U.S. patent application number 09/187502 was filed with the patent office on 2002-02-21 for low voltage/low power temperature sensor.
Invention is credited to YIN, RONG.
Application Number | 20020022941 09/187502 |
Document ID | / |
Family ID | 22689252 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020022941 |
Kind Code |
A1 |
YIN, RONG |
February 21, 2002 |
LOW VOLTAGE/LOW POWER TEMPERATURE SENSOR
Abstract
The present invention is a temperature sensor which is based on
the actual temperature coefficients of a device in the circuit,
rather than a predetermined threshold voltage that varies across
different devices. This temperature sensor includes a circuit which
determines the temperature of a device. More particularly, CMOS
circuit is provided which uses a current source to generate charge
and discharge voltages applied to a capacitor. These voltages are
dependent on the temperature coefficient of a resistor in the
current source. The charge and discharge times are then used to
determine a frequency which is dependent on the temperature
coefficient of the resistor. Thus, the temperature is sensed based
on the output frequency of the circuit. Additionally, the present
invention includes a mechanism which allows the temperature sensor
to be activated or deactivated as needed.
Inventors: |
YIN, RONG; (COPPELL,
TX) |
Correspondence
Address: |
Lisa K. Jorgenson, Esq.
STMICROELECTRONICS INC
1310 ELECTRONICS DRIVE
MAIL STOP 2346
CARROLLTON
TX
75006
US
|
Family ID: |
22689252 |
Appl. No.: |
09/187502 |
Filed: |
November 6, 1998 |
Current U.S.
Class: |
702/130 ;
374/E7.035; 702/136 |
Current CPC
Class: |
G01K 7/01 20130101 |
Class at
Publication: |
702/130 ;
702/136 |
International
Class: |
G01K 001/00 |
Claims
1. A temperature sensor, comprising: a current source having a
plurality of transistors and at least one resistor; and means for
converting an electrical current output from said current source to
a temperature dependent frequency signal; wherein said temperature
dependent frequency signal is independent of a threshold voltage
across any of said plurality of transistors.
2. A sensor according to claim 1 wherein said temperature dependent
frequency signal is based upon a thermal coefficient of resistance
of said at least one resistor.
3. A sensor according to claim 2 wherein a frequency of said
temperature dependent frequency signal is proportional to a
temperature of said at least one resistor.
4. A sensor according to claim 1 wherein said means for converting
comprises: a capacitor coupled to an output of said current source
having a charge current and discharge current proportional to
charge and discharge voltages, respectively, which are related to a
resistance value of said at least one resistor; a comparator for
receiving an input signal from said capacitor and for outputting
differential phase shifted control signals based thereon; and a
circuit for combining said differential phase shifted control
signals and for outputting said temperature dependent frequency
signal.
5. A sensor according to claim 4 further comprising means for
monitoring said temperature dependent frequency signal, and for
regulating the operation of other circuits based upon a
predetermined temperature level.
6. A sensor according to claim 5 further comprising means for
deactivating said temperature sensor based upon an external control
signal.
7. A method of sensing a temperature in an integrated circuit
device, comprising the steps of: providing an electrical current
from a current source, included in said integrated circuit device,
said current source having a plurality of transistors and at least
one resistor; and converting said electrical current output from
said current source to a temperature dependent frequency signal;
wherein said temperature dependent frequency signal is independent
of a threshold voltage across any of said plurality of
transistors.
8. A method according to claim 7 wherein said temperature dependent
frequency signal is based upon a thermal coefficient of resistance
of said at least one resistor.
9. A method according to claim 8 wherein a frequency of said
temperature dependent frequency signal is proportional to a
temperature of said at least one resistor.
10. A method according to claim 9 wherein said step of converting
comprises the steps of: providing a capacitor coupled to an output
of said current source having a charge current and discharge
current proportional to charge and discharge voltages,
respectively, which are related to a resistance value of said at
least one resistor; receiving, by a comparator, an input signal
from said capacitor and outputting, by said comparator,
differential phase shifted control signals based thereon; and
combining said differential phase shifted control signals and
outputting said temperature dependent frequency signal.
11. A method according to claim 10 further comprising the steps of:
monitoring said temperature dependent frequency signal; and
regulating the operation of other circuits based upon a
predetermined temperature level.
12. A method according to claim 11 further comprising the step of
deactivating said temperature sensor based upon an external control
signal.
13. A data processing system for regulating the power consumption
of components included in said data processing system, comprising:
at least one integrated circuit device that performs a portion of
data processing functions in said data processing system; a
temperature sensor having a current source with a plurality of
transistors and at least one resistor, said sensor including means
for converting an electrical current output from said current
source to a temperature dependent frequency signal, wherein said
temperature dependent frequency signal is independent of a
threshold voltage across any of said plurality of transistors; and
a monitor for determining when said temperature dependent frequency
signal reaches a predetermined threshold and controlling an
operation of said at least one integrated circuit based thereon.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a circuit which determines
the temperature of a device. More particularly, a complementary
metal oxide semiconductor (CMOS) circuit is provided which uses a
current source to generate charge and discharge voltages applied to
a capacitor. These voltages are dependent on the temperature
coefficient of a resistor in the current source. The charge and
discharge times are then used to determine a frequency which is
dependent on the temperature of the resistor. Thus, the temperature
is sensed based on the output frequency of the circuit.
[0003] 2. Description of Related Art
[0004] In the computer and data processing industry there is an
ever increasing demand for higher processing speeds and systems
which are capable of performing multiple tasks in parallel. Often
times there are tradeoffs associated with this increased processing
performance. One example is an increased level of power consumption
and corresponding increase in the amount of heat generated by a
particular device or IC.
[0005] Temperature sensors have many applications. A large number
of circuits and/or functional units in today's electronic devices
are temperature sensitive and require accurate and reliable
temperature information in order to take corrective action when the
temperature becomes too high. For example, the system frequency may
be reduced when a certain temperature threshold is reached in order
to cause the temperature to be reduced below the critical point.
Further, systems, such as portable electronic devices (games,
laptops, notebook computers, personal digital assistants), and the
like are sensitive to power consumption and may need to shut down
all or part of their operations when the power, which is function
of temperature, reaches a certain level. Additionally, some
individual circuits may need to be disconnected or shut down when
the temperature reaches a predetermined level. Another application
is an oscillator, such as a crystal oscillator which is frequency
dependent. In this case a temperature sensor is required to adjust
the accuracy of the output frequency. Rechargeable battery
applications is yet another area wherein an accurate and reliable
temperature sensor will have utility.
[0006] Conventional temperature sensing techniques are typically
based on a predetermined value of a transistor threshold voltage.
In reality the integrated circuit (IC) fabrication process is not
exactly consistent between groups of wafers, or lots. Thus, a
threshold voltage for transistors in a particular lot of wafers
will not be the same as the threshold voltage for the transistors
in another lot. Thus, the correlation between the frequency and the
temperature will not be consistent between sensors fabricated in
different lots. The functional units relying on the temperature to
perform various data processing activities may operate at different
temperatures resulting in inconsistent results across the same
device fabricated in a different lot.
[0007] Therefore, it can be seen that a need exists for a
temperature sensor that provides greater consistency when
manufactured at different times and in different lots in order to
provide a temperature dependent output signal having increased
accuracy.
SUMMARY OF THE INVENTION
[0008] In contrast to the prior art, the present invention is a
temperature sensor which is based on the actual temperature
coefficients of a device in the circuit, rather than a
predetermined threshold voltage that varies across different
devices.
[0009] Broadly, the present invention relates to a circuit which
determines the temperature of a device. More particularly, CMOS
circuit is provided which uses a current source to generate charge
and discharge voltages applied to a capacitor. These voltages are
dependent on the temperature coefficient of a resistor in the
current source. The charge and discharge times are then used to
determine a frequency which is dependent on the temperature of the
resistor. Thus, the temperature is sensed based on the output
frequency of the circuit.
[0010] An additional feature of the present invention is a
mechanism which allows the temperature sensor to be activated or
deactivated as needed.
[0011] Therefore, in accordance with the previous summary, objects,
features and advantages of the present invention will become
apparent to one skilled in the art from the subsequent description
and the appended claims taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram of a data processing system
including components capable of implementing the present
invention;
[0013] FIG. 2 is a schematic diagram of the elements that make up a
preferred embodiment of the present invention;
[0014] FIG. 3 is a more detailed schematic diagram of the
activation mechanism of the present invention; and
[0015] FIG. 4 are timing diagrams showing the waveforms at
particular times which are present at various nodes in the circuit
schematic of FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] In order for the various data processing systems to utilize
the functions of the present invention, the temperature sensor is
provided in selected ones of the integrated circuits, or chips,
that make up the system. For example, the temperature sensor of the
present invention may be provided on an application specific
integrated circuit (ASIC) in the clocking portion. In this manner,
the frequency output from the clock circuit can be lowered when the
sensor of the present invention determines that a temperature above
a predetermined threshold has been reached. Thus, control signals
can be provided to the clock circuit, such as a phase locked loop
(PLL) in order to regulate the temperature of the chip. This clock
circuit may be used to drive the frequency of a microprocessor,
microcontroller, digital signal processor (DSP) or like embedded on
the ASIC. In another application, the sensor of the present
invention can determine when a temperature threshold is reached in
order to turn off various non-critical portions of an IC to reduce
the power consumption and corresponding temperature. Those skilled
in the art will be familiar with numerous other uses of the
temperature sensor of the present invention.
[0017] Referring to FIG. 1, a typical data processing system is
shown which may be used in conjunction with the present invention.
This data processing system could include virtually any system
having a need to regulate the temperature of an included device or
circuit, including a laptop computer, PDA, desktop computer, or the
like. A central processing unit (CPU) 10 such as the Pentium II
microprocessor, commercially available from Intel Corp. may be
provided, although other microprocessors from other manufacturers,
such as the PowerPC microprocessor, commercially available from IBM
Corporation may also be used. Microprocessor 10 is interconnected
to the various other components by system bus 12 read only memory
(ROM) 16 is connected to CPU 10 via bus 12 and includes the basic
input/output system (BIOS) that controls the basic computer
functions. Random access memory (RAM) 14, I/O adapter 18 and
communications adapter 34 are also interconnected to system bus 12.
I/O adapter 18 may be a small computer system interface (SCSI)
adapter that communicates with a disk storage device 20.
Communications adapter 34 interconnects bus 12 with an outside
network enabling the data processing to communication with other
such systems, via the internet, local area network (LAN), or the
like. Input/output devices are also connected to system bus 12 via
user interface adapter 22 and display adapter 36. Keyboard 24,
track ball 32, mouse 26 and speaker 28 are all interconnected to
bus 12 via user interface adapter 22. Display monitor 38 is
connected to system bus 12 by display adapter 36. In this manner, a
user is capable of inputting to the system through the keyboards
24, trackball 32, or mouse 26 and receiving output from the system
via speaker 28 and display 38. Additionally, an operating system,
such as one of the versions of Windows, commercially available from
Microsoft Corporation is used to coordinate the functions of the
various components shown in FIG. 1.
[0018] Referring to FIG. 2, a preferred embodiment of the
temperature sensor of the present invention is shown. In this
embodiment a switching mechanism is shown with allows the
temperature sensor to be turned on or off. In some instances it is
advantageous to have the ability to control whether or not the
temperature sensor is operating. For example, when a data
processing system is in a low power or "sleep" mode it is not
necessary for the temperature sensor to be operational, since
during "sleep" mode most functions of the system are turned off and
the temperature will be at an acceptable level.
[0019] More particularly, a switching circuit is shown which can be
used by the system microprocessor or controller to disable the
temperature sensor in order to further reduce the total power
consumption. An input signal is provided on node 50 to a first
inverter 51. Additionally, a second inverter 53, delay circuit 55
and third inverter 57 are also part of the switching circuit. A
P-type transistor 58 is shown with its gates connected to the
output of inverter 51. P-type devices will conduct electricity when
a logical "0" (absence of a voltage) is provided to their gate. An
N-type transistor 52 having its gate connected to the output of
inverter 53. N-type transistors will conduct electricity when a
logical "1" (voltage) is applied to their gate. P-type transistor
54 is also shown with its gate connected to the output of delay
circuit 55, and it can be seen N-type transistor 56 has its gate
connected to the output of inverter 57.
[0020] When a "stop" signal input to node 50 is set equal to
logical 1, then the current source formed by transistors 101, 102,
103, 104 and resistor 105 is turned off. Specifically, when the
output of inverter 51 transitions from a "1" to a "0" transistor 58
will conduct electricity and pull node 60 to Vcc. The output of
inverter 53 will be a "1" when the input to node 50 is set.
Therefore, transistor 52 will conduct electricity and pull node 61
down to the reference voltage (potential), in this case, Vss. It
can be seen that when node 60 is at Vcc, transistors 101 and 102
will not conduct and cannot supply the current needed for the
temperature sensor to operate. Transistor 106, 107, 108 and 109 are
P-type transistors and form current mirrors. Each of these
transistors has its gate connected to node 60 such that when
transistors 101 and 102 of the current source are off they will
also be turned off.
[0021] When it is desired for the system to turn on the temperature
sensor the input control signal at node 50 is switched from high
(1) to low (0). This causes a short pulse to be generated at the
gate of transistor 54 (from delay circuit 55). Also a pulse is
provided from inverter 57 to the gate of transistor 56. When
transistor 54 conducts, node 61 will then be pulled up to Vcc
causing transistors 103 and 104 of the current source to conduct.
Similarly, node 60 is pulled down to Vss when transistor 56 begins
to conduct and transistor 101 and 102 also begin to conduct and the
current source then operates.
[0022] Next, the operation of the temperature sensor will be
described, also in conjunction with FIG. 2. As noted above,
transistors 101, 102, 103, 104 and resistor 105 form a current
source which provides electrical current through transistors 102,
104 and resistor 105. All of the transistors, 101, 102, 103 and 104
are working at weak inversion.
[0023] The voltage (Va) at node 62 can be determined using the
following equation:
Va=kT/q In S.sub.104S.sub.101/S.sub.103S.sub.102. (1)
[0024] Where k is Boltzmann's constant, q is electron charge and T
is temperature in degrees Kelvin. This constant (kT/q) is about 26
millivolts at 300 degrees K. In equation (1), "S" represents the
transistor size, i.e. width/length (W/L), for the transistors in
the current source (101, 102, 103, 104). A current mirror is formed
by transistor 106 wherein the same current that flows through
transistors 102, 104 and resistor 105 will also flow through
transistor 106 and resistors 109 and 110. The voltage (Vd) at node
63 can be determined in accordance with the following equation:
Vd=(S.sub.106/S.sub.102)(R.sub.110/R.sub.105)(Va) (2).
[0025] And the voltage (Vc) at node 64 can be determined by the
following:
Vc=(S.sub.106/S.sub.102)((R.sub.109+R.sub.110)/R.sub.105)(Va)
(3).
[0026] Vc is the voltage drop across resistors 109 and resistor
110, and Vd is the voltage across resistor 110.
[0027] In a preferred embodiment of the present invention, the
capacitors are implemented by using N-type depletion transistors.
That is, the source and drain of an N-type transistor are coupled
to one another and a capacitance is created across the gate and the
connected source/drain of the transistor. Capacitors 120, 121 and
122 are such N-depletion transistors. The temperature sensor of the
present invention then utilizes capacitor 120 to determine the
output frequency. More particularly, when the current source is
active, transistor 108 will be turned on to conduct electricity.
When N-type transistor 115 is on, the current will be used to
charge capacitor 120. P-type transistor 107 will also conduct when
transistor 108 is turned on. This will cause transistors 111 and
112 to conduct such that capacitor 120 has a path to Vss for the
discharge current. The current used to charge capacitor 120 is
represented by the following equation:
Ic=(S.sub.108/S.sub.102)(Va/R.sub.105). (4)
[0028] The discharge current from capacitor 120 can be
characterized by:
Id=(S.sub.112/S.sub.111)(S.sub.107/S.sub.102)(Va/R.sub.105).
(5)
[0029] The voltages Vc and Vd, as noted above, are the charging and
discharging voltages, respectively.
[0030] The voltage at node 71 is switched between Vc and Vd through
two N-type transistor passgates 146 and 147. When passgate 146 is
turned on, the voltage on node 71 is at Vc (charge). Also, when
transistor 146 is turned on N-type passgate transistor 115 will
also be turned on allowing capacitor 120 to be charged to the Vc
voltage level through node 70. While the voltage at node 70 is
greater than the voltage at node 71, the voltage at node 72 is
approximately the same as the threshold voltage (Vtn) of an N-type
transistor, e.g. transistor 130 and the voltage at node 73 is
substantially zero (0). At the next transition, node 75 goes high
(1) and turns on passgate 147 and N-type pass gate transistor 117.
In this case, the voltage at node 71 then switches to the Vd
(discharge) level. When passgate 117 turns on, node 70 begins to
discharge to the Vd voltage level and the discharge current will
flow through transistor 112 to Vss.
[0031] In a preferred embodiment of the present invention a
comparator is used to as a current to frequency converter. More
particularly the comparator will transform the analog current
output sensor signal to a digital control signal. The comparator is
formed by P-type transistors 109, 125 and 126, along with N-type
transistors 127, 128, 129 and 130, where transistors 128 and 129
are provided, in a preferred embodiment, to add more gain to
transistors 127 and 130. As shown in more detail by FIG. 4, the
waveforms at nodes 72 and 73 are quasi square waves with a 180
degree phase shift. The frequency of these square waves carry the
temperature information. This frequency can be translated into a
digital number by counting the square wave pulses over a
predetermined period.
[0032] A differential to single converter (level shifter) is then
utilized in a preferred embodiment of the present invention to
translate the differential waveforms into a single temperature
dependent signal. This converter is formed by P-type transistors
133 and 134 in conjunction with N-type transistors 132 and 135.
From FIG. 4, it can be seen that when node 73 is at the threshold
voltage of an N-type transistor (Vtn), node 72 will be low and vice
versa. During the time period when node 72 is at the Vtn level,
transistor 132 will be turned on causing the gates of transistors
133 and 134 to be pulled to Vcc-Vtp. That is, the gates of these
transistors is pulled to the voltage level of the input voltage
(Vcc) minus the threshold voltage of a P-type transistor (Vtp).
This, in turn causes node 74 to be pulled up to voltage Vcc. Node
74 is effectively the output of the temperature sensor of the
present invention. However, this node is connected to a series of
inverters which are used to increase the speed of the signal on
node 74. In a preferred embodiment four (4) inverters are
connected. These inverters are formed by P-type transistors 136,
138, 140 and 142, connected with N-type transistors, 137, 139, 141
and 143, respectively. Thus, when node 72 is at the Vtn level, node
74 will also be high and the output of the temperature sensor at
node 145 will also be high. During this same time period, node 73
will is low and will not turn on transistor 135. However, during
the next time period, node 73 will be at the Vtn voltage level
turning on transistor 135 which causes node 74 to be pulled down to
Vss thereby turning on P-type transistor 136, This causes the
output of the inverter (formed by transistors 136 and 137) to be
high (1).
[0033] In this case the output of the temperature sensor at node
145 will be low (0). Thus, when node 73 is high, the output at node
145 will be low.
[0034] In this manner the temperature sensor of the present
invention will provide an output signal at node 145 having a
frequency that is dependent on the temperature of various
components in the circuit. The frequency at the output will be
based on two time periods, i.e. the time to charge the capacitor
120 and the time it takes to discharge the capacitor. The time to
charge the capacitor is shown by the following equation:
t.sub.c=(C.sub.120)(Vcd)/Ic; where (6)
Vcd=Vc-Vd=(S.sub.106/S.sub.102) (R.sub.109/R.sub.105)(Va). (7)
[0035] The time period for the sensor to discharge is determined by
the following:
t.sub.d=(C.sub.120)(Vcd)/Id. (8)
[0036] The frequency at the output is shown by:
Frequency=1/(t.sub.c+t.sub.d). (9)
[0037] Then, substituting equations (4), (5), (6), (7) and (8) into
equation (9), the following equation is generated:
Frequency=[(S.sub.108/S.sub.102)(S.sub.112/S.sub.111)(S.sub.107/S.sub.102)-
]/[(C.sub.120)(S.sub.106/S.sub.102)(R.sub.109)][(S.sub.108/S.sub.102)+(S.s-
ub.112/S.sub.111)(S.sub.107/S.sub.102)]. (10)
[0038] Therefore, it can be seen in equation (10) that R.sub.109 is
the only temperature dependent element. Since the temperature
coefficient of this resistance (TCR) is known, the frequency output
will be inversely proportional to the TCR. By monitoring the
frequency the temperature of the circuit can be determined. That
is, as the frequency changes the chip temperature is sensed. Those
skilled in the art will understand that a device, such as a
counter, or the like can be connected to the output node 145 to
monitor the frequency of the output signals, i.e. the number of
times capacitor 120 charges and discharges over a given time
period. For materials with a positive TCR, as the temperature
increases, the frequency will decrease. Similarly, as the
temperature decreases the frequency will correspondingly increase.
Thus, the frequency is inversely proportional to the temperature of
the sensing circuit, i.e. the thermal coefficient of the resistance
for resistor R.sub.109. Once the frequency is sensed it can be
determined if the temperature is above a predetermined threshold
level. If so, then corrective action can be taken to shut off
various functions in the device, turn off the entire device, or the
like. When the frequency decreases to correspond to a temperature
below the predetermined threshold, these functions can be turned
back on. Of course, more than one predetermined threshold level is
contemplated by the present invention wherein each level may
correspond to different functions on the device.
[0039] One advantage of the temperature sensor of the present
invention is that the frequency will be substantially supply
voltage independent. Further, the present invention is transistor
model independent. More particularly, the temperature sensor of the
present invention is not dependent on the threshold voltage of the
transistors, it is threshold voltage (Vt) independent. Equation
(10) depends entirely on the actual characteristics of the circuit
components, rather than a predetermined threshold voltage value for
the N-type and P-type devices in the circuit.
[0040] The present invention will function at very low voltages
since the current source includes only a single P-type transistor
101 and 102. Therefore, the current can be provided by applying
only the threshold voltage (Vtp) across these transistors, plus an
additional small amount of voltage (on the order of a few hundred
millivolts). It can be seen that the amount of power consumed by
the present invention will also be relatively low based on the
small amount of voltage needed for the temperature sensor circuit
to operate. That is, the power is directly proportional to the
voltage (P=VA).
[0041] In another preferred embodiment of the present invention, a
constant frequency oscillator can be provided. This oscillator will
also be a low power, low voltage system in accordance with the
previous discussion and the description of the switching circuit of
FIG. 3. By properly choosing the resistor R.sub.109, such as an
N-type resistor, to have a zero (0) temperature coefficient of
resistance at a particular ambient temperature, the frequency
output of the circuit will be constant. Thus, an accurate frequency
level can be maintained. Those skilled in the art will understand
that it may be necessary, for example, to alter the TCR for a
corresponding temperature, such as by laser trimming or the like,
in order to obtain a reference frequency at room temperature.
[0042] Referring to FIG. 3, a more detailed schematic of the
switching circuit of the present invention is shown and will be
described in conjunction with FIG. 2. Inverters 51 and 53 are shown
connected to pulse generator 55 which includes a delay circuit.
This delay circuit includes five (5) additional inverters, 300,
301, 302, 303 and 304 connected in series. The input to pulse
generator circuit 55 is also connected as one input to a NOR gate
305 with the output of the series of inverters from inverter 304
being the other input to NOR gate 305. As shown in FIG. 2, the
output of pulse generator circuit 55 is provided to inverter
57.
[0043] More particularly, when a logical zero (0) is input at node
50, inverter 51 outputs a logical one (1) to transistor 58 of FIG.
2 and inputs a one to inverter 53 which outputs a zero to
transistor 52 and to pulse generator circuit 55. In this case a
zero is input to NOR gate 305 at node A, while a one is output from
inverter 304 and input to NOR gate 305 at node B. Those skilled in
the art will understand that a time delay occurs for the binary
input to inverter 300 to be processed by each inverter 300, 301,
302, 303, 304 and then output to NOR gate 305 as a logical one. In
this manner, when a zero is input to node 50, a zero is also input
to inverter 300 and node A of NOR gate 305. Delay inverters 300,
301, 302, 303 and 304 will then cause a one to be input at node B
of NOR gate 305. At this time, a zero will be output from NOR gate
305 and a one will be output to P-type transistor 54 with a zero
output to N-type transistor 56. During this period, none of
transistors 52, 54, 56 or 58 are turned on. When a logical one (1)
is input at node 50, a one is output to transistors 52 (on) and 54
and a zero is output to transistors 56 and 58, i.e. transistors 54
and 56 will not be turned on, while transistors 52 and 58 will be
on to keep the sensor off. Specifically, a one input to NOR gate
305 on node A and a zero input to NOR gate 305 on node B causes a
zero to be output to inverter 306. This in turn causes a one to be
input to P-type transistor 54 (off) and inverter 57. The output of
inverter 57 is a zero which is then input to N-type transistor 56
(off).
[0044] When it is desired to turn on the temperature sensor of the
present invention, the input at node 50 transitions back to a
logical zero, which places a zero on node A of NOR gate 305 at the
same time the previous logical zero is still on node B of NOR gate
305. Therefore, during the delay time required for the logical one
(due to the logical zero now input to node 50) to traverse the
delay inverters (300, 301, 302, 303, 304) a zero, zero (0, 0) will
be present on nodes A and B of NOR gate 305. During this time a
logical one output pulse is generated from NOR gate 305. This pulse
will have a duration substantially equivalent to the amount of time
required for the zero input to inverter 300 to traverse the delay
inverters. The output pulse from NOR gate 305 will then cause the
temperature sensor of the present invention to begin operating.
That is, a logical one is output from NOR gate 305 thus causing a
logical zero to be provided from inverter 306 to P-type transistor
54, which turns this transistor on. Additionally, a one is output
from inverter 57 that will cause N-type transistor 56 to being to
conduct. As noted previously, transistor 54 will input Vcc to the
gate of transistors 103, 104 and transistor 56 will pull the gate
of transistors 101, 102 to Vss causing it to be turned on. The
current source of the temperature sensor will then begin operation.
Subsequent to the duration of the output pulse from generator 55,
the switching mechanism will remain off until the input to node 50
is changed to logical zero when transistors 52 and 58 are turned
off and the current generator ceases operation until a transition
to a logical one occurs at node 50 and a pulse is subsequently
generated from NOR gate 305 by changing the input to node 50 to a
zero.
[0045] The switching operation of the temperature sensor in
accordance with these output signals has been described above in
conjunction with FIG. 2. Thus, a control circuit can be used to
provide the input signals to node 50 that will cause the
temperature sensor of the present invention to be shut off in order
to conserve electrical power.
[0046] FIG. 4 is a timing diagram showing the waveforms present at
various ones of the nodes in the temperature sensor circuit of FIG.
2. It can be seen that the first waveform, present and node 70, is
substantially a sawtooth wave that represents capacitor 120 during
its charging state (upward slope) during the time when the voltage
charging voltage Vc is present on node 71 and then discharging
(downward slope) when the discharge voltage Vd is present on node
71. The waveform on node 70 is based upon the frequency of the
capacitor and the temperature coefficient of resistor R2. This
signal will then be transformed into a digital signal such that the
frequency can be monitored, and therefore, the current sensed by
basically counting the signal transitions at the output node
145.
[0047] The second waveform shows the voltage on node 71. It can be
seen that the charge voltage Vc corresponds to the charging of
capacitor 120 which occurs when transistor 146 of the pass gate is
turned on. Voltage Vd corresponding to the discharge of capacitor
120 and occurs when transistor 147 of the pass gate is turned
on.
[0048] The third waveform shows the voltage on node 72 which is an
output of the differential comparator circuit formed by transistors
125, 126, 127, 128, 129 and 130. The fourth waveform represents the
voltage on node 73 which is another output of the comparator
circuit. It can be seen from FIG. 4 that the output signals at
nodes 72 and 73 are 180 degrees out of phase with one another.
These signals are then input to a differential to single converter
circuit formed by transistors 132, 133, 134 and 135. Node 74 is the
output of this converter circuit and provides an output signal to
four (4) inverters.
[0049] The fifth waveform is the temperature sensor circuit output.
It can be seen that it follows the waveform at node 72. More
particularly, when node 72 is at Vtn, transistor 132 is turned on
and causes reference potential to be input to the gate of N-type
transistor 134 which places a logical one on node 74. This will
cause a logical one to be output on node 145 (an even number of
inverters is present between nodes 74 and 145). When node 73 is at
Vtn, N-type transistor 135 is turned on causing a reference
potential (logical 0) to be output on node 74 and ultimately on
node 145. Thus, it can be seen that the output on node 145 follows
the waveform on node 72, but is the complement of the waveform on
node 73.
[0050] Although certain preferred embodiments have been shown and
described, it should be understood that many changes and
modifications may be made therein without departing from the scope
of the appended claims.
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