TRANSCEIVER FOR LOCAL NETWORK USING CARRIER-SENSE MULTIPLE ACCESS/COLLISION DETECTION

This document is a 1983 United States Patent describing a transceiver for a Carrier-Sense Multiple Access/Collision Detection (CSMA/CD) communications network, such as those using coaxial cable. The invention specifically addresses the challenge of utilizing industry-standard emitter-coupled logic (ECL) for the transmitter's current source.

Traditional ECL circuits, typically operating within a 0 to -5 volt range, face compliance limit issues when generating the larger voltage swings (6-7 volts) required during collision detection on the network. The patent proposes operating the transmitter current source in a power supply range of -5 to -10 volts, while the receiver and collision detection circuits operate in a contiguous range of 0 to -5 volts. This arrangement prevents the current source from saturating during signal collisions, ensuring that the collision detection mechanism remains functional.

Additionally, the document describes:

• Protection Circuits: Guard circuitry with timers that short-circuit the transmitter output to ground if a station attempts to monopolize the network.
• Collision Detection Testing: An integral mechanism that simulates a collision at the end of each transmission to verify that the collision detection circuitry is operational.
• Signal Shaping: A staircase waveform generator that reduces high-frequency components in the transmission, minimizing phase distortion.
• Isolation: Circuitry to protect the network from transceiver short circuits.