This paper presents CMOS temperature sensor which is designed using starved voltage controlled ring oscillator at 180 nm CMOS technology. CMOS temperature sensor also consists a voltage level shifter, a counter, and a register that is designed using d flip flop. Temperature sensor occupies smaller silicon area with higher resolution than the conventional temperature sensor. Used VCRO has full range voltage controllability along with a wide tuning range and is most suitable for low-voltage operation due to its full range voltage controllability. Various parameters of circuits are calculated. Result shows that speed and power dissipation of circuit are directly proportional to power supply voltage. By increasing temperature we see that power dissipation of circuit increases while delay decreases.

1. IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 09, 2014 | ISSN (online): 2321-0613
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Design and Analysis of Temperature Sensor using CMOS Technology
Modhya Mehul1
Kumkum Verma2
Sanjay Kumar Jaiswal3
1,2,3
Department of Electronics and Communication
1,2,3
ITM, Bhilwara
Abstract— This paper presents CMOS temperature sensor
which is designed using starved voltage controlled ring
oscillator at 180 nm CMOS technology. CMOS temperature
sensor also consists a voltage level shifter, a counter, and a
register that is designed using d flip flop. Temperature
sensor occupies smaller silicon area with higher resolution
than the conventional temperature sensor. Used VCRO has
full range voltage controllability along with a wide tuning
range and is most suitable for low-voltage operation due to
its full range voltage controllability. Various parameters of
circuits are calculated. Result shows that speed and power
dissipation of circuit are directly proportional to power
supply voltage. By increasing temperature we see that power
dissipation of circuit increases while delay decreases.
Key words: CMOS, VCO, WSN
I. INTRODUCTION
Temperature is one of the most important fundamental
physical quantity which is almost common in our daily life
and do not depend upon of materials i.e. temperature has
intensive property. Nowadays for each & every application
new higher performance standard circuits are required. As
we know thousands or millions of component are integrated
on thin silicon wafers. Before the wafer is scribed and cut
into individual chips, they are usually laser trimmed. One
popular use of embedded temperature sensors in VLSI
implementation is in the emergence of RFID and wireless
sensor network (WSN) applications.
For such type of applications, power consumption,
instead of sensing range and accuracy requirements,
becomes more important. CMOS temperature sensor has
been designed for microprocessor application. The
advantage of this circuit is no need of any BJT component
.One of the popular method is by using the difference
between the two outputs of register. These sensors in
general achieve good accuracy, less power dissipation.
The temperature sensors have been realized using a
ring-oscillator, in a 180 nm technology. Temperature is a
physical quantity that is a measure of hotness and coldness
on a numerical scale. Output signal generated by the ring
oscillator is proportional to the change in temperature. The
positive rising edge of voltage level shifter is counted by the
counter and then it is saved in register i.e. d flip flop. The
difference between outputs of register is taken as
temperature. Block diagram of temperature sensor is given
below.
Fig.1: Block diagram of temperature sensor
II. DESIGN OF CIRCUIT
A. Ring Oscillator:
A voltage controlled oscillator (VCO) is one of the most
important building blocks in analog and digital circuits.
There are many different implementations of VCO’s. One of
them is a ring oscillator based VCO, which is commonly
used in the clock generation Subsystem. The ring oscillator
is mainly used for its direct consequence of Easy
integration. Due to the integrated nature ring oscillators,
they have become the main part of many digital
communication systems. They are used as voltage controlled
Oscillators (VCO’s) in applications such as clock recovery
circuits for serial data Communications.
A ring oscillator consists of number of gain stages
in a loop in which output of the last stage is fed back to the
input of the first. The ring oscillator must satisfy the
Barkhausen criteria, which says that it should provide a
phase shift of 2π and to achieve oscillation it must have a
unity gain. The voltage controlled oscillator is designed
using self-bias ring oscillator as shown in figure 2.
Fig.2: Voltage Controlled ring oscillator
In this, the MOSFETs M5 and M9 operate as
inverter while MOSFETs M2 and M12operate as current
sources. The current sources limit the current available to
the inverter or it can be said that the inverter is starved for
the current. So this type of oscillator is called current starved
voltage controlled oscillator. Here the drain currents of
MOSFETs M1 and M8 are the same and are set by the input
control voltage.
B. D Flip Flop
A register is a memory device that can be used to Store
more than one bit of information. A register is usually
realized as several flip-flops with common control signals
that control the movement of data to and from the register.
Flip-Flop stores a logical state of one or more data input
signals in response to a clock pulse. During recurring clock
intervals to receive and maintain data for a limited time
period sufficient for other circuits within a system to further
process data. Power dissipation is an important parameter in
the design of VLSI circuits, and the clock network is
responsible for a substantial part of it (up to 50%). When the
supply voltage is decreased the speed of the logic circuits

2. Design and Analysis of Temperature Sensor using CMOS Technology
(IJSRD/Vol. 2/Issue 09/2014/038)
All rights reserved by www.ijsrd.com 170
might be decreased due to reduction in effective input
voltage to the transistors. Circuit diagram of D flip flop is
shown below in fig 3.
Fig.3: Schematic Diagram of D Flip- Flop
It consists 4 nand gate and 1 not gate. D and clk are its
input. Clock pulse (clk) is used to control the data moving
from input to output.
C. Level Shifter
In this temperature sensor the reduced ring oscillator output
is extended by voltage level shifter to full-scale so that the
counter counts the number of its rising edge. A binary input
signal having low voltage level to a binary signal having
different output is translated by a level shifter in an
integrated circuit. The level shifter is controlled by the low
state voltage translation circuits. Schematic diagram of level
shifter is shown in fig 4.
Fig.4: Level Shifter
D. Temperature Sensor
A temperature sensor is a device that gathers data
concerning the temperature from a source and converts
it to a form that can be understood either by an observer
or another device. . Schematic diagram of Temperature
Sensor is shown above in fig. 5.
Fig.5: Temperature Sensor
III. RESULT AND DISCUSSION
A. Ring Oscillator
The voltage controlled oscillator is used to generate a
specific frequency signal. The VCO is designed by 3-stage
ring oscillator which gives better VCO
Fig. 6: Voltage Controlled Ring Oscillator
Fig. 7: Characteristic of VCO
characteristic and frequency range. The simulated waveform
of VCO and the characteristic is shown above in fig 6 and
fig 7.Power dissipation and delay of ring oscillator at
different power supply voltage is shown below in table 1
when W/L ration of PMOS transistor is equal to 3 times of
NMOS W/L ratio.
Table 1: Power Dissipation & Delay of Ring
Oscillator at different Voltage
Vdd(V)
Delay (10-15
s) Power(µW)
PDP
1 1.3130 15.83 20.784
1.2 1.1896 67.14 79.869
1.4 1.0662 83.38 88.899
1.6 0.9428 92.60 87.303
1.8 0.8194 92.42 75.728
Here we see that by increasing power supply voltage delay
of the circuit decreases while power dissipation increases as
power dissipation of circuit is directly proportional to square
of power supply voltage.
B. D Flip Flop
Waveform of D flip flop is shown below in fig 8. When
input D is low & clock pulse is 0, then Qb will be low & Q
will be high. If input D is high & clock pulse is 0. Then Qb
will be low & Q will be high. Simulated waveform of D flip
flop is shown below in fig 8.
Fig.8: Simulated waveform of D flip flop

3. Design and Analysis of Temperature Sensor using CMOS Technology
(IJSRD/Vol. 2/Issue 09/2014/038)
All rights reserved by www.ijsrd.com 171
C. Level Shifter
Waveform of voltage level shifter is shown below in fig 9.
When the input signal Vin is low then output will also low
& if input signal Vin is high then the output will be high.
Fig.9: Waveform voltage level shifter
D. Temperature sensor
Ring oscillator-based temperature sensors provide a
good indication of circuit speed. Its waveform is shown
below in fig 10.
Fig.10: Waveform voltage level shifter
Power dissipation & delay of temperature sensor at different
threshold voltage and at different temperature is shown
below in table 2 and table 3.
Table 2: Delay and Power at different VTH
VTH(V) Delay (10-15
s) Power(µW)
0.37 199.43 227.585
0.47 200.17 161.83
0.57 199.91 146.41
0.67 198.57 44.22
0.77 195.88 75.74
Table3: Power, Delay and PDP at Different Temperature
Temperature
Delay
(10-15
s)
Power(µW)
PDP
37º 1.3130 40.35 53.003
47º 1.1896 112.08 133.33
57º 1.0662 241.175 257.13
67º 0.9428 245.175 231.15
77º 0.8194 344.39 282.19
IV. CONCLUSION
A ring oscillator-based CMOS temperature sensor has been
presented. Temperature sensor occupies smaller silicon area
with higher resolution than the conventional temperature
sensor based on band gap reference. Extremely low power
consumption is achieved through charge recycling. Ring
oscillators are basic building blocks of complex integrated
circuits. They are mainly used as clock generating circuits.
Used VCRO has full range voltage controllability along
with a wide tuning range and is most suitable for low-
voltage operation due to its full range voltage controllability.
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