Table of contents
1. Sampling
(1) Continuous time signal
The independent variable t is continuous, and there are corresponding function values on the independent variable. The function value (magnitude) can be continuous or discontinuous. If the amplitude is continuous, it is called an analog signal.
An example of a continuous-time signal with a discontinuous amplitude: the unit step signal is discontinuous at t=0.
(2) Discrete time signal
The independent variable t is discrete and the magnitude is continuous.
(3) Sampling : The process of sampling is the process of converting an analog signal into a discrete time signal .
There is no quantization after sampling, so the amplitude is continuous. The concept of continuity here is different from the concept of function continuity in mathematics. Function continuity means that the curve is smooth and can be guided everywhere. The continuity of the signal here means that any value in the value range of the original analog signal can be taken.
Example: For a sine wave voltage signal
| If the peak value of the signal is plus or minus 1.4V. Then the voltage obtained by sampling may be any value between -1.4V and +1.4V. The value itself is not quantized, so a continuous value is obtained. |
The sampling process is as follows ( see the vertical line ):
2. Quantification
Quantization : Use a set of numbers (such as binary numbers) to approximate the amplitude of a discrete signal and convert a discrete-time signal into a digital signal.
Quantization involves an important concept, that is "sampling bit depth". Sampling bit depth means that the value of each sampling point is represented by several bits . It is easy to understand that the more bits, the wider the range of numbers that can be represented, and it can be closer to analog signals. It can be intuitively understood. If the sampling rate and bit The depth is very large, and the discrete sequence of samples can be approximately equal to the analog signal.
Commonly used sampling bit depths are as follows:
| 8bit: 256 values, from 0 to 255 16bit: 65536 values, from 0 to 65535 24bit：……………………………… 32bit：………………………………. |
The quantization process is as shown in the figure below ( see the horizontal line ): q1=2, q2=3, q3=4, q4=5
After quantization, the analog signal with continuous time and continuous amplitude becomes a digital signal with discrete time and amplitude.
3. Coding
Coding is the third stage of analog signal digitization. The process of transforming the quantized sampling signal into a binary code stream with a given word length is called the coding process. As shown in the figure below: the output of the ADC chip is the audio data stream of 0 and 1.
4. Summary
(1) Analog signal digitization includes three processes: sampling + quantization + encoding
(2) Sampling turns continuous-time signals into discrete-time signals
(3) The digital signal is obtained after quantization and encoding. At this time, both the independent variable and the dependent variable are discrete values
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