Design Techniques for Radiation Hardened Phase Locked Loops

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Design Techniques for Radiation Hardened Phase Locked Loops Anantha Nag Nemmani, Martin Vandepas, Kerem

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 Total Ionization Dose (TID) Single Event Effects (SEE) 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 ↑ Digital PLL Tuning curves of Lee/Kim Ring oscillator before and after radiation. • Transient error currents • Modelled as sum of exponential current sources SEE on last stage of frequency divider • Digitally controlled analog oscillator (DCAO) • Time-to-digital converter (TDC) • Digital loop filter Analysis • Lee/Kim delay cell • Fine/Coarse tuning Digital Loop Filter Time-to-digital converter Digitally controlled analog oscillator • Fine tuning current DAC • 6 fine bits + 6 coarse bits • • Exponential delay chain Latches Sign detection Pseudo-thermometor encoder Operation of a TDC • Type – II loop filter Analysis Verification DCAO resolution 1. DCAO: SEE on control node Openloop gain For optimum performance Phase margin - ΦM Incremental phase accumulated 2. Phase detector: 3. Loop filter: Control word CPPLL Analogy Proportional Integral gain Radiation Hardening Self-Calibration TDC Output Response to frequency step at the input. Simulink Agrees with mathematical model Normalizing gain Redundancy & Majority Voting Layout Single Event Hardening • Loop parameters – f. LSB & d. T – Process dependent – Gn, α & β – Digital constants • Loop dynamics are dependent only dependent on: • Self calibration – Calibrate Kdig to the desired value Time-to-digital converter Frequency Divider MAPLD 2005/228 Accumulator