Abstract: A method comprising maintaining (A, B), by a device (6), communication with a monitoring unit (7); determining, by the device, an absence of communication from the monitoring unit; based at least on a result of said determining, starting monitoring (F) of at least one variable related to distance moved by the device and/or time elapsed; if the at least one variable meets at least one criterion, determining that the absence of communication from the monitoring unit is not due to a blind spot. A device securely attachable to a person (5) may be configured to carry out this method, which may be user in offender monitoring.

Abstract: A frequency calibration apparatus and method are provided. A frequency calibration method includes determining a frequency band according to results of frequency comparisons between a synchronized reference signal whose phase is synchronized to a phase of a prescale signal and a divided signal, and performing a Phase Locked Loop (PLL) operation on a reference signal and the divided signal at the determined frequency band to lock the divided signal.

Abstract: A method and apparatus are provided for analog-to-digital conversion, which uses switched capacitors for quantizing an input current. The apparatus for analog-to-digital conversion includes a plurality of charge units configured for being input with a current signal in an analog form, being sequentially charged with the input current signal, and providing a high-level or low-level signal to each next sequentially connected charge unit according to whether or not the charged charge unit is charged above a predetermined threshold value. The apparatus also includes a latch register for receiving the high-level or low-level signals output from the plurality of charge units, converting the received high-level or low-level signals into a linear code, and outputting the converted linear code. The high-level signal is used for starting to charge the next connected charge unit.