什么是非归零码(英文解释)

NRZ (non-return-to-zero) refers to a form of digital data transmission in which the binary low and high states, represented by numerals 0 and 1, are transmitted by specific and constant DC (direct-current) voltage s.

In positive-logic NRZ, the low state is represented by the more negative or less positive voltage , and the high state is represented by the less negative or more positive voltage. Examples are: Logic 0 = +0.5 volts Logic 1 = +5.0 volts Logic 0 = -3.0 volts Logic 1 = 0.0 volts

In negative-logic NRZ, the low state is represented by the more positive or less negative voltage, and the high state is represented by the less positive or more negative voltage. Examples are: Logic 0 = +5.0 volts Logic 1 = +0.5 volts Logic 0 = 0.0 volts Logic 1 = -3.0 volts

Some people wonder why the name of this mode is preceded by\"non\" when one of the logic states might be represented by zero voltage.The answer becomes apparent from the comparative definition of RZ (return-to-zero). See also bipolar signaling , unipolar signaling , and RZ .

RZ

RZ (return-to-zero) refers to a form of digital data transmission in which the binary low and high states, represented by numerals 0 and 1, are transmitted by voltage pulses having certain characteristics. The signal state is determined by the voltage during the first half of each data binary digit . The signal returns to a resting state (called zero) during the second half of each bit. The resting state is usually zero volts, although it does not have to be.

In positive-logic RZ, the low state is represented by the more negative or less positive voltage, and the high state is represented by the less negative or more positive voltage. Examples are:

Logic 0 = 0 volts for 1 bit

Logic 1 = +5 volts for 1/2 bit, then 0 volts for 1/2 bit

Logic 0 = -4 volts for 1/2 bit, then 0 volts for 1/2 bit Logic 1 = 0 volts for 1 bit

In negative-logic RZ, the low state is represented by the more positive or less negative voltage, and the high state is represented by the less positive or more negative voltage. Examples are:

Logic 0 = +5 volts for 1/2 bit, then 0 volts for 1/2 bit Logic 1 = 0 volts for 1 bit

Logic 0 = 0 volts for 1 bit

Logic 1 = -4 volts for 1/2 bit, then 0 volts for 1/2 bit.

See also bipolar signaling , unipolar signaling , and NRZ .

bipolar signaling

See also unipolar signaling .

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 below 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.

unipolar signaling

Unipolar signaling, also called unipolar 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 unipolar signal as it might appear on the screen of an oscilloscope . Each horizontal division represents one bit (binary digit). The logic 0 state is approximately 0 volts and logic 1 is

approximately +5 volts. (There is some room for error.) This is positive logic . Alternatively, logic 0 might be approximately +5 volts, and logic 1 might be approximately 0 volts; this would be negative logic . The bandwidth of a unipolar 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.

See also bipolar signaling .