Patent Publication Number: US-9893914-B2

Title: Apparatus and method for changing frequency deviation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. application Ser. No. 14/185,511 filed Feb. 20, 2014, and PCT Application No, PCT/US2015/016176, filed Feb. 17, 2015. The disclosure of the above applications are incorporated herein by reference. 
     TECHNICAL FIELD 
     This application relates to tire pressure sensors and, more specifically transmissions made to and from these devices. 
     BACKGROUND OF THE INVENTION 
     Tire pressuring monitoring (TPM) devices are used in today&#39;s vehicles. A tire pressure sensor senses the tire pressure reading (or other conditions, such as the temperature of the tire). These sensed readings may be communicated to a TPM receiver that is disposed in the vehicle. A display screen may also be coupled to the receiver. When the tire pressure reading falls below a particular threshold, the driver of the vehicle may be alerted, for example, by an alert message being displayed to the driver on the screen. The driver can then take any required action. 
     Most TPM sensors have a specific frequency deviation when they transmit frequency-shift keying (FSK) data. For example, the frequency deviation may be 315 Mhz +/−20 hz or 40 khz of deviation (or range). Thus, 314.98 Mhz may be used for transmission of a logic “0” (in the FSK scheme) while 315.02 Mhz may represent a logic 1. The exact frequency deviation is chosen when the TPM sensor is engineered and must be in accordance with the bandwidth and frequency discrimination of the receiver used to receive the FSK data. 
     Many TPM sensors have a FSK frequency deviation of between +/−30 Khz to +/−50 Khz. This means that the bandwidth of the receiver must be around 200 kHz. A wide receiver bandwidth is cost effective, but is linked to more in-band noise coming from different sources. This in-band noise decreases the sensitivity of the sensor in some cases. 
     Some original equipment manufacturers (OEMs) require a smaller bandwidth receiver. Thus, the TPM sensor working with such a receiver must also limit its frequency deviation. In some cases, a TPM sensor with a wide frequency deviation may not be received at all by a narrow band receiver or can be attenuated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein: 
         FIG. 1  comprises a block diagram of a system that changes FSK frequency deviation on the fly according to various embodiments of the present invention; 
         FIG. 2A  comprises a block diagram of a FSK switching arrangement for a TPMS monitor with capacitors inside the PLL according to various embodiments of the present invention; 
         FIG. 2B  comprises a block diagram of a FSK switching arrangement for a TPMS monitor with capacitors outside the PLL according to various embodiments of the present invention; 
         FIG. 2C  comprises a frequency response graph showing frequency deviations according to various embodiments of the present invention; 
         FIG. 3  comprises a flowchart of an approach for FSK switching according to various embodiments of the present invention; 
         FIG. 4  comprises a block diagram of an apparatus that changes FSK frequency deviation on the fly according to various embodiments of the present invention. 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. 
     DETAILED DESCRIPTION 
     Approaches are provided that implement a frequency-shift keying (FSK) frequency deviation switch for multi-application tire pressure monitoring (TPM) sensors or for any different radio frequency (RF) transmitters requiring different frequency deviations. The frequency deviation of the transmitted FSK signal is adjusted based upon the protocol to be transmitted. The TPMS sensors (or monitors or wheel units) may include processing devices and memories and execute computer instructions to sense and transmit tire pressure (or other) data. In these regards, the TPMS sensors may themselves include structures, devices, or apparatus that actually sense the pressure (or other types of data) in the tire, and make transmissions of the sensed information. 
     In one aspect, the TPM sensor uses a phase locked loop (PLL) to modulate and transmit the FSK data to the receiver. In some cases, the PLL offers the ability to use internal capacitors instead of external capacitors to create the desired frequency deviation. Typically. TPM sensor manufacturers prefer to use external load capacitors to the crystal oscillator as these represent fixed values. 
     In the present approaches, a bank of capacitors is offered by a PLL of the TPM sensor and this bank of capacitors can be either switched on or off depending upon the frequency deviation that is required. The bank of capacitors can be implemented with discrete components. 
     In many of these embodiments, a protocol that is to be used in the transmission is determined. Based upon the protocol, the transmission frequency range (or deviation) of a clock is selectively altered. TPMS data is transmitted according to the altered transmission frequency range (or deviation) of the clock. 
     In some aspects, selected ones of a plurality of capacitors that are coupled to the clock are selectively switched in and out of the transmission circuit. In other aspects, the transmissions are performed according to a frequency-shift keying (FSK) approach. In still other examples, the protocol is a selected protocol from a plurality of protocol and each of the plurality of protocols is associated with a different automobile manufacturer. 
     In other aspects, the clock is a crystal oscillator. In yet other aspects, the approaches are performed by a phase-locked loop (PLL). 
     In others of these embodiments, an apparatus for transmitting tire pressuring monitoring system (TPMS) data includes an interface and a controller. The interface has an input and an output. The controller is coupled to the interface. The controller is configured to determine a protocol to be used in the transmission and, based upon the protocol, selectively produce control signals that alter the transmission frequency range (or deviation) of a clock. The controller is further configured to transmit TPMS data according to the altered transmission frequency range (or deviation) of the clock at the output. 
     Referring now to  FIG. 1 , a system  100  that changes FSK frequency deviation on the fly for a multi-application TPMS sensor is described. The system  100  includes a first TPMS monitor (or sensor or unit or wheel unit)  104 , a second TPMS monitor  106 , a third TPMS monitor  108 , and a fourth TPMS monitor  110 . The monitors  104 ,  106 ,  108 , and  110  communicate with a receiver  112 . The communication between the TPMS monitors  104 ,  106 ,  108 , and  110  and the receiver  112  is accomplished in one aspect via wireless, radio frequency (RF) links. 
     The TPMS monitors  104 ,  106 ,  108 , and  110  may include processing devices and memories and execute computer instructions to sense and transmit tire pressure (or other) data. In these regards, the TPMS monitors  104 ,  106 ,  108 , and  110  may themselves include structures, devices, or apparatus that actually sense the pressure (or other types of data) in the tire. 
     The receiver  112  includes hardware and/or software to receive (and in some examples transmit) information from the TPMS monitors  104 ,  106 ,  108 , and  110 . The receiver  112  is disposed at an appropriate location within the vehicle  102 . 
     The TPMS monitors  104 ,  106 ,  108 , and  110  each implement at a minimum a FSK frequency deviation switch and are multi-application sensors. The sensors may also attenuate using amplitude-shift keying (ASK). That is, the monitors can change frequency deviation on the fly. In other words, the frequency deviation or range of the transmitted FSK signals from the TPMS monitors  104 ,  106 ,  108 , and  110  are adjusted based upon the protocol to be transmitted. 
     In one aspect, the TPMS monitors  104 ,  106 ,  108 , and  110  utilize a phase locked loop to modulate and transmit the FSK data to the receiver  112 . In some cases, the PLL offers the ability to use internal capacitors instead of external capacitors to create the desired frequency deviation. More specifically, a bank of capacitors is offered by a PLL and this bank of capacitors can be either switched on or off depending upon the frequency deviation that is required. The bank of capacitors can be implemented using discrete components. 
     Referring now to  FIGS. 2A and 2C , one example of a circuit  200  for changing FSK frequency deviation on the fly is described. The circuit  200  includes a phase locked loop (PLL)  202 , a clock (e.g., crystal oscillator)  204 , a FSK switch  206 , a first capacitor (C 1 )  208 , a second capacitor (C 2 )  210 , a first frequency deviation selection switch  212 , a second frequency deviation selection switch  213 , a third capacitor (C 3 )  214 , and a fourth capacitor (C 4 )  216  where C 1 , C 2 , C 3  and C 4  are the values of the capacitors. 
     The oscillator  202  oscillates at a certain frequency. If a high signal (a “1”) is applied to the FSK switch  206 , the switch  206  closes and the second capacitor (C 2 )  210  is shorted. A low “tone” with frequency equal to f 1  is transmitted. If a low signal (a logic “0”) is applied to the FSK switch  206 , the switch  206  is open and the second capacitor (C 2 )  210  is not shorted. A high “tone” with frequency equal to f 2  can also be transmitted. F 2  is higher than f 1  because the equivalent capacitance (CA) is (C 1 )(C 2 )/(C 1 +C 2 ) and this is less than C 1 . Consequently, f 2  is greater than f 1 . The frequency deviation is f 2 −f 1 . These examples assume low signals are applied to the first frequency deviation selection switch  212  and the second frequency deviation selection switch  213 . 
     If a smaller frequency deviation is desired, f 1  remains the same since it is driven by C 1 . F 2  is changed to a smaller value (f 3 ) so the frequency deviation (f 3 −f 1 ) is smaller than f 2 −f 1 . In particular, a high signal is applied to first frequency deviation selection switch  212 , a low signal is applied to the second frequency deviation selection switch  213 , and a low signal is applied to FSK switch  206 . Then, the equivalent capacitance (CB) becomes C 1 /(C 2 +C 3 ). 1/CB=1/C 1 +1/(C 2 +C 3 )=(C 2 +C 3 )/C 1 (C 2 +C 3 )+C 1 /C 1 (C 1 (C 2 +C 3 )=(C 1 +C 2 +C 3 )/C 1 C 2 +C 1 C 3 . Thus, CB=(C 1 C 2 +C 1 C 3 )/(C 1 +C 2 +C 3 ). CB is greater than CA. Thus f 3  (the new “High tone” frequency is less than f 2 . With the first frequency deviation being f 2 −f 1 , and the second deviation (with the addition of the capacitor bank being f 3 −f 1 , it can be appreciated that the second frequency deviation is less than the first frequency deviation. The fourth capacitor  216  may also be added to decrease the deviation further. Alternatively, the third capacitor  214  may be switched out and the fourth capacitor  216  switched in to give another frequency deviation. 
     The controller  222  determines when to switch in or out third capacitor  214  (via line  220 ) and the fourth capacitor  216 . In this example, the third capacitor  214  and the fourth capacitor  216  are located in the PLL  202 . Similarly, controller  272  and line  270  in  FIG. 2B  provide frequency deviation selection. 
     Referring now to  FIGS. 2B and 2C , another example of a circuit  250  for changing FSK frequency deviation on the fly is described. The circuit  250  includes a phase locked loop (PLL)  252 , a clock (e.g., crystal oscillator)  254 , a FSK switch  256 , a first capacitor (C 1 )  258 , a second capacitor (C 2 )  260 , a frequency deviation selection switch  262 , and a third capacitor (C 3 )  264 , C 1 , C 2 , C 3  and C 4  are the values of the capacitors. 
     The oscillator  252  oscillates at a certain frequency. If a high signal (a “1”) is applied to the FSK switch  256 , the switch  256  closes and the second capacitor (C 2 )  260  is shorted. A low “tone” with frequency equal to f 1  is transmitted. If a low signal (a logic “0”) is applied to the FSK switch  256 , the switch  256  is open and the second capacitor (C 2 )  260  is not shorted. A high “tone” with frequency equal to f 2  can also be transmitted. F 2  is higher than f 1  because the equivalent capacitance (CA) is (C 1 )(C 2 )/(C 1 +C 2 ) and this is less than C 1 . Consequently, f 2  is greater than f 1 . The frequency deviation is f 2 −f 1 . These examples assume low signals are applied to the frequency deviation selection switch  262 . 
     If a smaller frequency deviation is desired, f 1  remains the same since it is driven by C 1 . F 2  is changed to a smaller value (f 3 ) so the frequency deviation (f 3 −f 1 ) is smaller than f 2 −f 1 . In particular, a high signal is applied to frequency deviation selection switch  262 , and a low signal is applied to FSK switch  256 . Then, the equivalent capacitance (CB) becomes C 1 /(C 2 +C 3 ). 1/CB=1/C 1 +1/(C 2 +C 3 )=(C 2 +C 3 )/C 1 (C 2 +C 3 )+C 1 /C 1 (C 1 (C 2 +C 3 )=(C 1 +C 2 +C 3 )/C 1 C 2 +C 1 C 3 . Thus, CB=(C 1 C 2 +C 1 C 3 )/(C 1 +C 2 +C 3 ). CB is greater than CA. Thus f 3  (the new “High tone” frequency is less than f 2 . With the first frequency deviation being f 2 −f 1 , and the second deviation (with the addition of the capacitor bank being f 3 −f 1 , it can be appreciated that the second frequency deviation is less than the first frequency deviation. Other capacitors may be added in parallel to the third capacitor (C 3 )  256  and as showed in the example of  FIG. 2A . 
     As shown in both  FIG. 2A  and  FIG. 2B , the PLL  202  and  252  provides a fixed frequency deviation. The first capacitor  208  or  258  (C 1 ) is the load capacitor for the crystal oscillator  204  or  254  resulting in the lower carrier of the FSK signal. During, the low carrier transmission, the FET (FSK switch)  206  or  256  shorts the second capacitor  210  or  260  (C 2 ) to ground. For the high frequency carrier, the FET switch  206  or  256  is opened and the second capacitor  210  or  260  (C 2 ) is in series with the first capacitor  208  or  258  (C 1 ) creating a different load on the crystal and a different carrier transmission frequency. 
     Referring now to  FIG. 3 , one example of an approach for FSK switching is described. At step  302 , it is determined if the protocol to transmit includes a high frequency deviation. For example, a threshold may be used and if the transmission protocol has a frequency deviation that exceeds this threshold then the step is answered in the affirmative. On the other hand, if the desired protocol falls below the threshold then the answer is negative. 
     If the answer at step  302  is affirmative, then at step  304  additional capacitors in parallel with a loading capacitor (e.g., the second capacitor  208  or  258  in  FIG. 2A  and  FIG. 2B ) are not switched in parallel with the loading capacitor. This action maintains a relatively high frequency deviation. 
     If the answer at step  302  is affirmative, then at step  306  additional capacitors in parallel with a loading capacitor (e.g., the second capacitor  208  or  258  in  FIG. 2A  and  FIG. 2B ) are switched in parallel with the loading capacitor. This action decreases a high frequency deviation. For example, if the center frequency is  315  +/−20 khz, this action may decrease the deviation to +/−10 khz. In this way, the approaches accommodate a frequency range that the receiver in the vehicle is expecting. 
     Referring now to  FIG. 4 , an apparatus  400  for transmitting tire pressuring monitoring system (TPMS) data includes an interface  402  and a controller  404 . The interface  402  has an input  406  and an output  408 . 
     The controller  404  is coupled to the interface  402 . The controller  404  is configured to determine a protocol  416  to be used in the transmission and, based upon the protocol  416 , selectively produce control signals  410  that alter the transmission frequency of a clock  412 . The protocol  416  may be received from a memory  420  at the input  406 . The controller  404  is further configured to transmit TPMS data  414  according to the altered transmission frequency of the clock  412  at the output  408 . The control signals  408  may control a control circuit  411  that actually changes the clock frequency. 
     Still referring to  FIG. 4 , a transmission  448  is shown and includes a first portion  450 , a second portion  452 , and a third portion  454 . The first portion  450  is at a high frequency and represents a logic 1; the second portion  452  is at a lower frequency and represents a logic 0, and the third portion  454  is at the same high frequency as the first portion  450  and also represents a logic 1. 
     In the approaches described herein the range or deviation between high and low frequencies is altered on the fly based upon the protocol needed. For example, the difference between high frequency (of portions  450  and  454 ) and low frequency (portion  454 ) may need to be 20 khz for some transmission protocols and 30 khz for other protocols. As described herein, capacitors in a capacitor bank may be switched in or out of the transmission circuit. This switching of capacitors alters the “High tone” or high transmission frequency. Thus, if initially the low transmission frequency is f 1 , and the high transmission frequency is f 2  (f 2 &gt;f 1 ), then the deviation is f 2 −f 1 . Inserting a capacitor into the transmission circuit changes f 2  to f 3  with f 3 &lt;f 2  and f 1 &lt;f 3 . Thus, the second frequency deviation is f 3 −f 1  and the second frequency deviation is less than the first frequency deviation. 
     As mentioned, the frequency deviation used can be selected according to the protocol used. By protocols, it is meant any parameter or group of parameters or characteristics that describes a transmission including, for example, data formats (e.g., positioning and meaning of bits), baud rates, to mention two examples. Other examples are possible. 
     It should be understood that any of the devices described herein (e.g., the programming or activation devices, PLLs, the wheel units, the controllers, the receivers, the transmitters, the sensors, any presentation devices, or the external devices) may use a computing device to implement various functionality and operation of these devices. In terms of hardware architecture, such a computing device can include but is not limited to a processor, a memory, and one or more input and/or output (I/O) device interface(s) that are communicatively coupled via a local interface. The local interface can include, for example but not limited to, one or more buses and/or other wired or wireless connections. The processor may be a hardware device for executing software, particularly software stored in memory. The processor can be a custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the computing device, a semiconductor based microprocessor (in the form of a microchip or chip set) or generally any device for executing software instructions. 
     The memory devices described herein can include any one or combination of volatile memory elements (e.g., random access memory (RAM), such as dynamic RAM (DRAM), static RAM (SRAM), synchronous dynamic RAM (SDRAM), video RAM (VRAM), and so forth)) and/or nonvolatile memory elements (e.g., read only memory (ROM), hard drive, tape, CD-ROM, and so forth). Moreover, the memory may incorporate electronic, magnetic, optical, and/or other types of storage media. The memory can also have a distributed architecture, where various components are situated remotely from one another, but can be accessed by the processor. 
     The software in any of the memory devices described herein may include one or more separate programs, each of which includes an ordered listing of executable instructions for implementing the functions described herein. When constructed as a source program, the program is translated via a compiler, assembler, interpreter, or the like, which may or may not be included within the memory. 
     It will be appreciated that any of the approaches described herein can be implemented at least in part as computer instructions stored on a computer media (e.g., a computer memory as described above) and these instructions can be executed on a processing device such as a microprocessor. However, these approaches can be implemented as any combination of electronic hardware and/or software. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.