One by one, sensors are activated by sending an n-bit long word. The demultiplexer (DEMUX) selects one of the 2n output lines and enables the input (EN) of the chosen ring oscillator (Fig.4) for a period of time determined by the /STR signal. Frequency signal fosc from the activated oscillator, via addressable multiplexer (MUX) and frequency divider is given on the output as a fout signal.