Abstract:
A method and system of establishing an offset for a receiver. In one embodiment, a method includes receiving an input signal and generating a first signal. The method can further include integrating the input signal and the first signal at a reference node. In addition, the method can include comparing the input signal to a signal at the reference node and generating an output signal, analyzing the output signal to determine whether the output signal contains noise, and modifying the first signal based on the analysis of the output signal.

Description:
RELATED APPLICATIONS 
     This application claims priority to provisional application No. 60/579,634 filed on Jun. 15, 2004. 
    
    
     FIELD OF INTEREST 
     Embodiments of the invention relate to receivers configured to adapt to the magnitude of noise in input signals. Some embodiments of the invention may be used as receivers in remote-control systems, such as remote keyless entry (“RKE”) or similar systems used in vehicles. 
     BACKGROUND 
     When designing a high-sensitivity receiver, it is often desirable to set the data detection sensitivity of the receiver close to the level of the noise in the signals that one is interested in receiving. However, even when the sensitivity is set at this level, noise may still interfere with operation of the receiver. 
     SUMMARY 
     Noise interference with receiver operation is particularly prevalent in environments with variable noise. Variable noise may be generated, for example, by microprocessors cycling on and off or by electric motors. Variable noise can cause a receiver to “wake up” even when a signal of interest is not present. In applications where low-current receivers are used, activity by a receiver in the absence of a signal of interest can cause the receiver to exceed the current consumption requirements that a user or manufacturer may specify. For example, in vehicles, the operation of remote door locks, alarms, and other accessories draws current from a battery or batteries with limited capabilities to supply current. Receivers that are unnecessarily active add to the current demands placed on vehicle batteries. In modern vehicles, there are numerous control units, accessories, and other devices that may require a current, voltage, or power source. Thus, even relatively small levels of unnecessary current usage can adversely impact a vehicle battery or electrical system. 
     In view of the above, embodiments of the invention provide an adaptable receiver configured to adjust in a varying noise environment. Embodiments of the invention provide a reference input to a comparator controlled by a processor. The processor adjusts the reference input to adapt to variable noise. Embodiments of the invention inject a pulse-controlled signal to a comparator to create an adaptable reference. 
     In one embodiment, the invention provides a method of establishing an offset for a receiver. The method may include receiving an input signal; generating a first signal; directing the input signal and the first signal to a reference node; coupling a capacitor to the reference node; integrating the input signal and the first signal at the reference node; comparing the input signal to a signal at the reference node and generating an output signal; analyzing the output signal to determine whether the output signal contains noise or information that conforms to a predetermined information format; and modifying the first signal based on the analysis of the output signal. 
     In another embodiment, the invention provides a receiver having a comparator. The comparator is configured to receive an input signal, to compare the input signal to a signal at a reference node, and to generate an output signal. The receiver also includes a processor configured to generate a pulse-controlled signal having a pulse width. The processor is coupled to the comparator so that the pulse-controlled signal is delivered to the reference node and the output signal of the comparator is delivered to the processor. The processor analyzes the output signal to determine whether the output signal contains noise or information that conforms to a predetermined information format, and modifies the pulse width of the pulse-controlled signal based on the analysis of the output signal. A capacitor is coupled to the reference node. The pulse-controlled signal provided to the reference node is integrated with the input signal to provide a stable reference. 
     Additional aspects of embodiments of the invention are illustrated in the drawings and provided in the subsequent description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a circuit diagram of an exemplary embodiment of the invention. 
         FIG. 2  is a flow chart illustrating the signal processing of the processor of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Before embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of the examples set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or carried out in a variety of applications and in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “mounted,” “connected,” and “coupled” are used broadly and encompass both direct and indirect mounting, connecting, and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
       FIG. 1  illustrates an exemplary receiver  10 . The receiver  10  may be configured to obtain and process input signals or messages. In some embodiments, the receiver  10  may be configured to process tire pressure messages, keyless entry messages, or the like in a vehicle. The receiver  10  may be configured to receive radio-frequency signals, although configuring the receiver to receive other signals is possible. 
     An input signal may be received by a reception device or element  12 . The reception element  12  may be an antenna. Alternatively, signals of interest may be fed from another source, such as a cable or network. The input signal may be filtered or unfiltered. A filter may be used, for example, to remove signals outside a certain frequency band. Regardless of whether the input signal is filtered, the input signal may still include noise. The input signal may be considered as having a desired signal or information portion and a noise portion. 
     The input signal received at the reception element  12  is directed to an input node  14  coupled to a comparator  16 . Although a direct connection is shown between the element  12  and the input node  14 , components such as resistors, amplifiers, or the like may be situated between the element  12  and the input node  14 . Thus, the signal present at the input node  14  may be the same as the input signal received at reception element  12  or a version thereof. A number of components such as de-multiplexers, filters, amplifiers, delays, or the like may process the input signal between the reception element  12  and the input node  14  to create a version of the input signal at the input node  14 . 
     As should be understood by one of ordinary skill in the art, a variety of signal conditioning elements could be connected between various components of the embodiments described herein. Strictly speaking, the output of a signal conditioning circuit is not identical to its input, for example, an output signal differs in at least timing or phase from an input signal even in the simplest of components, although the time or phase difference may be very small. In any event it should be understood that the use of additional circuitry is within the scope of embodiments of the invention. Thus, unless the context indicates otherwise, the term “signal” encompasses an original signal and versions of that signal that might be created through the use of conditioning circuitry placed between two components. 
     The comparator  16  has a data input  18 , a reference input  20 , and an output  22 . In some embodiments, the comparator  16  may be constructed using an integrated circuit such as integrated circuit model LMV  324  manufactured by National Semiconductor. In some embodiments, the data input  18  is coupled to the input node  14  and receives a signal from the input node  14 . In some embodiments, the comparator  16  is configured to perform a selection of the signals at the data input  18  and the reference input  20 . More specifically, the comparator  16  may compare a signal received at the data input  18  to a signal received at the reference input  20  and generate an output signal at the output  22  by performing a selection of the signal having the greatest amplitude. As a consequence, the signal at the data input  18  or the reference input  20  having the greatest amplitude is output as the output signal on output  22 . 
     The comparator  16  may also be configured to generate one of two possible logic signals. The two possible output signals may correspond to one of two logic states. For example, the comparator  16  may generate a logic high output signal of 5 volts if the amplitude of the signal received at the data input  18  is greater than the amplitude of the signal received at the reference input  20  and may generate a logic low output signal of 0 volts if the amplitude of the signal received at the reference input  20  is greater than the amplitude of the signal received at the data input  18 . Other variations in the operation of the comparator  16  should be apparent to those skilled in the art. 
     In the embodiment shown, the receiver  10  also includes a processor  30 . The processor  30  may be a microprocessor, macroprocessor, or other processing chip or unit. The processor  30  may also be implemented using an application specific integrated circuit (“ASIC”) or other hardware circuit. The processor  30  has a processor input  32  and a processor output or port  34 . In some embodiments, the processor  30  may be an 8-bit programmable microprocessor manufactured by Microchip. In some embodiments, the processor  30  is configured to generate an adaptive-controlled signal. The processor  30  may be configured to adaptively control the amplitude, duration, frequency, or any combination thereof, of the generated signal. In some embodiments, the processor  30  generates a pulse-controlled signal and outputs or injects the signal on the processor output  34 . In some embodiments, the pulse-controlled signal contains a number of pulses where each pulse has similar amplitude but a varying width. The processor  30  may be configured to vary the pulse widths or pulse durations. The processor  30  may also be configured to switch between a set of predetermined set of pulse widths. In some embodiments, the input  32  of the processor  30  is coupled with the output  22  of the comparator  16 , and the processor  30  may be configured to vary the pulse widths based on the signal received from the comparator  16 . 
     In the embodiment shown, the pulse-controlled signal generated by the processor  30  is directed to a regulating resistor  36  configured to limit the current of the pulse-controlled signal. Specifically, the regulating resistor  36  may be used to protect the comparator  16  from receiving a current at an amplitude or level above the comparator&#39;s rating. One benefit of the regulating resistor  36  or similar conditioning circuitry is that it allows a generic or off-the-shelf processor to be used, since the conditioning circuitry modifies the signal to be compatible with the comparator  16 . Otherwise, a specialized or specific processor capable of inherently generating a compatible signal would be required 
     The regulating resistor  36  is coupled to a reference node  40 . The reference input  20  of the comparator  16  is also coupled to the reference node  40 . The reference input  20  of the comparator  16  may be configured to receive a reference signal from the reference node  40 . As previously described, in one embodiment, the comparator  16  compares the amplitudes of the signals at the data input  18  and the reference input  20  and outputs the signal with the greater amplitude. 
     In the embodiment shown, a capacitor  42  is coupled to the reference node  40  and a reference resistor  50  connects the input node  14  and the reference node  40 . 
     The output signal of the processor  30 , as limited by the regulating resistor  36 , injects charge into the reference input  20  to set the signal level where a signal of interest is detected. For example, in a keyless entry system, the charge sets the level where RF data will be detected. The activity of the capacitor  42  is also affected by this signal. Specifically, the current provided to the capacitor  42  sets the voltage at the reference node  40 , and therefor the voltage level at the reference input  20 . The voltage on the capacitor  42  is proportional to the magnitude of the injected current and the time duration that the current is injected as shown by the following equation.
 
 V =( I*t )/ C , where V is the voltage measured across the reference node 40 and ground (in FIG. 1), I is the current flowing through the regulating resistor 36, and C is the capacitance of the capacitor 42.
 
     In the embodiment shown in  FIG. 1 , the voltage level on the capacitor  42  settles to the average voltage of the signal input to data input  18 . The settling time is set by the RC time constant of the capacitance of the capacitor  42  and the resistance value of the reference resistor  50 . During some portion of the reference voltage settling time, the voltage level at the reference node  40  may exceed the voltage level at the input node  14 . As a consequence, only a positive excursion of the input signal delivered to the input node  14  causes the comparator  16  to output a “high” signal, i.e., to output the signal input to the data input  18 . The processor  30  may also be configured to reject the artificial high pulse as noise when output by the comparator  16 . 
     The magnitude of the reference voltage offset (i.e., the voltage level at reference node  40 ) is set by the value of the regulating resistor  36 , the capacitance value of the capacitor  42 , the differential voltage measured from the output  34  of the processor  30  to node  40  (i.e., the voltage of the capacitor  42 ), and the duration of the time that the processor  30  outputs a logic high signal (i.e., the width of a pulse). In the embodiment shown, it is the width of the pulse of the signal output by the processor  30  that is varied to control the level of the reference voltage. Other elements or components could be varied. For example, variable capacitors or resistors could be implemented. However, generating a pulse-width controlled signal may be accomplished relatively cheaply and easily using a relatively simple microprocessor. Adjusting other components is likely to be more expensive and complicated. 
     During a high amplitude pulse of the pulse-controlled signal injected by the processor  30 , the capacitor  42  receives a majority of the current contained in the signal injected by the processor  30  in combination with an integrated version of the data signal received by the data input  18  of the comparator  16 . In some embodiments, the reference input  20  of the comparator  16  has high resistance in comparison to the capacitor  42 , and while the capacitor  42  is charging, little current is received by the reference input  20  of the comparator  16 . Since little current, or a low amplitude signal, is received by the reference input  20 , the amplitude of the signal received by the data input  18  of the comparator  16  is likely to exceed the amplitude of the reference signal. If so, the comparator  16  outputs the signal present at the data input  18  or a version thereof. For example, the comparator  16  may output an amplified and clipped version of the signal received from the data input  18 . 
     During a low amplitude pulse of the pulse-controlled signal, the capacitor  42  may discharge. As the stored charge on the capacitor  42  decays, the current received at the reference node  40  increases, as does the amplitude of the reference signal received by the reference input  20  of the comparator  16 . During the capacitor  42  decay, the amplitude of the reference signal received by the reference input  20  may increase to a point where the amplitude of the reference signal matches or exceeds the average amplitude of the data signal. At this point, the comparator  16  no longer automatically outputs the data signal since the amplitude of the data signal may no longer always be greater than the amplitude of the reference signal. The reference signal may decay to a point where the amplitude of the reference signal is similar to the average amplitude of the data signal, and only portions of the data signal having amplitudes greater than the average amplitude will have amplitudes greater than the amplitude of the reference signal and will be output by the comparator  16 . 
     The processor  30  may be configured to output a high voltage at output  34 , and, when not injecting current, the processor  30  may be configured to set output  34  into a high impedance state where it has no impact on the reference level. Setting the output  34  into a high impedance state mimics disconnecting the input of the processor  30  from the receiver  10 . 
     As previously indicated, the comparator output  22  is coupled to the processor input  32 . If the comparator  16  outputs the data signal, or a version thereof, the processor  30  may be configured to determine whether the data signal output by the comparator  16  contains data of interest. The processor  30  may determine if the data signal output by the comparator  16  contains data of interest by determining if the information received conforms to a predetermined format. For example, each pulse in the data signal may have a particular amplitude, width, or the like. In some embodiments, if the data signal output by the comparator  16  and received by the processor  30  only contains noise, the processor  30  may increase the reference signal so that the data signal received at the data input  18  is not output by the comparator  16 . By increasing the amplitude of the reference signal, a higher amplitude data signal is required to cause the comparator  16  to output the data signal. 
     As indicated above, in the embodiment shown, the duration of the signal output on output  34  of the processor  30  sets the quantity of charge delivered to capacitor  42 . If the processor  30  detects excessive noise in the signal from the output  22  of the comparator  16 , the pulse durations are increased. Increases in pulse durations increase the value of the offset or signal at the reference node  40  and increases the amplitude of the noise required to trigger the comparator output  22 . The processor  30  continuously samples input information while turning the output  34  of the processor  30  from the +5 V output state (logic high) to the high impedance state. 
     If the comparator output  22  is quiet for too long, the charge pulse duration is reduced to lower the comparator reference voltage offset and increase the sensitivity of the receiver  10 . 
       FIG. 2  is a flow chart illustrating exemplary signal processing performed by the processor  30 . Starting at block  60 , the processor  30  initializes the pulse width. For example, the processor  30  may set the initial pulse width to 100 microseconds. The processor  30  may also initialize other aspects of the processing performed by the processor  30  such as setting the frequency of the pulse, such as generating a pulse every 12 milliseconds. After the pulse width and other aspects have been initialized, the processor  30  begins to output the pulse-controlled signal and process the signal received from the comparator  16 . At block  62 , the processor  30  determines whether the output received from the comparator  16  contains noise. (A way to determine whether a signal contains noise is to determine whether the signal contains information that conforms to a predetermined format. If the signal does not conform, it is assumed to have noise or at least too much noise in order to process). If the received signal does contain noise, the processor  30  determines if the pulse width can be increased or if the pulse width has already been increased to a maximum amount (block  64 ). The pulse width may have a maximum value such as 130 microseconds. Increasing the pulse width to a value more than the predetermined limit may cause the receiver to malfunction or operate inaccurately or incorrectly. If the pulse width has already been increased to the maximum amount allowed, the processor  30  may wait or delay a predetermined amount of time (block  66 ) and then may recheck the output received from the comparator  16  (block  62 ). The delay may be used to set a limit on the amount of current or power the processor  30  consumes. Without the delay, the receiver may continuously loop and process the signal received from the comparator  16 . The processor  30  may be configured or programmed to wait 5, 10, or more seconds between checking the signal received from the comparator  16 . 
     Alternatively, if the pulse width has not already been increased to the maximum value, the processor  30  increases the pulse width at step  68 . As previously indicated, increasing the pulse width raises the offset to the comparator  16 , which raises the required amplitude of the data signal needed to be output by the comparator  16 . In some embodiments, the processor  30  may increase the pulse width by 10 microseconds. After the processor  30  increases the pulse width, the processor  30  delays a predetermined amount of time before determining if the adjusted offset value is sufficient to quiet the noise on the output  22  of the comparator  16  (block  66 ). 
     If the processor  30  determines that the output received from the comparator  16  does not contain noise (block  62 ), the processor  30  determines whether the pulse width has already been reduced to a minimum value at block  70 . The processor  30  may be configured with a minimum limit that regulates the smallest pulse width that should be used. For example, the processor  30  may be configured to prohibit the pulse width from being lower than 70 microseconds. If the processor  30  determines that the pulse width is currently set at the lowest allowed value, such as 70 microseconds, the processor  30  may leave the pulse width unmodified and wait or delay a predetermined amount of time as previously described before checking for noise again (block  66 ). 
     If, on the other hand, the processor  30  determines that the current pulse width is not set at the minimum value, the processor  30  decreases the pulse width at block  72 . The processor  30  may be configured to decrease the pulse with by a predetermined amount, such as 10 microseconds. After decreasing the pulse width, the processor  30  then delays a given amount of time (block  66 ) before rechecking the received signal for noise (block  66 ). 
     If the processor  30 , however, determines that the output received from the comparator  16  does not contain noise, or otherwise, possibly contains data, the processor  30  may be configured to forward the received signal to other processing components or may perform signal processing itself. The received signal may be processed to determine whether an action, such as unlocking the doors of a vehicle, should be taken in light of the data or information present in the received signal. 
     Various features and aspects of embodiments of the invention are set forth in the following claims.