0TC Voltage Ref

8/3/2019 0TC Voltage Ref

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1

A CMOS Voltage Reference Based on Weighted

Difference of Gate-Source Voltages between PMOS

and NMOS Transistors for Low Dropout Regulators

Ka Nang Leung and Philip K. T. Mok

Department of Electrical and Electronic Engineering

The Hong Kong University of Science and Technology



2

Outlines

• Brief Review on Conventional MOS VoltageReference Based on Threshold Voltages

• Proposed CMOS Voltage Reference

• Conclusions



3

Conventional MOS Voltage ReferenceBased on Threshold Voltages

2 th1thref V V V -

[1] B.-S. Song and P. R. Gray, “Threshold-Voltage Temperature Drift in Ion-Implanted MOS

Transistors”, IEEE Journal of Solid-State Circuits, vol. SC-17, pp. 291-298, Apr. 1982.



4

Requirements of Conventional Reference

• Good matching of TC of Vth for low-TC Vref èRequire extensive process controls

èExpensive

• Require NMOS (PMOS) transistors with different Vth

èRequire multi-threshold-voltage process or

depletion-enhancement transistor process

èNot compatible in standard CMOS process



5

General Idea of Proposed CMOS Reference

NMOS ThresholdNMOS Threshold

Voltage Generator Voltage Generator

PMOS ThresholdPMOS Threshold

Voltage Generator Voltage Generator

ScalingScaling

Factor k Factor k

S+

TempTemp

VREF VREFTempTemp

|VTHP||VTHP|

THPTHNref VkVV -

TempTemp

VTHN VTHN

Controlled by circuit

parameters



6

Core Circuit

VREF

PMOS

NMOS

R1

R2

IB

VCC

ú

úúú

û

ù

ê

êêê

ë

é

-

÷ø

ö

çè

æ

÷ø

öçè

æ

÷ø

öçè

æ+

÷ø

ö

çè

æ

ú

û

ùê

ë

é-÷

ø

öçè

æ+

-÷ø

öçè

æ+

1

L

W

L

W

R

R 1

L

W

C

I 2

V V

R

R 1

V V R

R 1V

N N

P P

2

1

P OX P

B

THP THN 2

1

)PMOS ( GS )NMOS ( GS 2

1REF

m

m

m



7

Proposed CMOS Voltage Reference

GSpGSn2

1ref V V

R

R 1V -÷

ø

öçè

æ+

• Implemented in 0.6-mm CMOS process

• Simple and OpAmp-less structure



8

Minimum Supply Voltage

)sat ( 5 DS o

GSn2

1mins V C 0 @ V

R

R 1V +÷

ø

öçè

æ+

• Vsmin = 1.4V(Vthn » |Vthp| » 0.9V@0oC)

• Sub-1-V supply

voltage is possible for

Vth < 0.6V



9

Design Considerations

)mobilitiesand current ( F )voltagethreshold ( F

T

V

T

V

R

R 1

T

V

2 1

GSpGSn

2

1ref

+

¶

¶-

¶

¶÷ø

öçè

æ+

¶

¶

linear temp dependence non-linear temp dependence

1R

R

vthn

vthp

2

1-

b

b

2

p

n2

vthn

vthp

o

r

o p

on

n

p

2 2

1

T

T

)T (

)T (

L

W

L

W n p

÷ø

ö

çè

æ+÷

ø

öçè

æ

÷ø

öçè

æ

=÷ø

öçè

æ

÷ø

öçè

æ-

m

m

b

b

b

b

b

m

mm



10

Experimental Results

With optimum resistor ratio - TC = 24 ppm/oC

312.3

312.4312.5

312.6

312.7

312.8

312.9

313.0

313.1

313.2

313.3

0 20 40 60 80 100

Temperature (degree C)

R e

f e r e n c e v o l t a g e ( m

V )

Vs = 1.40 V Vs = 2.00 V Vs = 3.00 V



11

Resistor Ratio Sensitivity

1

R

R

vthn

vthp

2

1-

b

b

Typically, 0 < R1/R2 < 1 since bvthp is close to bvthn

(~1.2 to 4 mV/K)

So, the error on the resistance ratio in the proposeddesign is better than that in bandgap reference since

2

1

2

1

2

1

2

1

R

R R

R

R

R 1

R

R

÷ø

ö

çè

æ

<<

+

÷ø

ö

çè

æ D



12

Comparison with Bandgap Reference

-100%

0%

100%

200%

300%

400%

500%

600%

1% 2% 3%

Resistor Ratio Variation

V r e

f T C

V a r

i a t i o

n

BGVEF CMOSVREF

Comparison on Resistor Ratio Variation



13

Experimental Results on Change of R Ratio

312.3

312.4

312.5

312.6

312.7

312.8

312.9

313.0

313.1

313.2

313.3

0 20 40 60 80 100


R e f e r e n c e v o l t a g

e ( m V )

Vs = 1.40 V Vs = 2.00 V Vs = 3.00 V

331.5

332.0

332.5

333.0

333.5

334.0

334.5

0 20 40 60 80 100


R e f e r e n c e v o l t a g e

( m V )

Vs = 1.40 V Vs = 2.00 V Vs = 3.00 V

With optimumresistor ratio

TC = 24 ppm/oC

Resistor ratio off by6.23%

TC = 50 ppm/oC



14

Summary of the Measurement Results

~ ±0.03%/V (typical)±0.17%/V (max)

Line regulation

~ 25 ppm/oC (typical)

62 ppm/oC (max)

TC (0 to 100 oC)302.24±12 mVReference voltage

9.7 mA (max)Supply current

1.4 to 3 VSupply voltage

Measured results of 11 samples of 2 runs



15

Applications of the Proposed Voltage Reference

• Low Supply Voltage (down to 1.5V)• True CMOS Technology

• Output Voltage is adjusted by resistor network



16

Conclusions

A CMOS Voltage Reference is proposed• Compatible and reproducible in standard CMOStechnology

• Simple and OpAmp-less structure

• Temperature dependence is controlled by circuitparameters instead of requiring extensive processcontrols

• Low sensitivity on the resistor ratio

• Small size

• Good TC performance for power converter applications

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0TC Voltage Ref