A PWM Buck Converter with Load-Adaptive Power Transistor Scaling Scheme Using Analog-Digital Hybrid Control for High Energy Efficiency in Implantable Biomedical Systems

Sung Yun Park, Jihyun Cho, Kyuseok Lee, Euisik Yoon

Research output: Contribution to journalArticle

4 Citations (Scopus)


We report a pulse width modulation (PWM) buck converter that is able to achieve a power conversion efficiency (PCE) of >80% in light loads (< 100μ A) for implantable biomedical systems. In order to achieve a high PCE for the given light loads, the buck converter adaptively reconfigures the size of power PMOS and NMOS transistors and their gate drivers in accordance with load currents, while operating at a fixed frequency of 1 MHz. The buck converter employs the analog-digital hybrid control scheme for coarse/fine adjustment of power transistors. The coarse digital control generates an approximate duty cycle necessary for driving a given load and selects an appropriate width of power transistors to minimize redundant power dissipation. The fine analog control provides the final tuning of the duty cycle to compensate for the error from the coarse digital control. The mode switching between the analog and digital controls is accomplished by a mode arbiter which estimates the average of duty cycles for the given load condition from limit cycle oscillations (LCO) induced by coarse adjustment. The fabricated buck converter achieved a peak efficiency of 86.3% at 1.4 mA and > 80% efficiency for a wide range of load conditions from 45 μ A to 4.1 mA, while generating 1 V output from 2.5-3.3 V supply. The converter occupies 0.375 mm2 in 0.18 μ m CMOS processes and requires two external components: 1.2 μ F capacitor and 6.8 μ H inductor.

Original languageEnglish
Article number7370953
Pages (from-to)885-895
Number of pages11
JournalIEEE Transactions on Biomedical Circuits and Systems
Issue number6
Publication statusPublished - 2015 Dec


All Science Journal Classification (ASJC) codes

  • Biomedical Engineering
  • Electrical and Electronic Engineering

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