Oscillator and transmitter arrangement for power specific applications having parasitic impedances

A transmitter system for transmitting an output signal having an output level and a signal to noise ratio. The transmitter system comprises a balanced oscillator comprised of a resonator for generating a reference signal, and for creating a parasitic impedance. Moreover, the balanced oscillator comprises a first oscillator comprising a first amplifier for amplifying the reference signal, and a first feedback circuit for generating a first oscillating output signal in response to the reference signal amplified by the first amplifier. Similarly, the balanced oscillator comprises a second oscillator comprising a second amplifier for amplifying said reference signal, and a second feedback circuit for generating a second oscillating output signal in response to the reference signal amplified by the second amplifier. The transmitter system additionally comprises an antenna comprising the parasitic impedance created by the resonator for radiating the output signal corresponding with the first and second oscillating output signals to decrease the output level while increasing the signal to noise ratio.

FIELD OF THE OF INVENTION 
This invention relates generally to radio frequency ("RF") transmitters 
and, more particularly, to a balanced oscillator and transmitter 
arrangement for power specific applications. 
BACKGROUND OF THE INVENTION 
Compact radio frequency ("RF") transmitters are widely employed in 
connection with remote signal communication systems. Compact transmitters 
are commonly used for remotely controlling automatic garage door systems, 
electronic sound systems, televisions and VCRs. In the automotive 
industry, compact transmitters are commonly used in remote keyless entry 
systems to provide remote control access to a vehicle, as well as 
controlling other vehicular functions such as alarm system features, trunk 
release, for example. Ideally, compact hand held transmitters are battery 
operated, energy efficient and intended to accommodate a compact 
enclosure. 
In one known compact remote system design, the 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 control signal to control a function or feature of 
the system. 
Currently, a number of compact remote RF transmitters employ a single 
oscillator system for providing a local oscillation signal are known. In 
light of their cost and simplicity, single oscillator circuits have been 
the transmitter component of choice in automotive, remote controlled, 
keyless entry systems. 
Single oscillator systems are well suited for the RF signal transmission 
applications of a remote keyless entry system. However, these known single 
oscillator designs have several limitations regarding power output in 
particular applications. Traditional single oscillators, moreover, are 
overly sensitive to unwanted parasitic impedances created by the grasp of 
a user's hand on the transmitter's housing, the housing itself or the 
material to which the transmitter is fixedly adjoined, such as an 
automobile headliner or visor. This sensitivity is attributable to the 
additional impedance created by these parasitic effects which reduce the 
amount of transmitted energy towards the receiver due to the limited power 
available from these known single oscillator designs. In certain 
environments, such as those dictated by the European market, an output 
signal with a higher signal to noise ratio, and relatively greater power 
strength is required. In other applications, the remote keyless entry 
("RKE") systems; requirements driven by the international customer 
necessitate a low power design. In powering down the known balanced 
oscillator designs, the gain margin is reduced to the point where the 
small reductions in the gain of the transistors or output tank center 
frequency prevent the overall operation of the oscillation of the circuit. 
Thus, too much power would be radiated for particular markets, such as 
Japan, by providing a minimally operational balanced oscillator, and in 
other markets, too little power would be generated by traditional means. 
In view of these problems, a demand exist for an oscillator circuit for use 
in a transmitter having a diminished power output. A need further exists 
for an oscillator circuit having an increased signal to noise ratio. 
SUMMARY OF THE INVENTION 
The primary advantage of the present invention is to overcome the 
limitations of the prior art. 
In order to achieve the advantages of the present invention, a transmitter 
system for transmitting an output signal having an output level and a 
signal to noise ratio is disclosed. The transmitter system comprises a 
balanced oscillator comprised of a resonator for generating a reference 
signal, and for creating a parasitic impedance. Moreover, the balanced 
oscillator comprises a first oscillator comprising a first amplifier for 
amplifying the reference signal, and a first feedback circuit for 
generating a first oscillating output signal in response to the amplified 
reference signal amplified by the first amplifier. Similarly, the balanced 
oscillator comprises a second oscillator comprising a second amplifier for 
amplifying said reference signal, and a second feedback circuit for 
generating a second oscillating output signal in response to the amplified 
reference signal amplified by the second amplifier. The transmitter system 
additionally comprises an antenna comprising the parasitic impedance 
created by the resonator for radiating the output signal corresponding 
with the first and second oscillating output signals to decrease the 
output level while increasing the signal to noise ratio. 
In a further embodiment of the present invention, the transmitter system 
comprises a resonator interface having a lead, wire, trace or connector 
providing the parasitic impedance which forms the antenna for radiating 
the output signal. 
In still another embodiment of the present invention, the transmitter 
system comprises a filter for phase shifting the output signal comprised 
of an inductor and a filter parasitic impedance. 
In yet another embodiment of the present invention, a transmitter circuit 
for transmitting an output signal having a singular frequency is detailed. 
The transmitter circuit comprises an output impedance and a buffered 
oscillator. The buffer oscillator comprises a resonator for generating a 
reference signal, an amplifier coupled with the resonator for amplifying 
the reference signal, a first resonant tank for generating an oscillating 
output signal in response to the amplified reference signal, and a buffer 
circuit for buffering the oscillating output signal. Moreover, the 
transmitter circuit comprises an antenna for radiating the output signal 
corresponding with the oscillating output signal.

It should be emphasized that the drawings of the instant application are 
not to scale but are merely schematic representations 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 EMBODIMENTS 
Referring FIG. 1, a block diagram of a balanced oscillator and transmitter 
system 10 is illustrated according to the preferred embodiment of the 
present invention. System 10 comprises a balanced oscillator having a 
resonator 12 for generating a reference signal. Preferably, resonator 12 
comprises a surface acoustic wave ("SAW") device. However, in an alternate 
embodiment, resonator 12 is realized by a bulk acoustic wave ("BAW") 
device. 
Further, the balanced oscillator comprises a first and a second oscillator, 
18 and 24, each of which are coupled to resonator 12 by means of an 
interface. This interface comprises a lead, wire, trace, socket or 
connector to facilitate coupling with resonator 12 and to enable both 
oscillators 18 and 24 to receive the reference signal generated by the 
resonator. Each oscillator interface characteristically comprises a 
parasitic impedence, as shown by parasitic impedances 14 and 16. 
First oscillator 18 comprises an amplifier 22 for amplifying an input 
corresponding with the reference signal provided by resonator 12. 
Additionally, oscillator 18 comprises a first feedback circuit 20 for 
generating a first oscillating signal in response to the output of 
amplifier 22. To that end, first feedback circuit 20 is coupled with 
amplifier 22 and preferably comprises a pair of capacitors. Moreover, 
amplifier 22 is coupled with a biasing circuit 30. 
Similarly, second oscillator 24 comprises an amplifier 28 for amplifying an 
input corresponding with the reference signal provided by resonator 12. 
Second oscillator 24 also comprises a second feedback circuit 26 which is 
also preferably realized by two capacitors. Feedback circuit 26 is coupled 
with amplifier 28 for generating a second oscillating signal in response 
to output of amplifier 28. Amplifier 28 is also coupled with biasing 
circuit 30. 
To provide a balanced design, the outputs of both oscillators 18 and 24 are 
180 degrees out of phase with one another, yet equal in magnitude. It 
should be noted that while both oscillators 18 and 24 preferably comprise 
identical functional components, alternate oscillator designs which 
achieve the advantages of the present invention may be apparent to one of 
ordinary skill in the art. 
System 10 moreover comprises an antenna which in turn preferably comprises 
parasitic impedances 14 and 16. These parasitic elements 14 and 16 
functionally operates to radiate the balanced oscillator output signal. By 
utilizing this system design, the signal level of the balanced oscillator 
output signal radiated by antenna is substantially lower power than other 
oscillator designs employing inductors or the like to radiate energy 
because of the reduced loop area required for the current flow and the 
limiting inductive effect of the parasitic impedance. Furthermore, with 
respect to the fundamental and harmonic components of the output signal, 
the proportionality of the reduction of the signal power is relatively 
equal. Thus, the signal to noise ratio of the resultant balanced 
oscillator output signal is substantially enhanced. It should be apparent 
that this embodiment is ideal for particular environments where a lower 
power, high signal to noise ratio output signal is required, though 
applications may be apparent to one of ordinary skill. 
Referring to FIG. 2, a preferred circuit realization 40 of the preferred 
embodiment of the present invention is depicted. Circuit 40 comprises a 
first and second oscillator. Both oscillators are balanced with respect to 
one another and share an oscillating current signal I. Circuit 40 
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 40 comprises a balanced 
oscillator configuration having two independent oscillator circuits for 
producing a local oscillation signal. The first and second oscillator 
circuits each comprise a first and second transistor, Q.sub.1 and Q.sub.2, 
respectively, and are both coupled with a first resonator device 32 
positioned therebetween. Resonator device 32 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, Q.sub.1 and Q.sub.2, are each preferably 
realized by a bipolar junction transistor ("BJT"). Alternatives, however, 
such as a heterojunction bipolar transistor ("HBT") or a field effect 
transistor ("FET"), should be apparent to one of ordinary skill in the 
art. According to a further embodiment, transistors Q.sub.1 and Q.sub.2 
are each MMBTH10 type bipolar transistors. 
Transistors Q.sub.1 and Q.sub.2 each operate as an amplification stage to 
provide a unity loop gain for steady state operations. First transistor 
Q.sub.1 comprises a base, a collector, and emitter, Q.sub.1b, Q.sub.1c, 
and Q.sub.1e, respectively. Likewise, second transistor Q.sub.2 comprises 
a base, a collector, and emitter, Q.sub.2b, Q.sub.2c, and Q.sub.2e, 
respectively. Transistors Q.sub.1 and Q.sub.2 each have resistors, R.sub.1 
and R.sub.2, respectively, which are coupled between Q.sub.1e and 
Q.sub.2e, respectively, and a ground node. Moreover, transistors Q.sub.1 
and Q.sub.2 are each configured as a tuned circuit having positive 
feedback. It should be understood by one of ordinary skill in the art that 
various other transistor oscillator configurations may be substituted into 
the above arrangement to achieve the same functional purpose. 
Resonator device 32 is coupled between a pair of nodes each comprising the 
base terminals Q.sub.1b and Q.sub.2b of transistors Q.sub.1 and Q.sub.2, 
respectively, via resonator output lines 32a and 32b. By this design, each 
of the outputs lines, 32a and 32b, of resonator 32 are coupled with a 
respective amplifier stage. Thus, first output line 32a is coupled with 
transistors Q.sub.1, while second output line 32b is coupled with 
transistors Q.sub.2 to enable the reference signal created by resonator 32 
to be amplified. To provide a balanced design, as desired in the preferred 
embodiment, the outputs of both oscillators are 180 degrees out of phase 
with one another, yet equal in magnitude. 
Resonator 32 may comprise an array of metallic fingers formed on a 
piezoelectric substrate. Resonator 32 advantageously operates to stabilize 
oscillations of the carrier signal. Resonator 32 preferably comprises a 
surface acoustic wave ("SAW") device. However, according to a further 
embodiment, resonator 32 is a RO2073 SAW resonator manufactured and sold 
by RF Monolithics, Incorporated. Yet in still another embodiment, 
resonator 32 comprises a bulk acoustic wave ("BAW") device. 
Each oscillator of circuit 40 further comprises a feedback circuit. Each 
feedback circuit comprises a resonating circuit section which in turn 
preferably comprises a capacitor pairing and one half of resonator 32. The 
first capacitor pairing, C.sub.1 and C.sub.2, are employed to functionally 
generate a first oscillating output signal in response to the reference 
signal amplified by the transistor Q.sub.1. Here, capacitor C.sub.1 is 
coupled at the node comprising Q.sub.1b and first output line 32a, while 
capacitor C.sub.2 is coupled to a node comprising a second end of 
capacitor C.sub.1, and node coupling Q.sub.1e with resistor R.sub.1. 
Similarly, the second capacitor pairing, C.sub.3 and C.sub.4, and one half 
of resonator 32 generate a second oscillating output signal in response to 
the reference signal amplified by the transistor Q.sub.2 Capacitor C.sub.3 
is coupled at the node comprising Q.sub.2b and second output line 32b, 
while capacitor C.sub.4 is coupled to a node comprising a second end of 
capacitor C.sub.3, and node coupling Q.sub.2e with resistor R.sub.2. 
Capacitor pairings C.sub.1 and C.sub.2, as well as C.sub.3 and C.sub.4 are 
also incorporated so as to establish a voltage divider network for each 
respective oscillator. 
Furthermore, circuit 40 also comprises a DC bias voltage input source 
B.sub.1, typically 3V, along with an impedance network which are coupled 
with both first and second oscillators. With respect to the first 
oscillator circuit, the positive lead of input source B.sub.1 is coupled 
to Q.sub.1c. Likewise, the positive lead of input source B.sub.1 is also 
coupled to a node which includes Q.sub.2c in the second oscillator 
circuit. The negative lead, it should be noted, of input source B.sub.1 is 
coupled to ground. 
Both first and second oscillator circuits receive a data input signal, 
V.sub.DATA, for encoding an RF carrier signal, by means of a resistor 
network which forms a divider circuit. The data input signal, V.sub.DATA, 
encodes a carrier signal with a modulation scheme to provide information 
on the carrier signal. The preferred modulation format is amplitude 
modulation ("AM"), though pulse width modulation or frequency shift key 
modulation, and others may be easily substituted by one of ordinary skill 
in the art. The information provided on the carrier signal may control 
and/or initiate various system operations, such as a door lock actuation 
mechanism, as well as the on/off operations of circuit 40. Application of 
data input signal V.sub.DATA may be initiated by manual control through an 
actuation mechanism such as, for example, a push-button pad, switch or 
other pulsed activation device. 
Data input signal, V.sub.DATA, feeds directly to a node comprising a first 
end of resistors R.sub.4 and R.sub.6. The second end of resistor R.sub.4 
is coupled to a node including interface 32a of resonator 32, Q.sub.1b, 
first capacitor C.sub.1, and a resistor R.sub.5. The second end of 
resistor R.sub.6, likewise, is coupled to a node which includes interface 
32b of resonator 32, Q.sub.1b, capacitor C.sub.3, and a resistor R.sub.5. 
Resistors R.sub.3 and R.sub.4, as well as R.sub.5 and R.sub.6 are 
incorporated so as to establish a divider network for each respective 
oscillator. The second ends of the resistor R.sub.3 and R.sub.5 are 
coupled to a ground node along with the negative lead of input source 
B.sub.1. Resistor R.sub.3 is further coupled with second capacitor 
C.sub.2, while resistor R.sub.5 is further coupled with second capacitor 
C.sub.4. 
Circuit 40 additionally comprises an antenna for radiating the output 
signal corresponding with the first and second oscillating output signals 
in response to the commonly shared oscillating current signal I. The 
antenna is preferably realized by the parasitic impedances created by 
interfaces, 32a and 32b, of resonator 32. Interfaces, 32a and 32b comprise 
a lead, wire, trace, socket or connector. Parasitic impedances 32a and 32b 
each operate as an antenna for transmitting and radiating an 
electromagnetic field exhibiting the oscillating signal with the 
predetermined carrier frequency. Energy is efficiently stored in 
capacitors C.sub.1, C.sub.2, C.sub.3 and C.sub.4 to enhance radiation 
efficacy by reducing the amount of energy that may otherwise be required 
for each cycle of transistors Q.sub.1 and Q.sub.2. 
It should be noted that incorporating the above circuit design several 
benefits are derived. By employing this configuration utilizing parasitic 
impedances 32a and 32b as the antenna, the packaging of the resultant 
circuit 40 is substantially reduced. This is in part because a 
specifically realized antenna, such as an inductor, is not required to 
facilitate transmission. As such, the current flow between both 
oscillators requires a reduced path which thereby provides the basis for 
an electromagetic radiation having reduced field strength. By utilizing 
this design, therefore, the signal level of the balanced oscillator output 
signal radiated by antenna is substantially low power because of the 
reduced loop area required for the current flow and the limiting inductive 
effect of the parasitic impedance. Furthermore, with respect to the 
fundamental and harmonic components of the output signal, the 
proportionailty of the reduction of the signal power is relatively equal. 
Thus, the signal to noise ratio of the resultant balanced oscillator 
output signal is substantially enhanced. It should be apparent that this 
embodiment is ideal for particular environments where a lower power, high 
signal to noise ratio output signal is required, though applications may 
be apparent to one of ordinary skill. 
Referring to FIG. 3, a block diagram of a balanced oscillator and 
transmitter system 50 according to a further embodiment of the present 
invention. System 50 comprises a balanced oscillator having a resonator 52 
for generating a reference signal. Preferably, resonator 52 comprises a 
surface acoustic wave ("SAW") device. However, in an alternate embodiment, 
resonator 52 is realized by a bulk acoustic wave ("BAW") device. 
Further, the balanced oscillator comprises a first and a second oscillator, 
58 and 64, each of which are coupled to resonator 52 by means of an 
interface. This interface comprises a lead, wire, trace, socket or 
connector to facilitate coupling with resonator 52 and to enable both 
oscillators 58 and 64 to receive the reference signal generated by the 
resonator. Each oscillator interface characteristically comprises a 
parasitic impedence, as shown by parasitic impedances 54 and 56. 
First oscillator 58 comprises an amplifier 62 for amplifying an input 
corresponding with the reference signal provided by resonator 52. 
Additionally, oscillator 58 comprises a first feedback circuit 60 for 
generating a first oscillating signal in response to the output of 
amplifier 62. To this end, first feedback circuit 60 is coupled with 
amplifier 62 and preferably comprises two capacitors. Moreover, amplifier 
62 is coupled with a biasing circuit 70. 
Similarly, second oscillator 64 comprises an amplifier 68 for amplifying an 
input corresponding with the reference signal provided by resonator 52. 
Second oscillator 64 also comprises a second feedback circuit 66 which is 
coupled with amplifier 68. Second feedback circuit 66 generates a second 
oscillating signal in response to the output of amplifier 68 and 
preferably comprises two capacitors. Amplifier 62 is also coupled with 
biasing circuit 70. It should be noted that while both oscillators 58 and 
64 preferably comprise identical functional components, alternate 
oscillator designs which achieve the advantages of the present invention 
may be apparent to one of ordinary skill in the art. 
To provide a balanced design, the outputs of both oscillators 58 and 64 are 
180 degrees out of phase with one another, yet equal in magnitude. This 
feature is further facilitated by the inclusion of a filter 74. Filter 74 
provides phase shifting of the output signal transmitted by the antenna 
and is coupled between first oscillator 58 and second oscillator 64. 
System 50 moreover comprises an antenna composed of several elements. 
First, the antenna comprises parasitic impedances 54 and 56. The antenna 
is further realized by filter 74 comprising impedance which includes any 
of the following: a fixed inductor, a fixed capacitor, and/or a trace 
parasitic. Parasitic elements 54 and 56 in conjunction with filter 74 
functionally operate to radiate the balanced oscillator output signal. 
By utilizing this system design, the signal level of the balanced 
oscillator output signal radiated by antenna is substantially higher 
power, relative to the preferred embodiment of FIGS. 1 and 2, than other 
oscillator designs employing inductors or the like to radiate energy 
because of the reduced loop area required for the current flow and the 
limiting inductive effect of the parasitic impedance. This distinction 
over the preferred embodiment is attributable to incorporation of filter 
74. Furthermore, with respect to the fundamental and harmonic components 
of the output signal, the proportionality of the reduction of the signal 
power is relatively equal. Thus, the signal to noise ratio of the 
resultant balanced oscillator output signal is substantially enhanced. It 
should be apparent that this embodiment is ideal for particular 
environments where a higher power, high signal to noise ratio output 
signal is required, though applications may be apparent to one of ordinary 
skill. 
Referring to FIG. 4, a circuit realization 100 of the embodiment of FIG. 3. 
Circuit 100 comprises a first and second oscillator. Both oscillators are 
balanced with respect to one another and share an oscillating current 
signal I. Circuit 100 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 100 comprises a balanced 
oscillator configuration having two independent oscillator circuits for 
producing a local oscillation signal. The first and second oscillator 
circuits each comprise a first and second transistor, Q.sub.11 and 
Q.sub.12, respectively, and are both coupled with a first resonator device 
132 positioned therebetween. Resonator device 132 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, Q.sub.11 and Q,.sub.12, are realized by a 
bipolar junction transistor ("BJT"). Alternatives, however, such as a 
heterojunction bipolar transistor ("HBT") or a field effect transistor 
("FET"), should be apparent to one of ordinary skill in the art. According 
to a further embodiment, transistors Q.sub.11 and Q.sub.12 are each 
MMBTH10 type bipolar transistors. 
Transistors Q.sub.11 and Q.sub.12 each operate as an amplification stage to 
provide a unity loop gain for steady state operations. First transistor 
Q.sub.11 comprises a base, a collector, and emitter, Q.sub.11b, Q.sub.11c 
and Q.sub.11b, respectively. Likewise, second transistor Q.sub.12 
comprises a base, a collector, and emitter Q.sub.12b, Q.sub.12c, and 
Q.sub.12e, respectively. Transistors Q.sub.11 and Q.sub.2 each have 
resistors, R.sub.11 and R.sub.12, respectively, which are coupled between 
Q.sub.11e and Q.sub.12e, respectively, and a ground node. Moreover, 
transistors Q.sub.11 and Q.sub.12 are each configured within a circuit 
having feedback. It should be understood by one of ordinary skill in the 
art that various other transistor oscillator configurations may be 
substituted into the above arrangement to achieve the same functional 
purpose. 
Resonator device 132 is coupled between a pair of nodes each comprising the 
base terminals Q.sub.11b and Q.sub.12b of transistors Q.sub.11 and 
Q.sub.12, respectively, via resonator output lines 132a and 132b. By this 
design, each of the output lines, 132a and 132b, of resonator 132 are 
coupled with a respective amplifier stage. Thus, first output lines 132a 
is coupled with transistors Q.sub.11, while second output line 132b is 
coupled with transistors Q.sub.12 to enable the reference signal created 
by resonator 132 to be amplified. To provide a balanced design, as desired 
in the preferred embodiment, the outputs of both oscillators are 180 
degrees out of phase with one another, yet equal in magnitude. 
Resonator 132 may comprise an array of metallic fingers formed on a 
piezoelectric substrate. Resonator 132 advantageously operates to 
stabilize oscillations of the carrier signal. Resonator 132 preferably 
comprises a surface acoustic wave ("SAW") device. However, according to a 
further embodiment, resonator 132 is a RO2073 SAW resonator manufactured 
and sold by RF Monolithics, Incorporated. Yet in still another embodiment, 
resonator 132 comprises a bulk acoustic wave ("BAW") device. 
Each oscillator of circuit 100 further comprises a resonating tank circuit. 
Each resonating tank circuit preferably comprises a capacitor pairing and 
one half of the resonator 132. The first resonating tank circuit capacitor 
pair, C.sub.11 and C.sub.12, are employed to functionally generate a first 
oscillating output signal in response to the reference signal amplified by 
the transistor Q.sub.11. Here, capacitor C.sub.11 is coupled at the node 
comprising Q.sub.11b and first output line 132a, while capacitor C.sub.12 
is coupled to a node comprising a second end of capacitor C.sub.11, and 
node coupling Q.sub.11e with resistor R.sub.11. Similarly, second 
resonating tank circuit capacitor pair, C.sub.13 and C.sub.14, and one 
half the resonator 132 generate a second oscillating output signal in 
response to the reference signal amplified by the transistor Q.sub.12 
Capacitor C.sub.13 is coupled at the node comprising Q.sub.12b and second 
output line 132b, while capacitor C.sub.14 is coupled to a node comprising 
a second end of capacitor C.sub.13, and node coupling Q.sub.12e with 
resistor R.sub.12. Capacitor pairings C.sub.11 and C.sub.12, as well as 
C.sub.13 and C.sub.14 are also incorporated so as to establish a divider 
network for each respective oscillator. 
Furthermore, circuit 100 also comprises a DC bias voltage input source 
B.sub.11, typically 3V, along with an impedance network which are coupled 
with both first and second oscillators. With respect to the first 
oscillator circuit, the positive lead of voltage input source B.sub.1 is 
coupled to Q.sub.11c. Likewise, the positive lead of voltage input source 
B.sub.11 is also coupled to a node which includes Q.sub.12c in the second 
oscillator circuit. The negative lead, it should be noted, of voltage 
input source B.sub.11 is coupled to ground. 
Both first and second oscillator circuits receive a data input signal, 
V.sub.DATA, for encoding an RF carrier signal, by means of a resistor 
network which forms a voltage divider circuit. The data input signal, 
V.sub.DATA, encodes a carrier signal with a modulation scheme to provide 
information on the carrier signal. The preferred modulation format is 
amplitude modulation ("AM"), though pulse width modulation or frequency 
shift key modulation, and others may be easily substituted by one of 
ordinary skill in the art. The information provided on the carrier signal 
may control and/or initiate various system operations, such as a door lock 
actuation mechanism, as well as the on/off operations of circuit 100. 
Application of data input signal V.sub.DATA may be initiated by manual 
control through an actuation mechanism such as, for example, a push-button 
pad, switch or other pulsed activation device. 
Data input signal, V.sub.DATA, feeds directly to a node comprising a first 
end of resistors R.sub.14 and R.sub.16. The second end of resistor 
R.sub.14 is coupled to a node including interface 132a of resonator 132, 
Q.sub.11b, first capacitor C.sub.11, and a resistor R.sub.13. The second 
end of resistor R.sub.16, likewise, is coupled to a node which includes 
interface 132b of resonator 132, Q.sub.12b, capacitor C.sub.13, and a 
resistor R.sub.15. Resistors R.sub.13 and R.sub.14 as well as R.sub.15 and 
R.sub.16 are incorporated so as to establish a voltage divider network for 
each respective oscillator. The second ends of the resistor R.sub.13 and 
R.sub.15 are coupled to a ground node along with the negative lead of 
voltage input source B.sub.11. Resistor R.sub.13 is further coupled with 
second capacitor C.sub.12, while resistor R.sub.15 is further coupled with 
second capacitor C.sub.14. It should be noted that in the preferred 
embodiment, the data input section is designed to receive amplitude 
modulation ("AM") data, while in an alternate embodiment, the data input 
section is preferably designed to receive frequency shift key ("FSK") 
modulation data. 
Furthermore, circuit 100 additionally comprises a filter for phase shifting 
the circuit's resultant output signal. As such, the filter is coupled 
between Q.sub.11e and Q.sub.12e of transistors Q.sub.11 and Q.sub.12, 
respectively. It should be noted that the following elements ideally are 
mounted on a printed circuit board ("PCB") to realize certain benefits, 
including specific trace parasitics characteristics. 
The filter, as illustrated in FIG. 4, comprises a first and second fixed 
capacitor, C.sub.20 and C.sub.22, which are directly coupled to Q.sub.11e 
and Q.sub.12e, respectively, on one end, and to ground on the other end. 
Also coupled to the node coupling Q.sub.11e, and capacitor C.sub.20, as 
well as other elements, is a first fixed inductor L.sub.1. The other end 
of first inductor L.sub.1 is coupled to a first capacitance, C.sub.PCB1, 
as well as a first conductive trace parasitic inductance, L.sub.PCB. The 
further end of first capacitance, C.sub.PCB1, is then coupled to ground. 
Moreover, the other end of first trace parasitic inductance, L.sub.PCB, is 
coupled to a second capacitance, C.sub.PCB2, which like first capacitance, 
C.sub.PCB1, is also coupled to ground. Coupled between the non-ground ends 
of both second capacitance C.sub.PCB2 and fixed capacitor C.sub.22 is a 
second inductor, L.sub.2. The node wherein fixed capacitor C.sub.22 and 
second second inductor L.sub.2 adjoin is further coupled with Q.sub.12e of 
transistor Q.sub.12. It should be noted that first and second capacitances 
C.sub.B1, and C.sub.B2, are preferably realized by capacitors. However, 
alternately, first and second capacitances, C.sub.PCB1, and C.sub.PCB2, 
preferably may be conductive traces that created parasitic capacitances. 
Circuit 100 additionally comprises an antenna for radiating the output 
signal corresponding with the first and second oscillating output signals 
in response to the commonly shared oscillating current signal I. The 
antenna is realized by the parasitic impedances created by interfaces, 
132a and 132b, of resonator 132, as well as the filter elements, including 
first and second fixed capacitor, C.sub.20 and C.sub.22, first and second 
fixed inductors, L.sub.1 and L.sub.2, first and second trace parasitic 
capacitances, C.sub.PCB1 and C.sub.PCB2, and first trace parasitic 
inductance, L.sub.PCB. As detailed herein, Interfaces, 132a and 132b 
comprise a lead, wire, trace, socket or connector. Parasitic impedances 
132a and 132b, and the filter components--first and second fixed 
capacitor, C.sub.20 and C.sub.22, first and second fixed inductors, 
L.sub.1 and L.sub.2, first and second trace parasitic capacitances, 
C.sub.PCB1 and C.sub.PCB2, and first trace parasitic inductance, L.sub.PCB 
--each operate as an antenna for transmitting and radiating an 
electromagnetic field exhibiting the oscillating signal with the 
predetermined carrier frequency. Energy is efficiently stored in 
capacitors C.sub.11, C.sub.12, C.sub.13 and C.sub.14 to enhance radiation 
efficacy by reducing the amount of energy that may otherwise be required 
for each cycle of transistors Q.sub.11 and Q.sub.12. 
It should be noted that incorporating the above circuit design several 
benefits are derived. By employing this configuration utilizing parasitic 
impedances 132a and 132b and the filter components--first and second fixed 
capacitor, C.sub.20 and C.sub.22, first and second fixed inductors, 
L.sub.1 and L.sub.2, first and second trace parasitic capacitances, 
C.sub.PCB1 and C.sub.PCB2, and first trace parasitic inductance, L.sub.PCB 
--as the antenna, the signal level of the balanced oscillator output 
signal radiated by antenna is substantially higher power than the 
preferrred embodiment because of the increased loop area required for the 
current flow and the limiting inductive effect of the parasitic impedance 
in conjunction with the filter elements. Furthermore, with respect to the 
fundamental and harmonic components of the output signal, the 
proportionality of the reduction of the signal power is relatively equal. 
Thus, the signal to noise ratio of the resultant balanced oscillator 
output signal is substantially enhanced. It should be apparent that this 
embodiment is ideal for particular environments where a higher power, high 
signal to noise ratio output signal is required, though applications may 
be apparent to one of ordinary skill. 
Referring to FIG. 5, a further alternate embodiment is illustrated 
depicting a buffered oscillator and transmitter circuit 160. Circuit 160 
comprises three functional stages: an oscillator 162, a buffer 164 and an 
output system 166. Circuit 160 described herein is particularly applicable 
with automotive remote keyless entry systems. Other applications, however, 
are clearly foreseeable to one of ordinary skill in the art. 
According to a more detailed description, oscillator 162 comprises a 
transistor Q.sub.20 configuration and an input resonant tank circuit. The 
tank circuit comprises a resonator 172, such as a surface acoustic wave 
("SAW") device, a pair of feedback capacitors, C.sub.26 and C.sub.27, as 
well as a capacitor C.sub.29 for providing a large capacitance to maintain 
a constant DC voltage. Further, the oscillator also includes a number of 
biasing resistors to facilitate the proper operation of transistor 
Q.sub.20. Transistor Q.sub.20 functionally provides a unity loop gain for 
steady state operations. 
Structurally, transistor Q.sub.20 comprises a base, Q.sub.20b, collector, 
Q.sub.20c, and an emitter Q.sub.20e. Q.sub.20b is coupled with a node 
comprising surface acoustic wave resonator 172 and feedback capacitor 
C.sub.27, and collector Q.sub.20c is coupled with a DC bias voltage input 
source B.sub.111, while Q.sub.20e is coupled to ground through a first end 
of resistor R.sub.24. Additionally, feedback capacitor C.sub.27 is coupled 
to another node comprising Q.sub.20e, the first end of resistor R.sub.24, 
and feedback capacitor C.sub.26. Feedback capacitor C.sub.26, moreover, is 
coupled in parallel with resistor R.sub.24. The second ends of capacitor 
C.sub.26 and resistor R.sub.24 are both coupled to ground. Capacitor 
C.sub.29 is coupled between ground and DC bias voltage input source 
B.sub.111. 
Transistor Q.sub.20c is coupled to the voltage input source B.sub.111 to 
receive a DC bias input B.sub.111, typically 3V. Oscillator 162 also 
receives a data input signal V.sub.DATA for encoding the RF carrier 
signal, by means of a resistor network forming a voltage divider circuit. 
Data input, V.sub.DATA, encodes the carrier signal with a modulation 
scheme to provide information on the carrier signal. The preferred 
modulation format is amplitude modulation ("AM"), though pulse width 
modulation for example, and others may be easily substituted by one of 
ordinary skill in the art. The information provided on the carrier signal 
may control and/or initiate various system operations, such as a door lock 
actuation mechanism, as well as the on/off operations of circuit 160. 
Application of data input sign V.sub.DATA may be initiated by manual 
control through an actuation mechanism such as, for example, a push-button 
pad, switch or other pulsed activation device. By this configuration, 
transistor Q.sub.20, acting as an amplifier, in combination with the 
resonating tank circuit, generates a oscillating output signal. 
Transistors, Q.sub.20 and Q.sub.21, each preferably comprise a bipolar 
junction transistor ("BJT"). Alternatives, however, such as a 
heterojunction bipolar transistor ("HBT"), should be apparent to one of 
ordinary skill in the art. According to a further embodiment, transistors 
Q.sub.20 and Q.sub.21 are each MMBTH10 type bipolar transistors. 
Resonator device 172 is coupled between base 176 of transistor Q.sub.20 and 
ground. Resonator 172 advantageously operates to stabilize oscillations of 
the carrier signal. Resonator device 172 preferably comprises a series 
resonant input tank circuit surface acoustic wave ("SAW") device. However, 
according to a further embodiment, SAW resonator 172 is a RO2073 SAW 
resonator manufactured and sold by RF Monolithics, Incorporated. 
Buffer 164 functionally minimizes the effects of parasitic impedances 
created by a user's hand when grasping an RKE fob, by the filler plastics 
created by the RKE's housing, as well as the headliner or other interior 
materials in the event the fob is fixably mounted within the interior of 
an automobile. To realize this benefit, buffer 164 comprises a transistor 
Q.sub.21, as well as a buffer resonant tank of inductor L.sub.9 and 
capacitor C.sub.28. Transistor Q.sub.21 comprises a base, Q.sub.21b, an 
emitter, Q.sub.20e, and a collector, Q.sub.20c. Buffer 164 is coupled with 
oscillator. 162 at two nodes. First, buffer 164 receives a DC bias input 
from B.sub.111 at Q.sub.20c, wherefrom oscillator 162 is also biased. 
Buffer 164 is also coupled with amplifier 162 along Q.sub.20e of 
transistor Q.sub.20 and base of transistor Q.sub.21. 
Output stage 166 is coupled with buffer 164 for the purpose of transmitting 
the oscillating signal. The output of buffer 164, having an oscillating 
output at the resonant frequency, is transmitted across to stage 166. 
Stage 166 additionally comprises a matching device 174 for matching the 
output impedance of the circuit. Finally, output stage 166 comprises an 
antenna in the form of inductor L.sub.10 for transmitting the resultant 
oscillating signal. 
It should be noted that the oscillator and transmitter circuits of the 
present invention may be mounted within a compact enclosure and 
advantageously employed to transmit control signals, especially for use in 
connection with a remote controlled keyless entry system. For such an 
application, the user may manually activate the V.sub.DATA input to encode 
the carrier signal with selected information. The carrier signal and 
modulating information are then radiated from the transmitter circuits by 
means of the output tanks. A receiver which is generally mounted within a 
vehicle will receive the radiating signal, decode the modulating 
information and initiate and/or execute the selected operation such as 
locking or unlocking a vehicle door, activating or deactivating an alarm 
system, for example. In contrast to conventional approaches, these 
circuits advantageously achieve increased output power and maintain an 
efficient power usage therewith. 
Furthermore, it should also be apparent that the embodiments of the present 
invention may use various sized components which may be modified without 
departing from the invention. As one example, inductor L.sub.9 provides an 
inductance of approximately 40 nH. Capacitors C.sub.27 and C.sub.28 each 
may have a capacitance of approximately 4.7 pF, while capacitor C.sub.26 
has a capacitance of about 22 pF. Resistor R.sub.23 may have a resistance 
of about 15 k.OMEGA.. Resistor R.sub.22 may have a resistance of about 6.8 
k.OMEGA., while resistor R.sub.24 has a resistance of about 180 k.OMEGA.. 
While the particular invention has been described with reference to 
illustrative embodiments, this description is not meant to be construed in 
a limiting sense. It is understood that although the present invention has 
been described in a preferred embodiment, various modifications of the 
illustrative embodiments, as well as additional embodiments of the 
invention, will be apparent to persons skilled in the art upon reference 
to this description without departing from the spirit of the invention, as 
recited in the claims appended hereto. Thus, for example, it should be 
apparent to one ordinary skill in the art while the transmitter herein has 
been detailed as operating in the RF frequency range, other formats are 
available which would take full advantage of the present invention. 
Similarly, while bipolar junction transistors are described herein as one 
potential realization of an amplifier, other designs are available which 
utilize other transistor types, such as field effect transistors ("FETs"), 
JFETs and MOSFETs, for example, known to one of ordinary skill in the art. 
Moreover, the antenna of the present invention may also be realized by a 
patch antenna design, as would be apparent to one of ordinary skill in the 
art in view of the present invention. It is therefore contemplated that 
the appended claims will cover any such modifications or embodiments as 
fall within the true scope of the invention. 
All of the U.S. Patents cited herein are hereby incorporated by reference 
as if set forth in their entirety.