U.S. patent number RE34,179 [Application Number 07/538,932] was granted by the patent office on 1993-02-16 for temperature controlled hybrid assembly.
This patent grant is currently assigned to John Fluke Mfg. Co., Inc.. Invention is credited to Larry E. Eccleston.
United States Patent |
RE34,179 |
Eccleston |
February 16, 1993 |
Temperature controlled hybrid assembly
Abstract
A hybrid circuit structure includes an electrical circuit and a
heating circuit therefor, both mounted on a single substrate.
Valuable substrate space is saved by mounting the electrical
circuit components on one surface of the substrate and the heating
circuit elements on the opposite surface. A temperature control
circuit is included, preferably mounted on the same surface as the
electrical circuit components. Precision resistors for gain control
and other functions may be provided on a separate substrate which
may be mounted directly to the single substrate or to a separator
therebetween. The precision resistors are in thermal contact with
the temperature controlled heating circuit, thereby further
increasing the stability of the circuit.
Inventors: |
Eccleston; Larry E. (Edmonds,
WA) |
Assignee: |
John Fluke Mfg. Co., Inc.
(Everett, WA)
|
Family
ID: |
27065970 |
Appl.
No.: |
07/538,932 |
Filed: |
June 15, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
939522 |
Dec 8, 1986 |
04841170 |
Jun 20, 1989 |
|
|
Current U.S.
Class: |
327/512; 257/467;
327/564 |
Current CPC
Class: |
H01L
25/167 (20130101); H05K 1/0212 (20130101); G05D
23/1919 (20130101); G05D 23/24 (20130101); H05K
2203/165 (20130101); H05K 1/0306 (20130101); H05K
1/144 (20130101); H05K 1/167 (20130101); H05K
2201/043 (20130101); H05K 2201/10151 (20130101); H05K
2203/1115 (20130101); H05K 2203/1581 (20130101); H01L
2924/0002 (20130101); H01L 2924/0002 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
G05D
23/20 (20060101); G05D 23/24 (20060101); H01L
25/16 (20060101); H05K 1/02 (20060101); H05K
1/03 (20060101); H05K 1/14 (20060101); H05K
1/16 (20060101); H01L 027/00 () |
Field of
Search: |
;307/310,303,303.1
;357/28,81 ;323/289,369,907 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2354719 |
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May 1975 |
|
DE |
|
1029322 |
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May 1966 |
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GB |
|
1187595 |
|
Apr 1970 |
|
GB |
|
1307818 |
|
Feb 1973 |
|
GB |
|
2038102 |
|
Jul 1980 |
|
GB |
|
2057761 |
|
Apr 1981 |
|
GB |
|
2163008 |
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Feb 1986 |
|
GB |
|
Primary Examiner: Zazworsky; John
Attorney, Agent or Firm: Koske; Richard A. Gopstein;
Israel
Claims
I claim: .[.
1. A hybrid electronic circuit arrangement comprising:
a substrate;
an electrical circuit formed on said substrate;
a temperature control means formed on said substrate; and
heat generating circuit means formed on said substrate for heating
said electrical circuit to operate at predetermined temperature
conditions,
said heat generating circuit means connected to and responsive to
said temperature control means,
said heat generating circuit means in close thermal conductivity
with said electrical circuit for eliminating requirement of heat
enclosure therefor,
at least one element of said electrical circuit, said temperature
control means, and said heat generating circuit means comprising an
integrated circuit and at least another element of said electrical
circuit, said temperature control means, and said heat generating
circuit means comprising a film resistor..]. .[.
2. A hybrid electronic circuit arrangement as recited in claim 1,
wherein
said electrical circuit includes at least one component mounted on
said substrate,
said temperature control means includes a further circuit mounted
on said substrate, and
said heat generating circuit means comprises a plurality of film
resistors on said substrate..]. .[.3. A hybrid electronic circuit
as recited in claim 2 wherein said electrical circuit component is
mounted on one surface of said substrate forming a component
bearing surface, and
said plurality of film resistors of said heat generating circuit
means are formed on the opposite surface of said substrate..].
.[.4. A hybrid electronic circuit as recited in claim 2 wherein
said electrical circuit
component comprises an integrated circuit chip..]. 5. .[.An
electronic circuit arrangement as recited in claim 1.]. .Iadd.A
hybrid electronic circuit arrangement comprising:
a substrate;
an electrical circuit arranged on said substrate, .Iaddend.wherein
said electrical circuit comprises a plurality of components, at
least one component mounted on said substrate and at least one
component mounted on a separate substrate, said substrates
separated from one another by a spacer, said substrate and said
spacer comprising a material common thereto, whereby thermally
caused relative displacement between said substrate and said spacer
is reduced;
a temperature control means arranged on said substrate; and
heat generating circuit means arranged on said substrate for
heating said electrical circuit to operate at predetermined
temperature conditions,
said heat generating circuit means connected to and responsive to
said temperature control means,
said heat generating circuit means in close thermal conductivity
with said electrical circuit for eliminating the requirement of a
heat enclosure therefor,
at least one of said electrical circuit, said temperature control
means, and said heat generating circuit means comprising an
integrated circuit mounted on said substrate and at least one of
said electrical circuit, said temperature control means, and said
heat generating circuit means
comprising a film resistor formed on said substrate. 6. An
electronic circuit arrangement as recited in claim 5 wherein said
material common to
said substrate and to said spacer comprises a ceramic. 7. An
electronic circuit arrangement comprising:
a substrate;
an electrical circuit formed on said substrate;
a temperature control means formed on said substrate; and
heat generating circuit means formed on said substrate for heating
said electrical circuit to operate at predetermined temperature
conditions,
said heat generating circuit means connected to and responsive to
said temperature control means,
said heat generating circuit means being in close thermal
conductivity with said electrical circuit for eliminating
requirement of a heat enclosure therefor,
said electrical circuit including at least one component mounted on
said substrate;
said temperature control means including a further circuit mounted
on said substrate, and
wherein said electrical circuit component is mounted on one surface
of said substrate forming a component bearing surface, and
said heat generating circuit means is formed on the opposite
surface of said substrate; and
further comprising a separate network formed of components matched
to each other and comprising a high precision portion of said
electrical circuit,
said separate network formed on a separate substrate,
said separate substrate mounted to said opposite surface of said
first
mentioned substrate. 8. An electronic circuit as recited in claim 7
wherein said separate substrate is bonded to said opposite surface
of said
first mentioned substrate. 9. An electronic circuit as recited in
claim 7 further comprising separator means bonded to said opposite
surface of said first mentioned substrate, said separator means
having high thermal conductivity,
wherein said separate substrate is bonded to said separator means.
10. An electronic circuit as recited in claim 9 wherein said first
mentioned substrate is bonded to one surface of said separator
means and said separate substrate is bonded to an opposite surface
of said separator
means. 11. An electronic circuit as recited in claim 7 wherein said
separate network is sealed in a glass housing for improved
stability and
operation. 12. An electronic circuit as recited in claim 7 wherein
a plurality of connector pins are provided along one edge of said
first mentioned substrate and a plurality of separate connector
pins are
provided along an edge of said separate substrate. 13. An
electronic circuit as recited in claim 12 wherein said separate
substrate is mounted to said first mentioned substrate in an
arrangement selected to form a DIP
structure. 14. An electronic circuit as recited in claim 13 wherein
said separate substrate is mounted to said first mentioned
substrate to form a combined structure having a pair of parallel
edges,
said one edge of said first mentioned substrate and said one edge
of said separate substrate being along opposite ones of said pair
of edges of the
combined structure. 15. An electronic circuit as recited in claim
12 wherein said separate substrate is mounted to said first
mentioned
substrate in an arrangement selected to form a SIP structure. 16.
An electronic circuit as recited in claim 15 wherein said separate
substrate is mounted to said first mentioned substrate to form a
combined structure having a pair of parallel edges,
said one edge of said first mentioned substrate and said one edge
of said separate substrate being along a common one of said pair of
edges of the
combined structure. 17. An electronic circuit as recited in claim 7
wherein said separate network comprises a resistive network of film
resistors screened onto said separate substrate for controlling
operation of said electrical circuit components on said component
bearing surface of
said first mentioned substrate. 18. An electronic circuit as
recited in claim 17 wherein
said heat generating circuit means comprises film resistors
screened on
said substrate. 19. An electronic circuit as recited in claim 7
wherein said heat generating circuit means comprises film resistors
screened on
said substrate. 20. An electronic circuit as recited in claim 7,
wherein said arrangement comprises a hybrid circuit structure
wherein at least one element of said temperature control means and
said heat generating circuit means and/or at least one component of
said electrical circuit comprises an integrated circuit and another
element of said temperature control means and said heat generating
circuit means and/or another component of
said electrical circuit comprises a film resistor. 21. An oven
arrangement for heating an electrical circuit to operate at a
predetermined temperature for stabilizing electrical parameters
thereof, comprising:
a thermally conductive substrate;
an electrical circuit formed on said substrate;
a temperature control means formed on said substrate; and
heat generating circuit means formed on said substrate for heating
said electrical circuit via said thermally conductive substrate to
operate at predetermined temperature conditions,
said heat generating circuit means connected to and responsive to
said temperature control means,
said thermally conductive substrate maintaining said heat
generating circuit means in close thermal conductivity with said
heated electrical circuit for eliminating requirement of a heat
enclosure therefor;
said electrical circuit including at least one component adhesively
mounted on said substrate by an adhesive having high thermal
conductivity,
said temperature control means includes a further circuit
adhesively mounted on said substrate by an adhesive having high
thermal conductivity, and
said heat generating circuit means comprising a plurality of
resistors formed on said substrate,
said electrical circuit component mounted on one surface of said
substrate forming a component bearing surface.
said heat generating resistors formed on the opposite surface of
said substrate,
said temperature control means including at least one component
mounted on
said component bearing surface of said substrate. 22. An oven
arrangement as recited in claim 21, further including a hybrid
electrical circuit structure wherein at least one element of said
temperature control means and said heat generating circuit means
and/or at least one component of said electrical circuit comprises
an integrated circuit and another element of said temperature
control means and said heat generating circuit means and/or another
component of said electrical circuit comprises a film resistor,
and
further comprising a separate network formed of components matched
to each other and comprising a high precision portion of said
electrical circuit,
said separate network formed on a separate substrate,
said separate substrate adhesively mounted to said opposite surface
of said first mentioned substrate by said adhesive having high
thermal conductivity.
Description
TECHNICAL FIELD
This invention relates to electrical circuits, and more
specifically to arrangements for maintaining electrical circuits at
controlled temperatures to provide precisely controllable
temperature dependent operational characteristics to components of
the circuits.
BACKGROUND ART
It is known that electrical characteristics of circuit components,
whether discrete or integrated, are frequently sensitive to and
variable with temperature. It has accordingly been known in the
prior art to try to stabilize operational characteristics and
electrical parameters of electronic circuits by attempting to
maintain a relatively constant ambient temperature for the
circuit.
Typically, electrical parameters of circuit components, such as
resistors, are measured at and remain substantially constant at
known, constant, temperatures. It is thus known to operate a
circuit at a predetermined temperature to maintain the electrical
characteristics thereof at fixed values. However, temperature
control and stabilization has previously been expensive to
implement because of the need for additional circuitry and the
increased space requirements therefor.
Difficulties encountered in prior art efforts to attain temperature
stabilized operations have often related to obtaining an
arrangement of the electronic circuit to be stabilized together
with apparatus for controlling the ambient temperature.
Additionally, and more specifically, it has been difficult to
combine the circuit to be controlled with specific heating
apparatus to provide the desired operating temperature.
Accordingly, in the prior art it has become accepted to control the
ambient temperature of a circuit by enclosing the circuit within an
oven structure.
Such a prior art approach, however, is expensive and thus tends to
discourage operation of electronic circuits at desired
temperatures. In addition to requiring the heat generating
circuitry, the prior art temperature control arrangements require
an enclosure. Such enclosures, even if limited to surround a
particular circuit board or arrangement, add both to the expense of
fabricating the device and to the space and volume required
thereby.
Accordingly, temperature stabilized operation has been unavailable
in inexpensive electronic circuits and devices. The precision
available by operation of electrical circuits at known and
controlled temperatures has been relegated to more expensive
devices and has been generally unavailable in less expensive
devices, such as used in consumer electronics.
There has thus been a need in the prior art for easily implemented
and inexpensive temperature control arrangements for electronic
circuits. More specifically, there has been a need for heat
generating and heat control circuits which do not require expensive
ovens or excessive space and volume for implementation.
DISCLOSURE OF INVENTION
It is thus an object of the present invention to overcome the
difficulties of the prior art and to provide an inexpensive
electronic temperature control arrangement for controlling the
ambient operating temperature for electrical devices.
It is a more specific object of the invention to provide a heat
control arrangement for electrical devices, wherein the heat
controlling structure does not require substantial increases in
space and volume for implementation.
A more particular object of the invention is the provision of a
temperature control and heat generating arrangement for an
electronic circuit which does not require an enclosure.
It is yet another object of the invention to provide a structure
for implementing a compact electronic circuit, including therein on
a single circuit board both an operating circuit and a temperature
controlled heat generating circuit therefor.
Yet another object of the invention is the provision of a sandwich
structure wherein an electronic circuit is provided on one surface
of a substrate and a heat generating resistive circuit is provided
on an opposite surface of the substrate.
It is still a further object of the invention to provide a hybrid
circuit including an electronic circuit on one surface of a
substrate and a heat generating circuit on an opposite surface of
the substrate.
Still another object of the invention is to provide a hybrid
circuit including an electronic circuit on one surface of a
substrate and a heat generating circuit on an opposite surface of
the substrate, together with an arrangement wherein thin or thick
film resistive networks are formed on a separate substrate, and
wherein the separate substrate including the resistive network is
mounted to the heat generating circuit on the opposite surface of
the first mentioned substrate.
Yet a further object of the invention is to mount a hybrid circuit
assembly including both an electronic circuit and a heat generating
circuit on one side of, and in good thermal conductance with, a
ceramic separator having a known heat conductivity and to mount to
the other side of the separator a resistive network of matched
resistors used in the electronic circuit.
In accordance with these and other objects of the invention, there
is generally provided an electronic circuit arrangement comprising
an electrical circuit formed on a substrate, a temperature control
component formed on the substrate, and a heating circuit formed on
the substrate for heating the electrical circuit to operate under
predetermined temperature conditions. The heat generating circuit
is connected to and responsive to the temperature control
component, while the heat generating circuit is in close thermal
conductivity with the electrical circuit for eliminating
requirement of a heat enclosure housing therefor.
Preferably, the arrangement includes a hybrid electrical circuit
structure, and the electrical circuit includes at least one
component, such as an integrated circuit chip, mounted on the
substrate. The temperature control component includes a further
circuit mounted on the substrate, which may also be an integrated
circuit. The heat generating circuit includes film resistors
screened on the substrate.
In accordance with the preferred embodiment of the invention, the
integrated circuit component of the electrical circuit is mounted
on one surface of the substrate while the heat generating film
resistors are formed on the opposite surface of the substrate.
The temperature control component, which is mounted on the
substrate, is preferably mounted on the same surface of the
substrate as the electrical circuitry component.
In accordance with another aspect of the invention, there is also
provided a separate network, for controlling gain, for example, of
the components of the electrical circuit. The separate circuit is
preferably formed of components matched to each other, such as
precision matched resistors having a one ppm/.degree.C. matching,
for example. The separate network is preferably formed on a
separate substrate, mounted to the opposite surface of the
component and heater substrate.
The separate substrate may be bonded to the opposite surface of the
component and heater substrate. Alternatively, a high thermal
conductivity ceramic separator may be bonded along one surface
thereof to the opposite surface of the component and heater bearing
substrate, and the separate substrate may be bonded to the opposite
surface of the ceramic separator.
Moreover, the separate network may be sealed in a glass housing for
improved stability and operation, by excluding dust, humidity and
the like from affecting the various components thereof.
The separate substrate and the component and heater substrate are
each provided with contact connectors along a respective edge of
each. The separate substrate may be mounted to the component
substrate so that both sets of leads are along one edge of the
combined structure, thus forming a SIP (single-in-line-package).
Alternatively, the two substrates may be mounted so that the
connectors are formed on opposite edges of the combined structure,
thus forming a DIP (dual-inline-package).
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features and advantages of the
present invention will become more readily apparent to those
skilled in the art to which the invention pertains upon reference
to the following detailed description of one of the best modes for
carrying out the invention, when considered in conjunction with the
accompanying drawing in which a preferred embodiment of the
invention is shown and described by way of illustration, and not of
limitation, wherein:
FIG. 1 shows a hybrid circuit board incorporating the present
invention;
FIG. 2 shows a side view of a sandwich structure including the
hybrid of FIG. 1 and a separate substrate including a precision
resistance network thereon;
FIG. 3 illustrates the resistance network formed on the separate
substrate of FIG. 2; and
FIG. 4 shows a schematic representation of a circuit
interconnection between a component included on the hybrid of FIG.
1 and the resistance network of FIG. 3.
BEST MODE FOR CARRYING OUT THE INVENTION
In accordance with applicant's invention, there is thus provided a
hybrid circuit board, as shown at FIG. 1, which incorporates both
an electrical circuit and a heat generating circuit and a
temperature control circuit therefor.
Referring now to FIG. 1, there is shown a structural arrangement
10, which includes a substrate 12, on which is formed an electrical
circuit, symbolized by a component amplifier 14.
The electrical circuit and various of its components may be formed
of any of a number of different electrical and electronic devices
known in the art. Thus, discrete, film, or integrated components
may be used. Substrate 12 is thus preferably a hybrid circuit board
which may be used to mount discrete or integrated components, as
well as to form screened film components.
In one circuit utilizing the invention, a digital-to-analogue
converter (DAC) is formed, incorporating therein an integrated
circuit chip which includes amplifier 14. As hereinbelow described,
gain control networks, and particularly resistive networks for
controlling the gain of amplifier 14, may also be included on the
substrate 12.
In accordance with the invention, there is provided on substrate 12
a heater control circuit 16 as well as a heating circuit 18.
Preferably, heating circuit 18 is comprised of a weaving pattern of
film resistors, whether thin or thick, screened onto the substrate
12. In the following description, the term "component" will refer
to the electrical circuit components, such as amplifier 14, in
opposition to the various elements of the heating circuit 18.
As further shown in FIG. 1, the electrical circuit components, such
as amplifier 14, are mounted (or formed) on one surface of
substrate 12, hereinafter identified as a component bearing surface
of the substrate. The elements of the heating circuit 18,
illustrated by dashed lines, are preferably formed on the opposite
surface of the substrate. In this arrangement, substrate 12 is
preferably formed of a high thermal conductivity material, such as
ceramic material, to provide good thermal contact between the
heating circuit and the heated components and temperature control
circuit .Iadd.(i.e., heat control circuitry 16).Iaddend..
A significant advantage of the inventive arrangement is the
productive utilization of substrate space which is wasted in prior
art structures. More particularly, use of the rear surface of a
substrate to support a heating circuit reduces the space required
by the entire heated electronic circuit and thus reduces the size
of the substrate. As a result, the heating requirements are reduced
and the control requirements are simplified, thus advantageously
reducing the complexity of the heat control circuitry 16.
The reduced size of the hybrid arrangement 10 further enables the
heating circuit 18 to heat the circuit components without requiring
an enclosure therefor, thus further reducing the expense of forming
a heated electrical circuit.
In accordance with another aspect of the invention, precision of
operation of the various components formed and mounted on the
component bearing surface of substrate 12 is increased by providing
a separate network of precision matched components.
Thus, the gain of the amplifier 14 of a DAC incorporating the
present invention may be precisely controlled with the aid of a
resistive network of matched film resistors, illustrated at 20 in
FIG. 3. The resistors of the network 20 may be thin film or thick
film resistors. The separate resistive network may be provided on a
separate substrate 22, as illustrated at FIG. 2.
In the separately provided substrate 22, resistances (or other
circuit components) may be matched to track one another as closely
as 1 ppm/.degree.C., and the separate substrate 22, including
thereon the matched network 20, may be separately mounted to the
substrate 12.
As will be understood from the following description, the separate
substrate may be mounted directly to the rear surface of substrate
12. Alternatively, as illustrated in FIG. 2, a high thermal
conductivity ceramic spacer 24 may be used between the two
substrates. In the sandwich structure of FIG. 2, component bearing
substrate 12 is mounted to one surface of the ceramic spacer 24,
while the separate substrate incorporating the precision control
network thereon is mounted to the other surface of the spacer.
The circuit arrangement implemented by the inventive structure is
shown schematically in FIG. 4. As shown therein, amplifier 14, for
example, is mounted on the component bearing surface of substrate
12, illustrated at 23. The gain control circuit 20, which may be
comprised of two 10-K resistors, for example, is mounted on the
separate substrate 22. The resistive network 20 on substrate 22 may
be connected to the components of the electrical circuit on
substrate 12 in any manner known in the art.
In accordance with another aspect of the invention, it is noted
that in the arrangement of FIG. 2, the two substrates 12 and 22 are
each bonded to a respective surface of spacer 24 by a thin
molecular layer of thermally conductive epoxy, or the like.
Thus, the heating circuit 18 is in good thermal contact both with
the components mounted on the component bearing surface of
substrate 12 and with the resistive network of substrate 22,
providing for improved temperature control for the circuits on each
substrate. In that regard, the high thermal conductivity of the
ceramic separator, combined with the heated environment for
substrate 22 and the gain control circuitry thereon, results in a
heat gain of 20 to the resistive network 20.
Accordingly, while a typical temperature coefficient for a matched
resistive network may be in the range of 1 to 5 ppm/.degree.C., the
coefficient for the network 20 mounted on substrate 22 and in
thermal contact with heating circuit 18 of substrate 12 as shown in
FIG. 2 in accordance with the invention was reduced to a level of
several tenths ppm/.degree.C.
It should be noted, however, that the substrate 22 may be bonded
directly to the rear surface of substrate 12, without the
intervening ceramic separator 24.
Separator 24 is used in the embodiment of FIG. 2 to assure that the
resistors in resistive network 20 and in the heating circuit 18 do
not scratch one another or otherwise interfere with proper
operation of each. By preventing such inadvertent contact and by
providing ample clearance for leads and connectors on both
substrates, manufacturability of the device is simplified by the
ceramic separator 24. However, by providing sufficient clearance
between the two substrates and by providing sufficient thickness of
the bonding epoxy, for example, substrate 22 may be mounted
directly onto substrate 12, as above noted.
In the preferred embodiment, resistive network 20 is sealed by a
glass cover over substrate 22, in order to improve stability of the
network by eliminating exposure to humidity, dust, or other
contaminants.
As hereinabove mentioned, and as will be appreciated by those of
ordinary skill in the art to which the invention pertains, the
components and elements of each substrate are provided with leads
and connectors for contact with external devices, power sources,
and the like. Referring again to FIGS. 1 and 2, connecting pins 26
are provided at one edge of the substrate 12. Pins 26 provide
contact to the various electrical components on the component
bearing surface of the substrate as well as to the heating circuit
elements. As is also shown in FIG. 2, connecting pins 28 are
provided at an edge of substrate 22 for contacting the resistive
network 20 thereon.
In the arrangement of FIG. 2 the connecting pins 26 and 28 are
provided along the same edge of the combined structure. Thus, the
structure of FIG. 2 may be mounted in a circuit board socket as a
single-inline-package (SIP). However, it should be realized that
the connecting pins 26 and 28 may be provided at opposite edges of
the combined structure. Such an arrangement results in a
dual-inline-package (DIP) structure, and may be used to mount the
combined structure in a DIP socket of a circuit board. The DIP
structure may be more easily attained in an arrangement wherein
ceramic spacer 24 is not used.
There has thus been described an arrangement wherein an electrical
circuit and a heating circuit therefor are both mounted on a single
substrate. More particularly, there has been described an
arrangement wherein valuable space is saved by mounting the
electrical circuit components on one surface of the substrate and
the heating circuit elements on the opposite surface. A temperature
control circuit is included, preferably mounted on the same surface
as the electrical circuit components in order to monitor accurately
the temperature of the components. Precision resistors for gain
control and other functions are also provided, on a separate
substrate which may be mounted directly to the single substrate or
to a separator therebetween. The precision resistors are
accordingly also heated by the temperature controlled heating
circuit, thereby further increasing the stability of the
circuit.
The foregoing description of the preferred embodiment of the
invention has been presented for purposes of illustration and
description and is not intended to be exhaustive or to limit the
invention to the precise forms disclosed, since many modifications
and variations are possible in light of the above teaching. The
embodiment was chosen and described in order best to explain the
principles of the invention and its practical application, thereby
to enable others skilled in the art best to utilize the invention
in various embodiments and with various modifications as are suited
to the particular use contemplated therefor. It is intended that
the scope of the invention be defined by the claims appended
hereto, when interpreted in accordance with full breadth to which
they are legally and equitably entitled.
* * * * *