A 1-V 15 W High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van...

A 1-V 15W High-Precision Temperature SwitchD. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl

A 1-V 15 A 1-V 15 W High-Precision W High-Precision Temperature SwitchTemperature Switch

D. Schinkel, R.P. de Boer,

A.J. Annema and A.J.M. van Tuijl

Philips Research

University of Twente, Faculty of Electrical Engineering


ContentsContents

• Introduction

• Circuit fundamentals

• Design strategy

• Implementation

• Specifications

• Conclusions

• Introduction

• Circuit fundamentals

• Design strategy

• Implementation

• Specifications

• Conclusions


IntroductionIntroduction

– enable thermal protection (shutdown,clock frequency lowering etc.)

– use in integrated measurement or control devices

Why need integrated CMOS temperature

indicator?


IntroductionIntroduction

– Thermal protection only requires threshold temperature detection (125 °C)

– Multiple threshold values together form a digital temperature indicator

Why design switch and not a linear temperature dependent output?


Design goalsDesign goals

• Standard 0.18 m CMOS process

• Low voltage, Low power, Small area

• High accuracy

• Portable

• Switch temperature of 125 °C

• Extendable:adjustable switch temperaturemultiple switch temperatures

high accuracy over large T range


A

=

(1) (n)

R

IPTAT

k*R

Circuit FundamentalsCircuit Fundamentals

Use bandgap principle:

V

T

Vbe

V

T

Vgap,0

V

T

Vptat


Circuit FundamentalsCircuit Fundamentals

Detect crossing of Vptat with Vbe

A

=

(1) (n)

R1

IPTAT

R2

=

Binaryout

V

T

Vptat

V

T

Vbe


Design strategyDesign strategy

– Bipolar transistor Vbe spread

– Resistor matching & spread– Offset and noise of MOST devices

Establish quantitative relation for optimal MOST area distribution

Identify accuracy limitations:


Design strategyDesign strategy

A

=

(1) (n)

R1

R2

=

Binaryout

Vo1

Vo2

Io Io Io

2

2

2

122

2

1

2222

)ln(21

12R

n

RR

R

RooocompV IVV


Design strategyDesign strategyAssume:

WL

A

WL

A II

vV DGS

22 ,

Find equivalent offset (or flicker noise):

3

3

2

2

1

12

Area

X

Area

X

Area

Xtot

Minimal total given fixed Areatotal when:

23

322

221

1

Area

X

Area

X

Area

X


ImplementationImplementation

– High amplifier gain; speed may be low.– High supply and substrate noise rejection.

Implementation limitations:– Low supply voltage cascoding difficult.

– Folded cascodes not desirable

Implementation goals:



A

=

(1) (n)

R1

IPTAT

R2

=

Binaryout



A

Iout

Vdd

Iout

Vin-

Vin+

Positive feedback;

high gain, small bandwidth



– Robust circuit, easy to port

– Small flicker noise & offsetstraightforward use of large transistors instead of using

complex dynamic offset cancellation techniques.

– No cascoding or shielding low supply voltage

– All matched transistors have matched conditions at threshold temperature

Strong points:



Weak point:

– Nested inner loop stability analysis not straightforward


Chip photographChip photograph

Transconductance

amplifier

Comparator

Resistors Diode

connected

BJTs

150 m

190 m


SpecificationsSpecifications


ConclusionsConclusions

• Efficient & Robust Design strategy

• Very low power circuit– can decrease further with duty-cycle mode

• Good performance without calibration– 3 intra-batch deviation of only 1.1 C

• Design is well-suited for multiple thresholds extension


A 1-V 15 A 1-V 15 W High-Precision W High-Precision Temperature SwitchTemperature Switch

D. Schinkel, R.P. de Boer,

A.J. Annema and A.J.M. van Tuijl

Philips Research

University of Twente, Faculty of Electrical Engineering

A 1-V 15 W High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van...

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