Tire pressure monitoring system with low frequency initiation approach

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application Ser. No. 60/360,762 filed Mar. 1, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for an initiator oscillator for use in tire pressure monitoring systems.

2. Background Art

It is known in the automotive industry to provide for wireless monitoring of vehicle tire parameters, particularly tire pressure. In such tire pressure monitoring systems, tire pressure sensors and radio frequency (RF) transmitters including initiators that have high frequency pre-driver and signal conditioning circuitry. In each tire, at least one signal that corresponds to the tire pressure sensed by the tire pressure sensor is processed by the high frequency pre-driver and signal conditioning circuitry (e.g., initiator oscillator circuitry) prior to being transmitted by the transmitter through an antenna to a receiver/controller located on the vehicle. The tire pressure information delivered to the receiver/controller by the RF signals from the transmitters is subsequently conveyed to a vehicle operator or occupant, typically using a display unit. In such a fashion, tire pressure monitoring systems can help to improve vehicle safety. Exemplary tire pressure monitoring systems are described and shown in U.S. Pat. Nos. 6,112,587 and 6,034,597.

Some conventional approaches to initiator oscillators (or generators) as implemented in tire pressure monitoring systems use expensive microprocessors to achieve the desired oscillator frequency generation accuracy and data generation. Additionally, some conventional approaches to initiator generators as implemented in tire pressure monitoring systems use double-ended enable input circuitry. Conventional microprocessor controlled circuitry and double-ended circuitry can be expensive to implement.

Thus, there exists a need for a system and a method for a low frequency initiation generator (e.g., high frequency pre-driver and signal conditioning circuitry) for use in a tire pressure monitoring system that achieves the desired frequency accuracy at a lower cost than conventional microprocessor based approaches via a single enable input and an oscillator/divider integrated circuit having crystal accuracy.

SUMMARY OF THE INVENTION

The present invention provides a system and a method for a low frequency initiation generator (e.g., high frequency pre-driver and signal conditioning circuitry) for use in a tire pressure monitoring system that achieves the desired frequency accuracy at a lower cost than conventional microprocessor based approaches via a single enable input and an oscillator/divider integrated circuit having crystal accuracy.

According to the present invention, for use in a tire pressure monitoring system, an initiator generator is provided comprising an oscillator/divider configured to generate an output signal in response to a switched, regulated voltage. The output signal has a fundamental frequency and a gating frequency.

Also according to the present invention, for use in a tire pressure monitoring system, a method of generating an initiator output signal is provided, the method comprising generating the output signal at a fundamental frequency in response to a switched, regulated voltage, and gating the output signal at a gating frequency.

Further, according to the present invention, a reduced power consumption tire pressure monitoring system initiator generator is provided comprising a switching circuit, a regulator, and an oscillator/divider. The switching circuit may be configured to generate a switched, unregulated voltage in response to a supply voltage and an enable signal. The regulator may be configured to generate a switched, regulated voltage in response to the unregulated voltage. The oscillator/divider maybe configured to generate an output signal in response to the switched, regulated voltage. The output signal has a fundamental frequency and a gating frequency.

The above features, and other features and advantages of the present invention are readily apparent from the following detailed descriptions thereof when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a diagram of a pre-driver and signal conditioning circuit of the present invention; and

FIG. 2

is a detailed diagram of the pre-driver and signal conditioning circuit of FIG.

1

.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

With reference to the Figures, the preferred embodiments of the present invention will now be described in detail. As previously noted, it is known in the automotive industry to provide for wireless monitoring of vehicle tire parameters, particularly tire pressure. In such tire pressure monitoring systems, tire pressure sensors and radio frequency (RF) transmitters including initiators that have high frequency pre-driver and signal conditioning circuitry. In each tire, the tire pressure sensed by the tire pressure sensor is processed by the high frequency pre-driver and signal conditioning circuitry (e.g., initiator oscillator circuitry) prior to being transmitted by the transmitter through an antenna to a receiver/controller located on the vehicle. The tire pressure information delivered to the receiver/controller by the RF signals from the transmitters is subsequently conveyed to a vehicle operator or occupant, typically using a display unit.

Generally, the present invention provides a system and a method for a low frequency initiation generator (e.g., high frequency pre-driver and signal conditioning circuitry implemented as an initiator) for use in a tire pressure monitoring system that achieves the desired frequency accuracy at a lower cost than conventional microprocessor based or double-ended input approaches via a single enable input and an oscillator/divider circuit having crystal accuracy.

Referring to

FIG. 1

, a diagram illustrating a generator

100

in accordance with a preferred embodiment of the present invention is shown. The generator

100

may be configured as an oscillator/divider circuit. The generator

100

may be advantageously implemented as a pre-driver and signal conditioner (or initiator) for a vehicle tire pressure monitoring system. The generator

100

may be configured to generate an output signal having a fundamental frequency that is gated at a lower frequency than the fundamental frequency and switched on and off in response to an enable signal. The generator

100

generally presents the output signal to a driver circuit (not shown). The driver circuit may be implemented as a single transistor, an FET, or any appropriate high current and high voltage device to meet the design criteria of a particular application. The embodiment of the generator

100

illustrated in

FIGS. 1 and 2

may be advantageously implemented as an initiator for driving a differential FET current switch for powering a series RLC circuit for magnetic field generation in connection with a vehicle tire pressure monitoring system.

The generator

100

generally comprises a switching circuit (or block)

102

, a regulator circuit (or block)

104

, and an output circuit (or block)

106

. The output circuit

106

is generally implemented (or configured) as an oscillator/divider circuit.

The switching circuit

102

may have an input

110

that may receive a system voltage (e.g., BATT), an input

112

that may receive an enable signal (e.g., ENABLE), an input

114

that may receive a ground potential (e.g., GND), and an output

116

that may present a supply voltage (e.g., VCC). The system voltage BATT may be a battery voltage that is provided by a battery (i.e., an unregulated voltage source, not shown) that is configured to provide electrical power to the generator

100

.

The signal ENABLE may be a switching signal that switches the switching circuit

100

on (i.e., the signal ENABLE is asserted) when transmission of a signal (e.g., a tire pressure indication, not shown) generated in connection with the generator

100

is desired. The signal ENABLE is generally de-asserted when no signal transmission is desired. The generator

100

may, thus, conserve power (i.e., reduce power consumption) produced by the battery that provides the signal BATT. The supply voltage VCC is generally an unregulated or partially regulated voltage. For example, some transients on the signal BATT may be suppressed on the signal VCC. The switching circuit

102

generally switches the supply voltage VCC on and off in response to the assertion and de-assertion, respectively, of the signal ENABLE.

The regulator

104

may have an input

120

that may receive the signal VCC and an output

122

that may present a regulated supply voltage (e.g., VDD). The regulator

104

may be configured to present the regulated supply voltage VDD in response to the unregulated supply voltage VCC.

The oscillator/divider

106

may have an input

130

that may receive the supply voltage VDD and an output that may present a signal (e.g., OUT). The signal OUT generally has a fundamental frequency and is switched on an off (i.e., gated) at a gating frequency. The signal OUT is generally presented to additional circuitry (e.g., a driver circuit, not shown). In one example, the signal OUT may be implemented as an initiator signal for driving a differential FET current switch for powering a series RLC circuit for magnetic field generation in connection with a vehicle tire pressure monitoring system. The oscillator/divider

106

may be configured to present the signal OUT in response to the signal VDD.

Referring to

FIG. 2

, a detailed diagram of the generator

100

is shown. In one example, the switching circuit

102

comprises a varistor V

1

, a diode (or a transistor configured as a diode) D

1

, transistors Q

1

, Q

2

and Q

3

, capacitances (e.g., capacitors, transistors configured as capacitors, etc.) C

1

, C

2

, C

3

, and C

4

, and resistances (e.g., resistors) R

1

, R

2

, R

3

, R

4

, R

5

, R

6

and R

7

. The varistor V

1

is generally configured to provide transient suppression to the input signal BATT. The transistors Q

1

, Q

2

and Q

3

are generally implemented as bipolar junction transistors (BJTs).

The varistor V

1

may have a first terminal that may receive the supply voltage BATT and a second terminal that may receive the ground potential GND. The diode D

1

may have an anode terminal that may receive the supply voltage BATT and a cathode terminal that may be connected to a node that includes a collector of the transistor Q

1

, an emitter of the transistor Q

2

, and a first terminal of the resistor R

2

. The capacitance C

1

may have a first terminal that may receive the supply voltage BATT and a second terminal that may receive the ground potential GND.

The transistor Q

1

may have a base that may be connected to a first terminal of the capacitance C

2

and a first terminal of the resistor R

4

, and an emitter that may be connected to a first terminal of the resistor R

1

. The resistor R

1

may have a second terminal that may be connected to a node that includes a second terminal of the resistor R

2

, a first terminal of the resistor R

3

and a base of the transistor Q

2

. The transistor Q

2

may have a collector that may be connected to a first terminal of the capacitance C

4

. The supply voltage VCC is generally presented at the collector of the transistor Q

2

.

The signal EN may be presented to a node that includes a second terminal of the resistor R

4

, a first terminal of the capacitance C

3

, and first terminals of the resistors R

5

and R

6

. The transistor Q

3

may have a collector that may be connected to a second terminal of the resistor R

3

, a base that may be connected to a second terminal of the resistor R

6

and a first terminal of the resistor R

7

, and an emitter that may receive the ground potential GND. The capacitances C

2

, C

3

and C

4

, and the resistors R

5

and R

7

may each have a second terminal that may receive the ground potential GND. However, the switching circuit

102

may be implemented as any appropriate switching circuit to meet the design criteria of a particular application.

In one example, the regulator

104

comprises an integrated circuit (IC)

150

and capacitances C

5

and C

6

. The IC

150

is generally implemented as a voltage regulation circuit. In one example the IC

150

may be implemented as an LM-

317

. The IC

150

may have an input that may receive the supply voltage VCC, an input that may receive the ground potential GND, and output an output that may present the supply voltage VDD. The capacitances C

5

and C

6

may each have a first terminal that may be connected to the output of the IC

150

and a second terminal that may receive the ground potential GND. The capacitances C

5

and C

6

may be implemented as a single capacitance or as two or more capacitances. However, the regulator

104

may be implemented as any appropriate voltage regulation circuit to meet the design criteria of a particular application.

The oscillator/divider

106

generally comprises an IC

160

, an element X

1

, a transistor Q

4

, capacitances C

7

, C

8

, C

9

and C

10

, and resistors R

8

, R

9

, R

10

and R

11

. In one example, the IC

160

may be implemented as a 4060 14-stage ripple carry binary counter (e.g., a Fairchild Semiconductor™ CD4060BC, or the like). However, the IC

160

may be implemented as any appropriate IC or discrete components that may be configured as an oscillator/divider to meet the design criteria of a particular application. The element X

1

is generally implemented as an oscillator (e.g., a crystal oscillator, a ceramic resonator, etc.). The transistor Q

4

is generally implemented as a BJT.

In a standard configuration, the IC

160

may be implemented as a 16-lead IC. The IC

160

may have inputs

170

,

172

,

174

,

176

,

178

and

180

, and outputs

182

and

184

that may correspond to leads

16

,

10

,

11

,

9

,

8

,

12

,

5

and

3

, respectively. The inputs

172

,

174

and

176

may be implemented as clock (e.g., clocking signal) inputs. The input

170

may receive the supply voltage VDD. The input

172

may receive a signal (e.g., X_FREQ_B) and may be connected to a node that includes a first terminal of the resistors R

8

and R

9

. The input

174

may receive a signal (e.g., X_FREQ) and may be connected to a node that includes a second terminal of the resistor R

8

and first terminals of the element X

1

and the capacitance C

7

. The signals X_FREQ and X_FREQ_B are generally complementary clocking signals having an oscillation frequency. The signals X_FREQ and X_FREQ_B may be generated by the element X

1

.

The element X

1

may have a second terminal that may be connected to a second terminal of the resistor R

9

and a first terminal of the capacitance C

8

. The input

176

may be connected to a first terminal of the capacitance C

9

. The inputs

178

and

180

, second terminals of the capacitances C

7

, C

8

and C

9

, and first terminals of the capacitance C

10

and the resistor R

11

may receive the ground potential GND.

The output

182

may present a signal (e.g., F_FUND) and may be connected to a collector of the transistor Q

4

. The output

184

may present a signal (e.g., F_GATE) and may be connected to a first terminal of the resistor R

10

. The transistor Q

4

may have a base that may be connected to a node that includes second terminals of the capacitance C

10

and the resistors R

10

and R

11

. An emitter of the transistor Q

4

generally presents the signal OUT.

The signals F_FUND and F_GATE may be generated having frequencies that are related to (e.g., the same as, a multiple of or a dividend of) the oscillation frequency of the element X

1

(i.e., the frequency of the signals X_FREQ and X_FREQ_B). The IC

160

may be configured to generate the signals F_FUND and F_GATE in response to the signals X_FREQ and X_FREQ_B. The signal F_FUND generally has a frequency that is the fundamental frequency of the signal OUT. The signal F_GATE generally has a frequency that is the gating frequency of the signal OUT. The frequency of the signal F_GATE is generally lower than the frequency of the signal F_FUND. While the IC

160

has been shown having the signals F_FUND and F_GATE presented by the terminals

5

and

3

, respectively, other terminals of the IC

160

(e.g., terminals

1

,

2

,

5

,

7

,

8

, or

13

-

15

) may be implemented to present one or the other or both of the signals F_FUND and F_GATE to meet the design criteria of a particular application.

The generator

100

generally presents the signal OUT having a fundamental frequency that is determined by the frequency of the signal F_FUND and gated (e.g., switched on ad off) at the frequency of the signal F_GATE when the signal ENABLE is asserted. The generator

100

is generally disabled when the signal ENABLE is de-asserted.

As is readily apparent from the foregoing description, then, the present invention generally provides a system (e.g., the generator

100

) and a method for low frequency initiation circuitry (e.g., high frequency pre-driver and signal conditioning circuitry configured as an initiator oscillator) for use in a tire pressure monitoring system that achieves the desired frequency accuracy via a single enable input (e.g., via the signal ENABLE) and an oscillator/divider circuit (e.g., the output circuit

106

) having crystal accuracy and stability (i.e., accuracy and stability derived from the crystal X

1

) and, thus, at a lower cost than conventional microprocessor based and double-ended input approaches.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.