Tire pressure detector having reduced power consumption mechanism

A tire pressure detector employs a reduced power consumption mechanism comprising a PLL circuit including a VCO, that is operated in response to the logic states of an input data stream and a power amplifier configured to be externally located to an integrated circuit. The input data stream includes tire pressure information and is configured to be encoded to have multiple logic states. A micro-controller is employed to control the VCO, turning the VCO, and/or the amplifier, on and off for a certain period, according to the pattern of each data bit of the input data stream thus providing reduced current consumption. This tire pressure detector thus embodies an optimized circuit arrangement in terms of power efficiency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a tire pressure detector, and in particular to tire pressure detectors employing a reduced power consumption mechanism.

2. Related Art

In a vehicle, a tire pressure detector may be used in conjunction with a Tire Pressure Monitoring System (TPMS) to measure air pressure in tires. Tires having low tire pressure may raise safety concerns. The tire pressure detector may be attached to a tire, or the wheel on which the tire is mounted, and may detect low tire pressure. Upon detection, the tire pressure detector may transmit this information to a driver via a TPMS or the like. The transmission of the tire pressure information is often performed wirelessly. For instance, a radio frequency transmission may be used to transmit tire pressure detector readings.

In a tire pressure detector, sensors in addition to a pressure sensor such as a temperature sensor and/or a speed sensor may be included. A battery is also typically used to power components of the tire pressure detector. The tire pressure detector may also include communication components such as a phase locked loop (PLL) circuit, a crystal oscillator, an RF antenna that sends radio transmissions to a central control unit and possibly receives radio transmissions, etc. A power amplifier may also be included such that tire pressure signals may be amplified for transmission.

In a conventional tire pressure detector, the PLL circuit and the power amplifier are often installed on a single integrated circuit (IC) chip.FIG. 1is a block diagram of a conventional PLL circuit10. The conventional PLL circuit10typically includes a phase detector20, a voltage controlled oscillator (VCO)30and an amplifier40, as one of ordinary skill in the art will appreciate. The PLL circuit10may be constructed as a single integrated circuit. Although not shown inFIG. 1, the power amplifier is typically disposed on the same IC chip that defines the PLL circuit10.

The conventional PLL circuit10operates as follows. The phase detector20compares two input frequencies, “fin” and “fvco”, and generates output that corresponds to a phase difference of the two input frequencies. If “fin” does not equal to “fvco”, a phase-error signal is generated. The phase-error signal may be filtered by a suitable filter50and amplified by the amplifier40. In response to the phase-error signal, “fvco” is deviated in the direction of “fin”. If the “fin” does equal to “fvco”, the VCO30will lock to “fin”. The phases of the two input frequencies, “fin” and “fvco” become in phase.

In the conventional PLL circuit10, the VCO30is always powered-on regardless of logic states of input data bits. Even if input data bits have a zero state, the VCO30remains on and consumes current. Further, various components on the IC chip may not be separately controllable. The PLL circuit10and a power amplifier formed on the single IC chip may also generate noise.

SUMMARY

The present invention is directed to systems and methods which provide tire pressure detectors employing a reduced power consumption mechanism. In embodiments of the present invention the tire pressure detector VCO employed may be powered in response to logic states of input data bits. For example, in accordance with the present invention, a tire pressure detector VCO may not be powered when input data bits have a zero state. Further, various components on a tire pressure detector IC chip may be separately controllable. Also, in accordance with embodiments of the present invention, the PLL circuit and a power amplifier for a tire pressure detector may not be formed on the same IC chip. This, in addition to other advantages, might reduce noise in transmissions from, and to, the tire pressure detector.

By way of example only, in some embodiments of the present invention, a tire pressure detector includes a pressure sensor, an integrated circuit, a power amplifier and a radio frequency (RF) antenna. The pressure sensor measures air pressure in a tire. The integrated circuit receives tire pressure information and processes the tire pressure information as an RF signal for transmission. The power amplifier receives the RF signal from the integrated circuit and amplifies the RF signal. The power amplifier is preferably configured to be externally disposed to the integrated circuit. The RF antenna is connected to the power amplifier and transmits the RF signal.

In other embodiments, a tire pressure detector includes a pressure sensor, a data processing circuit, a PLL circuit, and an RF antenna. Again, the pressure sensor measures pressure of a tire. The data processing circuit receives the tire pressure from the pressure sensor and generates an input data stream. The input data stream is preferably configured to be encoded to represent a first logic state and a second logic state. The data processing circuit modulates the input data stream for radio frequency transmission. The PLL circuit includes a VCO. In accordance with the present invention, the VCO may be configured to be powered on according to the first logic state and powered off according to the second logic state. Again, the RF antenna transmits the modulated input data stream.

In still other embodiments, a reduced power consumption mechanism of a tire pressure detector is provided. The tire pressure detector is configured to detect and process tire pressure information. The reduced power consumption mechanism includes an input data stream, a PLL circuit and a power amplifier. The input data stream includes tire pressure information and is configured to be encoded to have multiple logic states. The PLL circuit includes a voltage controlled oscillator that is operated in response to logic states of the input data stream. The PLL circuit is implemented in an integrated circuit. The power amplifier is preferably configured to be externally located to from the integrated circuit.

DETAILED DESCRIPTION

FIG. 2is a block diagram of an embodiment of tire pressure detector100of the present invention. Tire pressure detector embodiment100includes pressure sensor160, main IC chip150, crystal oscillator170, battery180, power amplifier200, and RF antenna250. Alternatively, detector100may be self-powered and not include a battery. Crystal oscillator170, power amplifier200and battery180are connected to main IC chip150. Power control circuit110, phase-locked loop (PLL) circuit120, microcontroller125and memory130are preferably formed on main chip IC150. In this embodiment, crystal oscillator170is disposed off of main IC chip150. In another embodiment, crystal oscillator170may be disposed on the main IC chip150. Power amplifier200is preferably located off of main IC chip150in these embodiments.

Other sensors165, detecting various physical parameters in a tire including tire temperature, speed, rotation, rotation direction, tilt, etc., may be included on main IC chip150. For instance, other sensors165may include a temperature sensor, a speed sensor, an acceleration sensor, a shock sensor etc. Circuit block140indicates various other circuits that may be formed on the main IC chip150such as a timer, a low power detection circuit, a modulator, etc.

A tire pressure detector may be installed on each tire of a vehicle. Although not shown, a central control unit may be provided at a suitable location on a vehicle. The central control unit may be in communication with the tire pressure detectors and may inform a driver of various physical parameters of the tires including low tire pressures.

RF antenna250receives and sends information between a tire pressure detector100and other devices such as the central control unit. RF antenna250may be a planar RF antenna. Alternatively, RF antenna250may be a valve stem RF antenna. The valve stem RF antenna may use a tire valve as an RF antenna. For purposes of illustration only, RF antenna250is shown in the present Figures as internally formed within tire pressure detector100.

Pressure sensor160measures or detects tire pressure. In illustrated tire pressure detector100, pressure sensor160is a stand-alone sensor. In other embodiments, pressure sensor160may be integrated onto main IC chip150. Pressure sensor160sends pressure information to the main IC chip150for processing. When other sensors165are included on main IC chip150, physical parameter information detected by these sensors may be processed along with the pressure information from pressure sensor160. The physical parameters information may be used to identify a mounting location of a tire sending the tire pressure information, or the like. Such information is transmitted to main IC chip150for processing. The tire pressure information, which may be in the form of raw data, with or without the physical parameters, becomes an input data stream to main IC chip150. The input data stream may be manipulated internally and is preferably generated internally to main IC chip150. The input data stream may be communicated to microcontroller125by main IC chip150.

Preferably, microcontroller125controls various circuit elements on IC chip150to process the tire pressure information, such that the tire pressure information may be encoded. For instance, the tire pressure information may be encoded using the Manchester encoding technique. The Manchester encoding technique involves logic transition from high to low or low to high at half of the bit width of each bit. The logic transition from high to low corresponds to logic 1 and the logic transition from low to high corresponds to logic 0. Further, the tire pressure information may be formatted and patterned to be associated with an identification of a tire, a vehicle, etc. Additionally, the tire pressure information may be encrypted.

Microcontroller125might also control a modulator, such as contained in other circuit block140, to modulate an RF carrier frequency with tire pressure information for RF transmission. In one embodiment, the input data stream of the tire pressure information may be used to modulate an RF carrier frequency of 433.92 MHz while in another embodiment an RF carrier frequency such as 315 MHz may be used. Preferably, the RF carrier frequency is generated by VCO320included in PLL circuit120, as shown inFIG. 3. The input data stream preferably has a predetermined data rate, such as 4 KHz, which is generated internally to main IC Chip150.

Further, microcontroller125preferably controls and supervises the circuit elements formed on main IC chip150. The tire pressure information and other physical parameter information from other sensors165may be stored in memory130. Power control circuit110may distribute power from battery180or other power supply to circuit elements on main IC chip150.

FIG. 3is a block diagram of an embodiment of present PLL circuit120. PLL circuit120includes phase detector310, VCO320, frequency divider330and filter and amplifier340. PLL circuit120is in communication with crystal oscillator170and power amplifier200. Phase detector310presently receives two input frequencies, one from crystal oscillator170and one from VCO320through frequency divider330. Crystal oscillator170generates an input reference frequency. Phase detector310generates a phase-error signal if the phases of the two input frequencies do not equal. Filter and amplifier340operates to filter and amplify the phase-error signal. The frequency of VCO320is caused to be deviated toward the input frequency from crystal oscillator170. Frequency divider330is placed between phase detector310and the output of VCO320. The frequency divider operates such that a multiple of the input reference frequency is generated.

As shown inFIG. 3, VCO320receives a control signal from microcontroller125. The control signal may cause VCO320to turn on and turn off at the transition of each data bit. As described above, the input data stream of the tire pressure information may be encoded according to the Manchester encoding. Each data bit experiences the logic transition at half of the bit width. The input data stream of the tire pressure information is generated internally to tire pressure detector100. Formats and patterns of this data stream may already be known to microcontroller125. Thus, microcontroller125may control VCO320to be turned on and off according to the transition of the input data stream.

VCO320and the PLL circuit120are preferably implemented for use with a particular input data stream configuration. On the other hand, PLL circuits which are generic with regard to input data encoding format and data rates may not operate or be operated to turn on and off voltage controller oscillators. Turning on and off VCO320may substantially reduce current consumption. For example, at each transition from logic 1 to logic 0 in the input data stream VCO320is preferably turned off. Before each transition from logic 0 to logic 1 in the input data stream the VCO is preferably turned on. In prior PLL designs the VCO typically remains on for periods of logic 0 in the input data stream. In accordance with embodiments of this invention for periods of logic 0 in the input data stream the VCO320is preferably switched off. This may lead to a reduction in current consumption by removing the current which the VCO consumes when powered on. Manchester encoding, as described above is a method of encoding which utilizes a logic state change at half of the bit width of a bit. Thus, VCO current consumption may be reduced by up to 50% in embodiments of the present invention compared to current used when the VCO remains on in conventional tire pressure detectors.

Referring back toFIG. 2, power amplifier200is preferably configured to be external to main IC chip150. Because power amplifier200is external, any type of an amplifier may be used. For instance, amplifiers such as Class A type amplifiers or Class B type amplifiers may be used. Additionally, Class C type amplifiers are available. Class A type or Class B type amplifiers may provide good linearity of input signal and output signal but may have relatively poor power efficiency. In conventional tire pressure detectors, Class A and B type amplifiers are not typically used due to the relatively poor power efficiency, despite other advantages.

Embodiments of the present tire pressure detector100may employ Class A type and Class B type power amplifiers due to tire pressure detector100using current consumption reduction mechanisms such as PLL circuit120in conjunction with external amplifier200as described above. It is noted that power amplifier200, being separated from IC chip150, may not be affected by activation or operation of other circuit elements on the main IC chip150. For instance, attempting to define the power amplifier200along with PLL circuit120on a single IC chip may be problematic, may produce more noise and may tend to consume more current. Further, deploying power amplifier200off the main IC chip150may provide more space for configuring and designing main IC chip150.

Because power amplifier200is external to main IC chip150, selection and replacement of power amplifier200may be flexible. A power amplifier that consumes a relatively high current, may be replaced with a lower current amplifier. Alternatively, or additionally, a power amplifier with relatively poor power efficiency may be replaced with an amplifier having better power efficiency. In accordance with the present invention, the power amplifier200is preferably selected to accommodate the most efficient power transfer between main IC chip150and RF antenna250.

Like VCO320ofFIG. 3, power amplifier200may be turned on and off according to the input data stream. For logic 1, power amplifier200is turned on and for logic 0, power amplifier200is turned off. Thus, operation of power amplifier200in accordance with embodiments of the present invention may allow the power amplifier200to be activated only when needed. As a result, current consumption by power amplifier200may be reduced.

FIG. 4is a block diagram illustrating reduced power consumption mechanism400of tire pressure detector100. Mechanism400may include VCO on/off operation in PLL circuit410, an off-chip power amplifier and its on/off operation420, and optimized power transfer between the off-chip power amplifier and RF antenna430. As noted above, the on/off operation of the VCO and the power amplifier according to a pattern of each data bit may substantially minimize current consumption. Use of an off-chip power amplifier may provide advantages for selecting power efficient amplifiers when designing a tire pressure detector, or the like. For example, off-chip power amplifiers may be selected with consideration for efficient power transfer with the RF antenna. This flexibility further may contribute to reduced power consumption.

As noted above, tire pressure detectors may employ a current consumption reduction mechanism such as mechanism400ofFIG. 4. The VCO of the PLL may be controlled to be turned off for a certain period according to the pattern of each data bit. Further, the off-chip power amplifier may provide reduced current consumption. Moreover, the off-chip power amplifier may provide advantages including flexibility in selecting power amplifiers and easy replacement. The power amplifier also may be separately controllable. More efficient power transfer between the power amplifier and the RF antenna is possible because the power amplifier may be selected to match specifications and functions of the RF antenna. The off-chip power amplifier may provide flexible configuration and implementation of the IC chip and the entire tire pressure detector. Accordingly, the tire pressure detector may embody an optimized circuit arrangement in terms of power efficiency and reduced production expenses.