Martin Vandepas, Kerem Ok, Anantha Nag Nemmani, Merrick Brownlee, Kartikeya Mayaram, Un-Ku Moon

1. Characterization of 1.2GHz PhaseLocked Loops and Voltage Controlled Oscillators in a Total Dose Radiation Environment Martin Vandepas, Kerem Ok, Anantha Nag Nemmani, Merrick Brownlee, Kartikeya Mayaram, Un-Ku Moon Oregon State University Department of Electrical and Computer Engineering MAPLD 2005 September 7-9, 2005

2. Outline • Test chip description • Radiation test setup • Results • Conclusion

3. Test Chip (Honeywell MOI-5) • PLLs • LC oscillator PLL • Ring oscillator PLL • LC oscillators • NMOS current source • PMOS current source • Complementary current source • Ring oscillators • Maneatis delay cell • Linear-load modified Maneatis delay cell • Lee-Kim delay cell

4. Test Chip Die Photo LC oscillators Ring oscillators LC PLL Ring PLL

5. Prototype PLLs • Ring-VCO PLL • Programmable “N” & “ICP” • LC-VCO PLL • Programmable “N” & “ICP”

6. Prototype PLL Summary

7. Prototype LC VCOs PMOS current source Complementarycurrent sources NMOS current source

8. Prototype Ring Oscillators Maneatis cell Linear-load Lee/Kim cell • Maneatis delay cell: symmetric & linear loads • Lee/Kim delay cell: traditional & signal-delay-optimized layout • Body ties in SOI: with body ties & without (floating body)

9. Radiation Test Setup • Two tests • 500krad(SiO2) at a dose rate of 500 rad/sec • One exposure • Characterize the oscillators before and after the dose • 25krad(SiO2) to 6.4Mrad(SiO2) doubling dosage each step • Tested current and lock range of ring PLL vs. total radiation dose • Quantify effect of annealing 35 days after radiation at room temperature

10. Radiation Equipment at AFRL • Phillips low energy X-Ray (LEXR) tube • Shown with cryo chamber (not used) • Chip irradiated directly with IC lid removed • All circuits biased except buffers

11. First Test • Current consumption about constant throughout irradiation • Suggests leakage current is not significant for the given dose • One notable observation • Shifted tuning range for ring-based oscillators • Annealing until measurement of VCOs • Dependence on process makes characterization of annealing difficult

12. PMOS Source LC VCO

13. NMOS Source LC VCO

14. Complementary Source LC VCO

15. Lee/Kim Traditional Layout

16. Lee/Kim Signal-Path-Optimized Layout

17. Linear-Load Modified-Maneatis Oscillator

18. Period Jitter: LC VCOs

19. Period Jitter: Ring VCOs

20. Period Jitter: LC VCOs

21. Period Jitter: Ring VCOs

22. Second Test – Ring PLL • Circuit current vs. total dose • Very little annealing After 35 days annealing

23. Second Test – Ring PLL • Lock range vs. total dose • Still locks at 6.2MRad(SiO2) • Gaps are due to test setup After 35 days annealing

24. Total Dose Effect on PLLs • Digital blocks • Can tolerate large shifts in threshold voltages • Immune to large doses of radiation • Continue functioning until transistors cannot be turned on • Charge Pump and Loop Filter • Performance degradation • Current mismatch & leakage • Eventual functional failure • VCO • Tuning curve (fOSC, KVCO) changes

25. Total Dose Hardening • Self calibration/tuning • Analog tuning mechanisms are susceptible to total dose • Digital blocks can inherently resist large doses of radiation before functional failure • All digital PLLs ideal for total dosage hardening • Architectures with loop parameters independent of environment

26. Conclusions • Analog PLL’s can be sensitive to total dose radiation • Designing with threshold shifts in mind can harden them • New all-digital PLL techniques may present total dose hardened by design PLLs

27. Acknowledgment • We would like to thank Ken Merkel, Steve Clark, Dave Alexander, and Bill Kemp of the Air Force Research Lab in Albuquerque, NM for their direct support of the radiation testing • Thanks to AFRL for sponsoring this project