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Proportional. Control word. Integral gain. TDC Output. Normalizing gain. Design Techniques for Radiation Hardened Phase Locked Loops. Anantha Nag Nemmani, Martin Vandepas, Kerem Ok, Kartikeya Mayaram and Un-Ku Moon Oregon State University Electrical Engineering and Computer Science.
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Proportional Control word Integral gain TDC Output Normalizing gain Design Techniques for Radiation Hardened Phase Locked Loops Anantha Nag Nemmani, Martin Vandepas, Kerem Ok, Kartikeya Mayaram and Un-Ku Moon Oregon State University Electrical Engineering and Computer Science 2005 MAPLD International Conference ◊ Ronald Reagan Building and International Trade Center Washington, D.C. ◊ September 7-9, 2005 Effects Single Event Effects (SEE) Total Ionization Dose (TID) Effect on Phase Locked Loops (PLLs) SEE on PLLs • VCO tuning curves shift • Change in nominal frequency and VCO gain • Change in chargepump current • Loop parameters changed as a result • Loop transfer function altered • Accumulation of charge in gate oxide • Vth NMOS ↓ & Vth PMOS ↑ • Transient error currents • Modelled as sum of exponential current sources Digital PLL Tuning curves of Lee/Kim Ring oscillator before and after radiation. SEE on last stage of frequency divider SEE on control node Digital Loop Filter Time-to-digital converter Digitally controlled analog oscillator • Digitally controlled analog oscillator (DCAO) • Time-to-digital converter (TDC) • Digital loop filter • Exponential delay chain • Latches • Sign detection • Pseudo-thermometor encoder • Lee/Kim delay cell • Fine/Coarse tuning • Fine tuning current DAC • 6 fine bits + 6 coarse bits • Type – II loop filter Analysis Operation of a TDC Analysis Verification DCAO resolution 1. DCAO: Openloop gain For optimum performance Phase margin - ΦM Incremental phase accumulated 2. Phase detector: 3. Loop filter: CPPLL Analogy Response to frequency step at the input. Simulink Agrees with mathematical model Radiation Hardening Self-Calibration Layout Redundancy & Majority Voting Single Event Hardening • Loop parameters • fLSB & dT – Process dependent • Gn, α & β – Digital constants • Loop dynamics are dependent only dependent on: • Self calibration • Calibrate Kdig to the desired value Accumulator Time-to-digital converter Frequency Divider MAPLD 2005/228