traces for data and 6 / 16 mil traces
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for power. Where nessesary the traces All via are 0.3mm (12mil) drill.
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\section{Components}
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\subsection{Development}
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\section{Design}
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\subsection{GPS}
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\subsection{ESD Proctection}
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The GPS Antenna input is particularly sensitive to ESD damage. Options
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for protecting against this are outlines in the uBlox hardware
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intergration manual \bibitem{ublox8hw}
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One
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option to protect against this is to use an LNA with integrated ESD
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protection, such as.
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\subsection{TCXO}
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Flight UBSEDS2 clocked the Si4060 directly from a 16 MHz crystal
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osciallator. This was with about 6.5pF of internal capactance from the
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Si4060.
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\subsection{HF Clock}
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This is synthesised in the SAM D20E and used to drive the XIN input of
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the SI4060. The design frequency for the XIN input is 25 - 32MHz
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(30MHz by default) but UPU reports success with 16.369MHz. The maximum
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output clock frequency from the SAM D20E is 48MHz so this would be a
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useful design limit.
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No input capacitance value is given for the XIN pin but 2pF typical is
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given for out pins and this is probably about the same.
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The maximum rise/fall time for 48MHz is 10ns, around 5ns would be
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good, giving a knee = 100MHz.
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Path inductance is maybe 10nH total (1+1+1 x 2 for pad/gnd-pad/via, 4
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for trace)
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Maximum output current from the SAM D20E is 1mA (with DRVSTR=0, 1.8V),
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so output impedance = 1800Ω
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Worst case Q
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\begin{equation}
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Q = {\sqrt{10nH/2pF} \over 100} = 0.22 (good)
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\end{equation}
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Time constant
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\begin{equation}
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tc = RC = 1800*2pF = 3.6ns (good)
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\end{equation}
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In any case the SI4060 tune API allows ramping up the internal
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capacitance to 11pF, which will drop Q at the expense of the time
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constant.
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\subsection {Firmware}
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Check flight WG2 on habhub for gps string formatting gone wrong
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Get so much test data.
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\begin{thebibliography}{9}
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\bibitem{ublox8hw}
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uBlox 8 Hardware integration manual,
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http://www.u-blox.com/images/downloads/Product_Docs/MAX-M8_HardwareIntegrationManual_(UBX-13004876).pdf
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\end{thebibliography}
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\end{document}
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