Fully Integrated Buck Converter With Fourth-Order Low-Pass Filter

Fully integrated buck converters are typically operated with a second-order LC low-pass filter and a switching frequency beyond 100 MHz. The motivation for such design choices is to reduce the size of passive components in the LC low-pass filter required for small output voltage ripple. However, in a buck converter with on-chip planar spiral inductors, a fourth-order filter can deliver better performance characteristics without area penalty. This paper presents a comparative study of a fourth-order LC low-pass filter versus a second-order LC low-pass filter with on-chip planar spiral inductors and on-chip capacitors. A fully integrated buck converter is then designed with a quasi-V2 controller to demonstrate the benefits of a fourth-order LC low-pass filter. The prototype chip, which is implemented in a 65-nm CMOS process, produces a nominal voltage of 0.7 V from a 1-V supply. The fourth-order LC low-pass filter uses a total inductance of 1.8 nH and a total capacitance of 4 nF. Measurement results demonstrate fast transient response on the order of nanoseconds. A peak efficiency of 76.1% is achieved, and the output voltage ripple is kept below 15 mV over the entire range of load current from 40 to 180 mA.

[1]  Partha Pratim Pande,et al.  DVFS Pruning for Wireless NoC Architectures , 2015, IEEE Design & Test.

[2]  Cheng Huang,et al.  A 100 MHz 82.4% Efficiency Package-Bondwire Based Four-Phase Fully-Integrated Buck Converter With Flying Capacitor for Area Reduction , 2013, IEEE Journal of Solid-State Circuits.

[3]  Luca P. Carloni,et al.  A 2.5D integrated voltage regulator using coupled-magnetic-core inductors on silicon interposer delivering 10.8A/mm2 , 2012, ISSCC.

[4]  W.G. Dunford,et al.  A Fully Integrated 660 MHz Low-Swing Energy-Recycling DC–DC Converter , 2009, IEEE Transactions on Power Electronics.

[5]  M Wens,et al.  A Fully Integrated CMOS 800-mW Four-Phase Semiconstant ON/OFF-Time Step-Down Converter , 2011, IEEE Transactions on Power Electronics.

[6]  Jose A. Cobos,et al.  $v^1$ Concept: Designing a Voltage-Mode Control as Current Mode With Near Time-Optimal Response for Buck-Type Converters , 2015, IEEE Transactions on Power Electronics.

[7]  Bruno Allard,et al.  A 100 MHz 91.5% Peak Efficiency Integrated Buck Converter With a Three-MOSFET Cascode Bridge , 2016, IEEE Transactions on Power Electronics.

[8]  Vivek De,et al.  A 500 MHz, 68% efficient, fully on-die digitally controlled buck Voltage Regulator on 22nm Tri-Gate CMOS , 2014, 2014 Symposium on VLSI Circuits Digest of Technical Papers.

[9]  Fred C. Lee,et al.  Unified Equivalent Circuit Model and Optimal Design of $V^{2}$ Controlled Buck Converters , 2016, IEEE Transactions on Power Electronics.

[10]  Chen-Yu Wang,et al.  A fast-transient quasi-V2 switching buck regulator using AOT control , 2011, IEEE Asian Solid-State Circuits Conference 2011.

[11]  Song Qu,et al.  Modeling and design considerations of V/sup 2/ controlled buck regulator , 2001, APEC 2001. Sixteenth Annual IEEE Applied Power Electronics Conference and Exposition (Cat. No.01CH37181).

[12]  Qiang Li,et al.  V2 control with capacitor current ramp compensation using lossless capacitor current sensing , 2013, 2013 IEEE Energy Conversion Congress and Exposition.

[13]  Robert W. Erickson,et al.  Fundamentals of Power Electronics , 2001 .

[14]  S. Narendra,et al.  A 233-MHz 80%-87% efficient four-phase DC-DC converter utilizing air-core inductors on package , 2005, IEEE Journal of Solid-State Circuits.

[15]  Meeta Sharma Gupta,et al.  System level analysis of fast, per-core DVFS using on-chip switching regulators , 2008, 2008 IEEE 14th International Symposium on High Performance Computer Architecture.

[16]  Rongxiang Wu,et al.  High-Efficiency Silicon-Embedded Coreless Coupled Inductors for Power Supply on Chip Applications , 2012, IEEE Transactions on Power Electronics.

[17]  T. Qian,et al.  Analysis of the ramp compensation approaches to improve stability for buck converters with constant on-time control , 2012 .

[18]  Wing-Hung Ki,et al.  Digitally assisted quasi-V2 hysteretic buck converter with fixed frequency and without using large-ESR capacitor , 2009, 2009 IEEE International Solid-State Circuits Conference - Digest of Technical Papers.

[19]  Jian Sun.  Characterization and performance comparison of ripple-based control for voltage regulator modules , 2006, IEEE Transactions on Power Electronics.

[20]  Hou-Ming Chen,et al.  A Two-Phase Fully-Integrated DC–DC Converter With Self-Adaptive DCM Control and GIPD Passive Components , 2015, IEEE Transactions on Power Electronics.

[21]  Gu-Yeon Wei,et al.  A Fully-Integrated 3-Level DC-DC Converter for Nanosecond-Scale DVFS , 2012, IEEE Journal of Solid-State Circuits.

[22]  Jose A. Cobos,et al.  Design-oriented stability criteria of a v2 control compensated with inductor current of a boost converter for shipboard power systems , 2015, 2015 IEEE Applied Power Electronics Conference and Exposition (APEC).

[23]  Philip K. T. Mok,et al.  A Constant Frequency Output-Ripple-Voltage-Based Buck Converter Without Using Large ESR Capacitor , 2008, IEEE Transactions on Circuits and Systems II: Express Briefs.

[24]  Michiel Steyaert,et al.  A fully-integrated 0.18μm CMOS DC-DC step-down converter, using a bondwire spiral inductor , 2008, 2008 IEEE Custom Integrated Circuits Conference.

[25]  N. M. Ibrahim,et al.  Analysis of current crowding effects in multiturn spiral inductors , 2001 .

[26]  Paolo Mattavelli,et al.  Small-Signal Analysis and Optimal Design of Constant Frequency $V^{2}$ Control , 2015, IEEE Transactions on Power Electronics.

[27]  Paolo Mattavelli,et al.  Small-Signal Analysis and Optimal Design of External Ramp for Constant On-Time V $^{\bf 2}$ Control With Multilayer Ceramic Caps , 2014, IEEE Transactions on Power Electronics.

[28]  Stephen P. Boyd,et al.  Simple accurate expressions for planar spiral inductances , 1999, IEEE J. Solid State Circuits.

[29]  R. Harjani,et al.  A High-Efficiency DC–DC Converter Using 2 nH Integrated Inductors , 2008, IEEE Journal of Solid-State Circuits.