Bipolar Signalling - Telecommunications
Bipolar signaling, also called bipolar transmission, is a baseband method of sending binary data over wire or cable. There are two logic states, low and high, represented by the digits 0 and 1 respectively.
The illustration shows a bipolar signal as it might appear on the screen of an oscilloscope. Each horizontal division represents one bit (binary digit). The logic 0 state is -3 volts and logic 1 is +3 volts. This is positive logic. Alternatively, logic 0 might be +3 volts, and logic 1 might be -3 volts; this would be negative logic. Whether positive or negative logic is used, the voltages representing the low and high states are equal and opposite; over time, the average voltage is approximately equal to 0.
A bipolar signal resembles an alternating current (AC) rectangular wave, except that the frequency is not constant. The bandwidth of the signal is inversely proportional to the duration of each data bit. Typical data speeds in baseband are several megabits per second (Mbps); hence the duration of each bit is a fraction of a microsecond.