U.S. patent application number 11/767467 was filed with the patent office on 2007-10-11 for beta variation cancellation in temperature sensors.
This patent application is currently assigned to National Semiconductor Corporation. Invention is credited to Mehmet Aslan, John W. Branch.
Application Number | 20070237207 11/767467 |
Document ID | / |
Family ID | 37946245 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070237207 |
Kind Code |
A1 |
Aslan; Mehmet ; et
al. |
October 11, 2007 |
BETA VARIATION CANCELLATION IN TEMPERATURE SENSORS
Abstract
An apparatus and method for canceling variations in the beta for
a bipolar junction transistor so that the diode equation can be
employed to accurately measure the temperature of the transistor
based at least in part on a ratio of two target collector currents
and two measurements of the base-emitter voltage of the transistor.
If the determined collector current of the transistor is relatively
equivalent to one of the first and second target collector
currents, the transistor's base-emitter voltage is measured and
stored. An analog feedback circuit can be employed to change the
determined collector current to be relatively equivalent to the
first and second target collector currents. The analog feedback
circuit can include an optional sample and hold component to
further reduce power consumption and reduce noise. A digital
circuit can be employed to change the determined collector current
to be relatively equivalent to the first and second target
collector currents. Additionally, the transistor can be remotely
located in another integrated circuit.
Inventors: |
Aslan; Mehmet; (Sunnyvale,
CA) ; Branch; John W.; (Seattle, WA) |
Correspondence
Address: |
National Semiconductor Corporation;c/o DARBY & DARBY P.C.
P.O. BOX 770
Church Street Station
NEW YORK
NY
10008-0770
US
|
Assignee: |
National Semiconductor
Corporation
Santa Clara
CA
|
Family ID: |
37946245 |
Appl. No.: |
11/767467 |
Filed: |
June 22, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10865609 |
Jun 9, 2004 |
|
|
|
11767467 |
Jun 22, 2007 |
|
|
|
Current U.S.
Class: |
374/178 ;
374/E7.036 |
Current CPC
Class: |
G01K 7/015 20130101 |
Class at
Publication: |
374/178 |
International
Class: |
G01K 7/00 20060101
G01K007/00 |
Claims
1. An apparatus for remotely measuring a temperature of a
transistor disposed in a separate integrated circuit, comprising: a
first circuit that is arranged to adjust a determination of a
collector current of the transistor to be relatively equivalent to
a first target collector current and is also arranged to adjust
another determination of the collector current to be relatively
equivalent to a second target collector current, wherein the
determination of the collector current that is relatively
equivalent to the first target collector current is based on at
least one measurement of a first base current for the transistor,
and wherein the other determination of the collector current that
is relatively equivalent to the second target collector current is
based on at least one measurement of a second base current for the
transistor; and a second circuit that is arranged to measure a
first base-emitter voltage for the transistor if the determined
collector current of the transistor is relatively equivalent to the
first target collector current and is also arranged to measure a
second base-emitter voltage for the transistor if the determined
collector current of the transistor is relatively equivalent to the
second target collector current.
2. The apparatus of claim 1, further comprising circuitry that is
arranged to determine the temperature of the transistor based at
least in part on the measured first and second base-emitter
voltages.
3. The apparatus of claim 2, further comprising circuitry that is
arranged to at least reduce an effect on determining the
temperature of the transistor caused by at least one resistive
element coupled in series with the transistor.
4. The apparatus of claim 2, further comprising circuitry that is
arranged to communicate a representation of the determined
temperature.
5. The apparatus of claim 1, further comprising circuitry that is
arranged to adjust an emitter current provided to the transistor,
wherein a first adjustment of the emitter current enables the
determined collector current to be relatively equivalent to the
first target collector current and wherein a second adjustment of
the emitter current enables the determined collector current to be
relatively equivalent to the second target collector current.
6. The apparatus of claim 1, further comprising circuitry that is
arranged to bias the transistor above a common mode voltage.
7. The apparatus of claim 1, wherein the first circuit that adjusts
the determinations of the collector current further comprises at
least one digital component that is arranged to iteratively change
the determinations for the collector current of the transistor to
be relatively equivalent to at least one of the first and second
target collector currents.
8. The apparatus of claim 1, wherein the first circuit that adjusts
the determinations of the collector current further comprises an
analog feed back loop that is arranged to change the determinations
of the collector current of the transistor to be relatively
equivalent to at least one of the first and second target collector
currents.
9. The apparatus of claim 1, further comprising circuitry that is
arranged to sample and hold an emitter current for the transistor
if the transistor's determined collector current is relatively
equivalent to at least one of the first and second target collector
currents.
10. The apparatus of claim 1, wherein a value for the first target
collector current is at least a magnitude greater than another
value for the second target collector current.
11. The apparatus of claim 1, further comprising: a third circuit
that is arranged with a first ratio to provide the first target
collector current and is also arranged with a second ratio to
provide the second target collector current, wherein the first
ratio and the first target collector current are respectively
greater than the second ratio and the second target collector
current; and a fourth circuit that is arranged to adjust an input
of the third circuit employing the first ratio, wherein the
adjustment causes a difference of a selected target emitter current
and the first target collector current to be relatively equivalent
to a third base current of the transistor, and wherein the fourth
circuit applies the adjustment to the input of the third circuit if
the third circuit is providing the second target collector
current.
12. An apparatus for remotely measuring a temperature of a
transistor located within a separate integrated circuit,
comprising: a first circuit that is arranged to change an emitter
current provided to the transistor to cause a determined collector
current of the transistor to be relatively equivalent to a first
target collector current and is also arranged to change the emitter
current provided to the transistor to cause the determined
collector current of the transistor to be relatively equivalent to
a second target collector current; a second circuit that is
arranged to measure a first base-emitter voltage for the transistor
if the determined collector current of the transistor is relatively
equivalent to the first target collector current and is also
arranged to measure a second base-emitter voltage for the
transistor if the determined collector current of the transistor is
relatively equivalent to the second target collector current; and a
third circuit that is arranged to determine the temperature of the
transistor based at least in part on the measured first and second
base-emitter voltages.
13. The apparatus of claim 12, further comprising circuitry that is
arranged to measure a first base current for the transistor to
enable the determination of the collector current to be relatively
equivalent to the first target collector current, and is also
arranged to measure a second base current for the transistor to
enable the determination of the collector current to be relatively
equivalent to the second target collector current.
14. The apparatus of claim 12, wherein the first circuit that
changes the emitter current further comprises at least one digital
component that is arranged to iteratively adjust the emitter
current for changing the determined collector current of the
transistor to be relatively equivalent to at least one of the first
and second target collector currents.
15. The apparatus of claim 12, wherein the first circuit that
changes the emitter current further comprises an analog feed back
loop that is arranged to adjust the emitter current to change the
determined collector current of the transistor to be relatively
equivalent to at least one of the first and second target collector
currents.
16. The apparatus of claim 12, further comprising circuitry that is
arranged to sample and hold the emitter current if the transistor's
determined collector current is relatively equivalent to at least
one of the first and second target collector currents.
17. The apparatus of claim 12, further comprising: a fourth circuit
that is arranged with a first ratio to provide the first target
collector current and is also arranged with a second ratio to
provide the second target collector current, wherein the first
ratio and the first target collector current are respectively
greater than the second ratio and the second target collector
current; and a fifth circuit that is arranged to adjust an input of
the fourth circuit employing the first ratio, wherein the
adjustment causes a difference of a selected target emitter current
and the first target collector current to be relatively equivalent
to a base current of the transistor, and wherein the fifth circuit
applies the adjustment to the input of the fourth circuit if the
fourth circuit is providing the second target collector
current.
18. A method for remotely measuring a temperature of a transistor
that is located within a separate integrated circuit, comprising:
enabling a determination of the collector current of the transistor
to be relatively equivalent to a first target collector current; if
the determined collector current of the transistor is relatively
equivalent to the first target collector current, measuring a first
base-emitter voltage for the transistor; enabling the determined
collector current of the transistor to be relatively equivalent to
a second target collector current; and if the determined collector
current of the transistor is relatively equivalent to the second
target collector current, measuring a second base-emitter voltage
for the transistor, wherein the temperature of the transistor is
determined based at least in part on the measured first and second
base-emitter voltages.
19. The method of claim 18, further comprising: changing an emitter
current of the transistor to cause the determined collector current
of the transistor to be relatively equivalent to the first target
collector current; and changing the emitter current of the
transistor to cause the determined collector current of the
transistor to be relatively equivalent to the second target
collector current.
20. The method of claim 18, further comprising: changing a base
current of the transistor to cause the determined collector current
of the transistor to be relatively equivalent to the first target
collector current; and changing the base current of the transistor
to cause the determined collector current of the transistor to be
relatively equivalent to the second target collector current.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This Application is a Continuation of U.S. patent
application Ser. No. 10/865,609, filed on Jun. 9, 2004 and
currently pending, which is incorporated by reference herein and
the benefits of which are claimed under 35 U.S.C. .sctn.120.
FIELD OF THE INVENTION
[0002] The invention is generally directed to the measuring the
temperature of an electronic device, and more particularly, to
improving the accuracy of measuring a temperature signal provided
by a transistor disposed in an electronic device.
BACKGROUND OF THE INVENTION
[0003] An electronic temperature sensor circuit can be arranged to
measure the temperature on a remote (separate) silicon chip by
providing one or more known currents to a p-n junction located on
the remote chip. This circuit measures a diode voltage of this p-n
junction and processes the diode voltage to determine the actual
temperature at the remote location. Most p-n junctions employed for
this purpose are parasitic vertical p-n-p silicon based
transistors. Also, the temperature sensor circuit is usually
arranged to control the emitter currents of the transistor.
[0004] The classic diode equation is often employed to determine
the actual temperature at the remotely located p-n-p transistor
based on a ratio of approximated collector currents. So long as the
emitter current and collector current are substantially equivalent
for this remotely located transistor, the determined temperature
can be relatively accurate. However, if the beta (ratio of
collector current over base current) of the p-n-p transistor varies
with a varying emitter current, a determined temperature based on
the diode equation can be less accurate. Recently, process
variations and the ever shrinking physical size of process
geometries for silicon devices are causing the beta to vary
significantly with a varying emitter current.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Non-limiting and non-exhaustive embodiments of the present
invention are described with reference to the following drawings.
In the drawings, like reference numerals refer to like parts
throughout the various figures unless otherwise specified.
[0006] For a better understanding of the present invention,
reference will be made to the following Detailed Description of the
Invention, which is to be read in association with the accompanying
drawings, wherein:
[0007] FIG. 1 illustrates a schematic diagram of an exemplary
circuit that provides two known emitter currents for a remotely
located transistor;
[0008] FIG. 2 shows a schematic diagram of an exemplary circuit for
determining collector currents for a remotely located
transistor;
[0009] FIG. 3A illustrates a flow chart for determining the
temperature of a remotely located transistor based on separate
measurements of its base-emitter voltage for two determined target
collector currents;
[0010] FIG. 3B illustrates a flow chart for determining the
temperature of a remotely located transistor based on separate
measurements of its base-emitter voltage for two determined
collector currents;
[0011] FIG. 4A illustrates a schematic diagram of an exemplary
circuit that employs digital components to determine target
collector currents for a remotely located transistor;
[0012] FIG. 4B shows a schematic diagram of an exemplary circuit
that employs digital components to determine collector currents for
a remotely located transistor;
[0013] FIG. 5 illustrates a schematic diagram of an exemplary
circuit that employs analog components to determine collector
currents for a remotely located transistor;
[0014] FIG. 6 illustrates a schematic diagram of an exemplary
circuit that employs analog components to determine collector
currents for a biased and remotely located transistor;
[0015] FIG. 7 illustrates a flow chart for determining two target
collector currents that can be employed in the determination of the
temperature for a remotely located transistor;
[0016] FIG. 8 shows a schematic diagram of an exemplary circuit for
determining a first and a second target collector current for the
process described for FIG. 7;
[0017] FIG. 9 illustrates an overview of a block diagram for
components that measure the temperature of remotely located
transistor in accordance with determined target collector currents
and base-emitter voltages for the transistor; and
[0018] FIG. 10 illustrates a block diagram for an exemplary circuit
for measuring the base-emitter voltage of a remotely located
transistor in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, which form
a part hereof, and which show, by way of illustration, specific
exemplary embodiments by which the invention may be practiced. This
invention may, however, be embodied in many different forms and
should not be construed as limited to the embodiments set forth
herein; rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the invention to those skilled in the art. Among other
things, the present invention may be embodied as methods or
devices. Accordingly, the present invention may take the form of an
entirely hardware embodiment, an entirely software embodiment or an
embodiment combining software and hardware aspects. The following
detailed description is, therefore, not to be taken in a limiting
sense.
[0020] Briefly stated, the present invention is directed to an
apparatus and method for canceling variations in the beta for a
transistor so that the diode equation can be employed to accurately
measure the temperature of the transistor based at least in part on
a ratio of two target collector currents (Ictarget1, Ictarget2) and
two measurements of the base-emitter voltage (Vbe1, Vbe2) of the
transistor. If the determined collector current of the transistor
is relatively equivalent to one of the first and second target
collector currents, the transistor's base-emitter voltage is
measured and stored. An analog feedback circuit can be employed to
change the determined collector current to be relatively equivalent
to the first and second target collector currents. The analog
feedback circuit can include an optional sample and hold component
to further reduce power consumption and reduce noise. A digital
circuit can be employed to change the determined collector current
to be relatively equivalent to the first and second target
collector currents. Additionally, the transistor whose currents are
measured/determined to determine its temperature can be remotely
located in another integrated circuit (chip) or disposed in the
same integrated circuit as the invention.
[0021] The classic diode equation determines a change in the base
emitter voltage (.DELTA.Vbe ) for a p-n-p transistor as follows:
.DELTA. .times. .times. Vbe = .eta. .times. .kappa. .times. .times.
T q .times. ln .function. ( Ic .times. .times. 1 Ic .times. .times.
2 ) Equation .times. .times. 1 ##EQU1##
[0022] where .eta. is a non-ideality constant substantially
equivalent to 1.00 or slightly more/less, .kappa. is the well known
boltzmann's constant, q is the electron charge, T is the
temperature in Kelvin, Ic1 is a first collector current, and Ic2 is
a second collector current that are present at the measurement of a
first base-emitter voltage and a second base-emitter voltage.
[0023] In the past, since a ratio of collector currents tended to
be relatively equivalent to a ratio of known emitter currents (Ie),
the diode equation could be accurately approximated in a rewritten
form that follows: T = .DELTA. .times. .times. Vbe / ( .eta.
.times. .kappa. .times. .times. T q .times. ln .function. ( Ie
.times. .times. 1 Ice .times. .times. 2 ) ) ; where .times. Ic
.times. .times. 1 Ic .times. .times. 2 = Ie .times. .times. 1 I
.times. .times. e .times. .times. 2 Equation .times. .times. 2
##EQU2##
[0024] However, due in part to process variations for integrated
circuits with smaller process geometries, the assumption regarding
relatively equivalent ratios may no longer be valid. The beta
(ratio of collector current over base current) has been shown to
vary as much as 10 percent or more between two known emitter
currents for p-n-p transistors in integrated circuits manufactured
from relatively smaller process geometries.
[0025] In an exemplary integrated circuit based on a smaller die
size, a beta of 0.77 was measured for a 10 microamp emitter current
provided to a transistor. For the same transistor, the measured
beta was 0.83 when the emitter current was changed to 170
microamps. Thus, the diode equation approximation (Equation 2)
regarding the ratios of collector and emitter currents for a
transistor can cause relatively inaccurate temperature measurements
in an integrated circuit based on smaller process geometries.
Relatively significant inaccurate temperature measurements can
occur in integrated circuits that have process geometries of 90
nanometers or less.
[0026] The invention provides for a more accurate temperature
measurement for a transistor with a rewritten form of the diode
equation (Equation 3) that provides for actually measuring or
controlling the ratio of collector currents instead of the ratio of
emitter currents. T = .DELTA. .times. .times. Vbe / ( .eta. .times.
.kappa. q .times. ln .function. ( Ic .times. .times. 1 Ic .times.
.times. 2 ) ) Equation .times. .times. 3 ##EQU3##
[0027] FIG. 1 illustrates a schematic diagram of overview 100 for
an exemplary circuit that provides two known emitter currents for a
remotely located p-n-p transistor (Q1). Current sources 102 and 104
are separately coupled between a voltage source (Vdd) and
multiplexer 106. As each current source is selected, it provides a
known emitter current to the remotely located transistor Q1. The
provided emitter currents induce base-emitter voltages across the
transistor that can be measured (Vmeasured) and employed to
determine the temperature based on an approximation of the diode
equation (Equation 2).
[0028] FIG. 2 shows a schematic diagram of general overview 200 of
components for determining collector currents for a remotely
located transistor Q1. Current sensor 206 is coupled to the base of
transistor Q1 where it is employed to measure the base current of
this transistor. Current sensor 206 provides the measured base
current to control circuit 204 which in turn controls the operation
of variable current source 202. For two separate ranges of emitter
current, the variable current source is varied so that the
determination of the collector current (Icurrent=Iemitter-Ibase) is
equivalent to a first target (predetermined) collector current and
a second target collector current. The base-emitter voltage
(Vmeasured) for the remotely located transistor Q1 is measured when
the determined collector current is equivalent to one of the target
collector currents. The arrangement of these components enable the
temperature for a remotely located transistor to be determined
based on an actual ratio of predetermined target collector
currents, not an approximation. Additionally, substantially the
same arrangement of these components could be employed to determine
the temperature of a transistor that was disposed locally, i.e.,
the transistor can be disposed in the same integrated circuit as
the components employed to measure its currents.
[0029] FIG. 3A illustrates a flow chart for determining the
temperature of a remotely located transistor based on separate
measurements of its base-emitter voltage for two iteratively
determined target collector currents. Moving from a start block,
the process steps to block 302 where the emitter current provided
to the remotely located transistor is adjusted to a first value.
Also, a first target value is provided for comparing to a
determined collector current. At block 304, the base current for
the remotely located transistor is measured. Flowing to block 306,
the collector current is determined by the difference between the
first value of the emitter current and the measured base current,
i.e., Ic=Ie-Ib. Advancing to decision block 308, a determination is
made as to whether or not the determined collector current is
equivalent to the first target value. If false, the process moves
to block 310 where the emitter current is adjusted. Next, the
process returns to block 304 and performs substantially the same
actions discussed above. This process substantially loops until the
determined collector current is relatively equivalent to the first
target value.
[0030] If the determination at decision block 308 had been true,
the process would have stepped to block 312 where the base-emitter
voltage of the remotely located transistor for the first target
value would be measured and stored. Moving to decision block 314,
another determination is made as to whether or not the value of the
determined collector current is equivalent to a second target
value. If false, the process steps to block 316 where the second
target value is provided for comparing to the determined collector
current. The process returns to block 304 and performs
substantially the same actions discussed above except for the
second target value.
[0031] Once the determination at decision block 314 is true, the
process moves to block 318 where the diode equation (discussed
above) is employed to determine the temperature of the remotely
located transistor based on the measured base-emitter voltages for
two predetermined (target) values for the collector currents. Next,
the process returns to performing other actions.
[0032] The determined temperature may be converted into a
representation of the temperature that may be displayed or employed
by other devices to control the temperature of the integrated
circuit that includes the remotely located transistor.
Additionally, substantially the same process can be employed to
determine the temperature of a transistor that is disposed locally,
i.e., in the same integrated circuit as the components employed to
measure the transistor's currents.
[0033] FIG. 3B illustrates a flow chart for determining the
temperature of a remotely located transistor based on separate
measurements of its base-emitter voltage for two determined
collector currents. Moving from a start block, the process steps to
block 322 where a first emitter current that has a known value,
e.g., "X" milliamps, is provided to the remotely located
transistor. At block 324, a first base current is measured. Also,
the known first emitter current and the measured first base current
are employed to determine a first collector current, i.e., the
collector current is equivalent to the emitter current minus the
base current. Moving to block 326, the process measures a first
base-emitter voltage for the transistor.
[0034] Next, the process advances to block 328 where a second
emitter current that has a known value, e.g., "Y" milliamps, is
provided to the remotely located transistor. At block 330, a second
base current is measured. Also, the known second emitter current
and the measured first base current are employed to determine a
second collector current. Stepping to block 332, the process
measures a second base-emitter voltage for the transistor. Flowing
to block 334, the process employs the diode equation to determine
the temperature of the transistor which is based in part on a ratio
of the determined first and second collector currents and the
difference between the first and second measured base-emitter
voltage. Next, the process returns to performing other actions.
[0035] The determined temperature may be converted into a
representation of the temperature that may be displayed or employed
by other devices to control the temperature of the integrated
circuit that includes the remotely located transistor.
Additionally, substantially the same process can be employed to
determine the temperature of a transistor that is disposed locally,
i.e., in the same integrated circuit as the components employed to
measure the transistor's currents.
[0036] FIG. 4A illustrates a schematic diagram of overview 400 for
employing digital components to determine collector currents for a
remotely located transistor Q1 in accordance with the process
discussed above for FIG. 3A. Current sensor circuit 402 measures
the base current for transistor Q1 and converts the measured
current into an analog voltage signal. This voltage signal is
provided to analog-to-digital converter (ADC) 404 where the analog
signal is converted into the digital domain. ADC 404 provides this
digitalized signal to control logic 406. Also, control logic 406
receives a value of the emitter current presently provided to
transistor Q1 and a target value (first or second) for the
determined collector current.
[0037] Control logic 406 is coupled to digital-to-analog converter
(DAC) 408 and provides a digital signal to the DAC to increase,
decrease, or remain constant in regard to the emitter current for
transistor Q1. The analog output signal from DAC 408 is coupled to
the gate of MOSFET M1 which in turn provides the emitter current to
transistor Q1. Changes in the analog signal output of DAC 408
causes MOSFET M1 to either increase or decrease the emitter current
provided to transistor Q1. Additionally, substantially the same
arrangement of these components in FIG. 4A could be employed to
determine the temperature of a transistor that is disposed locally,
i.e., the transistor can be disposed in the same integrated circuit
as the components employed to measure its currents.
[0038] FIG. 4B illustrates a schematic diagram of overview 410 for
employing digital components to determine collector currents for a
remotely located transistor Q1 in accordance with a process
discussed above for FIG. 3B. Current sensor circuit 402 measures
the base current for transistor Q1 and converts the measured
current into an analog voltage signal. This voltage signal is
provided to analog-to-digital converter (ADC) 404 where the analog
signal is converted into the digital domain. ADC 404 provides this
digitalized signal to logic circuit 412. An output of logic circuit
412 is coupled back to ADC 404 to save power by de-energizing the
ADC if it is not actively employed to measure the base current.
Known emitter currents are separately provide to transistor Q1 by
current sources 414 and 416 through multiplexer 418. An
analog-to-digital converter (ADC) 420 is coupled across the base
and emitter of the remotely located transistor Q1 for measuring the
transistor's base-emitter voltage. Another output of logic circuit
412 is coupled to ADC 420 to save power by de-energizing this ADC
if it is not actively employed to measure the base-emitter voltage
current. The output of ADC 420 and another output of logic circuit
412 are coupled to temperature logic 422 to determine the
temperature of transistor Q1 and provide a representation of the
determined temperature with status bit(s), pin(s) serial
interface(s), parallel interface(s) bus(es), and the like.
[0039] In one embodiment, the resolution for ADC 404 to measure the
base current might be configured to be substantially less than the
resolution of ADC 420 to measure the base-emitter voltage of
transistor Q1. Also, since the first and second determined
collector currents are employed to determine temperature, gain
correction is automatically provided for measuring the base-emitter
voltage of the transistor Q1, i.e., increase, decrease, or remain
constant based on the determined collector current of the
transistor. Also, in yet another embodiment, a variable current
source could be employed to perform substantially the same actions
as current sources 414 and 416 and multiplexer 418.
[0040] Additionally, substantially the same arrangement of these
components in FIG. 4B could be employed to determine the
temperature of a transistor that is disposed locally, i.e., the
transistor can be disposed in the same integrated circuit as the
components employed to measure its currents.
[0041] FIG. 5 illustrates a schematic diagram of overview 500 for
employing analog components to determine collector currents for a
remotely located transistor Q1 in accordance with the process
discussed above. A pair of substantially matched MOSFET transistors
M1 and M2 have their sources coupled to a voltage supply (Vdd) and
their gates coupled to an output of opamp 502. The drain of MOSFET
M2 is coupled to the emitter of remotely located transistor Q1 and
arranged to provide an emitter current (Ie). The drain of MOSFET M1
is similarly arranged to provide a relatively equivalent current
(Ie') to a node "N", i.e., Ie'=Ie.
[0042] Node N is coupled to the non-inverting input of opamp 502,
an end of resistor R2 (other end of resistor R2 is coupled to
ground) and the drain of MOSFET M3. MOSFETs M4 and M3 are
substantially matched to each other and configured in a current
mirror arrangement where their sources are coupled to ground and
their gates are coupled together. Further, the gate of MOSFET M4 is
coupled to its drain and the base of remotely located transistor Q1
so that the base current Ib of transistor Q1 is mirrored by another
current Ib' flowing through MOSFET M3, i.e., Ib=Ib'. Since the
non-inverting input to opamp 502 has a relatively infinite
impedance at Node N, the current (Ic') that flows through
transistor R2 is equivalent to Ie'-Ib', which in turn is relatively
equivalent to the collector current. One terminal of variable
current source 506 is coupled to the voltage supply (Vdd) and
another terminal of the variable current source is coupled at Node
"B" to both an end of resistor R1 and the inverting input to opamp
502. The other end of resistor R1 is coupled to ground; and the
impedance values of resistors R1 and R2 are relatively equivalent
to each other. However, in another embodiment, the impedances of
resistors R1 and R2 can be significantly different values so long
as a ratio of their impedances is known, e.g., the impedance of R1
could be equivalent to several multiples of the impedance of R2,
and vice versa.
[0043] Since the inverting input to opamp 502 has a relatively
infinite impedance, a target collector current (Ictarget) provided
by the variable current source flows primarily through resistor R1
to ground. Based on the difference in voltage drops at its
non-inverting and inverting inputs caused by the flow of Ictarget
through resistor R1 and the flow of Ic' through resistor R2, opamp
502 adjusts its output to drive the gates of MOSFETs M1 and M2
until these voltage drops are relatively equivalent, such that
Ic'=Ictarget. Once Ic' is relatively equivalent to Ictarget, the
base-emitter voltage (Vmeasured) for transistor Q1 is measured for
a first target collector current. This process is repeated for a
second target collector current and a second measurement of the
base-emitter voltage for transistor Q1 is performed. Additionally,
once Ic' is adjusted to be relatively equivalent to a target
collector current (Ictarget), optional sample and hold circuit 504
enables the base-emitter voltage of transistor Q1 to be measured
while at least opamp 502 is de-energized to conserve power and
reduce noise. Furthermore, the diode equation can be employed to
determine the temperature of transistor Q1 based on the two
measurements of the base-emitter voltage for this transistor and a
ratio of the two target collector currents (Ictarget1 and
Ictarget2). Additionally, substantially the same arrangement of
these components could be employed to determine the temperature of
a transistor that is disposed locally, i.e., the transistor can be
disposed in the same integrated circuit as the components employed
to measure its currents.
[0044] FIG. 6 illustrates a schematic diagram of overview 600 for
employing analog components to determine collector currents for a
biased and remotely located transistor Q1 in accordance with the
process discussed above. The operation of this embodiment is
similar in some ways to the embodiment discussed in FIG. 5, albeit
different in other ways such as biasing. The sources of a pair of
substantially matched MOSFET transistors M1 and M2 are coupled to a
voltage supply (Vdd) and both of their gates are coupled to an
output of opamp 602. The drain of MOSFET M1 is coupled to the
emitter of remotely located transistor Q1 and arranged to provide
an emitter current (Ie) to this transistor. The drain of MOSFET M2
is similarly arranged to provide a relatively equivalent current
(Ie'=Ie) at one end of resistor R2 and the inverting input of opamp
602. This particular end of resistor R2 is also coupled to one
terminal of variable current source 608 whose other terminal is
coupled to ground. Also, the other end of resistor R2 is coupled to
the output of bias opamp 604.
[0045] At Node M, the base of transistor Q1 is coupled to one end
of resistor R1 whose other end is coupled to the output of bias
opamp 604. Also, the base of transistor Q1 is coupled to the
non-inverting input of opamp 602 and the inverting input of bias
opamp 604.
[0046] The impedance values for resistors R1 and R2 are
substantially equivalent to each other. Also, a bias voltage Vbias
is coupled to the non-inverting input of bias opamp 604.
[0047] In operation, Vbias is applied to the non-inverting input of
bias opamp 604 to bias the operation of the listed components above
the common mode voltage and MOSFET M1 provides the emitter current
(Ie) to the remotely located transistor Q1 so that a base current
(Ib) flows through resistor R1. A similar current (Ie') is provided
by MOSFET M2 to the other components in the circuit such that
variable current source 608 sinks a target collector current
(Ictarget) and the current (Ib') flowing through resistor R2 is
substantially equivalent to Ie'-Ictarget. The output of opamp 602
is adjusted until the base current (Ib) flowing through resistor R1
is relatively equivalent to the current (Ib') flowing through
resistor R2 for the target collector current (Ictarget).
[0048] Additionally, the operation of bias opamp 604 ensures that
the voltage at Node M (base of transistor Q1) is relatively
equivalent to a predetermined bias voltage Vbias. Also, the
operation of opamp 602 ensures that the collector current for the
remotely located transistor Q1 is adjusted to the value of the
target collector current.
[0049] Once Ib' is relatively equivalent to Ib, the base-emitter
voltage (Vmeasured) for transistor Q1 is measured for a first
target collector current. This process is repeated for a second
target collector current and a second measurement of the
base-emitter voltage for transistor Q1 is performed. Additionally,
once Ib' is adjusted to be relatively equivalent to Ib for a given
target collector current (Ictarget), optional sample and hold
circuit 606 enables the base-emitter voltage of transistor Q1 to be
measured while at least opamp 602 is de-energized to conserve power
and to reduce noise. Furthermore, the diode equation can be
employed to determine the temperature of transistor Q1 based on the
two measurements of the base-emitter voltage for this transistor
and a ratio of the two target collector currents (Ictarget1 and
Ictarget2). Additionally, substantially the same arrangement of
these components could be employed to determine the temperature of
a transistor that is disposed locally, i.e., the transistor can be
disposed in the same integrated circuit as the components employed
to measure its currents.
[0050] FIG. 7 illustrates a flow chart for determining two target
collector currents that can be employed in the determination of the
temperature for a remotely located transistor. Moving from a start
block, the process steps to block 702 where a target emitter
current is selected and applied to the remotely located transistor
and other components employed to measure at least one of this
transistor's collector and base currents. Also, an adjustable ratio
of one MOSFET transistor in a current mirror that provides a target
collector current is set equal to M where M is equivalent to a
ratio of a first target collector current over a second target
collector current. In one embodiment, M is set equal to 16.
[0051] At block 704, the process adjusts the value of the target
collector current until the target emitter current minus the target
collector current is equivalent to the base current of the remotely
located transistor. Also, the code for a Digital to Analog
Converter (DAC) that enables the adjustment of the target collector
current is set equal to zero; and the DAC code is incremented until
a comparator changes state and indicates that the base current of
the remotely located transistor is equivalent to the target emitter
current minus the target collector current. This incremented DAC
code is latched at the state change of the comparator.
[0052] Moving to block 706, the process enables an exemplary beta
variation cancellation circuit with a first target collector
current that is equivalent to the Ictarget at the latched DAC code.
Exemplary beta variation cancellation circuits and their operation
are taught in FIGS. 2, 4-6, and 8-9 and the related discussion. At
block 708, the base-emitter voltage Vbe1 for the first target
collector current (Ictarget) is measured and stored.
[0053] Advancing to block 710, the process changes the adjustable
ratio from M to one for the one MOSFET transistor in the current
mirror that provides the target collector current so that the
second target collector current is substantially smaller than the
first target collector current. At block 712, the process enables
an exemplary beta variation cancellation circuit with a second
target collector current that is equivalent to the Ictarget at the
second latched DAC code. At block 714, the base-emitter voltage
Vbe2 for the second target collector current (Ictarget2) is
measured and stored. Next, the process steps to block 716 where the
diode equation is employed to determine the temperature of the
remotely located transistor. The process subsequently returns to
performing other actions. Additionally, substantially this same
process could be employed to determine the temperature of a
transistor that is disposed locally, i.e., the transistor can be
disposed in the same integrated circuit as the components employed
to measure its currents.
[0054] FIG. 8 shows a schematic diagram of overview 800 for
determining a first and a second target collector current in a
manner substantially similar to the process described for FIG. 7.
Also, the arrangement and operation of the electronic circuit shown
in FIG. 8 is substantially similar to the electronic circuit shown
in FIG. 6, albeit different in some ways. In particular, FIG. 8
teaches enabling the first and second target collector currents to
be determined based on a selected target emitter current and an
adjustable ratio for a variable current mirror prior to measuring
the base-emitter voltage for the remotely located transistor. The
variable current mirror provides the target collector currents and
is formed by the arrangement of MOSFET transistors M4 and M5 where
the impedance of M5 is adjustable.
[0055] Additionally, the inputs to comparator 806 are coupled to
the inverting inputs of bias opamp 804 and opamp 802. The output of
the comparator is coupled to control logic 808 which outputs a code
for DAC 810. The output of the DAC is coupled to the gates of the
MOSFETs M4 and M5. Also, MOSFET M3 is configured to provide a
target emitter current and operate as another current mirror with
MOSFET transistors M1 and M2. This other current mirror ensures
that the target emitter current (Ietarget) flowing through MOSFET
M3 is substantially equivalent to the currents flowing through
MOSFETS M1 (Ie) and M2 (Ie').
[0056] During the determination of the first and second target
collector currents, the output of opamp 802 may be disconnected
from the gates of MOSFETs M1 and M2 by the opening of analog switch
S1. Also during this determination, MOSFET M3 is connected to the
gates of MOSFETs M2 and M1 by the closing of analog switch S2.
After the first and second target collector currents are
determined, S1 closes and connects the output of opamp 802 to the
gates of MOSFETs M1 and M2; and S2 opens and disconnects MOSFET M3
from the gates of MOSFETs M1 and M2.
[0057] Although not shown, a sample and hold circuit could also be
provided that disconnects the output of opamp 802 from the circuit
during the determination of target collector currents and the
measurement of the base-emitter voltage for the remotely located
transistor. Additionally, substantially the same arrangement of
these components could be employed to determine the temperature of
a transistor that is disposed locally, i.e., the transistor can be
disposed in the same integrated circuit as the components employed
to measure its currents.
[0058] FIG. 9 illustrates an overview of block diagram 900 for
components to measure the temperature of remotely located
transistor Q1 by determining target collector currents and
base-emitter voltages for the transistor. In another integrated
circuit, the remotely located transistor's base and emitter
currents are coupled to beta variation cancellation circuit 902
(exemplary embodiments are discussed above). The analog signal
output of circuit 902 is coupled to signal conditioner 904 which
can include buffers, low pass filters, and the like, for
damping/removing noise. The output of signal conditioner 904 is
coupled to the inputs of analog to digital converter (DAC) 906
whose output is coupled to logic component 908.
[0059] The output of logic component 908 is coupled to one of the
inputs for comparators 910 and 912. The output of these comparators
can be provided as external status bits and/or pins for the
integrated circuit. Another input to comparator 910 is coupled to
an output of Temperature Limit2 (914). Also, the other input to
comparator 912 is coupled to an output of Temperature Limit1 (916).
Serial interface 920 is coupled to both of the temperature limits
(914 and 916) and control logic 918. This control logic is also
coupled to circuit 902, signal conditioner 904 and ADC 906.
[0060] Additionally, serial interface 920 is arranged so that an
interface external to the integrated circuit can be employed to
configure the operation of the control logic and the values of the
two temperature limits (914 and 916). The serial interface can also
be configured to provide a digitized value that represents a
relatively accurate temperature of the remotely located transistor.
Furthermore, substantially the same arrangement of these components
could be employed to determine the temperature of a transistor that
is disposed locally, i.e., the transistor can be disposed in the
same integrated circuit as the components employed to measure its
currents.
[0061] FIG. 10 illustrates a block diagram of overview 1000 for an
exemplary circuit for measuring the base-emitter voltage
(Vmeasured) of a remotely located transistor. The Vmeasured is
coupled to optional low pass filter 1002 which provides for
reducing/eliminating noise in the measured voltage. The outputs of
filter 1002 is coupled to the inputs of analog to digital converter
(ADC) 1004 whose output is coupled to logic circuit 1006. The logic
circuit converts the digitized measurement of the base-emitter
voltage into a format that can be displayed by digitized
temperature display 1008. Display 1008 can include numerical
displays, colors, pictures, graphics, bar graphs, sounds, status
bits, status pins, interfaces, and the like, as a representation of
the digitized temperature for the remotely located transistor.
[0062] Additionally, in another embodiment, where the remotely
located transistor is disposed in series with and/or accessed
through one or more resistors, a resistive cancellation circuit may
be provided in addition to the circuits discussed above. If these
resistive cancellation circuits are used, likely more than two
measurements of the base currents and/or base-emitter voltages may
be performed to accurately determine the temperature of the
resistor.
[0063] Moreover, it will be understood that each block of the
flowchart illustrations discussed above, and combinations of blocks
in the flowchart illustrations above, can be implemented by
computer program instructions. These program instructions may be
provided to a processor to produce a machine, such that the
instructions, which execute on the processor, create means for
implementing the actions specified in the flowchart block or
blocks. The computer program instructions may be executed by a
processor to cause a series of operational steps to be performed by
the processor to produce a computer-implemented process such that
the instructions, which execute on the processor, provide steps for
implementing the actions specified in the flowchart block or
blocks.
[0064] Accordingly, blocks of the flowchart illustration support
combinations of means for performing the specified actions,
combinations of steps for performing the specified actions and
program instruction means for performing the specified actions. It
will also be understood that each block of the flowchart
illustration, and combinations of blocks in the flowchart
illustration, can be implemented by special purpose hardware-based
systems, which perform the specified actions or steps, or
combinations of special purpose hardware and computer
instructions.
[0065] The above specification, examples, and data provide a
complete description of the manufacture and use of the composition
of the invention. Since many embodiments of the invention can be
made without departing from the spirit and scope of the invention,
the invention resides in the claims hereinafter appended.
* * * * *