a2) United States Patent
`US 6,225,873 Bl
`(10) Patent No.:
`May1, 2001
`(45) Date of Patent:
`Hill
`
`US006225873B1
`
`(54) FREQUENCY SHIFT KEY MODULATING
`OSCILLATOR
`
`(75)
`
`Inventor:
`
`John P. Hill, Westland, MI (US)
`
`(73) Assignee: Lear Automotive Dearborn, Inc.,
`Southfield, 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.: 08/566,270
`
`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 & David Kenny, “Basic Crystal Oscillator
`Design Considerations” RFdesign Oct. 1992 pp. 75-79.
`Fred Brown, “Stable LC Oscillators” rfdesign Mar. 1987 pp.
`54-61.
`
`
`
`Harvey L. Morgan, “An Emitter Follower Oscillator” rfde-
`sign Oct. 1988 pp. 61-62.
`D. L. Ash, “Saw Devices In Wireless Communication Sys-
`tems”, Oct. 31, 1993, p. 115-124, 1993 [EEE Ultrasonic
`Symposium.
`(22) Filed:—Dee. 1, 1995
`Siemens Components, “Cost—Attractive, Reliable Remote
`Controls Use Saw Resonators”, vol. 25, No. 4, Aug. 1990,
`p. 142-145.
`Gee Plessey Semiconductor—Preliminary Information Kes-
`rxol 290-460MHz Ask Receiver Sep. 1995 p, 245-251.
`Temic—Telefunken Semiconductors—Preliminary Infor-
`mation UHF AM/FM Transmitter U2740B Rev. Al; 23,03,
`1995.
`
`C51) WE MOUsrrcsiccciasesectcctcestasiessisessasciste HO03C 3/00
`(52) US. Ce seesssssssnesnsseneen 332/102; 332/100; 332/101;
`375/272; 375/303; 375/304; 375/306; 375/307;
`331/107 A; 331/179
`(58) Field of Search 0.0.0.0... 332/100, 101,
`332/102; 375/272, 303, 304, 306, 307;
`331/107 A, 179
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`Temic—Telefunken Semiconductors—Preliminary Infor-
`mation UHF AM/FM Transmitter U2741B Rev. Al; 02,05,
`1995.
`
`2,930,991 *
`3,451,012 *
`3,560,881 *
`
`3/1960 Edwards ....ccsccssseseessenness 332/102
`
`6/1969 Spiro...
`ew 332/102
`2/1971 Fredricsson.
`..eesssssreesessess 332/102
`
`Primary Examiner—Sicgfried H. Grimm
`(74) Altorney, Agent, or Firm—Brooks & Kushman P.C.
`
`(57)
`
`ABSTRACT
`
`The present invention teaches a system for selectably oscil-
`lating at a first or a secondoscillating frequency. The system
`comprises an oscillator for providing an oscillating output.
`«3/1984 (DE).
`3332307
`Moreover,
`the system comprises a switching device for
`2/1986 (DE).
`3429574
`selectingafirst or a second impedance in response to a select
`0459781
`12/1991 (EP).
`signal having a voltage. Each of the first and second imped-
`ancesis fixed independently ofthe 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 secondoscillating frequency when the second
`impedance is provided.
`
`(List continued on next page.)
`FOREIGN PATENT DOCUMENTS
`
`(List continued on next page.)
`OTHER PUBLICATIONS
`
`Branislav Petrovic, “A Balanced RF Oscillator”, rfdesign
`Dec. 1989 pp. 35-38.
`Robert Matthys, “A High Performance VHF Crystal Oscil-
`lator Circuit” rfdesign Mar. 1987 pp. 31-38.
`
`2 Claims, 6 Drawing Sheets
`
`
`
`
`
`Roku EX1021
`U.S. Patent No. 9,911,325
`
`Roku EX1021
`U.S. Patent No. 9,911,325
`
`

`

`US 6,225,873 B1
`
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`FOREIGN PATENT DOCUMENTS
`
`4,189,676
`4,794,622
`5,103,221
`5,138,284
`5,367,537
`5,422,605
`5,532,654 *
`
`2/1980 Arias et al. .
`.
`12/1988 Isaacmanet al.
`4/1992 Memmola ...........0..0000 340/825 .31
`8/1992 Yabuki et ab.
`..cccsceseserseeeeees 331/56
`
`11/1994 Anderson ......
`wore DTS/65
`
`331/116 R
`6/1995 Yang et al.
`......ccccsccsssssssssesees 332/102
`7/1996 Teki et al.
`
`0626772
`1603627
`W0O9%6/16473
`91/4063
`93/4726
`
`11/1994 (EP).
`11/1981
`(GB).
`5/1996 (WO).
`5/1991 (ZA).
`7/1993 (ZA).
`
`* cited by examiner
`
`

`

`U.S. Patent
`
`May 1, 2001
`
`Sheet 1 of 6
`
`US 6,225,873 BI
`
`
` FIRST
`
`FG. 1
`(PLURAL
`
`
`SECOND
`RESONATING
`CIRCUIT
`
`RESONATING
`CIRCUIT
`
`17 - ANTENNA
`
`--
`
`eeepc ' é
`
`#
`
`f :
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`
`.
`
`

`

`U.S. Patent
`
`May 1, 2001
`
`Sheet 2 of 6
`
`US 6,225,873 BI
`
`FY F
`
`

`

`U.S. Patent
`
`May 1, 2001
`
`Sheet 3 of 6
`
`US 6,225,873 BI
`
`TIME 1 nsec/DIV
`Bt. 6
`
`VOLTS
`4
`
`RESONATING
`CIRCUIT
`‘ ‘
`
`RESONATING
`CIRCUIT\
`
`SG. 7
`
`0
`
`', RESONATING CIRCUIT /
`
`100 - ANTENNA
`
`

`

`
`
`146
`
`C13
`
`U.S. Patent
`
`May 1, 2001
`
`US 6,225,873 BI
`
`Sheet 4 of 6
`
`~ 144
`
`

`

`U.S. Patent
`
`May 1, 2001
`
`Sheet 5 of 6
`
`US 6,225,873 Bl
`
`
`
`FG 10
`
`200 ~\
`
`SWITCHING
`DEVICE
`
`OSCILLATOR
`
`225
`
`ee
`
`OR fo
`
`205
`
`210
`
`
`
`

`

`U.S. Patent
`
`May 1, 2001
`
`Sheet 6 of 6
`
`US 6,225,873 Bl
`
`woe ee eee ee ee ee ee ee ee eb a a ee eee eee
`
`i
`ee ee |
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`
`
`

`

`US 6,225,873 B1
`
`1
`FREQUENCYSHIFT KEY MODULATING
`OSCILLATOR
`
`RELATED APPLICATIONS
`
`The following application is related to application Ser.
`No. 08/342,721, filed on Nov. 21, 1994, now U.S. Pat. No.
`5,486,793, and pending application Ser. No, 08/448,759,
`filed on May 24, 1994.
`
`FIELD OF THE INVENTION
`
`This invention relates generally to remote transmitters
`and, more particularly, to a frequency modulated balanced
`oscillator.
`
`BACKGROUND OF THE INVENTION
`
`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 efficient 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 on/off 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 controlsignal 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 elementL.,. 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 Colpitts oscillator
`of circuit 5 comprises a Colpitts configuredtransistor Q, 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
`C,. Further, the oscillator also includes a numberofbiasing
`resistors to facilitate the proper operation of transistor Q,.
`Transmitter circuit 5 also comprises an inductor L, which
`acts as an antenna element for radiating the RF output signal.
`Structurally, transistor Q, comprises a base 4, collector 6
`and emitter 8. Base terminal 4 is coupled with surface
`acouslic wave resonator 2, and collector 6 is coupled with
`inductor L,, while emitter 8 is coupled to ground through a
`resistor R,. Additionally, feedback capacitor C, is coupled
`between emitter 8 and ground,and as such, is in parallel with
`resistor R,. Feedback capacitor C,
`is coupled between
`collector 6 and emitter 8. Moreover, a third capacitor C, is
`coupled between inductor L, and ground for providing a
`large capacitance to maintain a constant DC voltage.
`Circuit 5, and more particularly L, and C,, is coupled to
`a direct current (“DC”) voltage source to receive a DC bias
`input V,,,, typically 6 V. Transmitter circuit 5 also receives
`a data input signal V,,,47,4 for encoding the RF carrier signal.
`
`10
`
`15
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`As detailed hereinabove, circuit 5 generates a radiating
`output signal via inductor L,. In doing so, transistor Q,,
`acting as an amplifier, in combination with the resonating
`tank circuit, generates a resonating signal which is provided
`to inductor L, as an oscillating current signal I. The con-
`duction of current I through inductor L, in turn causes the
`radiating output signal to be transmitted as an electromag-
`netic field.
`
`The above described Colpitts oscillator is well suited for
`the RFsignal 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 L., 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 Q,
`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 transmilters are
`hand grasped and directed generally toward a receiver ofthe
`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 FSK
`oscillator is depicted in U.S. 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
`phenomenonis highly undesirable to the long term efficacy
`of a compact remote transmitter design.
`In view of these problems, a need remainsfor 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 knownart.
`
`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 inventionis to provide
`for a frequency shift key modulating oscillator circuit which
`is more cost effective.
`
`invention is to
`Sull 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.
`
`

`

`US 6,225,873 B1
`
`3
`In order to achieve the advantages of the present
`invention, a system for selectably oscillating at a first or a
`second oscillating frequencyis disclosed. The system com-
`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 ofthe first and second imped-
`ances are fixed independently of the select signal voltage
`such that the oscillating output oscillates at the first oscil-
`lating frequency when the first impedance is provided and
`oscillates at
`the second oscillating frequency when the
`second impedanceis 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-limitative
`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 illustratesa 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 for
`selectably oscillating at a first or second frequency;
`FIG, 12 illustratesa first circuit realization of the system
`of FIG. 11; and
`FIG. 13 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 oneof skill in the art by examination
`of the information herein.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`Referring to FIG, 2, a balanced oscillator and transmitter
`system 10 is illustrated according to a first embodiment of
`the present invention. System LO comprises a resonator 18
`for generating a reference signal having a resonating fre-
`quency. Resonator 18 preferably comprises a surface acous-
`
`~] ‘an
`2
`
`30
`
`35
`
`40
`
`45
`
`50
`
`60
`
`65
`
`4
`tic wave (“SAW”) 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 (“BAW”) device for example, may also be employed
`to realize the functional purpose of the resonator.
`System 10 additionally comprises a first and second
`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 amplify-
`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 be 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 LI for radiat-
`ing an output signal having a single frequency. The output
`signal of antenna 11 corresponds with the sum of both first
`and secondoscillating outputs. The relationship between the
`output signal and the first and second oscillating signals can
`be best understoodby 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 ofthis 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 10 differs from the sum ofthe 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 ofthe 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 IL preferably comprises an inductor having a
`direct current (“DC”) center point. This DC center point
`partitions the inductor into a first and second equivalent
`inductors. Furthermore, antenna LL comprises an alternating
`current (“AC”) balanced oscillating point which provides a
`location along antenna 11 where the AC voltage magnitude
`ofthe oscillating 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 balancedcircuit 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
`
`10
`
`15
`
`6
`5
`of transistor Q, and node 28. Accordingly, inductors L, and
`In a further embodiment ofthe present invention, antenna
`L, are coupled together at node 28 in a series connection. A
`11 comprises a primary winding of a center tapped trans-
`voltage input source 24 is coupled to node 28 between
`former for transmitting the oscillating outputs of both first
`inductors L., and L, for applying a DC voltage input V,,,
`and second oscillators 12 and 15 onto a secondary winding.
`thereto. According to one example of the present invention,
`Bythis arrangement, secondary winding may act as antenna
`voltage input signal V,,, is a +3 volt DC signal. Application
`itself by radiating the oscillating outputs. However,
`this
`of the +3 volts between inductors L, and L, biases transis-
`approach is preferred for low frequency operation. To sup-
`tors Q, and Q, to realize the necessary gain. Inductors L,
`port operation at other frequencies, an output inductor or the
`and L., each operate as an antenna for transmitting and
`like should be employed in conjunction with a filter and
`radiating an electromagnetic field exhibiting the oscillating
`matching circuit to radiate the oscillating outputs.
`signal with the predetermined carrier frequency.
`Referring to FIG. 3, a circuit realization 20 is depicted of
`Circuit 20 further comprises a data input 26 coupled to
`the balanced oscillator and transmitter system of FIG. 2.
`both resonator output
`lines 42 and 44 though respective
`Balanced oscillator and transmitter circuit 20 comprises a
`resistors R, and R,. Data input 26 is adapted to receive an
`first and second pseudo Colpitts oscillator. Both pseudo
`on/off data input signal V5.7, which is applied to both sides
`Colpitts oscillators are balanced with respect to one another
`of SAW resonator 22, Each of the resonator output lines 42
`and share a common tank circuit and oscillating current
`and 44 is also coupled to ground via respective resistors R.
`signal I for power output efficiency. Circuit 20 described
`and R,. The data input signal V,,,,, encodes the carrier
`signal with a modulation scheme to provide information on
`herein is particularly applicable with automotive remote
`the carrier signal. The preferred modulation format is fre-
`keyless entry systems. Other applications, however, are
`quency shift key (*FSK”), though other schemes including
`clearly conceivable to one of ordinary skill in the art.
`pulse width modulation (“PWM”) and amplitude modula-
`According to a more detailed description, circuit 20
`tion (“AM”) may be easily substituted by one of ordinary
`comprises a balanced oscillator configuration which
`skill
`in the art. The information provided on the carrier
`includes two pseudocolpitts oscillator circuits for producing
`signal may control and/orinitiate various system operations,
`a local oscillation signal. The oscillator circuitry includes a
`such as a door lock actuation mechanism, as well as the
`first transistor Q., and a second transistor Q, each coupled
`on/off operations of circuit 20. Application of data input
`with a resonator device 22 therebetween. Resonator device
`signal V,,474, May be initiated by manual control through an
`22 acts as a series resonant input tank for generating and
`actuation mechanism such as, for example, a push-button
`stabilizing the oscillating current signal I. By so doing, a
`pad, switch or other pulsed activation device.
`resonance RF carrier frequency is achieved.
`SAW resonator 22 providesfor an input tank circuit which
`First and second transistors, Q, and Q,, each preferably
`is commonly shared by the pair of pseudo Colpitts. Inductor
`comprise a bipolar junction transistor (“BJT”). Alternatives,
`L,, in combination with capacitors C, and C., furnishes a
`however, such as a heterojunction bipolar transistor
`first output tank circuit. Similarly, inductor L, in combina-
`(“HBT”), should be apparent to one of ordinary skill in the
`tion with capacitors C,, and C,, creates a second output tank
`art. According to a further embodiment, transistors Q, and
`circuit, While the series resonant input tank stabilizes oscil-
`Q, are each MMBTH1O type bipolar transistors.
`lation of the resonating signal, the output tanks provide for
`radiation of the RFoutput signal. Capacitors C, and C,; also
`Transistors Q., and Q, each operate as an amplification
`establish a voltage divider network, as well as a positive
`stage lo provide a unity loop gain for steady state operations.
`feedback path to transistor Q.. Likewise, capacitors C, and
`First transistor Q., comprises a base, a collector, and emitter
`C, creates a voltage divider and a positive feedback path to
`30, 32 and 34, respectively. Likewise, second transistor Q,
`transistor Q,. Energyis efficiently stored in the capacitors C,
`comprises a base, a collector, and emitter 36, 38 and 40,
`through C, and inductors L, and L, to enhance radiation
`respectively. Transistors Q, and Q, are each configured as a
`efficacy by reducing the amount of energy that may other-
`pseudo Colpitts oscillator having a tuned LC circuitry and
`wise be required for each cycle of transistors Q, and Q,.
`positive feedback.
`It should be understood by one of ordi-
`nary skill in the art that various other transistor oscillator
`Referring to FIG, 4, circuit 20 may alternately be config-
`configurations may be substituted into the above arrange-
`ured to include a center-tapped transformer 46 in lieu of first
`ment to achieve the same functional purpose.
`and second inductors L, and L,. To this end, center-tapped
`transformer 46 comprises a primary winding havingafirst
`Resonator device 22 is coupled between the base termi-
`primary winding portion 48a and second primary winding
`nals 30 and 36of transistors Q. and Q, via resonator output
`lines 42 and 44,respectively. Resonator 22 is shown having
`portion 48). Primary winding portions 48a and 485 prefer-
`ably are of substantially equal size. The voltage input source
`an array of metallic fingers formed on a piezoelectric sub-
`24is coupledto a center tap 49, located between the primary
`strate. Resonator 22 advantageously operates to stabilize
`winding portions 48a and 485, for supplying DC voltage
`oscillations of the carrier signal. Resonator device 22 pref-
`input V,,, thereto,
`erably comprises a series resonant input tank circuit surface
`acoustic wave (“SAW”) device. However, according to a
`Center-tapped transformer 46 further comprises a second-
`further embodiment, SAW resonator 22 is a RO2073 SAW
`ary winding 50 located adjacent
`to the primary winding
`resonator manufactured and sold by RF Monolithics, Incor-
`portions 48a and 48). Transformer 46 is adapted to form a
`porated.
`first magnetic coupling between primary winding portion
`48a and the secondary winding 50, and a second magnetic
`Circuit 20 further comprises a pair of output tank circuits.
`coupling between primary winding portion 48b and second-
`Each output tank circuit includes a capacitor and inductor;
`ary winding 50. The secondary winding 50 in turn is coupled
`first output
`tank comprises first
`inductor L, and second
`on both endsto a filter and matching network 52. A pair of
`output tank comprises second inductor L,. Inductors L, and
`output lines extending from the filter and matching network
`L, each operate as antenna radiating elements for radiating
`52 are coupled to a radiating inductor L, for radiating an
`an output signal in response to the commonly shared oscil-
`output electromagnetic field therefrom.
`lating current signal I. First inductor L, is coupled between
`collector terminal 32 oftransistor Q, and node 28, while
`According to the alternate embodimentof FIG. 4,thefirst
`second inductor L, is coupled between collector terminal 38
`and second primary winding portions 48a and 48b of the
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`US 6,225,873 B1
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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 electromagneticfields from
`each of primary winding portions 48a and 48b 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.,, 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
`Sseries-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. 2-4. Here, series resonant
`tank circuit 60
`comprises a resistor R,,, capacitor C,, and inductor L,,.
`Each of these components are coupled in series to create
`series resonanttank circuit 60. The resonant frequency ofthe
`tank circuit 60 is generally dependant on the size of the
`inductor Ly, and capacitor Cy,
`In operation,circuit 20 receives a DCinput voltage signal
`Vwthrough voltage input source 24. Data input Var, May
`also be received via data input 26 to encodethe carrier signal
`with a predetermined 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 Q, and Q, cycle between
`the collector terminal 38 and emitter terminal 40 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
`L, and L,. In addition,
`the feedback paths provided via
`capacitors C, and C, and capacitors C,, and C, create a phase
`delay which adjusts the loop time to realize the desired
`frequency.
`Referring to FIG. 6, a graphical representation of voltage
`waveformsachieved by the first embodiment of the present
`invention is depicted. Here,
`the inductors L, and L, of
`circuit 20 of FIG. 2 cach radiate a separate signal through
`separate electromagneticfields, 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 L. and L., and the total summedradiating output
`are illustrated by the waveforms 66 providedin FIG. 6. The
`first radiating output signal transmitted from inductor L. is
`shown as voltage waveform 62, while the second radiating
`output signal transmitted from inductor L, is depicted as
`voltage waveform 64. Voltage waveforms 62 and 64 are
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`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 therefore 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 ofthe present
`invention.
`
`Single radiating output signal 66 in one embodiment has
`a frequency of approximately 315 MHz. Additionally, the
`outputs from both inductor L, and inductor L, 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 buffered 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 (“SAW”) device, and the resonating
`frequency preferably falls within the radio frequency (“RF”)
`spectrum. It should be obviousto one of ordinary skill in the
`art, however, that other components, such as a bulk acoustic
`wave (“BAW”) 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 ofordinary skill in the art that
`alternate oscillator designs may be realized while still
`achieving the advantages of the present invention. To pro-
`vide a balanced design, the outputs