A 0.9-V 28-MHz Highly Digital CMOS Dual-RC Frequency Reference With ±200 ppm Inaccuracy From -40 °C to 85 °C

Woojun Choi, Jan Angevare, Injun Park, Kofi A.A. Makinwa, Youngcheol Chae

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This article presents an energy-efficient dual-RC frequency reference intended for wireless sensor nodes. It consists of a digital frequency-locked loop (FLL) in which the frequency of a digitally controlled oscillator (DCO) is locked to a temperature-independent phase shift derived from two different RC poly-phase filters (PPFs). Phase shifts with complementary temperature coefficients (TCs) are generated by using PPFs made from different resistor types (p-poly and silicided p-poly). The phase shift of each filter is determined by a zero-crossing (ZC) detector and then digitized by a digital phase-domain ΔΣ modulator (ϕ-ΔΣM). The results are then combined in the digital domain via fixed polynomials to produce a temperature-independent phase shift. This highly digital architecture enables the use of a sub-1-V supply voltage and enhances energy and area efficiency. The 28-MHz frequency reference occupies 0.06 mm² in a 65-nm CMOS process. It achieves a period jitter of 7 ps (1σ) and draws 142 μW from a 0.9-V supply, which corresponds to an energy consumption of 5 pJ/cycle. Furthermore, it achieves ±200 ppm inaccuracy from -40 °C to 85 °C after a two-point trim.

Original languageEnglish
Number of pages11
JournalIEEE Journal of Solid-State Circuits
Publication statusE-pub ahead of print - 2022


  • CMOS frequency reference
  • Detectors
  • digital frequency-locked loop (FLL)
  • digital phase-domain ΔΣ modulator (ϕ-ΔΣM)
  • digitally assisted
  • Frequency locked loops
  • Frequency modulation
  • RC poly-phase filter (PPF)
  • Resistors
  • Switches
  • temperature compensation
  • Temperature measurement
  • Temperature sensors
  • trimming
  • wireless sensor node
  • zero-crossing (ZC) detector.


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