Download A 1-V 15 mW High-Precision Temperature Switch

Philips Research
University of Twente, Faculty of Electrical Engineering
A 1-V 15 mW High-Precision
Temperature Switch
D. Schinkel, R.P. de Boer,
A.J. Annema and A.J.M. van Tuijl
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Contents
•
•
•
•
•
•
Introduction
Circuit fundamentals
Design strategy
Implementation
Specifications
Conclusions
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Introduction
Why need integrated CMOS temperature
indicator?
– enable thermal protection (shutdown,clock
frequency lowering etc.)
– use in integrated measurement or control
devices
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Introduction
Why design switch and not a linear
temperature dependent output?
– Thermal protection only requires threshold
temperature detection (125 °C)
– Multiple threshold values together form a
digital temperature indicator
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Design goals
•
•
•
•
•
•
Standard 0.18 mm CMOS process
Low voltage, Low power, Small area
High accuracy
Portable
Switch temperature of 125 °C
Extendable:
adjustable switch temperature
multiple switch temperatures
high accuracy over large T range
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Circuit Fundamentals
Use bandgap principle:
V
Vgap,0
=
IPTAT
k*R
T
V
Vptat
A
T
R
V
Vbe
(1)
(n)
T
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Circuit Fundamentals
Detect crossing of Vptat with Vbe
V
=
Vbe
=
IPTAT
T
Binary
out
A
R1
V
R2
(1)
(n)
Vptat
T
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Design strategy
Identify accuracy limitations:
– Bipolar transistor Vbe spread
– Resistor matching & spread
– Offset and noise of MOST devices
Establish quantitative relation for
optimal MOST area distribution
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Design strategy
Io
Io
=
Io
=
Vo2
Vo1
Binary
out
A
R1
R2
(1)
 2V
comp
(n)
R

  V2o 2   V2o1  2  1
 R1

2
2




R

R
2
2
2
1
  R2 
  I o  2 
  ln( n) 



A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Design strategy
Assume:

2
VGS
Av

WL
, 
2
ID
AI

WL
Find equivalent offset (or flicker noise):

2
tot
X3
X1
X2




Area1 Area2 Area3
Minimal total given fixed Areatotal when:
X3
X1
X2



2
2
2
Area1
Area2 Area3
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Implementation
Implementation goals:
– High amplifier gain; speed may be low.
– High supply and substrate noise rejection.
Implementation limitations:
– Low supply voltage  cascoding difficult.
– Folded cascodes not desirable
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Implementation
=
=
IPTAT
Binary
out
A
R1
R2
(1)
(n)
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Implementation
Vdd
Iout
Vin-
A
Vin+
Iout
Positive feedback;
high gain, small bandwidth
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Implementation
Strong points:
– Robust circuit, easy to port
– Small flicker noise & offset
straightforward 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
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Implementation
Weak point:
– Nested inner loop  stability analysis not
straightforward
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Chip photograph
Diode
Resistors
connected
BJTs
Transconductance
amplifier
Comparator
190 mm
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
150 mm
Specifications
This work
Other work
Supply voltage
1.0-1.8 V
2.2-5.5 V
Supply current
16mA
25mA DC
Technology
CMOS 0.18 mm
CMOS 2 mm
Area
0.03 mm2
1.5 mm2
Inaccuracy (3)
1.1C
1C
Calibration
No
Yes
DC supply sensitivity
0.05C/V
0.1C/V
Switch temperature
128.5C
-
Hysteresis
1.2C
-
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
Conclusions
• 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 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl
A 1-V 15mW High-Precision Temperature 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 mW High-Precision
Temperature Switch
D. Schinkel, R.P. de Boer,
A.J. Annema and A.J.M. van Tuijl
A 1-V 15mW High-Precision Temperature 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 mW High-Precision
Temperature Switch
D. Schinkel, R.P. de Boer,
A.J. Annema and A.J.M. van Tuijl
A 1-V 15mW High-Precision Temperature Switch
D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl