Home > Industry Information > Introduction And Principle Analysis Of Pulse Code Modulation
Pulse-code modulation (PCM) is a modulation method that converts analog signals into digital signals. Its function is to transform the continuously input analog signal into a quantity
that is discrete both in the time domain and amplitude, and convert it into code form for output.
The working principle of pulse code modulation is to sample, quantify and encode a series of analog signals, and convert them into binary codes to achieve the communication mode.
2.1 Sampling
Select a series of sample points at fixed time intervals in a continuous analog signal. The sampling rate refers to the number of samplings per second, with the unit being Hertz (Hz).
According to Nyquist's theorem, in order to reconstruct the original signal without distortion, the sampling rate should be at least twice the highest frequency of the signal.
2.2 Quantification
Quantization is the process of mapping continuous analog signal values to discrete amplitudes using sample values, and replacing the sampled values with the closest level values using a previously specified set of level values.
2.3 Coding
The quantization value of each fixed level is represented by A set of binaries. Coding faults are also called analog-to-digital conversion (A/D).
2.4 Channel Transmission
The digital signal encoded by PCM can be transmitted through digital channels, such as digital audio interfaces (such as S/PDIF) or network transmission.
2.5 Decoding
At the receiving end, the PCM signal undergoes a decoding process to convert binary codewords into quantization levels. The decoding process is the reverse process of the encoding process.
· Hardware components: sensors, circuit boards, display screens, etc
· Software system: Data processing algorithm, user interface design
At the transmitting end, the input analog signal m(t) is sampled, quantized and encoded. The encoded PCM signal is a binary digital sequence,
and the transmission mode can adopt digital baseband transmission or bandpass transmission after carrier modulation.
At the receiving end, the PCM signal is decoded and restored to a sequence of quantized values with errors. Then, the high-frequency components are
filtered out by a low-pass filter, and the reconstructed analog signal m(t) can be obtained.
Compared with analog signals, digital signals are less disturbed by noise during transmission, and error correction coding technology can be adopted to further improve the timeliness and reliability of signal transmission.
The storage and processing of digital signals are more convenient and efficient than those of analog signals. PCM converts analog signals into digital signals,
making the storage, processing and transmission of audio and video data more convenient.
PCM is one of the key technologies in the digitization process of analog signals. It converts continuous analog signals into discrete digital signals, enabling the signals to be stored,
processed and transmitted in digital form. This is of vital importance in modern communication and computer systems.
Prediction Coding refers to the prediction of a signal by using one or more signals in front, and then encoding the difference between the actual value and the predicted value
Differential pulse code modulation is a modulation method that quantitatively encodes the difference of amplitude sampling of analog signals, and is simply called difference coding.
This modulation method uses past sampling values to predict the current sampling values and encodes them. Difference encoding can increase the encoding frequency.
This technology is widely used in digital communication between analog signals.
In order to adaptively select the optimal parameters, the communication encodes the source data between partitions. During encoding, a set of predicted parameters is automatically
selected to minimize the mean square error between the actual value and the predicted value in this interval. Its characteristic is that, based on the uneven distribution of the signal,
the system has the ability to change the size of the quantization interval with the variation of the input signal to maintain the basic uniformity of the signal input to the quantizer. This ability is called adaptive quantization.
·Frequency division multiplexing: The frequency band of the transmission channel is divided into several narrow bands, and each narrow band is responsible for transmitting one signal.
For instance, if the frequency band of a channel is 1400Hz, this channel is divided into four sub-channels: 820-990Hz, 1230-1400Hz, 1640-1810Hz, and 2050-2220Hz.
The distance between adjacent sub-channels is 240Hz, which is used to ensure that the sub-channels do not interfere with each other and that each pair of users occupies only one sub-channel.
This is an important means of simulating carrier communication.
·Time-division multiplexing: It divides the transmission channel by time, assigns a time interval to each user, and transmits a part of the signal within each interval. This way, more users can use one transmission line.
Pulse Code Modulation (PCM), as an important digitalization technology for analog signals, converts continuous analog signals into discrete digital signals through the processes of sampling, quantization and coding.
This not only improves the efficiency and reliability of signal transmission, but also provides great convenience for the storage and processing of signals.
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