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`
`USUU6225873B1
`
`(12) United States Patent
`US 6,225,873 B1
`(10) Patent N0.:
`Hill
`
`(45) Date of Patent: May I, 2001
`
`(54) FREQUENCY SHIFT KEY MODULA'I‘ING
`OSCILLATOR
`
`(75)
`
`Inventor:
`
`John P. Hill, Weslland, M1 (US)
`
`(73) Assignee: Lear Automotive Dearborn, lnc.,
`Soullificld, MI (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent
`is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: ostsasg'to
`
`(22
`
`Filed:
`
`Dec. 1, 1995
`
`1m.c1.7 ....................................................... Heac star)
`(51)
`(52) U.S. c1.
`.......................... 332/102;332ttoo;332t1m;
`3757272; 375803; 375804; 375,306; 3757307;
`331(107 A; 331t179
`(58) Field of Search ..................................... 333100, 101,
`332! 102; 375,972, 303, 304, 306, 307;
`3317107 A, 179
`
`(56)
`
`References Cited
`U.S. PA’I‘EN'I' DOCUMEN'I'S
`
`Nick Demma, “Balanced Meissner Oscillator Circuits" RF
`design Dec. 1993 pp. 72—74.
`Gary A Breed, "A Basic Review of Feedback" RFdesign
`Apr. 1993, pp. 62—64.
`Craig Taylor 8:. David Kenny, “Basic Crystal Oscillator
`Design Considerations" RFdesign Oct. 1992 pp. 75—79.
`Fred Brown, “Stable LC Oscillators” ridesign Mar. 1987r pp.
`54-61.
`
`Harvey L. Morgan. “An Emitter Follower Oscillator“ rfde—
`sign Oct. 1988 pp. 6l-62.
`D. L. Ash, “Saw Devices In Wireless Communication Sys~
`tents”, Oct. 31, 1993, p. 115—124, 1993 lEEE Ultrasonic
`Symposium.
`Siemens Components, "Cost—Attractive, Reliable Remote
`Controls Use Saw Resonators”, vol. 25, No. 4, Aug. 1990,
`p. 142—145.
`Gee l’lessey Semiconductor#Preliminary Information Kes—
`rxol 290—460MI-Iz Ask Receiver Sep. [995 p. 245—251.
`'I'emic—Telel‘unken Semiconrluctors—l’relirninary Infor—
`mation UlIli AMIITM Transmitter U274-{ll3 Rev. A]; 23,03,
`1995.
`
`Ternic—Telel'unkcn Semiconductors—Prelirninary Infor-
`mation UHF AMt’FM Transmitter U274”? Rev. A]; 02,05,
`1995.
`
`2,930,991 *
`3,451,012 *
`3,560,881 *
`
`3t1960 Edwards ............................... 3327102
`
`611069 Spiro
`3327102
`I-‘redricsson
`2_t19?1
`332nm
`
`Printer? Examiner—Siegfried H. Grimm
`(74) Attorney, Agent, or Finn—Brooks & Kushman RC.
`
`(57)
`
`ABSTRACT
`
`{List continued on next page.)
`FOREIGN l’A’I‘EN'l' DOCUMEN‘lS
`
`3332307
`3429574
`045th
`
`3t1984 (Di-Z).
`271086 (DE).
`12(1991 (13?).
`
`(List continued on next page.)
`OTHER PUBLICATIONS
`
`Branislav Petrovic, “A Balanced RF Oscillator”, rfdcsign
`Dec. 1989 pp. 35—38.
`Robert Mallhys, "A Iligh Performance VIII: Crystal Oscil-
`lator Circuit” rfdesign Mar. 1987 pp. 31—38.
`
`The present invention teaches a system for selectably oscil-
`lating at a first or a secoan oscillating frequency. The system
`comprises an oscillator for providing an oscillating output.
`Moreover,
`the system comprises a switching device for
`sclccling a first or a second impedance in response to a select
`signal having a voltage. Each of the first and second imped-
`ances is fixed independently of the select signal voltage such
`that the oscillating output oscillates at the first oscillating
`frequency when the first impedance is provided and oscil—
`lates at the second oscillating frequency when the second
`impedance is provided.
`
`2 Claims, 6 Drawing Sheets
`
`
`
`
`
`Roku EX1022
`
`U.S. Patent No. 7,589,642
`
`Roku EX1022
`U.S. Patent No. 7,589,642
`
`

`

`US 6,225,873 B1
`
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`FOREIGN PATENT DOCUMENTS
`
`4,189,6T6
`4,?94,622
`5,103,221
`5,138,284
`5,367,537
`5,422,605
`5,532,654 ’
`
`2;"1980 Arias cl al. .
`.
`131988 Isaacman el al.
`4f1992 Memmola ....................... 340,825.31
`31’1992 Yabuki (:1 al,
`...... 33156
`
`llfl994 Anderson ......
`3T5f55
`
`3311116 R.
`Elf-1995 Yang el iii.
`............................. 3323102
`771996 Ieki at al.
`
`OGZGTTZ
`160362?
`W096f164?3
`91(4‘53
`93:“4726
`
`11;“1994 (E?) ,
`1U [98]
`(GB) .
`$1995 (W0) .
`5l1991 (22A) .
`7f1993 (7A) .
`
`* ciled by examiner
`
`

`

`US. Patent
`
`May 1,2001
`
`Sheet 1 0f 6
`
`US 6,225,873 B1
`
`
`
`(7",? I
`fl/flfi’fli’fl
`
`71 -ANTENNA
`
`
`
`
`
`
`
`FIRST
`RESONATING
`CIRCUIT
`
`SECOND
`RESONATING
`CiRCUIT
`
`

`

`US. Patent
`
`May 1,2001
`
`Sheet 2 0f 6
`
`US 6,225,873 B1
`
`5’???
`
`

`

`US. Patent
`
`May 1,2001
`
`Sheet 3 0f 6
`
`US 6,225,873 B1
`
`0
`
`4
`
`VOLTS
`CIRCUIT
`
`TIME 1 nsecmlv
`
`firm
`
`100 — ANTENNA
`RESONATING
`
`SECOND
`RESONATING
`
`

`

`US. Patent
`
`May 1,2001
`
`Sheet 4 0f 6
`
`US 6,225,873 B1
`
`’/,110
`
`f44
`
`120 132
`124
`R10
`
`R11
`
`146
`
`C13
`
`
`
`

`

`US. Patent
`
`May 1, 2001
`
`Sheet 5 of 6
`
`US 6,225,873 B1
`
`
`
`a"? I”
`
`200 \
`
`225
`
`OSCILLATOR
`
`a.“
`
`Ofifz
`
`SWITCHING
`DEVICE
`
`205
`
`210
`
`
`

`

`US. Patent
`
`May 1, 2001
`
`Sheet 6 of 6
`
`US 6,225,873 B1
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`37"} 1'3
`
`_._____________________L_.________-------——
`
`,--235
`
`IIIIIIIIIIIIIIIIIIIIII
`
`
`
`
`
`

`

`US 6,225 ,873 B1
`
`1
`FREQUENCY SHIFT KEY MODULATING
`OSCILLATOR
`
`RELATED APPLICATIONS
`
`The following application is related to application Ser.
`No, 08842921, filed on Nov. 21, [994, now US. Pat. No,
`5,486,793, and pending application Ser. No. 08l448,?59,
`filed on May 24, 1994.
`
`FIELD 017 THE INVENTION
`
`This invention relates generally to remote transmitters
`and, more particularly, to a frequency modulated balanced
`oscillator.
`
`BACKGROUND OF THE INVEN'I'lON
`
`5
`
`ill
`
`15
`
`2
`radiating
`As detailed hereinabove, circuit 5 generates a
`output signal via inductor I_,. In doing so, transistor 0,,
`acting as an amplifier, in combination with the resonating
`tank circuit, generates a resonating signal which is provided
`to inductor L1 as an oscillating current signal I. The con—
`duction of current I through inductor L ,
`in In rn causes the
`radiating output signal to be transmitted as an electromag-
`netic field.
`
`The above described Colpitts oscillator is well suited for
`the RF signal transmission applications of a remote keyless
`entry system. However, such an oscillator design provides a
`limited amount of power output. Further, the alternative of
`a greater inductance value for radiating inductor 1,, may not
`feasibly achieve a corresponding increase in power due to
`the inherent
`limitations of such components. Similar
`attempts to enhance output power through the optimization
`of component values has proved futile in view of the
`matching losses created thereby. Moreover, rail-to-rail volt-
`age swings in transistor 0, tend to confine the amount of
`current flow through the circuit which, in turn, diminishes
`the available power output realized by a given transmitter
`circuit.
`
`As a result of the limited power available from compact
`remote transmitters using Colpitts Oscillators, another prob-
`lem has arisen with their application in compact remote
`transmitters. Typically, compact
`remote transmitters are
`hand grasped and directed generally toward a receiver of the
`system. By so doing, a parasitic impedance is created by the
`user’s hand. This additional impedance reduces the amount
`of transmitted energy towards the receiver. This becomes an
`issue of particular significance in view of the limited power
`available from a traditional Colpitts oscillator.
`Moreover, present compact remote transmitters employ a
`frequency shift key ("FSK") modulation scheme. Realiza-
`tions of these designs have incorporated expensive compo-
`nents such as a PIN or varactor diode. One such ESK
`oscillator is depicted in US. Pat. No. 5,367,537. In these
`circuits, the PIN or varactor diode changes capacitance in
`response to a change in the control voltage applied.
`Unfortunately, this control voltage changes with the life of
`the battery supply voltage. As such, the center frequency of
`the FSK oscillator in turn drifts. This frequency drifting
`phenomenon is highly undesirable to the long term efficacy
`of a compact remote transmitter design,
`In view of these problems, a need remains for a frequency
`shift key modulating oscillator circuit having a predictable
`center frequency which is not prone to drifting. A demand
`further exists for a frequency shift key modulating oscillator
`circuit which is more cost effective. Moreover,
`industry
`requires a frequency shift key modulating oscillator circuit
`drawing less energy from the power supply, and as such
`having an extended life span.
`SUMMARY OF THE INVENTION
`
`The primary advantage of the present
`overcome the limitations of the known art.
`
`invention is to
`
`Another advantage of the present invention is to provide
`for a frequency shift key modulating oscillator circuit having
`a predictable center frequency which is not prone to fre-
`quency drifting.
`A further advantage of the present invention is to provide
`for a frequency shift key modulating oscillator circuit which
`is more cost effective.
`
`invention is to
`Still another advantage of the present
`provide for a
`frequency shift key modulating oscillator
`circuit drawing less energy from the power supply, and as
`such having an extended life span.
`
`Compact radio frequency (“RF") transmitters are widely
`employed in connection with remote signal communication
`systems, primarily for remotely controlling automatic
`garage door systems, electronic sound systems, televisions
`and VCRs. In the automotive industry, compact RF trans—
`mitters are commonly used in remote keyless entry systems
`to provide remote control access to a vehicle, as well as for
`enabling other vehicular functions including alarm system
`features and a trunk release, for example. Ideally, hand held —
`transmitters are battery operated, energy eflicient and
`intended to accommodate a compact enclosure.
`In one known compact remote system design, an RF
`transmitter radiates an RF signal with a predetermined
`carrier frequency encoded according to an onfofi' switched
`pattern. This radiating signal is subsequently received by a
`remote receiver. Once received, the signal is processed, if
`necessary, and then provided as a control signal to control a
`function or feature of the system.
`Currently, a number of compact remote RF transmitters
`employ a single oscillator design for providing a
`local
`oscillation signal. As illustrated in FIG. 1, a conventional
`transmitter circuit 5 is shown with a single oscillating circuit
`commonly referred to as the Colpitts oscillator. Transmitter
`circuit 5 generates a local oscillation signal which is trans-
`mitted from an antenna element 1.1. In light ofits simplicity,
`circuit 5 has been the transmitter component of choice in
`automotive, remote controlled, keyless entry systems.
`Referring to FIG. 1 in greater detail, the Colpitls oscillator
`ofcircuit 5 comprises a Colpitts configured transistor 01 and
`an input resonant tank circuit. The tank circuit
`typically
`comprises a
`resonator, such as a surface acoustic wave
`(“SAW") device 2, and a pair of feedback capacitors, C, and
`C2. Further, the oscillator also includes a number of biasing
`resistors to facilitate the proper operation of transistor 0,.
`Transmitter circuit 5 also comprises an inductor L1 which
`acts as an antenna element for radiating the RF output signal.
`Structurally, transistor 0, comprises a base 4, collector 6
`and emitter 8. Base terminal 4 is coupled with surface
`acoustic wave resonator 2, and collector 6 is coupled with
`inductor [.1, while emitter 8 is coupled to ground through a
`resistor R3. Additionally, feedback capacitor C2 is coupled
`between emitter 8 and ground, and as such, is in parallel with
`resistor R3. Feedback capacitor C]
`is coupled between
`collector 6 and emitter 8. Moreover, a third capacitor C3 is
`coupled between inductor L1 and ground for providing a
`large capacitance to maintain a constant DC voltage.
`Circuit 5, and more particularly L1 and C3, is coupled to
`a direct current ("DC“) voltage source to receive a DC bias
`input V,m typically 6 V. Transmitter circuit 5 also receives
`a data input signal V5,,“ for encoding the RF carrier signal.
`
`an
`
`35
`
`40
`
`45
`
`50
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`55
`
`60
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`65
`
`

`

`US 6,225 ,873 B1
`
`3
`In order to achieve the advantages of the present
`invention, a system for selectahly oscillating at a first or a
`second oscillating frequency is disclosed. The system corn-
`prises an oscillator
`for providing an oscillating output.
`Moreover.
`the system comprises a switching device for
`selecting a first or a second impedance in response to a select
`signal having a voltage. Each of the first and secoan imped—
`ances are fixed independently of the select sigtal voltage
`such that the oscillating output oscillates at the first oscil-
`Iating frequency when the first impedance is provided and
`oscillates at
`the second oscillating frequency when the
`second impedance is provided.
`These and other advantages and objects will become
`apparent to those skilled in the art
`from the following
`detailed description read in conjunction with the appended
`claims and the drawings attached hereto.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`invention will be better understood from
`The present
`reading the following description of non-[imitative
`embodiments, with reference to the attached drawings,
`wherein below:
`
`FIG. 1 illustrates a circuit diagram illustrating a conven-
`tional single Colpitts—type oscillator and transmitter circuit;
`FIG. 2 illustrates a block diagram of a balanced oscillator
`and transmitter system;
`FIG. 3 illustrates a first circuit realization of the balanced
`oscillator and transmitter system;
`realization of the
`FIG. 4 illustrates a second circuit
`balanced oscillator and transmitter system;
`FIG. 5 illustrates a circuit realization of a series resonant
`tank circuit;
`
`FIG. 6 illustrates a graphical representation of voltage
`waveforms achieved by the balanced oscillator and trans-
`mitter system of FIG. 2;
`FIG. 7 illustrates a block diagram of a preferred balanced
`oscillator and transmitter system;
`FIG. 8 illustrates a first circuit realization of the system of
`FIG. 7;
`FIG. 9 illustrates a second circuit realization of the system
`of FIG. '7;
`FIG. 10 illustrates a buffered oscillator and transmitter
`circuit;
`FIG. 11 illustrates a block diagram of a system [or
`selectably oscillating at a first or second frequency;
`FIG. 12 illustrates a first circuit realization of the system
`of FIG. 11; and
`FIG. l3 illustrates the preferred circuit realization of the
`system of FIG. 11.
`It should be emphasized that the drawings of the present
`disclosure are not to scale but are merely schematic repre-
`sentations and are not
`intended to portray the specific
`parameters or the structural details of the invention, which
`can be determined by one of skill in the art by examination
`of the information herein.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMEN'I‘S
`
`Referring to F IG. 2, a balanced oscillator and transmitter
`system 10 is illustrated according to a first embodiment of
`the present invention. System 10 comprises a resonator 18
`for generating a reference signal having a resonating fre-
`quency. Resonator 18 preferably comprises a surface acous-
`
`1E]
`
`15
`
`_
`
`an
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`tic wave (“SA ”) device, and the resonating frequency
`preferably falls within the radio frequency (“RF") spectrum.
`It should be obvious to one of ordinary skill
`in the art,
`however,
`that other components, such as a bulk acoustic
`wave ("HAW“) device for example, may also be employed
`to realize the functional purpose of the resonator.
`System 10 additionally comprises a first and see-end
`oscillator, 12 and 15, each for generating an oscillating
`output in response to the resonating frequency of the reso-
`nator 18. First oscillator 12 comprises an amplifier 14 for
`amplifying an input corresponding with the reference signal
`provided by resonator 18, and a resonating circuit 13,
`coupled with amplifier .14, for generating an oscillating
`signal
`in response to output of amplifier 14. Similarly,
`second oscillator 15 comprises an amplifier 16 for amplifyw
`ing an input corresponding with the reference signal pro»
`vided by resonator 18, and a resonating circuit 17, coupled
`with amplifier 16, for generating an oscillating signal
`in
`response to output of amplifier 16. While both oscillators
`preferably comprise identical
`functional components,
`it
`should be apparent to one of ordinary skill in the art that
`alternate oscillator designs may he realized while still
`achieving the advantages of the present invention. To pro—
`vide a balanced design. the outputs of both oscillators 12 and
`15 are 180 degrees out of phase with one another, yet equal
`in magnitude.
`System 10 moreover comprises an antenna 11 for radiat-
`ing an output signal having a single frequency. The output
`signal of antenna 11 corresponds with the sum of both first
`and second oscillating outputs. The relationship between the
`output signal and the first and second oscillating signals can
`be best understood by appreciating the output characteristics
`of system 10. Comprising an output impedance, system 10
`can be viewed using a voltage divider model. Using this
`illustration, both first and second oscillator outputs are
`representative of an input to the divider. The model further
`comprises a first impedance associated with the impedance
`seen by each oscillator to ground, as well as a second
`impedance in series with the first impedance. Second imped-
`ance is a model of the output impedance of system 10. By
`way of this voltage divider model, the output signal gener-
`ated by antenna 11 is representative of the voltage falling
`across the first
`impedance. Thus, in view of its balanced
`characteristics, the output signal transmitted by antenna 11
`of system ll] differs from the sum of the oscillating outputs
`in amplitude alone, though the current is the same.
`It is,
`nonetheless, conceivable that
`the output signal might be
`intentionally distinguishable from the sum of the oscillating
`outputs in frequency or phase, as well as a combination
`thereof,
`for example, as would be apparent
`to one of
`ordinary skill in the art.
`Antenna 1] preferably comprises an inductor having a
`direct current (“DC”) center point. This DC center point
`partitions the inductor into a {inst and second equivalent
`inductors. Furthermore, antenna 11 comprises an alternating
`current ("AC") balanced oscillating point which provides a
`location along antenna 11 where the AC voltage magnitude
`of the mcillating outputs of first and second oscillators 12
`and 15 are both substantially zero. In view of both the AC
`and DC center points, a "balanced" oscillator is realized.
`Tight tolerances for resonating circuits 13 and 17 are not
`required for the present balanced oscillator design. This
`benefit is achieved by way of the DC center point and the AC
`center point, as well as the balanced circuit itself. Moreover,
`as antenna 11 preferably transmits both oscillator outputs at
`a single primary frequency, the tolerances associated with
`resonating circuits 13 and 17 are less critical to the overall
`operation of system 10.
`
`

`

`US 6,225 ,873 B1
`
`ill
`
`15
`
`so
`
`35
`
`40
`
`5
`In a further embodiment of the present invention, antenna
`11 comprises a primary winding of a center lapped trans-
`former for transmitting the oscillating outputs of both first
`and second oscillators 12 and 15 onto a secondary winding.
`By this arrangement. secondary winding may act as antenna
`itself by radiating the oscillating outputs. However,
`this
`approach is preferred for low frequency operation. To sup—
`port operation at other frequencies, an output inductor or the
`like should be employed in conjunction with a filter and
`matching circuit to radiate the oscillating outputs.
`Referring to FIG. 3, a circuit realization 2|] is depicted of
`the balanced oscillator and transmitter system of FIG. 2.
`Balanced oscillator and transmitter circuit 20 comprises a
`first and second pseudo Colpitts oscillator. Both pseudo
`Colpitts oscillators are balanced with respect to one another
`and share a common tank circuit and oscillating current
`signal I for power output efficiency. Circuit 20 described
`herein is particularly applicable with automotive remote
`keyless entry systems. Other applications, however, are
`clearly conceivable to one of ordinary skill in the art.
`According to a more detailed description, circuit 20
`comprises a balanced oscillator configuration which
`includes two pseudo colpitts oscillator circuits for producing
`a local oscillation signal. The oscillator circuitry includes a
`first transistor Q2 and a second transistor 03 each coupled *
`with a resonator device 22 therebetween. Resonator device
`22 acts as a series resonant input tank for generating and
`stabilizing the oscillating current signal I. By so doing. a
`resonance RF carrier frequency is achieved.
`First and second transistors, 03 and 03, each preferably
`comprise a bipolar junction transistor (“BIT”). Alternatives,
`however, such as a heterojunction bipolar transistor
`(“HB’I‘”). should be apparent to one of ordinary skill in the
`art. According to a further embodiment, transistors 02 and
`03 are each MMBTl-l [0 type bipolar transistors.
`Transistors Q: and 03 each operate as an amplification
`stage to provide a unity loop gain for steady state operations.
`First transistor Q2 comprises a base, a collector, and emitter
`30, 32 and 34, respectively. Likewise, second transistor 03
`comprises a base, a collector, and emitter 36, 38 and 40,
`respectively. Transistors Q2 and Q3 are each configured as a
`pseudo Colpitts oscillator having a tuned [.C circuitry and
`positive feedback.
`It should be understood by one of ordin
`nary skill in the art that various other transistor oscillator
`configurations may be substituted into the above arrangew
`ment to achieve the same functional purpose.
`Resonator device 22 is coupled between the base termi-
`nals 30 and 36 of transistors Q2 and 03 via resonator output
`lines 42 and 44, respectively. Resonator 22 is shown having
`an array of metallic fingers formed on a piezoelectric sub-
`strate. Resonator 22 advantageously operates to stabilize
`oscillations of the carrier signal. Resonator device 22 pref-
`erably comprises a series resonant input tank circuit surface
`acoustic wave ("SAW”) device. However, according to a
`further embodiment, SAW resonator 22 is a R02073 SAW
`resonator manufactured and sold by RF Monolithics, Incor-
`porated.
`Circuit 20 in nher comprises a pair of output tank circuits.
`Each output tank circuit includes a capacitor and inductor;
`first output
`tank comprises first
`inductor L2 and second
`output tank comprises second inductor L3. Inductors L; and
`L3 each operate as antenna radiating elements for radiating
`an output signal in response to the commonly shared oscil-
`lating current Signal I. First inductor I,2 is coupled between
`collector terminal 32 of transistor Q2 and node 28, while
`second inductor L3 is coupled between collector terminal 38
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`of transistor 03 and node 28. Accordingly, inductors L2 and
`L, are coupled together at node 28 in a series connection. A
`voltage input source 24 is coupled to node 28 between
`inductors I.2 and [.3 for applying a DC voltage input Vrrv
`thereto. According to one example of the present invention.
`voltage input signal Vm is a +3 volt DC signal. Application
`of the +3 volts between inductors L2 and L3 biases transis-
`tors 02 and 03 to realize the necessary gain. Inductors L2
`and I.3 each operate as an antenna for transmitting and
`radiating an electromagnetic field exhibiting the oscillating
`signal with the predetermined carrier frequency.
`Circuit 20 further comprises a data input 26 coupled to
`both resonator output
`lines 42 and 44 though respective
`resistors Rb and [1,. Data input 26 is adapted to receive an
`ontolf data input signal VDATA which is applied to both sides
`of SAW resonator 22. Each of the resonator output lines 42
`and 44 is also coupled to ground via reSpective resistors R5
`and R8. The data input signal VD“, encodes the carrier
`signal with a modulation scheme to provide information on
`the carrier signal. The preferred modulation format is fre-
`quency shift key ("FSK"), though other schemes including
`pulse width modulation ("PWM") and amplitude modula-
`tion (“AM") may be easily substituted by one of ordinary
`skill
`in the art. The information provided on the carrier
`signal may control andior initiate various system operations,
`such as a door lock actuation mechanism, as well as the
`onioff operations of circuit 20. Application of data input
`signal me may be initiated by manual control through an
`actuation mechanism such as, for example, a push-button
`pad, switch or other pulsed activation device.
`SAW resonator 22 provides for an input tank circuit which
`is commonly shared by the pair ofpseudo Colpitts. Inductor
`Ly, in combination with capacitors C, and C5. furnishes a
`first output tank circuit. Similarly. inductor L3. in combina-
`tion with capacitors C6 and (2,, creates a second output tank
`circuit. While the series resonant input tank stabilizes oscil—
`lation of the resonating signal, the output tanks provide for
`radiation of the RF output signal. Capacitors C4 and C5 also
`establish a voltage divider network, as well as a positive
`feedback path to transistor 0:. Likewise, capacitors Ca and
`C7 creates a voltage divider and a positive feedback path to
`transistor 03. Energy is elliciently stored in the capacitors C4
`through (‘7 and inductors L2 and L3 to enhance radiation
`efficacy by reducing the amount of energy that may other-
`wise be required for each cycle of transistors 02 and 03.
`Referring to FIG. 4, circuit 20 may alternately be config-
`ured to include a center-tapped transformer 46 in lieu of first
`and second inductors L; and L_-,. To this end, center-tapped
`transformer 46 comprises a primary winding having a first
`primary winding portion 48a and second primary winding
`portion 48!). Primary winding portions 48a and 48b prefer-
`ably are of substantially equal size. The voltage input source
`24 is coupled to a center tap 49, located between the primary
`winding portions 48:: and 48b, for supplying DC voltage
`input V,” thereto.
`Center-tapped transformer 46 further comprises a second-
`ary winding 50 located adjacent
`to the primary winding
`portions 48a and 48b. Transfomter 46 is adapted to form a
`lirst magnetic coupling between primary winding portion
`480 and the secondary winding 50, and a second magnetic
`coupling between primary winding portion 43b and second
`ary winding 50. The secondary winding 50 in turn is coupled
`on both ends to a filter and matching network 52. A pair of
`output lines extending from the filter and matching network
`52 are coupled to a radiating inductor L,1 for radiating an
`output electromagnetic field therefrom.
`According to the alternate embodiment of FIG. 4, the first
`and second primary winding portions 48:: and 48b of the
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`US 6,225 ,873 B1
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`5
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`it]
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`15
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`7
`center-tapped transformer 46 each produce an electromag-
`netic field in response to the oscillating current signal I that
`is transmitted therethrough. The electromagnetic fields from
`each of primary winding portions 480 and 48!) are thereby
`transmitted and induced onto the secondary winding 50 of
`the center-tapped transformer 46. The signals induced onto
`secondary winding 50 are summed together. The summed
`signal is in turn filtered to eliminate undesirable noise, and
`is impedance matched via filter and matching network 52.
`The filtered and impedance matched signal is then passed
`through a radiating inductor L.l to transmit a single radiating
`output signal. Use of the center-tapped transformer 46
`advantageously separates out
`the even harmonics and is
`generally better able to achieve enhanced control of the
`transmission of the single radiating output signal.
`It should be understood that the SAW resonator 22 is a
`series-resonant
`input
`tank circuit which may be imple-
`mented with alternate comparable series resonant frequency
`stabilizing devices. As an alternative to the SAW resonator
`22,
`the series resonant
`tank circuit may include a bulk '
`acoustic wave (“BAW”) device, crystal device, microstrip or
`any other series-resonant structure or device that may
`achieve the desired stabilizing signal oscillation.
`With particular reference to FIG. 5, a series resonant tank
`circuit 60 is depicted as an alternative to the SAW resonator
`22 of FIGS. 24. Here, series resonant
`tank circuit 60
`comprises a resistor Rm capacitor CM and inductor LM.
`Each of these components are coupled in series to create
`series resonant tank circuit 60. The resonant frequency of the
`tank circuit 60 is generally dependant on the size of the
`inductor LM and capacitor CM.
`In operation, circuit 20 receives a DC input voltage signal
`Vm- through voltage input source 24. Data input V0,,“ may
`also be received via data input 26 to encode the carrier signal
`with a predeterminccl modulation scheme. Initially, circuit
`20 forms a resonating signal which starts up and builds to a
`steady state energy level having oscillations at a known
`frequency. In doing so, transistors Q3 and Q3 cycle between
`the collector terminal 38 and emitter terminal 4|] in response
`to noise or other induced signals and will build until the
`steady state is reached.
`During start up, each amplification stage provides a gain
`in excess of unity. At steady state, the gain of each ampli-
`fication stage is approximately equal to or slightly greater
`than unity to account for any energy loss. The series resonant
`tank circuit with SAW resonator 22 maintains and ensures
`the stability of the signal oscillation within the circuit 20.
`The oscillating signal in turn is exhibited by current signal
`I flowing through the antenna radiating elements, inductors
`L2 and 1.3. In addition,
`the feedback paths provided via
`capacitors C4 and C5 and capacitors C5 and C7 create a phase
`delay which adjusts the loop time to realize the desired
`frequency.
`Referring to FIG. 6, a graphical representation of voltage
`waveforms achieved by the tlrst embodiment of the present
`invention is depicted. Here,
`the inductors [.2 and 1.3 of
`circuit 20 of FIG. 2 each radiate a separate signal through
`separate electromagnetic fields, both of which have the same
`carrier frequency in response to the commonly shared oscil—
`lating current signal I. These radiating output signals from
`inductors L2 and L3 and the total summed radiating output
`are illustrated by the waveforms 66 provided in FIG. 6. The
`first radiating output signal transmitted from inductor L2 is
`shown as voltage waveform 62, while the second radiating
`output signal transmitted from inductor L3 is depicted as
`voltage waveform 64. Voltage waveforms 62 and 64 are
`
`8
`characterized as having equal amplitudes and an approxi-
`mate 180 degree phase shift relationship relative to one
`another. Radiating signals 62 and 64 emitted are measured
`with respect to voltage ground 28 and there fore exhibit the
`aforementioned phase shift of 180 degrees. As waveforms
`62 and 64 are both measured relative to node 28,
`the
`summation of both waveforms 62 and 64 relative to the
`commonly shared current signal
`I
`results in a voltage
`waveform representing a single radiating output signal 66.
`Accordingly, Output signal 66 may be achieved using the
`pair of balanced oscillators and output tanks of the present
`invention.
`
`Single radiating output signal 66 in one embodiment has
`a frequency of approximately 315 MHZ. Additionally, the
`outputs from both inductor L2 and inductor L3 of the first
`and second output tanks are balanced signals which are
`symmetrical relative to node 28 which is preferably set at +3
`volts DC. In contrast, the separate radiating signals created
`by center-tapped transformer 46 of one of the alternate
`embodiments of the present invention, may be summed and
`then filtered and impedance matched prior to transmission.
`Referring to FIG. 7. a bufi‘ered balanced oscillator and
`transmitter system 70 is illustrated. System 70 comprises a
`resonator 72 for generating a
`reference signal having a
`resonating frequency. Resonator 72 preferably comprises a
`surface acoustic wave ("SA ") device, and the resonating
`frequency preferably falls within the radio frequency (“RF”)
`spectrum. It should be obvious to one ofordinary skill in the
`art, however, that other components, such as a bulk acoustic
`wave ("RAW") device for example, may also be employed
`to realize the functional purpose of the resonator.
`System '70 additionally comprises a first and second
`oscillator, 74 and 76, each for generating an oscillating
`output in response to the resonating frequency of the reso-
`nator 72. First oscillator '74 comprises an amplifier 78 for
`amplifying an input corresponding with the reference signal
`generated by resonator 72, and a resonating circuit 80,
`coupled with amplifier 78, for generating an oscillating
`signal
`in response to output of amplifier 78. Similarly,
`second oscillator 76 comprises an amplifier 82 for amplify-
`ing an input corresponding with the reference signal gener-
`ated by resonator 72, and a resonating circuit 84, coupled
`with amplifier 82, for generating an oscillating signal in
`response to output of amplifier 82. While both oscillators
`preferably comprise identical
`functional components,
`it
`should be apparent to one of ordinary skill in the art that
`alternate oscillator designs