United States Patent [19J
`McClure
`
`I 1111111111111111
`11111 111111111111111 1111111111 11111 11111 111111111111111111
`
`
`US005898235A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,898,235
`Apr. 27, 1999
`
`[54]
`
`INTEGRATED CIRCUIT WITH POWER
`DISSIPATION CONTROL
`
`[75]
`
`Inventor: David C. McClure, Carrollton, Tex.
`
`[73] Assignee: STMicroelectronics, Inc., Carrollton,
`Tex.
`
`[21] Appl. No.: 08/775,611
`
`[22] Filed:
`
`Dec. 31, 1996
`
`Int. Cl.6
`H03K 5/153
`[51]
`.....................................................
`[52] U.S. Cl. ............................ 307/64; 327/544; 365/227;
`395/750.03; 364/707
`[58] Field of Search ........................ 307/64, 66; 327/544;
`365/227; 395/750.03; 364/273-273.5, 707
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,167,024 11/1992 Smith et al. ......................... 364/273.1
`5,483,464
`1/1996 Song
`......................................... 307/64
`5,513,361
`4/1996 Young ................................ 395/750.03
`
`Primary Examiner-Albert W. Paladini
`Attorney, Agent, or Firm-Theodore E. Galanthay; Lisa K.
`Jorgenson; Peter J. Thoma
`
`[57]
`
`ABSTRACT
`
`An integrated circuit device such as an SRAM operating in
`a battery backup mode, or operating in a quiescent mode
`when deselected in the operation of a portable electronic
`device, includes a power dissipation control circuit that
`reduces the voltage on an internal power supply node so that
`the memory array is powered at a minimum level sufficient
`to retain the data stored therein intact.
`
`4,683,382
`
`7/1987 Sakurai
`
`................................... 365/227
`
`19 Claims, 2 Drawing Sheets
`
`14
`
`10
`------------~
`,----~--------
`r--------------------1
`24
`
`22
`
`SW2
`
`CONTROL
`
`SW1
`
`\
`
`26
`
`VOLTAGE
`SHIFT
`ELEMENT
`
`30
`
`12
`~------------
`
`20
`
`MAIN
`CIRCUIT
`------------J
`GND
`16
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1021
`Page 1 of 8
`
`

`

`U.S. Patent
`
`Apr. 27, 1999
`
`Sheet 1 of 2
`
`5,898,235
`
`VEXT 14
`10
`r---~--------
`------------~
`r--------------------,
`
`CONTROL
`
`1
`
`26
`
`VOLTAGE
`SHIFT
`ELEMENT
`
`FIG. 1
`
`L----------------\---~
`MAIN
`CIRCUIT
`____________
`
`12
`
`L------------
`
`GND 16
`
`s
`
`50
`
`46
`
`40
`~
`
`Vee
`
`48
`
`Vern
`
`CONTROL
`
`44
`
`VINT
`
`20
`
`J
`
`60
`~
`
`Vee
`
`72
`
`68
`
`T1
`
`66
`
`70
`
`CONTROL
`
`T2
`
`Vern
`
`+
`VBAT-=-
`-
`
`64
`
`VINT
`
`42 MAIN CIRCUIT
`
`62 MAIN CIRCUIT
`
`Vss
`FIG. 2
`
`Vss
`FIG. 3
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1021
`Page 2 of 8
`
`

`

`U.S. Patent
`
`Apr. 27, 1999
`
`Sheet 2 of 2
`
`5,898,235
`
`R
`
`FIG. 4
`
`FIG. 5
`
`FIG. 6
`
`P-
`
`FIG. 7
`
`FIG. 8
`
`FIG. 9
`
`80\....
`
`82
`
`86
`
`90
`
`92
`
`P-
`
`FIG. 10
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1021
`Page 3 of 8
`
`

`

`5,898,235
`
`1
`INTEGRATED CIRCUIT WITH POWER
`DISSIPATION CONTROL
`
`BACKGROUND OF THE INVENTION
`
`5
`
`10
`
`The present invention relates to integrated circuit devices
`and more particularly to battery-powered integrated circuits
`with low power consumption.
`Many integrated circuits, such as static random access
`memory ("SRAM") devices, rely on batteries as backup
`power supplies to retain the data stored within them while
`the equipment in which they are used is turned off or the
`power supply to the equipment has failed. Such integrated
`circuits are becoming more complex, thus placing greater
`demands on such backup batteries. Although battery tech- 15
`nology is improving, increases in battery capabilities are not
`keeping up with the increasing power requirements of the
`integrated circuit devices they serve. There is, accordingly,
`a need to reduce the power consumption of integrated
`circuits when used in a battery backup mode.
`Additionally, portable electronic devices ( computers, cel(cid:173)
`lular phones, etc.) rely upon batteries to supply operational
`power during general use. Such devices employ integrated
`circuit devices, which contribute to battery power consump(cid:173)
`tion and reduced operating time between battery recharg(cid:173)
`ings. There is, accordingly, a need to reduce the power
`consumption of integrated circuits used in portable elec(cid:173)
`tronic devices in order to extend the time of operation on a
`single charge of the battery.
`
`2
`FIG. 7 is a cross-section of a PN junction diode used in
`the subcircuit of FIG. 6;
`FIG. 8 is another embodiment of a subcircuit of the
`present invention;
`FIG. 9 is another embodiment of a subcircuit of the
`present invention; and
`FIG. 10 is cross-section of a transistor specially fabricated
`to provide a relatively high threshold voltage, which may be
`useful in another embodiment of the present invention.
`
`20
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`Referring to FIG. 1, an integrated circuit device in accor(cid:173)
`dance with the present invention is indicated by reference
`numeral 10, designating the circuitry contained within the
`larger dashed outline. The integrated circuit device 10
`includes a main circuit 12, which is preferably a memory
`circuit such as an SRAM memory array. Conventional
`SRAMs include so-called "4T" and "6T" types, both being
`well known in the art. The 4T type SRAM uses four
`N-channel MOSFETs,
`(metal-oxide-semiconductor
`field
`effect transistors) and two resistors for each memory cell of
`the memory array. The resistors are typically high resistivity
`25 portions of polycrystalline silicon (polysilicon) lines run(cid:173)
`ning within
`the array. The 6T type SRAM uses six
`MOSFETs, two of which are P-channel transistors and four
`of which are N-channel transistors.
`The integrated circuit device 10 is connected between a
`30 high voltage terminal 14 and a low voltage terminal 16,
`(indicating an
`which are respectively
`labeled the VExr
`external voltage supply) and GND (indicating a ground
`terminal). Integrated circuit device 10 includes a power
`dissipation control circuit contained within the smaller
`35 dashed outline labeled by reference numeral 20. The power
`dissipation control circuit 20 has a first power supply leg 22
`connected in parallel with a second power supply leg 24. A
`first switch SWl is disposed in the first leg 22 and a second
`switch SW2 is disposed in the second leg 24. A voltage shift
`40 element 30 is also disposed in the second leg 24 in series
`with the second switch SW2.
`The first and second legs 22 and 24 provide alternative
`paths between the high voltage terminal 14 and an internal
`power supply node labeled VINr The main circuit 12 is
`45 connected between the internal power supply node VINT and
`the low voltage or GND terminal 16. The states of the
`switches SWl and SW2 are controlled by control circuitry
`26. When the main circuit 12 is in an active mode, which for
`an SRAM memory array consists of reading data in from
`50 external circuitry or writing data out to external circuitry, the
`main circuit 12 requires full power at a normal operating
`voltage
`level. However, when the main circuit is in a
`quiescent mode, which in the case of an SRAM memory
`means merely maintaining
`the status of the data stored
`55 therein, it does not need full power at the normal operating
`voltage level. Instead, in the quiescent mode, it can maintain
`the status of the information stored in the memory array by
`applying a minimum voltage necessary to maintain a tran(cid:173)
`sistor in each memory cell array turned on. Such minimum
`60 voltage, or "holding" voltage, may be only a few tenths of
`a volt above the threshold voltage of a typical transistor used
`in each memory cell of the array.
`For example, a typical memory cell transistor requires
`only about 0.6 volts to be maintained on. Some processes
`65 differentiate the doping used for making N-channel and
`P-channel transistors so that the N-channel transistor may
`require 0.6 volts to be maintained on, whereas the P-channel
`
`SUMMARY OF THE INVENTION
`
`In accordance with the principal object of the present
`invention, a power dissipation control circuit is included in
`an integrated circuit device for switching the power supplied
`to a main circuit of the device from full power to a reduced
`power depending on the mode of operation of the main
`circuit.
`Another object of the invention is to switch an integrated
`circuit memory device to a low-power dissipation mode
`when the device is deselected by external circuitry so that
`the device merely needs to maintain the status of the stored
`information without performing input/output operations.
`Another object of the invention is to switch an integrated
`circuit memory device to a low-power dissipation mode
`during battery backup operation so that a minimum holding
`voltage is applied to the device in order to maintain the data
`stored therein for an extended duration.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Other objects, features and advantages of the invention
`will be best understood
`from
`the following detailed
`description, read in conjunction with the accompanying
`drawings, in which:
`FIG. 1 is a generalized circuit diagram of a device of the
`present invention;
`FIG. 2 is a circuit diagram of one implementation of the
`present invention;
`FIG. 3 is a circuit diagram of another implementation of
`the present invention;
`FIG. 4 is one embodiment of a subcircuit of the present
`invention;
`FIG. 5 is another embodiment of a subcircuit of the
`present invention;
`FIG. 6 is another embodiment of a subcircuit of the
`present invention;
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1021
`Page 4 of 8
`
`

`

`5,898,235
`
`5
`
`3
`transistor may require about 0.8 volts to be maintained on.
`Thus, for a 4T type SRAM using all N-channel transistors,
`a holding voltage of about 1.0 volt applied to the internal
`power supply node VINT
`is sufficient to maintain the data
`stored in the memory array. For a 6T type SRAM memory,
`which uses both P-channel and N-channel transistors, a
`holding voltage of about 1.2 volts is sufficient to maintain
`the data stored in the memory array.
`Accordingly, it will be appreciated that applying the full
`normal operating voltage to the memory array unnecessarily
`causes excessive power dissipation when the memory array
`is operating in the quiescent mode. Therefore, when the
`memory array is in the quiescent mode, the control circuitry
`26 opens the first switch SWl and closes the second switch
`SW2 so that power is supplied to the main circuit through
`the second leg 24. In the second leg 24, the voltage shift
`element 30 causes a voltage drop from the level of the
`normal operating voltage to the desired holding voltage level
`needed to maintain the status of the data stored in the
`memory array of the main circuit 12.
`Referring to FIG. 2, a specific application of the invention
`will now be described. This application is useful for con(cid:173)
`serving battery power in a portable electronic device in
`which the main battery (not shown) supplies power at a
`normal operating voltage level designated Vee· The inte(cid:173)
`grated circuit device of FIG. 2 is designated generally by
`reference numeral 40 and includes a high voltage terminal,
`labeled Vee and a low voltage terminal labeled Vss· The
`device 40 includes a main circuit 42, which may be a
`memory array such as an SRAM or a DRAM or may be any 30
`of various other integrated circuits having an active mode
`and quiescent mode.
`The main circuit 42 is connected between an internal
`power supply node VINT
`and the low voltage terminal Vss·
`A power dissipation control circuit 44 is connected between 35
`the high voltage terminal Vee and the internal power supply
`node VINT· The power dissipation control circuit 44 has a
`first leg 46 connected in parallel with a second leg 48. The
`first leg 46 has a channel P-channel MOS transistor T1
`connecting the high-voltage
`terminal Vee to the internal 40
`power supply node VINT· The second leg 48 has a first
`N-channel MOS transistor T2 connected in series with a
`second N-channel MOS transistor T3 in a path connecting
`the high voltage terminal Vee to the internal power supply
`node VINT· Transistor T3 is connected in a well-known 45
`manner with its gate connected to its drain to function like
`a diode.
`Control circuitry 50 controls the on and off states of the
`transistors T 1 and T 2 by means of a control signal V CTR
`applied at a common connection between
`the gates of
`transistors T1 and T2 . Thus, when transistor T1 is on,
`transistor T 2 is off, and vice versa. Control circuitry 50
`operates in response to an external signal S applied to the
`integrated circuit device 40. For example, incoming signal S
`may transmit chip select and chip deselect signals from other 55
`circuitry external to the integrated circuit device. The control
`circuitry 50 interprets signal S to apply V CTR as a low
`voltage signal turning on transistor T 1 and turning off
`transistor T 2 when the integrated circuit device 40 has been
`selected or "enabled" by signal S for normal operation. 60
`Under such circumstances, the normal Vee operating voltage
`is applied to the main circuit 42, with essentially no drop
`across transistor T1 , because it is turned on hard. When the
`integrated circuit device 40 has been deselected by incoming
`signal S, the control circuitry 50 generates control signal 65
`V CTR at a high voltage level to turn off transistor T 1 and turn
`on transistor T2 . Under these circumstances, the voltage Vee
`
`4
`is reduced by the voltage drops across transistors T 2 and T 3
`before appearing that the internal power supply node VINr(cid:173)
`Although
`is specifically
`illustrated as an
`transistor T 2
`N-channel transistor, it could be implemented as a P-channel
`transistor driven by an inverted V CTR signal. However, the
`increased voltage drop provided by the N-channel transistor
`T2 as shown may be preferred in the particular implemen(cid:173)
`tation of the invention.
`Based upon the respective levels of the normal voltage
`10 supply Vee and the minimum holding voltage needed at node
`VINT, one or more additional transistors, such as transistor
`T3 , can be connected in series in the second leg 48. For
`example, referring briefly to FIG. 4, two N-channel transis(cid:173)
`tors TA and TB are shown connected in series and each with
`15 its gate connected to its drain to provide double the voltage
`drop of the single transistor T3 in FIG. 2. Accordingly, the
`voltage drop in the second leg 48 of the power dissipation
`control circuit 44 can be adjusted appropriately to reduce the
`voltage level down from Vee to approximately the minimum
`20 holding voltage necessary for maintaining the condition of
`the main circuit 42 in its quiescent state. It will be appre(cid:173)
`ciated that this application of the inventive circuit will
`extend the operating time of a battery-operated portable
`electronic device by reducing the power dissipation of
`25 integrated circuit devices such as SRAM memory devices
`when they are deselected and are merely maintaining data in
`a quiescent state.
`Now referring to FIG. 3, another implementation of the
`inventive circuit will be described in the context of a battery
`backed-up SRAM. FIG. 3 shows an integrated circuit device
`designated generally by a reference numeral 60. The inte(cid:173)
`grated circuit device 60 includes a main circuit 62, which in
`this case is an SRAM memory array. It may be either a 4T
`type or a 6T type SRAM as previously described.
`The main circuit 62 is normally powered by a conven(cid:173)
`tional external power supply (not shown) connected at a
`high voltage terminal Vee and a low voltage terminal Vss· A
`backup battery V BAT
`is connected to provide a source of
`power to the main circuit 62 when the external power supply
`fails. Typically, such a backup battery is a small battery
`attached directly to the housing (not shown) of the integrated
`circuit device 60.
`The backup battery V BAT has a negative terminal 64 and
`a positive terminal 66. The negative terminal 64 is connected
`to the low voltage terminal Vss· The main circuit 62 is
`connected between an internal power supply node VINT and
`the low voltage terminal Vss· A first power supply leg 68
`connects the high voltage terminal Vee to the internal power
`through a P-channel MOS transistor T 1 . A
`50 supply node VINT
`second power supply leg 70 connects the positive terminal
`66 of the backup battery V BAT to the internal power supply
`node VINT
`through series-connected N-channel transistors
`T2 and T3 .
`Control circuitry 72 connected to the high voltage termi(cid:173)
`nal Vee and the positive terminal 66 of the backup battery
`V BAT determines whether power will be supplied to the main
`circuit 62 through the first leg 68 or the second leg 70. The
`gates of transistors T 1 and T 2 are connected together at a
`node that receives a control signal V CTR generated by the
`control circuitry 72. The control circuitry 72 senses the level
`of the voltage on the high voltage terminal Vee and compares
`it to an internally generated reference voltage that indicates
`whether the voltage level on the high voltage terminal Vee
`has fallen to the level requiring backup battery operation.
`The control circuitry 72 generates control signal V CTR at a
`low level (i.e., at ground or Vss) whenever the voltage level
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1021
`Page 5 of 8
`
`

`

`5,898,235
`
`5
`
`10
`
`5
`on the high voltage terminal Vee is above the reference
`voltage. This keeps transistor T1 turned on and transistor T2
`turned off so that the main circuit 62 is powered directly
`from the external voltage source through the Vee connection.
`However, whenever the voltage level on the high voltage
`terminal Vee drops below the reference voltage, the control
`circuitry 72 generates control signal V crn at a high level
`sufficient to turn off transistor T 1 and turn on transistor T 2 so
`that power is supplied to the main circuit 62 by the backup
`battery V BAT through the second leg 70 and the series-
`connected transistors T 2 and T 3 therein.
`As in FIG. 2, the transistor T3 of FIG. 3 serves as a voltage
`shift element providing one turn-on threshold voltage drop
`to reduce the voltage level at the internal power supply node
`to a minimal holding voltage level required to maintain 15
`VINT
`the data stored in the memory of the main circuit 62. And as
`previously mentioned, two or more such diode-connected
`N-channel transistors (e.g., see FIG. 4) can be substituted for
`the single transistor T3 of FIG. 3. Furthermore, the voltage
`shift element 30 described generically in the context of FIG. 20
`1 need not be implemented as diode-connected MOS
`transistors, such as the transistor T 3 in FIGS. 2 and 3, but can
`instead be implemented by other circuit elements, such as
`those described below.
`FIG. 5 shows a resister R as an alternative to the diode(cid:173)
`connected MOS transistor T3 of FIGS. 2 and 3. The resister
`R can be fabricated in an integrated circuit device using
`various known techniques to provide a high resistance value.
`For example, the resistor R could be constructed in a strip of
`high resistivity polycrystalline silicon ("polysilicon"). Such
`high
`resistance
`polysilicon
`resisters
`are commonly
`employed as load elements in 4T type SRAM memory cells.
`However, a rectifying element, such as a diode or diode(cid:173)
`connected transistor, is preferred to a non-rectifying resistor
`as a voltage shift element, since a rectifying element will
`provide a more predictable voltage drop compared to a
`resistor. Furthermore, if the external power applied at the
`V
`terminal momentarily collapses and then returns to a
`n~crmal level, data could be lost but for the inclusion of a
`rectifying-type voltage shift element. For example, opera(cid:173)
`tion of the integrated circuit device 40 of FIG. 2 in the
`quiescent mode would benefit from the use of a rectifying(cid:173)
`type voltage shift element (i.e., transistor T 3 ) in the event
`that Vee momentarily collapses.
`FIG. 6 shows the alternative of using one or more
`series-connected diodes DA and DB in lieu of the transistor
`T3 in FIGS. 2 and 3. One or more such diodes DA and DB
`can serve as the voltage shift element 30 of FIG. 1 since each
`such diode would provide a voltage drop equal to one
`turn-on threshold of about 0.6 volts in a manner similar to
`the threshold voltage drop provided by transistor T 3 of
`FIGS. 2 and 3. The diodes DA and DB of FIG. 6 can be
`implemented in a conventional manner as depicted in FIG.
`7 wherein N+ and P+ doped regions are provided in a P-well 55
`76 formed in a substrate 78 using conventional techniques.
`FIGS. 8 and 9 show additional alternatives for making the
`equivalent of a diode in an integrated circuit by fabricating
`a bipolar transistor and connecting its base to its collector.
`FIG. 8 shows an NPN bipolar transistor TNPN connected to 60
`provide a diode equivalent. FIG. 9 shows a PNP bipolar
`transistor T PNP connected to provide a diode equivalent.
`Either of these diode-connected bipolar transistors can serve
`as a voltage shift element in a manner similar to the
`diode-connected N-channel transistor T3 of FIGS. 2 and 3. 65
`FIG. 10 shows an implementation of a transistor that
`provides a higher than normal threshold voltage and corre-
`
`6
`spondingly higher voltage drop when used in the circuit of
`the present invention. The transistor of FIG. 10, which is
`designated generally by reference numeral 80, is a modified
`form of a lightly doped drain ("LDD") type transistor. The
`transistor 80 is an N-channel MOSFET having a gate layer
`82 disposed above a gate oxide layer 84 and includes
`conventional LDD type oxide spacers 86 and 88 at the sides
`of the gate 82. The transistor 80 has source and drain regions
`90 and 92, which are entirely heavily doped. Dashed regions
`94 and 96 indicate the location where the lightly doped drain
`regions normally would have been formed, but in this case,
`no doping is provided in these regions. Therefore, the source
`and drain regions 90 and 92 do not extend under the gate 82
`as in the conventional MOSFET device. This modified form
`of an N-channel MOSFET provides a transistor having a
`higher than normal turn-on threshold voltage. For example,
`such a device of this type can be fabricated having a
`threshold voltage in the range from 1.2 to 2.0 volts.
`Using the transistor 80 ofFIG.10
`to advantage, the switch
`SW2 and voltage shift element 30 of FIG. 1 can be imple(cid:173)
`mented with a single high threshold transistor of this type.
`In the specific circuits of FIGS. 2 and 3, transistor T 2 can be
`implemented using such a high threshold voltage transistor
`so that it may not be necessary to include any additional
`25 transistor T 3 in series with it in order to achieve the desired
`voltage drop in that leg of the circuit.
`Although a preferred high threshold voltage transistor
`useful in the present invention is the type depicted in FIG.
`10, there are other ways of increasing the turn-on threshold
`30 voltage of a transistor. For example, the gate oxide can be
`made thicker or the doping in the channel can be adjusted.
`Such other types of high threshold voltage transistors can be
`substituted to provide the desired voltage drop achieved by
`transistors T2 and T3 of FIGS. 2 and 3.
`From the foregoing description, it will be appreciated that
`the integrated circuit device of the present invention can
`achieve significantly reduced power dissipation when oper(cid:173)
`ating in a quiescent or battery backup mode. In an SRAM
`implementation, the main operational circuit can be operated
`40 just above the minimum holding voltage level to maintain
`the data stored in the device. Because the main circuit is
`operated at a lower voltage, the power dissipation is signifi(cid:173)
`cantly reduced. Therefore, it will be appreciated that the
`present invention has advantageous application in integrated
`45 circuit devices having backup batteries as well as with
`integrated circuit devices used in portable electronic equip(cid:173)
`ment.
`Although preferred embodiments of the invention have
`50 been described in detail, it will be understood by those
`skilled in the art that various modifications can be made
`therein without departing from the spirit and scope of the
`invention as set forth in the appended claims.
`What is claimed is:
`1. An integrated circuit device for use with external power
`supplied by high and low voltage terminals, the high voltage
`terminal providing a normal operating voltage to the device,
`comprising:
`an internal power supply node;
`the internal power
`a main circuit connected between
`supply node and the low voltage terminal; and
`a power dissipation control circuit connected between the
`high voltage terminal and the internal power supply
`node, the power dissipation control circuit having first
`and second parallel
`legs connected
`to the internal
`power supply node, a first switch disposed in the first
`leg and a second switch disposed in the second leg, a
`
`35
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1021
`Page 6 of 8
`
`

`

`5,898,235
`
`25
`
`30
`
`7
`voltage shift element disposed in the second leg in
`series with the second switch and wherein the voltage
`shift element comprises at least one rectifying element
`providing a voltage drop in the second leg of at least
`one turn-on threshold when said second switch is on, 5
`and control circuitry controlling the operation of the
`first and second switches, the control circuitry turning
`the first switch on and the second switch off to connect
`the high voltage terminal directly to the internal power
`supply node when the main circuit is in an active mode, 10
`the control circuitry turning the first switch off and the
`second switch on to supply current through the voltage
`shift element to the internal power supply node when
`the main circuit is in a quiescent mode, whereby the
`voltage shift element lowers the voltage on the internal 15
`power supply node to a holding voltage below the level
`of the normal operating voltage.
`2. The integrated circuit device of claim 1 further com-
`prising:
`a backup battery connected to supply power to the main 20
`circuit though the second leg of the power dissipation
`control circuit.
`3. The integrated circuit device of claim 1 wherein the
`rectifying element comprises an N-channel MOSFET with
`its gate connected to its drain.
`4. The integrated circuit device of claim 1 wherein the
`rectifying element comprises a PN junction diode.
`5. The integrated circuit device of claim 1 wherein the
`rectifying element comprises an NPN bipolar transistor with
`its base connected to its collector.
`6. The integrated circuit device of claim 1 wherein the
`rectifying element comprises an PNP bipolar transistor with
`its base connected to its collector.
`7. An integrated circuit device for use with external power
`supplied by high and low voltage terminals, the high voltage 35
`terminal providing a normal operating voltage to the device,
`comprising:
`an internal power supply node;
`the internal power 40
`a main circuit connected between
`supply node and the low voltage terminal; and
`a power dissipation control circuit connected between the
`high voltage terminal and the internal power supply
`node, the power dissipation control circuit having first
`and second parallel
`legs connected
`to the internal
`power supply node, a first switch disposed in the first
`leg and a second switch disposed in the second leg, a
`voltage shift element disposed in the second leg in
`series with the second switch wherein the voltage shift
`element comprises a resistor, and control circuitry 50
`controlling
`the operation of the first and second
`switches, the control circuitry turning the first switch
`on and the second switch off to connect the high voltage
`terminal directly to the internal power supply node
`when the main circuit is in an active mode, the control 55
`circuitry turning the first switch off and the second
`switch on to supply current through the voltage shift
`element to the internal power supply node when the
`main circuit is in a quiescent mode, whereby
`the
`voltage shift element lowers the voltage on the internal 60
`power supply node to a holding voltage below the level
`of the normal operating voltage,
`and a backup battery connected to supply power to the
`main circuit through the second leg of the power
`dissipation circuit.
`8. The integrated circuit device of claim 7 wherein the
`resistor comprises high resistivity polycrystalline silicon.
`
`8
`9. An integrated circuit device for use with external power
`supplied by high and low voltage terminals, the high voltage
`terminal providing a normal operating voltage to the device,
`comprising:
`an internal power supply node;
`the internal power
`a main circuit connected between
`supply node and the low voltage terminal;
`a power dissipation control circuit connected between the
`high voltage terminal and the internal power supply
`node, the power dissipation control circuit having first
`and second parallel legs with first ends thereof con(cid:173)
`nected together at the high voltage terminal and with
`second ends thereof connected together at the internal
`power supply node, a first MOS transistor disposed in
`the first leg and a second MOS transistor disposed in
`the second leg and with the gates of the first and second
`transistors being commonly connected, a voltage shift
`element disposed in the second leg in series with the
`second transistor, and control circuitry connected to
`and providing control signals to the commonly con(cid:173)
`nected gates of the first and second transistors, the
`control circuitry turning on the first transistor and
`turning off the second transistor to connect the high
`voltage terminal directly to the internal power supply
`node when the integrated circuit device receives a chip
`select signal causing the device to operate in an active
`mode, the control circuitry turning off the first transistor
`and turning on the second transistor to supply current
`from the high voltage terminal to the main circuit solely
`through the second leg when the integrated circuit
`device receives a chip deselect signal causing the
`device to operate in a quiescent mode, whereby the
`voltage shift element lowers the voltage on the internal
`power supply node to a holding voltage below the level
`of the normal operating voltage when the device is in
`the quiescent mode.
`10. The integrated circuit device of claim 9 wherein the
`voltage shift element comprises at least one rectifying
`element providing a voltage drop in the second leg of at least
`one turn-on threshold when the second MOS transistor is on.
`11. The integrated circuit of claim 10 wherein the first
`MOS transistor is a P-channel MOSFET, the second MOS
`transistor is an N-channel MOSFET, and the rectifying
`45 element is an N-channel M OSFET with its gate connected to
`its drain.
`12. A battery backed-up integrated circuit device having
`power dissipation control capability, comprising:
`a backup battery having positive and negative terminals;
`high and low voltage supply terminals for connection to
`an external power source, the low voltage supply
`terminal being connected to the negative terminal of the
`backup battery;
`an internal power supply node;
`a control signal node;
`the internal power
`a main circuit connected between
`supply node and the low voltage supply terminal;
`a first power supply leg connecting
`the high voltage
`supply terminal to the internal power supply node;
`a second power supply leg connecting the positive termi(cid:173)
`nal of the backup battery to the internal power supply
`node;
`a first transistor disposed in the first power supply leg and
`connected to the control signal node to selectively drive
`the internal power supply node by an external voltage
`applied to the high voltage supply terminal;
`
`65
`
`MICROCHIP TECHNOLOGY INC. EXHIBIT 1021
`Page 7 of 8
`
`

`

`5,898,235
`
`9
`a second transistor disposed in the second power supply
`leg and connected to the control signal node to selec(cid:173)
`tively drive the internal power supply node by the
`voltage supplied by the backup battery;
`a voltage shift element disposed in the second power 5
`supply leg in series with the second transistor; and
`control circuitry connected to the high voltage supply
`terminal, the control signal node, and the positive
`terminal of the backup battery, the control circuitry
`generating a control signal to selectively turn on and 10
`turn off the first and second transistors in response to
`the voltage level on the high voltage supply terminal,
`whereby the first transistor is turned on and the second
`transistor is turned off whenever the voltage level is
`above a reference voltage, and whereby the first tran- 15
`sistor is turned off and t