Low-Dropout Regulator with

modest ripple and rugged performance in 180nm

INTRODUCTION

LINEAR REGULATOR CONCEPTS

CIRCUIT IMPLEMENTATION

PERFORMANCE ANALYSIS

CONCLUSION

Presentation Outline

INTRODUCTION

1Low-Dropout Regulator with modest ripple and rugged performance in 180nm

Supplying and conditioning power are the most fundamental functions of an electrical system.

A loading application cannot sustain itself without energy, and cannot fully perform its functions without a stable supply

Transformers, generators, batteries, and other off-line supplies incur substantial voltage and current variations across time and over a wide range of operating conditions

High frequency switching circuits CPU and DSP circuits utilized in an application usually load it.

Solution for above mentioned problems is to use a power converter

stable dc-bias voltage impervious to noise, temperature, and input-supply voltage variations

to sense and generate a correcting signal (high voltage gain)

pass device to mediate and conduct whatever load current is required from the unregulated input supply to the regulated output

reacts to offset and cancel effects of load current, input voltage, temperature, and an array of other variations on the output

to sense the output

LINEAR REGULATOR

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

CONCEPT OF LINEAR REGULATOR

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LINEAR REGULATOR

3Low-Dropout Regulator with modest ripple and rugged performance in 180nm

Transient response of LDO

LDO provide power to low-voltage digital circuits operating under different modes of operation --voltage transients-cannot be handled by digital circuits  Factors affecting transient response of an LDOThe internal compensation of the LDOThe amount of output capacitanceThe parasitics of the output capacitor

The faster local feedback n/w responds quicker to load changes than more complicated regulator loop

The additional loop has negligible effects on dc accuracy as its low frequency gain is kept well below that of the regulator

The additional loop also demand little to no current to have less impact on operational life of battery

LINEAR REGULATOR

4Low-Dropout Regulator with modest ripple and rugged performance in 180nm

REGULATING PERFORMANCE

Steady-state (dc) voltage variations in the output (ΔVOUT) resulting from dc changes in load current (ΔILOAD) define load regulation(LDR) performance

Systematic input-offset voltages, which result from asymmetric currents and volt-ages in the feedback error amplifier, further degrade load-regulation performance

  Even if the LDO were symmetric, its widely variable load would cause considerable voltage

swings at internal nodes, subjecting some of the devices to asymmetric conditions

LOAD REGULATION

LINE REGULATIONLine regulation(LNR) performance is a dc parameter and it refers to output voltage variations arising from dc changes in the input supply Power-supply variations affect the regulator in two waysDirectly through its own supply

Indirectly via supply-induced variations in reference VREF

LINEAR REGULATOR

5Low-Dropout Regulator with modest ripple and rugged performance in 180nm

PROCESS AND TEMPERATURE INDEPENDENT BIASING

The transconductance of MOSFETs determine performance parameters: small signal gain, speed and noise.

It is desirable to bias the transistors such that their transconductance is independent of process, supply voltage and temperature

LINEAR REGULATOR

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Circuit Implementation

ERROR AMPLIFIERERROR AMPLIFIER

PASS TRANSISTORPASS TRANSISTOR

FAST REACTING PATHSFAST REACTING PATHS

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

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Linear Regulator FIRST FAST REACTING PATH

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FIRST REACTING PATH

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

Linear Regulator SECOND FAST REACTING PATH

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FIRST REACTING PATH

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

When load current output voltage The loop results in of Vgs of Mf4

which is coupled through cm2 to input of M18

Its operation current leads to in drive for Mp restoring output voltage to its

original value

Linear Regulator THIRD FAST REACTING PATH

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FIRST REACTING PATH

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

Transistors Mf6-Mf9, Mp, and feedback resistors R1-R2 form the third self-reacting pathTransistors Mf6-Mf9 constitute an error amplifierWhen load current the output voltageThe output voltage of error amplifier leading to drive for M18Gate voltage of Mp thus restoring the output voltage

Linear Regulator AC ANALYSIS

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Parameter Iload(0mA) Iload(100mA)

Loop gain 62dB d 

Phase margin 92.61o 95.38o

The Phase Margin for this load current range The Phase Margin for this load current range is above 95is above 95OO, loop-gain is about 72dB, loop-gain is about 72dB

means a stable LDO and enough means a stable LDO and enough gain for a high output voltage accuracygain for a high output voltage accuracy

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

Linear Regulator DC ANALYSIS

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Parameter Measured units

Line Regulation 1 mV/V

 

Load Regulation 0.162 mV/mA

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

Linear Regulator TRANSIENT ANALYSIS

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Parameter Measured units

OVERSHOOT 97 mV

 

UNDERSHOOT 144 mV

For a load current pulse of 100mA step with 1s rise and fall times

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

Linear Regulator RIPPLE IN OUTPUT VOLTAGE

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It has ripple voltage equal to 0.9 mvIt has ripple voltage equal to 0.9 mv means a stable LDO and means a stable LDO and

high output voltage high output voltage accuracyaccuracy

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

Linear Regulator PSRR (POWER SUPPLY REJECTION RATIO)

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It has PSRR of 42dB @1KhzIt has PSRR of 42dB @1Khz At low frequencies the PSRR is very high At low frequencies the PSRR is very high

which results in high suppression of which results in high suppression of disturbances from the supply line. In the disturbances from the supply line. In the higher frequency area of > 1 MHz the higher frequency area of > 1 MHz the PSRR gets very small and even reaches 0 PSRR gets very small and even reaches 0 dB at 6 MHz. This means that a 1 MHz dB at 6 MHz. This means that a 1 MHz signal would pass through the regulator signal would pass through the regulator without attenuationwithout attenuation

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

LINEAR REGULATORS MEASURED PERFORMANCE

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Parameter Measured Units Technology 

0.18  

Loop gain@full load current@zero load current

 7162

 dBdB

Line regulation 0.989 mV/V

Load regulation 0.162 mV/mA

PSRR@1KHZ 42 dB

Δvout(Undershoot) 144 mV

Δvout(Overshoot) 144 mV

Summary of measured performanceSummary of measured performance

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

Conclusion

Low-Dropout Regulator with modest ripple and rugged performance in 180nm

LDO regulator targeted for SOC applications(optimized design for performance, board area, and cost)

LDO is stable for output current in the complete range from 0 to 100 mA

LDO with high regulation accuracy and fast transient response

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REFERENCES

Low-Dropout Regulator with modest ripple and rugged performance in 180nm 17

[1] Sai Kit Lau, K.N. Leung, and P.K.T. Mok,“Analysis of low-dropout regulatorTopologiesfor low-voltageregulation”,inIEEE Conference of Electron Devices and Solid-StateCircuits,December2003[2] P.Hazucha,T.Karnik,B.A Bradley,C. Parsons,D.Finan,and S.Borkar,”area –efficientlinear regulator withultra fast load regulation,” IEEE J. Solid-StateCircuits, vol. 40, no. 4, pp.933-940, Apr. 2005[3] P. Y. Or and K. N. Leung, “An output-capacitorless low-dropout regulator with direct voltage-spike detection,” IEEE J. Solid-State Circuits, vol. 45, no. 2, pp. 458-466, Feb. 2010.[4] T. Y. Man, K. N. Leung, C. Y. Leung, P. K. T. Mok, and M. Chan,“Development of single-transistor control LDO based on flipped voltage follower for SoC,” IEEE Trans.Circuits Sys. I, vol. 55, no. 5, pp. 1392-1401, Jun. 2008.[5]Texas Instruments, “Fundamental theory of PMOS low-dropout voltage regulators”,TexasInstruments Inc., SLVA068, Dallas, TX, USA, April 1999.[6]Chester Simpson, “Linear and switching voltage regulator fundamentals”, NationalSemiconductor Corporation, Santa Clara, CA, USA, 1995.[7] Chia-Min Chen,Chung-Chih Hung, “A Fast Self-Reacting Capacitor-less Low-Dropout Regulator, ” IEEE Trans. Circuits Syst. I, pp. 375-378, Sept. 2011[8]Frederik Dostal, “How and when to use low dropout linear regulators”, Embedded ControlEurope Magazine, pp. 16-19. March 2004 Issue.[9]R. J. Milliken, J. Silva-Martinez and E. Sanchez- Sinencio, “Full onchipCMOS low-dropout voltage regulator,” IEEE Trans. Circuits Syst. I,vol. 54, no. 9, pp. 1879-1890, Sept. 2007.[10]S. K. Lau, P. K. T. Mok, and K. N. Leung, “A low-dropout regulator forSoC with Q-reduction,” IEEE J. Solid-State Circuits, vol. 42, no. 3, pp.658-664, Mar. 2007.[11] D.A.Johns, K.Martin, “Analog Integrated Circuit Design,” John Wiley and Sons Inc, U.K.,246-251(1997)

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