United States Patent (19)
`McGlinchey
`
`USOO.5677558A
`Patent Number:
`11
`45 Date of Patent:
`
`5,677.558
`Oct. 14, 1997
`
`54 LOW DROPOUT LINEAR REGULATOR
`75 Inventor: Gerard F. McGlinchey, Enniskerry,
`Ireland
`
`Primary Examiner Stephen Meier
`Attorney, Agent, or Firm-Koppel & Jacobs
`57
`ABSTRACT
`
`73 Assignee: Analog Devices, Inc., Norwood, Mass.
`
`21 Appl. No.: 688,557
`22 Filed:
`Jul. 30, 1996
`Related U.S. Application Data
`63 Continuation of Ser. No. 397,901, Mar. 3, 1995, abandoned.
`(51) Int. Cl. ........... HO1, 29/76; HO1L 29/94;
`HO1L 31/062; HO1L 3/119
`52 U.S. Cl. .......................... 257/370; 257/373; 3271564
`(58) Field of Search ................................. 257/370, 373,
`257/547; 327/564
`
`56
`
`References Cited
`U.S. PATENT DOCUMENTS
`3/1989 Bingham ................................... 35i/35
`4,812,891
`1/1990 Miyazawa et al. .
`... 257f742
`4,893,157
`5,245.202 9/1993 Yasazaka ................................. 257/133
`OTHER PUBLICATIONS
`Sedra et al, Micro Electronic Circuits, p. 795. (O1982.
`Muller et al, Device Electronics for IC's, p. 122, C1986.
`Sedra, Microelectronic Circuit.sp. 798, 1986.
`
`A low dropout linear regulator utilizing a vertical PNP
`transistor as its pass element, integrated with CMOS cir
`cuitry. The vertical PNP transistor includes a P-well formed
`in a lightly doped N type substrate for its collector. An
`N-type region formed in the P-well is its base and a P-type
`region formed in the N-type region is its emitter. The emitter
`receives a variable input supply and the collector provides a
`regulated output signal to the load being driven. As the input
`voltage diminishes to less than a diode drop above the output
`voltage, the vertical PNP transistor tries to saturate and its
`associated parasitic NPN transistor turns on. To limit the
`effects of the parasitic NPN transistor and maintain a regu
`lated output, a current limiter is connected between the input
`and the collector of the NPN parasitic transistor. As the input
`voltage drops, the possibility of lateral current flow from the
`P-well of the vertical PNP transistor through the substrate to
`NMOS devices comprising the CMOS circuitry increases. A
`current diverter is connected to the body of each NMOS
`device to prevent the lateral currents from entering the
`sources and drains of the NMOS devices.
`
`14 Claims, 2 Drawing Sheets
`
`No
`
`o OUT
`
`Parasitic
`
`
`
`
`
`Reference
`Woltage
`Generator
`
`GND
`
`
`
`Q1
`
`PMOS Device 44
`
`NMOS Device 34
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1026
`Page 1 of 7
`
`

`

`U.S. Patent
`
`Oct. 14, 1997
`
`Sheet 1 of 2
`
`5,677,558
`
`Ea
`d
`O
`
`
`
`|ÞUIB ANCH
`
`o NII
`
`
`
`
`
`35 e??o A 90 UIÐJ???ÀI
`JO?e. Ieue?)
`
`
`CIN?) –
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1026
`Page 2 of 7
`
`

`

`U.S. Patent
`
`Oct. 14, 1997
`
`Sheet 2 of 2
`
`5,677.558
`
`
`
`r
`r
`
`()
`O
`a
`>
`O)
`A
`f
`O
`s
`2.
`
`w
`
`A
`f
`O
`s
`A.
`
`a.
`
`CN)
`CD
`m
`th
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1026
`Page 3 of 7
`
`

`

`5,677,558
`
`10
`
`15
`
`25
`
`30
`
`1.
`LOW DROPOUT LINEAR REGULATOR
`This application is a continuation of application Ser. No.
`08/397,901, filed Mar. 3, 1995, now abandoned.
`BACKGROUND OF THE INVENTON
`1. Field of the Invention
`The present invention relates to circuitry for regulating a
`variable input signal to provide a constant output signal, and
`more specifically to a series low dropout linear voltage
`regulating circuit (regulator) using a PNP transistor pass
`element with the capacity for integration into circuits using
`CMOS process technology.
`2. Description of the Related Art
`Many circuits, such as integrated circuits (ICs), require a
`power supply with a constant voltage level and a varying
`current to accommodate for varying load conditions. The
`problem is that typical power supplies, such as batteries,
`experience variations in their output voltage level as load
`conditions change and as the battery dies down. A variable
`power source therefore cannot be directly applied to an IC.
`The function of a regulator is to produce a regulated output
`from a variable power supply. The output of the regulator is
`then used as a power source for other circuits.
`One type of IC regulator is the linear voltage regulator,
`which includes error amplifiers, voltage reference generators
`and logic to control the voltage across a pass element that is
`connected in series with the load. Typically, the pass element
`is a power transistor. By operating the transistorin its linear
`region, it conducts current continuously and provides an
`uninterrupted output signal. Important features of a linear
`regulator include a low dropout voltage and a high maxi
`mum load capacity. The dropout voltage is the lowest input
`voltage at which a regulated output voltage is maintained.
`The output voltage level is determined by the requirements
`of the external circuitry being supplied. Below the dropout
`voltage, the regulator fails to provide a regulated output
`voltage.
`In implementing a linear regulator, both MOS and bipolar
`transistors may be used as the pass element, since they are
`both effective low on resistance switches for sourcing high
`currents. Bipolar transistors are preferable to MOS transis
`tors because they occupy less space on the IC, and thus allow
`for more efficient use of chip area and lower manufacturing
`costs. A disadvantage of bipolar transistors, however, is that
`many ICs are implemented using CMOS rather than bipolar
`circuitry. One problem with using bipolar technology on
`CMOS ICs is that PN junctions inherent in the IC may
`become forward biased, resulting in a loss of junction
`50
`isolation and resulting degradation of the circuit character
`istics. A requirement for integrating a bipolar pass element
`with CMOS circuitry, therefore, is to eliminate the effect of
`currents between the bipolar and MOS devices on the IC.
`Another problem when introducing bipolar technology into
`the CMOS process is that additional fabrication steps may
`be needed.
`One linear regulator which integrates a lateral bipolar
`transistor as the pass element into CMOS circuitry is dis
`closed in U.S. Pat. No. 4,812,891, Bingham, Mar. 14, 1989.
`It uses a dual serial collector lateral PNP pass-transistor.
`When the transistor's collector-base voltage approaches the
`emitter-base voltage the transistor saturates, which initiates
`the flow of minority carriers from the base to the dual
`collectors. The substrate acts as a barrier to the vertical flow
`of minority carriers (perpendicular to the surface of the
`substrate facing the emitter). The first collector collects the
`
`45
`
`35
`
`60
`
`65
`
`2
`laterally flowing minority carriers (parallel to the surface of
`the epitaxial layer in which the emitter is formed). Any
`lateral current not collected by the first collectoris collected
`by the second collector, preventing the flow of base-to
`collector current to the circuitry external to the lateral PNP
`pass-transistor region.
`To preserve junction isolation, a diode-connected
`N-channel transistor is positioned next to the lateral PNP
`transistor to prevent it from forward biasing with respect to
`the all Pregions in the substrate. The N-channel transistor is
`connected by its gate and drain to the highest voltage supply
`VIN+, and its source is connected to its body. The body is
`thus prevented from forward biasing with respect to the
`substrate.
`This circuit has a small geometry compared to MOS
`devices and is capable of supporting MOS circuitry.
`However, the lateral pass-transistor has only a limited cur
`rent capacity, current gain and maximum load capacity.
`Another problem is that in fabricating the pass-transistor, an
`extra step is added to the CMOS process.
`SUMMARY OF THE INVENTION
`The present invention is a low dropout linear regulator
`utilizing a vertical PNP transistor as the pass element. The
`PNP transistor may be integrated into CMOS circuitry
`without requiring complicated fabrication steps, and has a
`low dropout voltage and a high maximum load current
`capacity.
`The PNP transistor includes a P well formed in a lightly
`doped N type substrate for its collector. Within the P well is
`an N type base region of a higher concentration than the
`substrate. Inside the base is a Ptype region which serves as
`the emitter. The emitter of the PNP transistor is connected to
`the input supply terminal and its collectoris connected to the
`output terminal. The supporting circuitry of the regulator
`includes a reference voltage generator, a voltage divider and
`an error amplifier. By equating the midpoint voltage of the
`voltage divider to a reference voltage, the error amplifier
`monitors the PNP transistor collector current and voltage,
`drawing base current from the PNP transistor to maintain the
`collector current at the level required by the load. The base
`current drawn in turn forward biases the emitter-base junc
`tion of the PNP transistor and maintains the base voltage at
`a diode drop below the input voltage.
`When the input supply voltage is more than a diode drop
`above the output, the PNP transistor functions in its normal
`mode. In this mode the output voltage is kept constant and
`a low base current is drawn by the error amplifier to supply
`the collector current. As the input voltage drops to less than
`a diode drop, approximately 0.7V, above the collector
`voltage, the base voltage drops below the collector voltage
`and the PNP transistor begins to saturate. In the saturation
`mode, the PNP transistor continues to function as a linear
`pass element, but its current gain (B) drops and its required
`base drive increases.
`As the input voltage drops to approximately 0.17V above
`the predetermined output voltage, the error amplifier can no
`longer draw the required base current to supply the load
`current. The regulator thus drops out and the output voltage
`is no longer maintained at the constant predetermined level.
`As the input continues to drop, the output voltage tracks the
`input at 0.17W below it. This input to output relationship is
`continued until the input reaches 2.0V, at which point the
`regulator stops conducting between the input terminal and
`the output terminal.
`The regulator's PNP transistor has a parasitic NPN tran
`sistor effect associated with it which turns on as the PNP
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1026
`Page 4 of 7
`
`

`

`5,677.558
`
`3
`transistor base voltage drops below its collector voltage. The
`resulting parasitic NPN transistor currents retard the satu
`ration of the PNP transistor. A current limiter is connected
`between the input terminal and the collector of the parasitic
`NPN transistor to limit parasitic currents through it as the
`transistor Saturates. A side effect of the current limiter is that
`the voltage drop across it causes the substrate voltage to drop
`below the input voltage. This increases the possibility of the
`pass transistor's P well forward biasing with respect to the
`substrate and forming a parasitic lateral PNP transistor with
`other P wells formed on the substrate. A current diverter is
`used to prevent parasitic currents between P wells in the
`substrate from entering the sources and drains of CMOS
`circuitry integrated onto the substrate.
`DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic diagram illustrating the regulator of
`the present invention with a vertical PNP transistor as the
`pass element.
`20
`FIG. 2 is a cross-sectional diagram of the structure of the
`vertical PNP transistor pass element integrated with CMOS
`circuitry,
`
`10
`
`15
`
`4
`collector current and adjusts the voltage across R1 and R2.
`The base current drawn from Q1 is adjusted until its col
`lector current equals the required load current. As an
`example, when a disk drive connected to OUT turns on, the
`load current required at OUT increases. The current through
`R1 and R2 subsequently drops, resulting in an increased
`base current drawn from Q1 by the error amplifier 4. The
`increase in the base current drawn from Q1 is continued until
`Q1's collector current equals the required load current.
`The Q1 base drive drawn by the error amplifier 4 also
`forward biases Q1's emitter-base junction. This is due to the
`exponential relationship between the base current of a
`bipolar transistor and its emitter-base voltage. By drawing a
`current from Q1's base, the error amplifier 4 controls the
`current through Q1 and forward biases its emitter-base
`junction. The resulting voltage at the error amplifier output
`10 is the input voltage at IN minus the Q emitter-base
`junction diode drop of approximately 0.7V.
`Depending upon the input voltage, Q1 operates in either
`its normal mode or its saturation mode. When the input
`voltage is approximately a diode drop or more above the
`output voltage, Q1 operates in the normal mode. This is
`because its base-to-emitter junction is forward biased and its
`base voltage, which is a diode drop below the input voltage,
`is greater than its collector voltage. In the normal mode, the
`B of Q1 is approximately 100 and a low base drive is
`required to provide the necessary load current at OUT. The
`error amplifier 4 typically draws a 2 mA base current from
`Q1 when a maximum load current of 200 mA is required.
`As the input power supply depletes and the input voltage
`falls to less than a diode drop above the output voltage, Q1's
`base voltage drops below the output voltage. The emitter
`to-base junction of Q1 remains forward biased, however,
`and its collector voltage rises above its base voltage, forward
`biasing its collector-to-base junction. This pushes Q1 into its
`saturation mode and causes its B value to drop. A greater Q1
`base drive is then required by the error amplifier 4 to
`maintain a constant load current at OUT. The required base
`drive continually increases as the input voltage decreases
`because the emitter-to-collector voltage differential of Q1
`approaches zero and Q1's B decreases. The limit to the
`decrease in B and the increase in Q1's required base drive
`before the regulator drops out is the maximum output
`current of the error amplifier 4, which is approximately
`40-50 mA for an exemplary implementation. To provide a
`maximum load current of 200 mA with a maximum base
`drive of 40-50mA, the B of Q1 cannot drop below 4-5. Q1's
`B reaches 4-5 when its emitter voltage is approximately
`0.17V above its collector voltage. Therefore, the regulator
`maintains a constant output voltage and can provide a
`maximum load current of 200 mA as long as the input
`voltage is equal to or greater than approximately 0.17W
`above the predetermined output voltage level.
`When the input voltage drops to less than approximately
`0.17V above the desired output voltage, the output voltage
`linearly decreases with the input and remains 0.17W below
`the input. For example, if the desired output is 5.0V, once the
`input voltage drops below 5.17V, the output begins to
`linearly decrease with the input. Thus, if the input drops to
`5.07V, the output will fall to 4.9V. Many circuits can still
`operate as long as the output provided by the regulator does
`not vary significantly below the predetermined level. Thus.
`for some IC's normally requiring 5.0V, 4.9W is acceptable.
`One design constraint associated with the regulator as
`described is the development of parasitic effects. As Q1 tries
`to saturate, an associated parasitic vertical NPN transistor
`
`DETALED DESCRIPTION OF THE
`INVENTION
`FIG. 1 shows an embodiment of the present regulator,
`which uses a vertical PNP transistor Q1 as a pass element.
`The regulator includes supporting circuitry which controls
`the voltage across Q1 and pushes it into or out of saturation
`mode, depending upon the input voltage level at the input
`terminal N. Q1, by fluctuating into or out of saturation, can
`receive a varying input signal and supply a regulated output
`voltage and current to the output terminal OUT. The output
`terminal is connected to the load being driven.
`The supporting circuitry includes a reference voltage
`generator 2 which generates a predetermined reference
`voltage. The reference voltage generator 2 is preferably a
`Zener diode or a band-gap voltage reference circuit that
`includes PMOS and NMOS devices and PNP transistors,
`fabricated using conventional CMOS process technology. In
`a preferred embodiment, the reference voltage is approxi
`mately 1.255V. The supporting circuitry also includes an
`error amplifier 4 in the form of an operational amplifier
`which includes PMOS and NMOS devices fabricated using
`conventional CMOS process technology. The error amplifier
`4 has its inverting input connected to the reference voltage
`generator output and its non-inverting input connected to the
`midpoint 6 of a voltage divider circuit consisting of resistors
`R1 and R2 connected in series between OUT and ground
`GND. The error amplifier 4 holds the midpoint voltage equal
`to the reference voltage. This in turn maintains a constant
`output voltage at OUT, as determined by the relative resis
`tance values of R1 and R2. The predetermined voltage is set
`according to the requirements of the external circuitry being
`supplied; 5.0V is a common output for applications such as
`laptop computers.
`Another requirement of the external circuitry is that the
`load current supplied at OUT by Q1's collector must be
`adjustable to accommodate for variable load conditions such
`as a disk drive in a computer turning on or off. To supply a
`variable load current at OUT, the error amplifier output 10
`is connected to receive Q1's base current. When the load
`current varies the current through R1 and R2 also varies,
`changing the voltage across R1 and R2. The error amplifier
`4 corrects this by varying the base current it draws from Q1.
`This change in Q1's base current in turn changes Q1's
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1026
`Page 5 of 7
`
`

`

`5
`QP1 with a base at the collector of Q1, an emitter at the base
`of Q1 and a collector at the emitter of Q1 also turns on and
`draws current. This is due to QP1’s base voltage, which is
`at the same voltage as Q1's collector, increasing above
`QP1's emitter voltage and forward biasing QP1’s base-to
`emitter junction. QP1’s emitter then supplies current to the
`error amplifier 4, reducing the current it draws from Q1's
`base. This in turn reduces Q1's collector current, causing the
`current supplied to the load at OUT to drop. To control the
`effect of QP1, a current limiter 14 is connected between IN
`and QP1’s collector. The current limiter 14 limits the maxi
`mum saturation current through QP1 to an insignificant level
`compared to the current drawn from Q1's base. This pre
`vents the output current supplied to the load from being
`significantly reduced by the QP1 current.
`One implementation of the current limiter 14 is a resistor
`R3 as shown in FIG.1. The voltage across the resistor R3 is
`the input voltage less QP1's collector voltage. Since QP1's
`emitter is approximately 0.7V below the input (through the
`emitter-base junction of Q1) and QP1’s collector-to-emitter
`voltage during saturation is approximately 0.1V, the voltage
`across the resistor is approximately 0.6V. Considering that
`the error amplifier draws a maximum of 40-50 mA from
`Q1's base when Q1 is in saturation, a preferred resistor value
`of 200 ohms limits the current through QP1 to approxi
`25
`mately 3 mA (0.6V/200 ohms). 3 mA is a significantly small
`current compared to the maximum base current 40-50 mA
`that is supplied by the error amplifier 4. The resistor R3 can
`be either a discrete resistor, a diffused resistor, a JFET
`resistor, a thin-film resistor or a resistor that may be imple
`30
`mented into a CMOS process.
`FIG. 2 is a cross-sectional diagram of the vertical PNP
`transistor of this invention integrated with CMOS circuitry
`utilizing CMOS process technology. The vertical PNP struc
`ture Q1 includes a Pwell 22 formed in an N type substrate
`24 using a conventional CMOS process. P well 22 is the
`collector, within which is formed an N type base region 26.
`Inside the base is a P type region 28 which serves as the
`emitter. The emitter is connected to IN for receiving the
`input voltage to be regulated, and its collector is connected
`to OUT to provide the regulated output signal.
`The vertical parasitic NPN transistor QP1 of FIG. 1
`appears in FIG. 2 with the N type region 26 as the emitter.
`the P well 22 as its base, and the N type substrate 24 as its
`collector. As in the circuit of FIG. 1, a current limiter,
`interposed between IN and the substrate 24, limits the
`current to the emitter of the saturated parasitic NPN tran
`sistor QP1. In FIG. 2, the current limiter is a thin-film
`resistor R3. R3 is fabricated by sputtering and patterning a
`thin layer of silicon-chrome material onto the substrate 24.
`The advantage of a thin-film resistoris that it is fully isolated
`from the other semiconductor regions on the substrate. R3
`may also be implemented as a discrete resistor, a JFET
`resistor, a diffused resistor or a resistor that may be imple
`mented into a CMOS process.
`Aside effect of the use of a resistive current limiter is that
`the voltage drop across R3 causes the substrate voltage to
`fall below the input voltage by approximately 0.6V during
`the saturation of the parasitic NPN transistor, as described
`above. This causes the substrate voltage to drop below the
`output voltage when the input voltage drops to less than
`0.6V above the output voltage. This in turn means that the
`N type substrate 24 is at a lower voltage than the collector
`P well 22. As the input voltage continues to drop, the PN
`junction from the P well 22 to the substrate 24 forward
`65
`biases. Junction isolation is thus lost, initiating the formation
`of a lateral parasitic PNP transistor with the Pwell 22 acting
`
`55
`
`35
`
`45
`
`50
`
`5,677,558
`
`10
`
`15
`
`20
`
`6
`as an emitter and other PWells such as the Pwell 32 of the
`NMOS device 34 which is integrated into the same
`substrate, acting as a collector. The substrate 24 in between
`acts as the base. The effect of parasitic currents is to degrade
`the frequency response and current efficiency of the circuit.
`To eliminate the effect of the lateral parasitic PNP
`currents, a plurality of current diverters are used to channel
`parasitic currents away from the sources and drains of MOS
`circuitry formed in the substrate 24. A current diverter is
`implemented by connecting the body of P-wells formed in
`the substrate 24, other than the body of P well 22 and the
`body of other vertical PNP transistors, to ground. This
`implementation includes connecting the body of the NMOS
`devises included in the reference voltage generator2 and the
`error amplifier 4 circuits of FIG. 1 formed in the substrate 24
`to ground. As an example of the current diverter in FIG. 2,
`the body 36 of the NMOS device 34 is connected to ground
`GND. This safely diverts lateral parasitic PNP currents
`flowing from Pwell 22 to the Pwell32 of the NMOS device
`34 to ground, and the source 37 and drain 38 of the NMOS
`device 34 are not affected. PMOS devices are not affected by
`the loss of junction isolation because their sources and
`drains are at the same voltage as the substrate 24. For
`example, the source 40 and drain 42 of the PMOS device 44
`are at the same voltage as substrate 24 and will not forward
`bias with respect to the substrate. Thus, although the loss of
`junction isolation for NMOS devices is not prevented, the
`MOS circuitry with which the regulator is integrated into the
`substrate 24 is not contaminated by parasitic currents from
`Q1.
`While particular embodiments of the invention have been
`shown and described, numerous variations and alternative
`embodiments will occur to those skilled in the art.
`Accordingly, the invention is intended to be limited only in
`terms of the appended claims.
`I claim:
`1. A low dropout linear regulator integrated with CMOS
`circuitry, comprising:
`an input terminal for receiving a variable input signal,
`an output terminal for providing a regulated output signal,
`a vertical PNP pass transistor having an emitter connected
`to said input terminal, a collector formed as a P-well in
`an N-type substrate and being connected to said output
`terminal, and a base, and
`a current limiter connected between said input terminal
`and said n-type substrate to limit current between said
`input terminal and said substrate and to thereby permit
`said pass transistor to enter saturation and provide low
`dropout regulation.
`2. A low dropout linear regulator as in claim 1, wherein
`said current limiter comprises a resistor,
`3. A low dropout linear regulator for receiving a variable
`input signal at an input terminal and producing a regulated
`output signal at an output terminal, integrated with CMOS
`circuitry, comprising:
`a reference voltage generator for generating a reference
`voltage,
`a voltage divider connected to said output terminal,
`a vertical PNP pass transistor having an emitter connected
`to receive said variable input signal, a base, and a
`collector formed as a P-well in an N-type substrate and
`connected to provide said regulated output signal,
`a CMOS error amplifier connected to compare the voltage
`at said voltage divider tap to said reference voltage and
`to sinka variable current from said base, the magnitude
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1026
`Page 6 of 7
`
`

`

`7
`of said variable current being determined by said
`amplifier as a function of said comparison, and
`a current limiter connected between said input terminal
`and said N-type substrate to limit current between said
`input terminal and said substrate and to thereby permit
`said pass transistor to enter saturation and provide low
`dropout regulation.
`4. A regulator as in claim 3, wherein said current limiter
`comprises a resistor.
`5. A regulator as in claim3, wherein said CMOS circuitry
`10
`is comprised of PMOS and NMOS devices, said NMOS
`devices having source, drain, and body regions, and said
`regulator further comprising,
`a plurality of current diverters connected to respective
`ones of said NMOS devices to prevent current from the
`collector of said vertical PNP transistor from entering
`the source and drain regions of said NMOS devices.
`6. A regulator as in claim.5, wherein said current diverters
`comprise connections between the body region of each of
`said NMOS devices and ground.
`7. A low dropout regulator, comprising:
`an N-doped semiconductor substrate,
`a vertical PNP pass transistor, including
`a P-well formed in said substrate and forming the
`collector of said pass transistor, said collector for
`providing power at regulated output voltage,
`an N-type region formed in said P-well, with a doping
`concentration substantially greater than said
`substrate, said N-type region forming the base of
`said pass transistor, and
`a P-type region formed in said N-type region and
`forming the emitter of said pass transistor, said
`emitter for receiving power at an unregulated
`voltage,
`a CMOS error amplifier sharing said substrate and con
`nected to sink a variable current from the base of said
`pass transistor, and
`a current limiter connected between said emitter and said
`substrate to limit the current flowing from said sub
`strate to said base when said P-well forward biases with
`respect to said base.
`8. A regulator as in claim 7, further including:
`additional Ptype regions in said substrate comprising the
`sources and drains of respective PMOS devices,
`additional P-wells in said substrate,
`additional N-type regions in said additional P-wells, said
`additional N-type regions comprising the sources and
`drains of respective NMOS devices, and
`
`45
`
`15
`
`20
`
`25
`
`30
`
`35
`
`5,677.558
`
`5
`
`8
`a plurality of current diverters, coupled to said additional
`P-wells to prevent the flow of current from said P-well
`to said sources and drains of said NMOS devices.
`9. A regulator as in claim 8, wherein said current diverters
`comprise connections between said additional P-wells and
`ground.
`10. A regulator as in claim 7, wherein said current limiter
`comprises a thin-film resistor formed in said substrate.
`11. A low dropoutlinear regulator integrated with CMOS
`circuitry, comprising:
`an N-doped semiconductor substrate,
`a vertical PNP transistor, including
`a P-Well formed in said substrate,
`an N-type region formed in said P-well, with a doping
`concentration substantially greater than said
`Substrate,
`a P-type region formed in said N-type region,
`an input terminal connected to provide a variable signal
`to said P-type region,
`an output terminal connected to receive a regulated
`output signal from said P-well,
`a reference voltage generator for generating a reference
`voltage,
`a voltage divider connected to said P-well,
`a CMOS error amplifier supplied by said voltage refer
`ence generator and connected to said voltage divider to
`establish an output voltage at said P-well, said error
`amplifier connected to receive a variable current from
`said N-type region, and
`a current limiter connected between said P-type region
`and said substrate to limit the current flowing between
`said substrate and said N type region when said P-well
`forward biases with respect to said N type region.
`12. A regulator as in claim 11, wherein said current limiter
`comprises a thin-film resistor formed in said substrate.
`13. A regulator as in claim 11, wherein said CMOS
`circuitry is comprised of PMOS and NMOS devices formed
`in said substrate, said NMOS devices having source, drain,
`and body regions, and further comprising,
`a plurality of current diverters connected to respective
`ones of said NMOS devices to prevent current from
`said P-well from entering the source and drain regions
`of said NMOS devices.
`14. A regulator as in claim 13, wherein said current
`diverters comprise connections between the body region of
`each of said NMOS devices and ground.
`
`ck.
`
`:
`
`::
`
`*
`
`:
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1026
`Page 7 of 7
`
`