Passive keyless entry device

The present invention provides a passive keyless entry device having a switching element 4, which is switched on/off by a control signal, connected to a symmetrical low frequency transmission circuit, so that a transmission speed of a transmission signal is not lowered and a transmission efficiency of the transmission signal is not deteriorated. The passive keyless entry device comprises a vehicle-mounted transceiver and a portable transceiver. The vehicle-mounted transceiver comprises a clock circuit 9 for outputting a clock signal, a control circuit 10 for outputting a control signal, modulation circuits 7 and 8 for modulating the clock signal with the control signal to produce a modulation signal and an inverted modulation signal, transmission circuits 1 and 2 for supplying the modulation signal and the inverted modulation signal to a low frequency antenna 3, and a switching FET 4 driven by the control signal. The transmission circuits 1 and 2 are configured by first and second half-bridge circuits composed of a pair of FETs 1a and 1b and a pair of FETs 2a and 2b, respectively and the low frequency antenna 3 is connected between output terminals 5 and 6 of the first and second half-bridge circuits, and the switching FET 4 is connected in series to a transmission path of the low frequency signal and is switched off when transmission of the low frequency signal is stopped.