Four-level binary data transmission system - uses single-step level transition to code binary zero and double-step transition for binary one

摘要

The serial binary data transmission system uses four levels, denoted A.B.C. A binary zero is coded by a single-step level transition towards, or between, the two intermediate levels, B and C. A double-step transition from A to C or B to D is used to code binary one. Preferred encoding circuitry uses four flip-flops, each corresp. to one of the four possible levels. Logic circuitry responds to incoming data bits to set one of the flip-flops in accordance with the voltage level to be produced. Decoding circuitry may use a differentiator producing spikes of two different magnitudes, corresp. to a one or zero. These spikes feed comparators's driving a flip-flops with associated logic circuits. The transmission system allows completely asynchronous transmission since each new bit is immediately recognisable and avoids DC imbalance problems.