low voltage temperature sensor front end

Low Voltage Smart Temperature Sensor Front End

Design and Analysis of Analog IC

1

Shreyas Rao

R10357881

Satyabh Mishra

R10322331

Introduction

PTAT

Analog to

2

Voltage Reference

Analog to Digital Converter

Project Goals

� To Design a PTAT, varying with Temperature but independent of Power Supply.

� To Design a Voltage Reference Independent of

3

� To Design a Voltage Reference Independent of Temperature and Power Supply.

� Desired Temperature Range (0ºC~120ºC).

� Desired Voltage Range (1.2V~2V).

Design Principles

� Use of Subthreshold MOSFETs, where VGS < VTH.

4

� Achieved by increasing the Transistor Size(W/L) under a fixed current.

Design Principle For PTAT

� By Using the two NMOS in Subthreshold Region.

The Output Current of the PTAT varies exponentially.

� Id=Io exp (Vgs/ζ Vt)

5

� Id=Io exp (Vgs/ζ Vt)

;Vt=KT/q

� Transistor size is determined by keeping the PMOS in Active and NMOS in Subthreshold Region.

PTAT Output

Id=Io exp (Vgs/ζ Vt)

6

Design Principle for Voltage Ref.7

Design of Compensation Circuit

� The Compensation Current flowing through the resistor equals (VGS /R).

� As the temperature increases , for keeping the

8

increases , for keeping the Vgs constant under subthreshold the Compensation Current Decreases.

Compensation Circuit Output9

Final Schematic and Layout10

(167.250µm * 56.850µm)

Voltage Reference11

Voltage Reference12

Temperature VDD

Performance at Worst Corner

V=0.8V

PTAT ResponseVoltage Reference

13

Vref at 3V and 5V14

Design Challenges

� Keeping the Desired Transistors in Subthreshold Region and Others in Active Region.

� Determining the Correct (W/L) configuration for all

15

� Determining the Correct (W/L) configuration for all transistors and Resistance Value.

� Making the PTAT and Vref independent of Power Supply Variation.

Point of Concern

� The Voltage Reference and PTAT is not independent with variation of Power Supply.

16

� Getting the Exact Inverse Slope for PTAT and Compensation Circuit.

Future Work

� Design of PTAT source independent of Power Supply variation.

� An improved constant Gm Circuit with the property

17

� An improved constant Gm Circuit with the property of PTAT can be implemented.

� Increasing the Voltage and Temperature Range.

References

� Po-Hsuan Huang, Hongchin Lin and Yen-Tai Lin, “A Simple Subthreshold CMOS Voltage Reference Circuit with Channel-Length Modulation Compensation,” IEEE Transactions on Circuits and Systems-II, September 2006.

� B. Razavi, “Design and Analysis of CMOS Integrated Circuits”.

18

� B. Razavi, “Design and Analysis of CMOS Integrated Circuits”. (Text Book)

� G.Giustolisi, G.Palumbo, M.Criscione and F. Cutri, ”A Low-Voltage Low-Power Voltage Reference Based on Subthreshold MOSFETs,” IEEE Journal of Solid State Circuits, VOL.38, January 2003.

Thanks

19

Thanks