United States Patent 9
`Leach
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,560,954
`Dec. 24, 1985
`
`[54] LOW POWER OSCILLATOR CIRCUIT
`[75]
`Inventor:
`Jerald G. Leach, Houston, Tex.
`[73] Assignee: Texas Instruments Incorporated,
`Dallas, Tex.
`.
`[21] Appl. No.: 334,487
`[22] Filed:
`Dec. 24, 1981
`[51]
`Tint, C14 oeecsscseesscteeeesseneacseseesenes HO03B 5/12
`[52] U.S. CI, oeeeeeessscssssesesesssceneseee 331/108 B; 331/57;
`331/DIG.3; 307/448; 307/481
`[58] Field of Search ............scs0 331/45, 50, 55, 56,
`331/57, 104, 108 A, 108 B, 108 C, 111, 113 R,
`143, 144, DIG. 3; 307/445, 448, 480, 481, 482
`.
`.
`References Cited
`U.S. PATENT DOCUMENTS
`3,702,945 11/1972 Faith et al. sscscsssscssennse 307/481 x
`3,854,103 12/1974 Takarada esecsnssesnsseersees 331/55
`
`4,083,020 4/1978 Goldberg...
`331/DIG. 3 X
`4,236,121 11/1980 Semturia -cscsocvensessessteun 331/57
`FOREIGN PATENT DOCUMENTS
`
`[56]
`
`OTHER PUBLICATIONS
`Shepherd, I. E. “Oscillator Starts in a Defined State”,
`Electronic Engineering, Jun. 79, p. 31.
`Gordon,R. E. “Stable Wideband Relaxation Oscillator
`Using Three Inverting Amplifiers”, National Bureau of
`Standards, Technical Note #437, Nov. 67, pp. 21-22.
`Primary Examiner—Eugene R. LaRoche
`Assistant Examiner—Robert J. Pascal
`Attorney, Agent, or Firm—Thomas E. Tyson; Leo N.
`Heiting; Melvin Sharp
`[57]
`ABSTRACT
`A low poweroscillator circuit including a latch con-
`nected to two loops. Each loop includes dynamic in-
`verters and static inverters connected in cascade. The
`loops are connected to the latch such that the output of
`_the final stage is an inputto the latch. Aninitialization
`Circuit is included on one loop to initiate oscillation.
`Storage capacitors are included in the loops to provide
`an oscillator output voltage that is greater than the
`oscillator power supply voltage.
`
`30368
`
`3/1977 Japan...essssessssseseees 331/DIG.3
`
`2 Claims, 14 Drawing Figures
`
` -
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`MAIN OSCILLATOR
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`1
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`APPLE 1008
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`1
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`APPLE 1008
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`U.S. Patent Dec. 24, 1985
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`U.S. Patent Dec. 24, 1985
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`U.S. Patent Dec. 24, 1985
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`U.S. Patent Dec. 24, 1985
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`

`1
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`LOW POWER OSCILLATOR CIRCUIT
`
`RELATED APPLICATIONS
`
`U.S. patent applications that are related to the present
`application include U.S. Pat. Ser. No. 335,028 entitled,
`“Low Power Circuit For Microcomputer, U.S. patent
`application Ser. No. 335,029 entitled, “Low Power
`Display Circuit”, U.S. patent application Ser. No.
`335,852 entitled, “Low Voltage RAM Cell”, U.S. pa-
`tent application Ser. No. 334,486 entitled, “Low Power
`Clock Generator Circuit”, and U.S. patent application
`Ser. No. 334,850 entitled “Integrated On/Off Switch”.
`BACKGROUND
`1. Field of the Invention
`This invention relates to digital processing circuitry
`and moreprticularly to low power circuits for digital
`processing.
`2. Prior Art
`Electronic calculator systems of the type having all
`the main electronic functions within a single,
`large
`scaled integrated (LSI) semiconductor chip or small
`numbers of chips are described in the following prior
`applications or patents assigned to Texas Instruments
`Incorporated:
`U.S. Pat. No. 3,819,921 by Kilby et al for “Miniature
`Electronic Calculator”, based on an application origi-
`nally filed Sept. 29, 1967;
`U.S. Pat. No. 4,074,351 by Boone and Cochran for
`“Variable Function Program Calculator”;
`U.S. Pat. No. 3,819,957 by Bryant for “Digital Mask
`Logic in Electronic Calculator Chip”; and
`U.S. Pat. No. 3,987,416 by Vandierendonct, Fischer
`and Hartsell for “Electronic Calculator With Display
`and Keyboard Scanning”.
`These prior inventions madepossible vast reductions
`in cost and size and increases in functions of electronic
`calculators. Many millions of such calculators have
`been produced. The efforts to reduce manufacturing
`costs and increase the functions available to the user are
`continuing. Particularly it is desired to provide a basic
`chip structure that is quite versatile and can be used for
`many different types of calculators and similar digital
`processing equipment. This permits a single manufac-
`turing facility to produce a large quantity of the same
`devices, differing only in a single mask change, to pro-
`duce a dozen variations while still maintaining large
`volume cost advantages.
`The previous MOS/LSIcalculator chips as referred
`to above were generally register organized in that a
`single instruction word operated onall of the digits in a
`given register. A more versatile approach is to make the
`machine digit organized, operating on one digit at a
`time. For example, it may be desired to test or set a
`particular one bit flag. In a register machine, an entire
`13 digit register must be addressed and masked to imple-
`ment this, whereas a digit organized machine may ac-
`cess only the needed digit or bit. An example of such a
`processing chip is disclosed in U.S. Pat. No. 3,991,305
`by Caudelet al entitled, “Electronic Calculator or Digi-
`tal Processor Chip with Multiple Code Combinations of
`Display and Keyboard Scan Outputs”. This patent dis-
`closes what is commonly knownin industry as the TMS
`1000 architecture for a 4 bit microcomputer. Another
`approach using this same type of architecture is dis-
`closed in U.S. patent application Ser. No. 216,113 enti-
`tled, “Dual Register Digital Processor System” by Ko-
`
`4,560,954
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`2
`eppen, Rogers, Solimeno and Brown. Thearchitecture
`disclosed herein is similar to the TMS 1000 architecture,
`and the architecture disclosed in the above applications
`is implemented with low powercircuitry.
`FIG.1a illustrates a prior art attempt at low power
`operation using positive channel MOS (P-MOS)field
`effect transistor devices. This type of circuit is referred
`to as precharge and conditional discharge circuitry.
`The node 800 becomes charged during ¢ 3. It should be
`noted that since the circuitry is presented in P-MOS,the
`devices are active during the negative portions of the
`timing signals. This node remains charged until condi-
`tionally discharged by the input line during ¢ 1. If the
`input
`line remains high,
`then the node will remain
`charged and the output will remain at — V as shownin
`FIG. 1b. However, if the input is low, thus activating
`device 801, the node 800 will be discharged during } 1
`as shown. The disadvantage to this standard perchar-
`ge/discharge logic is that the precharge period can
`cause problems in other circuits, such as in addressing
`RAM cells. If percharge/discharge logic were con-
`nected directly in the addressing portion of the RAM
`cell, all the addresses would be ON during the pre-
`charge time. Therefore if precharge/discharge logic
`wereto be used to address a RAM,additional circuitry
`would be required to buffer the precharge intervals
`from the addressing lines of the RAM cells.
`FIG. 2 illustrates a static inverter which includes a
`device with the depleted region 802 to provide charge
`at the node connected to the output line. The static
`inverter removes the precharge problem; however, the
`static inverter also consumes a larger amount of d.c.
`current. The static inverter also requires that the size of
`the load device be muchlarger than any of the devices
`in the precharge/dischargecircuitry. This is a disadvan-
`tage when fabricating the circuitry on a small silicon
`chip.
`A third approach to the low powercircuit operation
`is shown in FIG. 3, which is a complementary MOS
`(CMOS)inverter. The clocked CMOSinverter does
`not have precharges and does not require constant d.c.
`current. However, the CMOS fabrication process is
`more expensive and more complex than a normal
`PMOSor NMOSfabrication process.
`The low power approach to many semiconductor
`display applications has included the use of CMOS,
`precharge/discharge and static devices. One such appli-
`cation is circuitry required for liquid crystal displays.
`Liquid crystal displays require low amounts of power
`and thus interface well with low power processing
`circuitry. A reference forliquid crystal display require-
`ments is the International Handbook of Liquid Crystal
`Displays 1975-76, Second Edition, with 1976 Supple-
`ment by Martin Tobias, published by Ovum Ltd. 14 Pen
`Road, London, NC 9RD, England. Another reference
`is “General Information on Liquid Crystal Display”,
`published by Epson America, Incorporated, 2990 West
`Lomita Boulevard, Tolerance, Calif. A third reference
`is an article entitled, “Liquid Crystal Displays” by L. A.
`Goodman,printed in the Journal of Vacuum Science and
`Technology, Vol. 10, No. 5, September/October 1973.
`In the past, the LCD devices have required the use of
`low power circuitry such as the precharge discharge
`logic, or CMOSlogic. This specification discloses an-
`other alternative, a low powercircuit that makes possi-
`ble a low powerinterface to LCD’s without the disad-
`vantages of the three prior art circuits.
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`3
`SUMMARYOF THE INVENTION
`
`4,560,954
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`In accordance with the present invention, an oscilla-
`tor circuit is provided that includes a latch connected to
`two loops. Each loop is made of several dynamic invert-
`ers connected in cascade with at least one static in-
`verter. The output of the final stage inverter of each
`loop is connected to the latch input. Each loop further
`includes a capacitor connected between the output of
`one of the inverters and the output ofthe latch. In addi-
`tion, initialization circuitry is connected to at least one
`of the loopsto start the circuit oscillating. The oscillator
`circuit output is characterized by having a voltage mag-
`nitude that is greater than the magnitude of the voltage
`provided to the oscillator circuit by the power supply.
`In a preferred embodimentofthis invention, an oscil-
`latorcircuit is provided that includes a latch connected
`to two loops of cascaded inverters. Each inverter is
`connected to each of the two latch outputs. The output
`ofthe final stage of each loop is connected to the two
`separate inputs of the latch. In this embodiment, the
`loops contain several dynamic inverters and onestatic
`inverter. The dynamic inverters further receive timing
`signals from the output of the latch. In addition, each
`loop has a capacitor connected to the output of one
`inverter and the other terminal of the capacitor con-
`nected to the output of the latch. The capacitor is pro-
`vided to bootstrap the voltage magnitude of the oscilla-
`tor circuit output higher than that magnitude of the
`voltage provided by the oscillator power supply. The
`oscillator circuit further includes initialization circuit
`tied to oneof the loopsto initiate oscillation upon powe-
`rup.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG.1a is a schematic diagram ofa prior art prechar-
`ge/dischargelogic.
`FIG.16 is a timing diagram for the precharge/dis-
`charge logic of FIG. 1a.
`FIG.2 is a schematic diagram of a prior art static
`inverter.
`FIG.3 is a schematic diagram of a prior art comple-
`mentary MOSinverter.
`FIG.4a is a schematic diagram of a low power MOS
`inverter.
`FIG.42 is a symbolic diagram of the low power MOS
`circuit shown in FIG. 4a.
`FIG.4c is a timing diagram of the low power MOS
`circuit in FIG. 4a.
`FIG. 5 is a block diagram ofthe oscillator and clock
`phase generator.
`FIG.6 is a logic diagram of the oscillator.
`FIG.7 is a schematic diagram ofthe tickler oscillator
`of FIG.5.
`FIG.8 is a schematic diagram of the ring counter of
`FIG.5.
`FIG.9 is a schematic diagram of a bootstrap circuit
`for use in the oscillator of FIG. §.
`And FIG.10 is a schematic diagram of the oscillator
`circuit of FIG.5.
`In the various figures of the drawing, like reference
`numerals are used to denote like or similar parts.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`FIG. 4a is the schematic drawing of the basic low
`powerinverter. The symbol for this circuit in FIG.4¢ is
`shownin FIG. 4. Timing diagramsfor this circuit are
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`shown in FIG.4c. Referring to FIG. 4a, the node 806is
`charged during the time frame @ A by device 805. Dur-
`ing @ B, the node 806 is discharged by the inputline and
`device 809 if the input is low for PMOScircuitry. If,
`however, the input is high, then the timing signal @ B
`provides an additional charge through capacitor 807 to
`node 806. Node 806 turns on device 813 if charged and
`¢ B likewise turns on devices 811 and 812. If the input
`is high, thus not turning on device 810, the lines marked
`“QUT 1” and “OUT 2”produce an output voltage of
`—V as shown. It should also be noted that node 806
`produces a voltage that is below —V since node 806
`receives charge from —V or the negative rail, plus
`charge from the clocking phase @ B through capacitor
`807. Therefore the voltage at node 806 is greater than
`~V. This type of circuitry results in a low power in-
`verter without the use of precharge/discharge logic or
`static inverters. In addition, all the devices shown in
`FIG.4a maybefabricated in a PMOSstructure as small
`devices.
`FIG.5 is a block diagram of a clock generatorcircuit.
`Block 311 represents a tickler oscillator which starts the
`oscillator 313 via line 312. Oscillator 313 then outputs
`two oscillator signals to the ring counter 315 which
`then outputs timing signals on line 316 to the delay
`buffers 317. The delay buffers provide 15 signals on
`lines 318 to the clock buffers as shown. Nine clock
`signals are output on lines 320. The logic diagram of the
`oscillator circuit and tickler circuit is shown in FIG.6.
`Block 311 contains logic for the tickler oscillator which
`includes a static NAND gate 321 connected to two
`static inverters 322 and 323. Note that capacitor 324 is
`connected from the output of the inverter 322 to an
`input of the static NAND gate 321. This capacitor adds
`chargeto the outputof devices 323 to drive devices 347,
`348 and 349 in the main oscillator. This technique is
`called “bootstrapping” or driving the value to a voltage
`that is greater than the negative power supply. The
`purposeof the tickler oscillator is to start the oscillator
`313 upon powerup. Oscillator 313is illustrated as two
`loops of inverters connected with NAND gatesthat are
`cross coupled. Note that capacitors 332 and 341 are
`provided in these inverter loops to provide extra charge
`for the oscillator outputs at 344 and 345. Inverters 330,
`334, and 338 are gated by OSC.Inverters 331, 337 and
`339 are gated by OSC.Inverters 335 and 340 aresimilar
`to the static inverters as illustrated in FIG. 2. NAND
`gates 328 and 329 are gated by Signal A and Signal B,
`respectively.
`Thestatic inverters 335 and 340 can be fabricated in
`the manner described above with reference to the prior
`art static inverters shown in FIG. 2 above, and the low
`powerinverters 330, 331, 334, 337, 338, and 339 can be
`fabricated in accordance with the invention as exempli-
`fied by the inverter circuit described with reference to
`FIG.4a.
`The block diagrams of FIGS. 5 and 6 can be accom-
`plished with a circuit fabricated in accordance with the
`schematic diagrams shown in FIGS.7,8,9 and 10. FIG.
`7 is a schematic diagram ofthe tickler circuit 311; FIG.
`8 is a schematic diagram of the ring counter 315 (see
`FIG.5); FIG. 9 is a schematic diagram of the bootstrap-
`ping circuit 975 which may be usedin theoscillators of
`FIG.6. FIG. 10 is a schematic diagram of one way of
`accomplishing the main oscillator circuit 313 of FIG.6,
`using precharge and discharge circuits similar to that
`described above with reference to FIG. 4¢ above. In
`FIG. 10, the NAND gate multivibrator 50 is located
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`means for establishing a precharge voltage on said
`between the digital oscillator channels 51 and 52 (the
`precharge/discharge node during a time when said
`upper and lower channels in FIG. 10 correspond re-
`precharge/discharge nodehas no currentflow, and
`spectively to the lower and upper channels of FIG.6).
`means for selectively allowing the current
`flow
`The various inverters and capacitors of FIG.6 are also
`through said precharge/discharge node for dis-
`shown generally in FIG. 10.
`Whatis claimedis:
`charging said precharge voltage to produce an
`inverter output; and
`1. A digital oscillator, comprising:
`each ofsaid low powerinverters comprises:
`first and second oscillator loops, each including a
`a first, second and third MOSFET device connected
`logical combination gate within the loop, a plural-
`in series from thefirst to third MOSFETdevicesin
`ity of low power inverters connected in cascade
`a first circuit,
`fromafirst low powerinverterto a last low power
`the control elements of a first and second of said
`inverter, and a feedback capacitor connected from
`MOSFETdevices being connected to receive re-
`an output of a second inverter of said plurality of
`spectivefirst and second out of phase clock pulses;
`the low powerinverter inverters to an input of the
`a capacitor connected between the control element of
`the second MOSFETdevice and a nodeatan inter-
`first low powerinverter the output of a last mem-
`connection between said first and second MOS-
`ber ofsaid plurality of low power inverters being
`connected to a first input of said logical combina-
`FETdevices said node being said precharge/dis-
`tion gate;
`charge node;-
`first and second connection means where the first
`said third MOSFETdevice having its control ele-
`ment connected to receive an input signal;
`connection means being for connecting the output
`at least three MOSFETdevices connected in series in
`of the logical combination gate of the first oscilla-
`a second circuit;
`tor loop to the inputofthefirst low powerinverter
`the control element of an outside one of said at least
`means of the first oscillator loop and to a second
`three MOSFETdevices being connected to said
`input of the logical combination gate of the second
`precharge/discharge node;
`oscillator loop and wherein the second connection
`the control elementof the other outside oneofsaid at
`means being for connecting the output ofthe logi-
`least three MOSFET devices being connected to
`cal combination gate of the second oscillator loop
`receive the input signal;
`to the input ofthe first low power inverter means
`the control elementof at least one central MOSFET
`of the secondoscillator loop and to a second input
`device of said at least three MOSFET devices
`of the logical combination gate of thefirst oscilla-
`being connected to receive the clock signal con-
`tor loop such that the logical combination gates of
`nected to said control element of said MOSFETin
`said first and second oscillator loops being con-
`said first series circuit to which said capacitor is
`nected together to form a bistable multivibrator to
`connected, an inverter output being developed at
`an interconnection between said at least one central
`producealternate pulses of oscillator outputsignals
`MOSFETdevice and the other outside one ofsaid
`at respective outputs of said logical combination
`at least three MOSFETdevices.
`gates;
`at least one of said inverters in each ofsaid oscillator
`2. Theoscillator circuit of claim 1 further comprising:
`timing signal means connected to the outputsof the
`loops including;
`logical combination gates of the first and second
`a precharge/discharge node;
`oscillator loops for generating timing signals.
`means
`for
`selectively preventing current
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`through said precharge/discharge node;
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