Reader/writer for performing efficient transmission/reception with no-battery information storage medium

A reader/writer which transmits power and modulated data to a no-battery information storage medium having a communication function in a noncontact state, and receives modulated data from said no-battery information storage medium, comprising:

• first and second drivers for transmitting the power and the modulated data;
• first and second loop antennas connected to respective output lines of said first and second drivers to respectively receive transmission carrier currents from said first and second drivers;
• first and second current detection means, arranged between said first and second loop antennas and the respective output lines of said first and second drivers, for extracting, as reception signals, changes in transmission carrier currents of said first and second loop antennas caused by signals of the modulated data received by said first and second loop antennas while the transmission carrier currents are supplied from said first and second drivers upon reception of the modulated data from said no-battery information storage medium;
• and
• addition means for adding the modulated data signal currents extracted from respective outputs from said first and second current detection means.

A reader/writer which transmits power and modulated data to a no-battery information storage medium having a communication function in a noncontact state, and receives modulated data from said no-battery information storage medium, comprising:

• a driver for transmitting the power and the modulated data;
• a loop antenna connected to an output line of said driver to receive a transmission carrier current from said driver;
• and
• current detection means, arranged between said loop antenna and the output line of said driver, for extracting, as a reception signal, a change in transmission carrier current of said loop antenna caused by a signal of the modulated data received by said loop antenna while the transmission carrier current is supplied from said driver upon reception of the modulated data from said no-battery information storage medium wherein, when a binary-phase-modulated signal having undergone binary phase modulation with a sub-carrier having a fraquency 1/n (n is an integer) a transmission carrier frequency used for transmission is received as the modulated data from said no-battery information storage medium, said reader/writer uses said current detection means to extract, as the modulated data received by said loop antenna, a signal current of the binary-phase-modulated signal having undergone binary phase modulation with the sub-carrier having the frequency 1/n the transmission carrier frequency used for transmission, and further comprises
• signal processing means for changing the binary-phase-modulated signal extracted by said current detection means into a binary signal;
• and
• demodulation means for starting counting from an edge of a pulse for an ON period of the pulse of the binary signal from said signal processing means on the basis of the transmission carrier frequency to detect a timing of substantially a center of a width of the pulse, and when the timing is continuously detected a predetermined number of times, turning on a gate for the demodulated output of the binary-phase-modulated signal to enable the demodulated output, or when the timing cannot be detected the predetermined number of times within a predetermined time, turning off said gate to disable the demodulated output.