Patent ID: 6531954
Filing Date: 2003-03-11
Classification: G08B

Abstract:
An anti-theft circuit for a portable device comprising:a transmission block disposed in the portable device having a transmission pseudo random number sequence generation block for generating a particular pseudo random number sequence and a multiplication block for always multiplying a relatively â€˜highâ€™ 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 from the transmission block, sampling the signal, multiplying a sampled value to a pseudo random number 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, the anti-theft sensing circuit including an RF reception block for receiving the signal from the transmission block, an analog-to-digital converting block for receiving a signal from the RF reception block and converting the signal into a digital signal, a sampling block for sampling one value from the digital signal output from the reception block, a pseudo random sequence generation block for generating a reception pseudo random number sequence, which is the same as the transmission pseudo random number sequence, a reception multiplication block for multiplying a sampled value from the sampling block with the output of the reception pseudo random sequence generation block, an adding block for accumulating outputs of the multiplication block for a time period and for summing the outputs, a threshold value comparing block for comparing an output of the adding block to a preset threshold value, to provide a â€˜lowâ€™ signal if the output of the adding block is relatively greater and a â€˜highâ€™ signal if the output of the adding block is relatively smaller, and an alarm means for selectively providing an alarm signal to an exterior of the portable device according to a signal from the threshold value comparing block.