Abstract: A surrounding circuit for the local area network transceiver comprises isolation transformer, electric resistance, Diodes, transmitting circuit, transistor, electric capacitor, and input circuit; in order to slow down the rising time and falling time of the signal, the circuit can effectively improve the output signal waveform at the secondary coil of the isolation transforming and make it similar to sine wave which decreases the possibility of high frequency radiation. The circuit also provides a receiving surrounding circuit connected to the output of the transmitting surrounding apparatus which can eliminate the Common Mode Noise, has the effect of isolation, and at the same time allows the low-frequency collision signal to enter the transceiving circuit and maintains enough high input impedance.

Abstract: The present invention relates to an apparatus for transmitting and receiving Manchester coded digital data for IEEE 802.3 Ethernet/Cheapernet type local area network. The apparatus mainly comprises, an isolation transformer, a signal converter with one end connected to one side of the isolation transformer, a receiver with its input connected to the other end of the signal converter, a capacitor located in the receiver and a transmitter with its output connected to the other side of the isolation transformer whereby the isolation transformer and the capacitor may isolate the external terminals from the main circuit. Moreover, the receiver and the transmitter can be integrally formed with a controller and thus to reduce the cost.