Abstract: A waveform shaping circuit wave-shapes a demodulated signal after FM demodulation to generate a binary value. A smoothing circuit smoothes the demodulated signal to generate a reference voltage. A comparator compares the reference voltage with the demodulated signal to output the binary value. A potential difference limiting circuit determines whether a potential difference between the demodulated signal and the reference voltage exceeds a set voltage. When the potential difference exceeds the set voltage, the potential difference is controlled to a value less than the set voltage. At the initiation of signal reception or after a jamming signal stops, the reference voltage follows the demodulated signal, thus allowing data reception to rapidly begin.

Abstract: When a vehicle door locking operation is conducted, an in-vehicle device checks the vehicle compartment to determine whether a mobile unit exists in the vehicle compartment. When the in-vehicle device receives a response from the mobile unit indicating its presence in the compartment, the in-vehicle device receives a response from the mobile unit, prohibits the door from locking, and activates a buzzer. The mobile unit thus can be prevented from being locked in the vehicle compartment. When the mobile unit receives the search signal, it sounds its buzzer, thereby making it possible to further indicate its location within the compartment.

Abstract: A waveform shaping circuit wave-shapes a demodulated signal after FM demodulation to generate a binary value. A smoothing circuit smoothes the demodulated signal to generate a reference voltage. A comparator compares the reference voltage with the demodulated signal to output the binary value. A potential difference limiting circuit determines whether a potential difference between the demodulated signal and the reference voltage exceeds a set voltage. When the potential difference exceeds the set voltage, the potential difference is controlled to a value less than the set voltage. At the initiation of signal reception or after a jamming signal stops, the reference voltage follows the demodulated signal, thus allowing data reception to rapidly begin.

Abstract: When a door locking operation is conducted in a vehicle, an in-vehicle device executes a vehicle compartment checking to check whether a mobile unit exists in the vehicle compartment. When the in-vehicle device receives a response from the mobile unit, the in-vehicle device transmits a search signal to the mobile unit, prohibits the door locking, and activates a buzzer, etc. The mobile unit can be prevented from being blocked in a vehicle compartment. When the mobile unit receives the search signal, it blows the buzzer, thereby making it possible to indicate the location of its existence.

Abstract: A mobile unit for an electronic key system includes an LF receiver unit that receives a radio signal transmitted from an in-vehicle device by an electric wave of an LF band, a UHF transmitter unit that transmits a radio signal to the in-vehicle unit by an electric wave of a UHF band. The mobile unit also includes a UHF receiver unit that receives a search signal transmitted from another mobile unit by an electric wave of the UHF band, and a buzzer that notifies outside existence thereof when the search signal is received by the UHF receiver unit. The UHF transmitter unit can transmit the search signal to the mobile unit in addition to the radio signal to the in-vehicle device.

Abstract: A transmission system is provided which includes a transmitter working to transmit data on a frame basis and a receiver. If two frames having the same data are inputted in sequence to the receiver, the receiver decides that it is unnecessary to decode a following one of the frames and stops receiving or decoding it. This results in decreases in operation load and power consumption of the receiver.

Abstract: A receiver includes a circuit board and a dielectric antenna. The circuit board has a receiving circuit on a first surface, and a ground pattern on a second surface. The circuit board is disposed close to a rear window of a vehicle so that the ground pattern faces a roof panel. The dielectric antenna extends from an edge of the circuit board toward and along the rear window. As a result, the roof panel capacitively couples with the ground pattern, so that the roof panel becomes imaginary ground. The dielectric antenna functions as a monopole antenna with the imaginary ground. It is not influenced with a metallic material of the vehicle.

Abstract: A receiver includes a circuit board and a dielectric antenna. The circuit board has a receiving circuit on a first surface, and a ground pattern on a second surface. The circuit board is disposed close to a rear window of a vehicle so that the ground pattern faces a roof panel. The dielectric antenna extends from an edge of the circuit board toward and along the rear window. As a result, the roof panel capacitively couples with the ground pattern, so that the roof panel becomes imaginary ground. The dielectric antenna functions as a monopole antenna with the imaginary ground. It is not influenced with a metallic material of the vehicle.

Abstract: A transmission system is provided which includes a transmitter working to transmit data on a frame basis and a receiver. If two frames having the same data are inputted in sequence to the receiver, the receiver decides that it is unnecessary to decode a following one of the frames and stops receiving or decoding it. This results in decreases in operation load and power consumption of the receiver.