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Linear Voltage Regulator

Presented By-Ashis Maity

Research Consultant

Advanced VLSI Laboratory

Indian Institute of Technology, Kharagpur

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Why do we need voltage regulator?

Scaling the device to reduce power, area,

increase speed.

W ,L , tox , Hence VDD.

For 0.25u technology, tox=50A

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Why do we need voltage regulator?

Faster Scaling of core supply than system

supply.

Voltage regulator required to fill the gap between

system supply and core supply.

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Applications & Properties of Linear

Voltage Regulator

Applications:

Used as voltage supply for highly analog

blocks like Sense amplifier, op-amp etc.

Properties:

Highly clean o/p voltage.

Lesser noise.

Poor efficiency.

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Transient Response of a Typical

Voltage Regulator

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Specifications / Requirements

ILOAD : ILOAD_max to ILOAD_min.

VDDINT : VDDINT_typ 10%.

Settling time : Time required to settle VDDINT

within tolerance band at ILOAD transitionsPower Efficiency : Ratio of output power and

input power.

LOAD Regulation: How VDDINT varies with

ILOAD.LINE Regulation: How VDDINT varies with

VDDEXT.

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Driver Circuit with P-type pass tr.

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Advantages & Disadvantages of

Driver ckt with P-type pass transistor

Advantages :

Low dropout (LDO) .

Lesser area ( n-well process, without body

effected ).Higher gain - lesser input referred dc offset.

Higher load regulation capability.

Disadvantages:Frequency compensation is not easy.

Settling time is large.

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Driver Circuit with N-type pass tr.

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Advantages & Disadvantages of

Driver ckt with N-type pass transistor

Advantages:

Frequency compensation is easy.

Self feedback- act as source follower.

O/P impedance is small. Faster Response.

Disadvantages :

Dropout is more.

More area ( with body effect ).Lesser gain - Input referred offset is more.

Lesser load regulation capability.

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Thank U!