U.S. patent number 3,571,630 [Application Number 04/773,059] was granted by the patent office on 1971-03-23 for two-terminal monolithic voltage regulator and reach-through transistor.
This patent grant is currently assigned to National Semiconductor Corporation. Invention is credited to Robert J. Widlar.
United States Patent |
3,571,630 |
Widlar |
March 23, 1971 |
TWO-TERMINAL MONOLITHIC VOLTAGE REGULATOR AND REACH-THROUGH
TRANSISTOR
Abstract
A double diffused transistor structure having a base region
which is sufficiently thin so that the reverse breakdown voltage
between the emitter and the collector (BV.sub.eco) is less than the
reverse breakdown voltage between the emitter and the base
(BV.sub.ebo). The transistor structure is connected in an
upside-down fashion as a two-terminal network, the terminals being
formed by the emitter and the collector in a manner similar to that
heretofore employed with Zener diodes to provide a "reach-through"
at a predetermined voltage thereacross. A circuit utilizing such a
"reach-through" transistor structure connected in the upside-down
fashion in conjunction with other components to operate the
transistor structure at a constant current to maintain the reverse
breakdown voltage constant.
Inventors: |
Widlar; Robert J. (Mountain
View, CA) |
Assignee: |
National Semiconductor
Corporation (Santa Clara, CA)
|
Family
ID: |
25097080 |
Appl.
No.: |
04/773,059 |
Filed: |
November 4, 1968 |
Current U.S.
Class: |
327/580;
257/E27.031; 322/4; 327/584 |
Current CPC
Class: |
H01L
27/00 (20130101); H01L 27/0716 (20130101); G05F
3/185 (20130101) |
Current International
Class: |
H01L
27/00 (20060101); H01L 27/07 (20060101); G05F
3/18 (20060101); G05F 3/08 (20060101); H03k
023/08 (); H01l 009/00 () |
Field of
Search: |
;317/235,222,30
;307/296,302,303,304 ;322/4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Craig; Jerry D.
Claims
I claim:
1. A two-terminal monolithic voltage regulator comprising:
a first terminal and a second terminal across which a voltage to be
regulated may be applied;
a first transistor means including a first region and a second
region of a first conductivity type separated by a third region of
a second conductivity type, at least a portion of said third region
being so thin that a depletion layer caused by reverse biasing the
junction formed between said first region and said third region
extends through said portion at a potential less than the avalanche
breakdown potential of said junction, said first region being
coupled to said first terminal;
resistance means coupling said second region to said second
terminal; and
a second transistor means having a first base, a first emitter and
a first collector, said first emitter being coupled to one of said
first and second terminals, said first collector being coupled to
the other of said first and second terminals and said first base
being coupled to said second region of said first transistor means,
said second transistor means being responsive to the current flow
through said first transistor means to regulate said voltage.
2. A two-terminal monolithic voltage regulator as recited in claim
1 wherein said resistance means includes a field effect transistor
having a gate, a source and a drain, said gate being coupled to one
of said first and second terminals, said source being coupled to
said second terminal and said drain being coupled to said second
region.
3. A two-terminal monolithic voltage regulator as recited in claim
2 and further including a third transistor means having a second
base, a second emitter and a second collector, said second emitter
being coupled to one of said first and second terminals, said
second collector being coupled to the other of said first and
second terminals and said second base being responsive to the
output of said second transistor means.
4. A two-terminal monolithic voltage regulator as recited in claim
3 and further including means coupling said third region to said
second terminal.
5. A two-terminal voltage regulator comprising:
a first terminal and a second terminal across which a voltage to be
regulated may be applied;
a first transistor means including a first emitter and a first
collector separated by a first base, and defining a first PN
junction between said first emitter and said first base, and a
second PN junction between said first base and said first
collector, the thickness of said base separating said first and
second junctions being so small that a depletion layer caused by
reverse biasing said first junction extends to said second junction
at a biasing potential less than that required to cause avalanche
breakdown across said first junction, said first emitter being
coupled to said first terminal;
resistance means coupling said first collector to said second
terminal; and
a second transistor means including a second base, a second emitter
and a second collector, said second base being coupled to said
first collector, said second collector being coupled to said first
terminal and said second emitter being coupled to said second
terminal.
6. A two-terminal voltage regulator as recited in claim 5 wherein
said resistance means includes a field effect transistor having a
gate, source and drain, said gate being coupled to said first
terminal, said drain being coupled to said first collector and said
source being coupled to said second terminal.
7. A two-terminal voltage regulator as recited in claim 6 and
further including a third transistor means having a third base, a
third emitter and a third collector, said third base being coupled
to said second collector, said third emitter being coupled to said
first terminal and said third collector being coupled to said
second terminal.
8. A two-terminal voltage regulator as recited in claim 7 wherein
said first transistor means and said second transistor means are of
a first conductivity type and said third transistor means is of the
opposite conductivity type.
9. A two-terminal voltage regulator as recited in claim 6 and
further including means coupling said first base to said second
terminal.
Description
STATEMENT OF THE INVENTION
This invention relates to voltage regulators, and, more
particularly, to a two-terminal monolithic voltage regulator
utilizing a reach-through transistor structure either alone or in
combination with other circuitry for maintaining the current
therethrough constant.
DESCRIPTION OF THE PRIOR ART
Low voltage regulators are required for numerous applications, such
as simple voltage regulation, level shifting, and the generation of
abrupt transitions for use in reproducing nonlinear transfer
functions. One device which is inexpensive and reliable and has
found very extensive use for low voltage regulation application is
the Zener diode. Zener diodes, however, have a rather soft
characteristic at low voltage, and do not have the speed of
response found desirable particularly in high-speed computer and
similar applications.
To overcome the limitations of Zener diodes, a narrow base, planar
junction, punch-through diode has been developed which is described
in U.S. Pat. No. 2,975,342 which issued on Mar. 14, 1961. In
accordance with this Pat., a single junction diode is provided
which has an ohmic contact located parallel to and spaced a very
small distance apart from the PN junction. When the applied voltage
across the junction is increased, the depth of the space charge
region or depletion layer produced by the voltage likewise
increases. When the voltage across a junction is increased to a
value at which the depletion layer depth punches through to the
ohmic contact, the diode develops a low dynamic impedance. This
punch-through diode has been found to be considerably faster than
the Zener diode, and has a somewhat sharper breakdown
characteristic.
However, the sharpness of the breakdown characteristic of the
punch-through diode still leaves something to be desired,
particularly where regulation is needed over a wide range of
currents, say from 10 microamps to 10 milliamps.
OBJECTS OF THE INVENTION
It is therefore a primary object of the present invention to
provide an improved low voltage regulator.
It is a further object of this present invention to provide a low
voltage regulator of the two-terminal monolithic type which is the
electrical equivalent of a breakdown diode.
It is also an object of the present invention to operate a
transistor structure, having a base region too thin for normal
operation, in a new mode to provide a two-terminal voltage
regulator which has a hard characteristic.
It is a further object of the present invention to provide a
two-terminal monolithic voltage regulator which has a sharp
breakdown characteristic over a current range extending from below
10 microamps to above 10 milliamps.
It is an additional object of the present invention to provide a
regulator device which includes a transistor structure which is
operated in a different than the normal mode to exhibit
reach-through breakdown at a predetermined voltage, the transistor
structure being combined in an integrated circuit chip with other
circuit elements to form a new and novel regulator device.
SUMMARY OF THE INVENTION
In accordance with the preferred embodiment of the present
invention, a double diffused planar transistor is constructed in
such a manner that the second diffusion is deeply diffused into the
first diffusion region so that the PN junction defining the
base-emitter boundary and the PN junction defining the
base-collector boundary have at least a portion in close proximity
to one another. The close proximity portion of these two junctions
is selected in such a manner that the application of a reverse
voltage (emitter more positive than collector for an NPN device)
across the emitter and the collector electrodes produces a
"reach-through" or breakdown of the transistor at a voltage which
is lower than the reverse voltage which will produce an avalanche
breakdown when applied between the emitter and the base
terminals.
In other words, the transistor structure of this invention is
operated in the upside-down mode in which the emitter of a NPN
structure, or the collector of a PNP structure, is maintained
positive with respect to the base. To avoid an avalanche breakdown
between the emitter and base when connected in this upside-down
configuration, the base region is made sufficiently thin so that
the depletion layer crosses the base-collector junction before an
avalanche is reached.
In accordance with one embodiment of the invention, this
reach-through transistor structure may be utilized in the
upside-down configuration as a two-terminal regulator, the
two-terminal networks being formed respectively by the emitter and
the collector. In accordance with another embodiment of the present
invention, the reach-through transistor is operated at a constant
reverse current and amplifier circuitry is used to regulate the
terminal voltage against variations in current.
Objects and advantages other than those set forth above will be
apparent from the following description, when read in connection
with the accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional diagram of a reach-through transistor
structure constructed in accordance with the present invention;
FIG. 2 is a schematic wiring diagram of an NPN reach-through
transistor structure of the type illustrated in FIG. 1, connected
for operation in the voltage regulator mode, in accordance with the
present invention;
FIG. 3 is a schematic circuit diagram of a regulator device
employing the reach-through structure of the present invention;
FIG. 4 is a graph comparing the performance characteristics of the
regulator device of FIG. 3 with that of a conventional
alloy-junction diode.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, there is shown a double diffused
transistor device 10 which includes an emitter (E) region 12, a
base (B) region 13 and a collector (C) region 14. The emitter
region is deeply diffused during the manufacture of device 10 into
the base region to produce the desired characteristics for
reach-through operation in accordance with this invention. Because
of this deep penetration during the second diffusion, the thickness
of base 13, defined as the distance between the NP junctions formed
by the emitter-base junction and the base-collector junction, is
less than found in ordinary transistors, a condition necessary for
the phenomena of reach-through to occur.
The phenomena of reach-through occurs when the depletion region of
the reverse biased emitter-base junction penetrates or "reaches
through" narrow base region 13 to collector region 14. This results
in an abrupt increase in current flow between the emitter and
collector. In accordance with this invention, the reach-through
phenomenon is utilized to produce a regulating action in the
circuit in which the device is connected.
It is important in the present invention that the device be
fabricated in such a manner that the voltage at which reach-through
occurs (between emitter and collector) is less than the voltage at
which avalanche breakdown occurs (between emitter and base). That
is, the reach-through voltage between the emitter and collector,
commonly designated as BV.sub.eco, must be less than the avalanche
voltage between the emitter and the base, commonly designated as
BV.sub.ebo. The condition that BV.sub.ebo must be greater than
BV.sub.eco usually makes the device of this invention unsuitable as
an ordinary transistor device, as the narrow base region causes a
low breakdown voltage in the normal operating mode of the
transistor.
To obtain a transistor device in which the BV.sub.ebo is greater
than the BV.sub.eco, the second diffusion must be carefully
controlled. In practice, a test sample is utilized and frequently
tested during the second diffusion and the diffusion is stopped
when the sample shows the desired breakdown voltage between the
emitter and collector.
The reach-through transistor of the present invention may be
utilized in a number of ways to provide voltage regulation. In
perhaps the simplest application, which is illustrated in FIG. 2 of
the drawing, a reach-through transistor device 15 has its emitter
15E connected through a resistance R to terminal 16. The collector
15C is connected to ground and the base 15B is preferably shorted
to the collector 15C, although it need not necessarily be so
connected. When an unregulated voltage is applied to the circuit at
terminal 16 the operating characteristics of the transistor 15, as
explained above, are such that a regulated output voltage can be
obtained at the emitter terminal 15E. Instead of using an NPN
configured reach-through transistor structure, the same effect can
be obtained using a PNP configured structure by simply reversing
the circuit polarities.
A somewhat more efficient voltage regulator is illustrated in FIG.
3. A reach-through transistor structure 20 is shown connected to
elements including a field effect transistor 17 which uses the base
diffusion of the NPN transistor as a channel and the NPN emitter as
a gate. Transistor 17 serves to establish the operating current of
device 20 at a level greater than the base current of a transistor
18, which may be an ordinary transistor, and provides most of the
gain for the regulator. Transistor 18 has an emitter 18a, a base 18
b which is connected to the emitter of device 20, and a collector
18c. The regulator also employs another transistor having an
emitter 19a, a base 19b and a collector 19c. From a practical
standpoint, all of the the transistor elements of FIG. 3 are
preferably formed on the same chip using integrated circuit
techniques. For example, the regulator may be fabricated on a
silicon die with the six-mask planar-epitaxial process used for the
great majority of linear and digital integrated circuits.
Transistor 19 may be a vertical PNP transistor which is made using
the NPN base and an emitter, the NPN collector as a base and the
P-type substrate of the integrated circuit as a collector. It will
be apparent that this PNP transistor, which is required to handle
large currents up to 10 mA, must be made quite large because of the
low emitter efficiency of the NPN base diffusion.
The regulator also includes a pinch resistor 21 which sets the
operating collector current of transistor 18. The resistance value
of resistor 21 may be chosen so that transistor 18 sees a minimum
variation of collector current in the midrange of operating
currents for the completed device, giving best regulation in this
region.
In operation of the regulator, as voltage is applied across the
device, the emitter-base junction of diode device 20 is reverse
biased. When a voltage is reached where the emitter depletion
region penetrates the base to the collector, reverse reach-through
occurs and device 20 beings to conduct, turning on transistor 18
which regulates the voltage across the terminals of the
regulator.
The characteristics of a regulator such as shown in FIG. 3,
relative to the characteristic of a typical alloy-junction diode,
are shown in the graphs of FIG. 4. Curve 23 represents the
characteristic of the alloy-junction device, while curve 24 shows
the characteristics of a regulator as shown in FIG. 2. These graphs
clearly illustrate the relatively soft characteristic of the
alloy-junction device compared with the hard and sharply breaking
characteristics of the regulator of the present invention.
In the operation of the regulator shown in FIG. 3 for reverse
voltages up to about further 1 volt of the nominal breakdown
voltage, the reverse current is primarily junction leakage current
in the low nanoampere range. Above this voltage, device 20 breaks
down, conducting into the On resistance of transistor 17. Any
further increase in voltage causes device 20 to conduct more, but
at the same time it pinches OFF transistor 17, giving rise to an
initial hump in the reverse characteristic. This continues until
transistor 18 turns ON, and its added gain initiates breakdown and
hardens the diode characteristic. The diode voltage will then vary
by about 60 mv./decade until the current rises to 50 .mu.A. At this
point, transistor 19 turns ON, providing even more gain and
reducing the voltage variation to approximately 15 mv./decade. At
currents much above 1 mA, the base current of the output PNP
transistor 19 becomes appreciable by comparison to the bleed
current through resistor 21, so that the reverse characteristic
softens somewhat.
The change of breakdown voltage with temperature is a nearly linear
3.3 mv./.degree. C., independent of the nominal breakdown voltage.
Because of this predictable temperature drift, the device can be
used in building relatively simple temperature compensated
regulators for operation with input voltages down to 3v. and output
voltages down to 1V. This is a distinct advantage, since it is
difficult to make any other type of temperature compensated
reference in the voltage range from 2V to 6v., and tunnel diodes
and most integrated circuits operate at voltages below that of
temperature-compensated references.
From the foregoing, it will be seen that there is provided a
two-terminal monolithic voltage regulator which is electrically
equivalent to a breakdown diode. At low voltages, the regulator
provides reverse characteristics which are more than 10 times
sharper than those obtainable with single-junction Zener diodes.
The regulator of this invention has been manufactured with
breakdown voltages from 1.8v. to 5.6v. As indicated above, the
regulator is well suited to fabrication using integrated circuit
techniques.
While the above detailed description has shown, described and
pointed out the fundamental novel features of the invention as
applied to various embodiments, it will be understood that various
omissions and substitutions and changes in the form and details of
the device illustrated may be made by those skilled in the art,
without departing from the spirit of the invention. It is the
intention, therefore, to be limited only as indicated by the scope
of the following claims.
* * * * *