Automatic answering system using transponder

摘要

The power feeding efficiency and the communicable range of an automatic answering system are improved in an automatic answering system using a transponder which performs code communication using amplitude modulation of a carrier with an electromagnetic coupling transponder mounted in a key 1 or the like. In a transceiver for performing the code communication with the transponder via an antenna coil 4, a circuit for driving the antenna coil 4 in a transceiver 510 based on clock CLK is implemented by a bridge-type complementary circuit of transistors 52a - 52d. Thereby, driving current is increased. Meanwhile, a circuit for controlling the driving mode based on a write signal WR is implemented by a parallel circuit of a transistor 51 to which a power-supply voltage Vcc is applied and a resistor 511. Thereby, a current corresponding to a resistance of the resistor 511 flows through the antenna coil 4 even during the minimum driving when the transistor 51 is turned off, thus improving the power feeding efficiency and the communicable range of the system.