Abstract:
Anti-theft circuit for a portable device, is disclosed, in which a correlation in a PN(Pseudo Random Number) sequence is employed for effective prevention of a portable device from being thieved, the anti-theft circuit including a transmission block disposed in the portable device having a block for generating a particular pseudo random number sequence and a multiplication block for always multiplying a ‘high’ value to an output of the block for generating a particular pseudo random number sequence, the transmission block for converting an output of the multiplication block into an analog value and transmitting the analog value, and an anti-theft sensing circuit separate from the portable device for receiving a signal transmitted form the transmission block, sampling the signal, multiplying a sampled value to a pseudo random number sequence identical to a case of the transmission block, summing for a time period, comparing to a preset threshold value, and selectively providing an alarm signal to outside thereof according to a result of the comparison.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an anti-theft circuit, and more particularly, to an anti-theft circuit for a portable device, in which a correlation in a PN(Pseudo Random Number) sequence is employed for effective prevention of a portable device from being thieved. 
     2. Background of the Related Art 
     FIG. 1 illustrates the steps of an exemplary generation of a general pseudo-random number sequence, with three bits of a delay bit size. If initial values of the delay bits are ‘1 0 0’, delay bits are shifted to repeat in an order of 0 0 1, 0 1 0, 1 0 1, 0 1 1, 1 1 1, 1 1 0, with a period of 2 3 −1, i.e., 7 chips. The pseudo-random number sequence generated in this case is ‘1 0 0 1 0 1 1’, which is repetitive. 
     As an exemplary related art anti-theft circuit, a car anti-theft circuit will be explained with reference to the attached drawings. FIG. 2 illustrates a block diagram of a transmission system in the related art anti-theft circuit, and FIG. 3 illustrates a block diagram of a reception system in the related art anti-theft circuit. 
     The related art car anti-theft circuit is provided with electrical systems in a car, a controller disposed between electrical components in each of the electrical systems and a power supply block, and a transmitter for transmitting an activating signal to the controllers. The controllers are supplied of power from the power supply block in the car. The controller maintains its power path to the electrical component cut-off until the controller receives an encoded and transmitted activating signal when the controller decodes and compares to a value stored in advance, to establish a power supply path and put the electrical component into regular operation if the value is same. When the encoded, and transmitted signal is not the same as the value stored in the controller under an irregular condition, the power supply path to the electrical component is not established. As a result, the electrical component is not put into regular operation, allowing a theft prevention signal to be transmitted from the transmitter with a signal of an audible frequency band or a low powered FM system signal. 
     The transmission system in the aforementioned related art car anti-theft circuit has a system as shown in FIG.  2 . 
     Referring to FIG. 2, the transmission system is provided with a power supply block  11 , a switching block  12  for switching a power supplied from the power supply block  11 , an encoder  13  for encoding a particular signal upon reception of the power under the switching of the switching block, and a transmitter  14  for transmitting the signal encoded in the encoder  13 . 
     FIG. 3 illustrates a reception system in the car anti-theft circuit. 
     Referring to FIG. 3, the reception system in the car anti-theft circuit has a voltage regulating unit  22  for regulating a voltage level supplied from a power supply unit  21 , a receiver  23  disposed between the electrical systems in the car for receiving the activating signal transmitted from a transmitter  22  in the transmission system, a decoder/comparator unit  24  for decoding the activated signal received through the receiver  23  and comparing to a value stored in advance, and a switching block  25  for selectively switching a voltage in the voltage regulating unit  22  according to a result of comparison in the decoder/comparator unit  24 . In the car anti-theft circuit having the transmission system and the reception system, a particular active signal is transmitted and sensed, to cut off a power supply circuit selectively in an action of theft prevention of a car. 
     However, because the related art anti-theft device should encode and decode a particular signal, for making an anti-theft action according to a result of the comparison, the related art anti-theft device requires a decoding block, and can not provide a particular signal source. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an anti-theft device for a portable device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide an anti-theft circuit for a portable device which can effectively prevent a portable device from being thieved. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the anti-theft circuit for a portable device, in which a correlation in a PN(Pseudo Random Number) sequence is employed for effective prevention of a portable device from being thieved by issuing an alarm when a portable device is out of preset range which causes a difference of a time offset in the PN sequence, includes a transmission block disposed in the portable device having a block for generating a particular pseudo random number sequence and a multiplication block for always multiplying a ‘high’ value to an output of the block for generating a particular pseudo random number sequence, the transmission block for converting an output of the multiplication block into an analog value and transmitting the analog value, and an anti-theft sensing circuit separate from the portable device for receiving a signal transmitted form the transmission block, sampling the signal, multiplying a sampled value to a pseudo random number sequence identical to a case of the transmission block, summing for a time period, comparing to a preset threshold value, and selectively providing an alarm signal to outside thereof according to a result of the comparison. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention: 
     In the drawings: 
     FIG. 1 illustrates the steps of an exemplary generation of a general pseudo- random number sequence; 
     FIG. 2 illustrates a system of a transmission system in a related art anti-theft circuit; 
     FIG. 3 illustrates a block system of a reception system in a related art anti-theft circuit; 
     FIG. 4 illustrates a block system of an anti-theft sensing circuit in accordance with a preferred embodiment of the present invention; 
     FIG. 5 illustrates a block system of a transmission system in an anti-theft circuit in accordance with a preferred embodiment of the present invention; 
     FIG. 6 a  illustrates a block diagram of a RF reception block; 
     FIG. 6 b  illustrates a block diagram of a RF transmission block; 
     FIG. 7 illustrates a block diagram of a PN sequence generation system in accordance with a preferred embodiment of the present invention; and, 
     FIG. 8 illustrates a correlation of PN generation of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. FIG. 4 illustrates a block system of an anti-theft sensing circuit in accordance with a preferred embodiment of the present invention, and FIG. 5 illustrates a block system of a transmission system in an anti-theft circuit in accordance with a preferred embodiment of the present invention. The anti-theft circuit for a portable device includes a transmission circuit in the portable device and a sensing circuit carried by a user. Herein, the portable device denotes various devices including personal portable telecommunication devices. The sensing circuit in the anti-theft circuit for a portable device will be explained. 
     Referring to FIG. 4, the sensing circuit in the anti-theft circuit for a portable device of one embodiment of the present invention to be carried by the user includes an A/D(analog-to-digital) converting block  31  for receiving an analog signal from the transmission circuit disposed in the portable device through a RF reception block  30  for converting into a digital signal; a sampling block  32  for sampling one of the digital signals from the A/D converting block  31 ; a first multiplication block  34  having an XOR(Exclusive OR) gate circuit for subjecting the sampled digital signal in the sampling block  32  and an output from a first pseudo random number sequence generation block  33  to multiplication block  34 ; an adding block  35  for adding the outputs of the first pseudo random number sequence generation block  33  for a period of time; a threshold value comparing block  36  for comparing an output of the adding block  35  to a preset threshold value to provide a ‘low’ signal if the output of the adding block is greater and a ‘high’ signal if the output of the adding block  35  is smaller, and an alarming means  37  for selectively providing an alarm signal according to the signal from the threshold value comparing block  36 . 
     Referring to FIG. 5, the transmission system in the anti-theft circuit of the preferred embodiment of the present invention disposed in the portable device includes a second multiplication block  39  for always multiplying ‘unity’ to an output of the second pseudo random number sequence generation block  38 , a D/A(Digital-to-Analog) converting block  40  for converting an output of the second multiplication block  39  into an analog value, a RF transmission block  41  for transmission of the analog value from the D/A converting block  40  in a RF. 
     The RF reception block  30  and the RF transmission block  41  in the sensing circuit and the transmission system have the following system. FIG. 6 a  illustrates a block diagram of a RF reception block, and FIG. 6 b  illustrates a block diagram of a RF transmission block. 
     The RF reception block  30  has a multiplier for multiplying a data received from a reception antenna and cos ωt, and a low pass filter for making a low pass filtering of an output of the multiplier and providing to the A/D converting block  31 . The RF transmission block has a multiplier for multiplying a value from the D/A converting block  40  and a cos ωt, and a transmission antenna for RF transmission of an output from the multiplier to outside. 
     Systems of the pseudo random number sequence generation blocks  33  and  38  will be explained in detail. FIG. 7 illustrates a block diagram of a PN sequence generation system in accordance with a preferred embodiment of the present invention, and FIG. 8 illustrates a correlation of PN generation of the present invention. 
     FIG. 7 illustrates an embodiment of a PN sequence generation system, wherein, if it is a 3 bit delay device, a first block is a delay MSB block  60 , a third block is a delay LSB block  61 . And, for identification of the user, a first block in a mask device block  64  composed of memories, such as EEPROM is a mask MSB block  62 , and a third block is a mask LSB block  63 . A pseudo random number sequence generation block has a first, a second, and a third AND operation block  65   a ,  65   b , and  65   c  each for subjecting initial values of respective bit digits in a delay block and a mask device blocks  64  to AND operation, and an adder  66  for adding operated values of the first, second, and third AND operation blocks  65   a ,  65   b , and  65   c.    
     FIG. 8 illustrates a correlation of a pseudo random number sequence generation in the aforementioned pseudo random number sequence generation block. 
     The anti-theft alarm giving operation in the anti-theft device for a portable device of the present invention will be explained. 
     If it is assumed that delay bits in a pseudo random number sequence generation is three bits, and mask bit is three bits, and value of the delay bits are ‘1 0 0’ and values of the mask bits for identification of the user is ‘0 1 1’, outputs of the second pseudo random number sequence generation block  38  will be ‘0 0 1 0 1 1 1, and 0 0 1 0 1 1 1, - - - , the transmission system disposed in the portable device will have a period of 2 3 −1, i.e., 7 chip. The chip is data bits generated according to a PN clock rate in a PN generation block. 
     The behaviour of the PN generation block in accordance with a preferred embodiment of the present invention will be explained. 
     When the pseudo-random number sequence has delay bits with initial values of ‘1 0 0’, since mask bits (seed values for identifying a user) are ‘0 1 1’, the first AND operation block  65   a  receives a delay bit ‘1’ and a mask bit ‘0’ to provide ‘0’. And, the second AND operation block  65   b  receives a delay bit ‘0’ and a mask bit ‘1’ to provide ‘0’. Accordingly, the adder  66  provides ‘0’. And, the next shifted delay bits ‘0 1 1’ are provided to the first, second, and third AND operation blocks  65   a ,  65   b , and  65   c  respectively, to provide ‘0 1 1’ respectively, causing the adder  66  to provide ‘0’. Thus, as the delay bits are repeated in an order of →1 0 0→0 1 1→1 1 0→1 1 1→1 0 1→0 0 1→0 1 0→, the adder  66  provides ‘0 0 1 0 1 1 1’, repeatedly. If the mask bits provided are, not ‘0 1 1’, but other values, the generated PN will differ. If sizes of the delay bits and the mask bits are, not 3 bits respectively, but larger, a size of the chip will also be larger, which is an extension of a number of numerals in the user identification code, it implies an increased admission capability of subscribers into the anti-theft circuit for a portable device of one embodiment of the present invention. 
     The PN generation block is a block generating 0&#39;s and 1&#39;s at random but with the same total numbers of 0&#39;s and 1&#39;s for a fixed period or interval, wherein, because, if seeds(mask bit values for user identification) which are sources for generating random numbers are different, sequences of 0&#39;s and 1&#39;s the seeds produce differ, provided the seed is unknown, the same sequence of 0&#39;s and 1&#39;s can not be produced. As shown in FIG. 5, since the value multiplied with the outputs of the second PN generation block  38  is always ‘1’, outputs of the second multiplication block  39  are always the same with the outputs of the second PN generation block  38 , which are provided to the RF transmission block  41  through the D/A converting block  40 . As shown in FIG. 4, values from the RF transmission block  41  in the transmission system of the anti-theft circuit of the preferred embodiment of the present invention are provided to the RF reception block  30  in the sensing circuit of the anti-theft circuit of the preferred embodiment of the present invention. The data received in the RF reception block  30  and demodulated of its phase is digitized in the A/D converting block  31 , and sampled in the sampling block  32 . A sampled value is multiplied with an output of the first PN generation block  33  generating an identical pseudo random number sequence to the second PN generation block  38  in the first multiplication block  34 . Outputs of the first multiplication block  34  are accumulated for a time period in the adding block  35 . In this instance, if the time period deviates more than 2 chip, i.e., if the portable device and the user are distanced away more than 2 chip from each other, the accumulated value in the adding block  35  is decreased to a value below the preset threshold value, so that the alarming means  37  issues a theft alarm signal to outside of the circuit (in the case when the threshold value is set to be a value when a 2 chip deviated). For example, if it is assumed that there is no time and distance deviations between the portable device and the anti-theft sensing circuit, and outputs of the sampling block  32  and outputs of the first PN generation block  33  are multiplied and summed for a time period ‘n’, a value provided to the threshold value comparing block  36  is n×2 3−1 , exactly. Herein, if it is defined that the threshold value is (n/2)×(2 3−1 ), an output of the threshold value comparing block  36  will be low, so that alarming means  37  provides no alarm signal to outside of the circuit. And, if there is a time difference of more than one chip in generation of random numbers from the first, and second PN generation blocks  33  and  38  in the transmission system in the portable device and the anti-theft sensing circuit the user carries, i.e., the transmission system and the anti-theft sensing circuit are distanced away corresponding to more than one chip, the value, multiplied, summed for a time period, of outputs of the sampling block  32  in the anti-theft sensing circuit and outputs of the first PN generation block  33 , and provided from the adding block  35  is substantially ‘0’ when a characteristic of the PN sequence is taken into consideration, to provide a ‘high’ from the threshold value comparing block  36 , for the alarming means  37  to issue an anti-theft alarm signal to outside of the device. 
     The aforementioned anti-theft circuit for a portable device of the present invention, in which an alarm signal is issued to the exterior of the device if distanced farther than a preset distance for prevention of the portable device, has the following advantages. 
     First, the use of a PN sequence correlation, which allows to dispense with a block decoding an activating signal, can simplify the system. 
     Second, a proper activating signal source that allows identification of each user can be assigned. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in an anti-theft circuit for a portable device of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.