RF tag, RF tag reader, and pulse code key detecting circuit, and RF tag system using them

An RF tag system for conducting radio communications between an RF tag reader and an RF tag using radio waves of VHF band or above (30 MHz or above), comprising:

• the RF tag configured as at least one of a remote start RF tag and a scheduled start RF tag, and
• the RF tag reader, the RF tag reader being constructed and arranged to send a tag activating command including RF tag ID code of an RF tag on the other end of communications in ASK modulation mode by using a CW radio wave at a query carrier frequency fo, and receiving a response signal as a return information, which is superimposed on a sub-carrier signal frequency-offset by a frequency fs from the query carrier frequency fo, from the RF tag,
• wherein the remote start RF tag includes a resonant stub voltage multiplier circuit that detects a query from the RF tag reader and a pulse code key detecting circuit that determines whether a pulse width is within a certain range,
• wherein the scheduled start RF tag includes a resonant stub voltage multiplier circuit that detects a query from the RF tag reader and a demodulation circuit that is driven by a timer at regular time intervals, and
• wherein the RF tag reader includes a quadrature and compensation circuit that directly conducts quadrature detection by the query carrier frequency fo and then corrects detection error, and a generating circuit that samples signals at a frequency 4 fs in order to obtain an MPSK demodulated signal from a detection signal.