| LionSAT Hybrid Plasma Probe | ||
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LionProbe Design 1.0 Introduction 2.0 Background 2.1 Langmuir Theory 2.2 PFP Theory 2.3 Plasma Sheath 3.0 Implementation 3.1 Microprocessor 3.2 A/D & D/A Convert 3.3 Electrometer 3.4 DDS & Comparator 3.5 Phase Detection 3.6 Signal Combination 3.7 Sensor Heads 3.8 Boom Selection 3.9 Other Schematics 4.0 Results 5.0 Project Value 6.0 Cost Analysis 7.0 Conclusion 8.0 Future Work 9.0 References |
 Direct Digital Synthesizer & Comparators A Plasma Frequency Probe is realized with the use of a direct digital synthesizer (DDS), electrometer and a phase detector. The DDS is an integrated circuit that generates an AC sinusoid at frequencies from 1 Hz to half of the crystal clock speed. It is expected that the LionSat DDS crystal will be 80 MHz. Possible output frequencies then range up to 40 MHz. According to the upper-hybrid frequency analysis discussed earlier, this is above the expected maximum. The output signal is filtered to eliminate higher order harmonics. This signal is sent to the plasma sensor head. The resonant frequency of the plasma is easily detected when the output voltage signal and returning current signal are matched in phase. Fast AD8561 comparators are used to transform the AC sinusoids into digital pulse trains. These comparators have only a 7ns propagation delay and have output swings near the supply rails. We can then use the resultant digital pulse train for relative phase analysis.
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