What Is Delta Modulation?

Incremental modulation is abbreviated as M or incremental pulse code modulation (DM), which is another method of digitizing analog signals after PCM. Proposed by French engineer De Loraine in 1946, the purpose is to simplify the digital method of analog signals. It is widely used mainly in military communications and satellite communications, and is sometimes used as an A / D converter in high-speed large-scale integrated circuits.

Incremental modulation is abbreviated as M or incremental pulse code modulation (DM), which is another method of digitizing analog signals after PCM. Proposed by French engineer De Loraine in 1946, the purpose is to simplify the digital method of analog signals. It is widely used mainly in military communications and satellite communications, and is sometimes used as an A / D converter in high-speed large-scale integrated circuits.

Chinese name

Incremental modulation

Short name

M

Category

Method of digitizing analog signal

Presenter

De Loraine

Research Progress of Incremental Modulation

The basic principle of incremental modulation was proposed in 1946. It is the simplest type of differential pulse coding. Early speech incremental modulation encoders consisted of discrete components. With the development of analog integrated circuit technology, integrated monolithic modules for syllabic compression amplification appeared in the late 1970s, and instantaneous companding integrated monolithic chips appeared in the 1980s. The monolithic chip includes switched capacitor filters and switched capacitor integrators. The degree of integration is continuously improved, which makes the encoder of incremental modulation smaller in size and lower in power consumption.

How Incremental Modulation Works

The principle of simple incremental modulation (DM) is shown in the figure. Figure

Incremental modulation

Middle: x ( n ) represents the nth sample value of the analog signal; ( n ) represents the predicted value of x ( n ); mercy ( n ) represents the approximate value of the nth sample value, and ( n ) = mercy ( n -1); d ( n ) represents the difference between the sample value x ( n ) and its predicted value ( n ), d ( n ) = x ( n )- ( n ); ( n ) represents the quantizer The output value. If the difference d ( n ) is positive, then ( n ) = , is called the magnitude; if d ( n ) is negative, then ( n ) =-.

Incremental modulation The digital formation rule of the transmitting end of the incremental modulation system is: if the quantizer outputs ( n ) = , then the digital c ( n ) = 1, also known as "1" code; otherwise ( n ) =-, then the number c ( n ) = 0, also known as "0" code. At the receiving end, the magnitude '( n ) is solved from the digital, and the decoding rule is: "1" code is received, c ( n ) = 1, and the magnitude ' ( n ) = is received; receive To the 0 code, c ( n ) = 0, giving the magnitude ( n ) =-. Output signal samples ( n ) = '( n ) + ' ( n -1). If the transmission channel is error-free, that is, c ( n ) = c '( n ), the receiving end ( n ) is the same as the transmitting end ( n ), and the original analog signal is restored after the sample-and-hold circuit and the low-pass filter. . In an actual circuit, an integrator can be used to implement the functions of an adder and a delay unit; a magnitude generator and a polarity switch can be used to form a quantizer; and the sampling and digital forming parts can be composed of shift registers.

Incremental modulation classification

The disadvantage of the early simple incremental modulation was that the dynamic range was very narrow and could not meet the requirements of practical telephone systems. Therefore, many different types of incremental modulation appeared. One of the more widely used is adaptive incremental modulation, which is characterized by that the magnitude of the quantizer can automatically follow the change in signal amplitude, thereby expanding the dynamic range. If the magnitude is controlled by directly detecting the average slope information (the average value within 10 ms of the syllable) in the output digital, it is called digital detection of the syllable pressure amplification amount modulation; if the magnitude control depends on The two digits are called instantaneous compression amplification modulation; if syllable companding is used in the large signal segment and instantaneous compression expansion is used in the small signal segment, it is called mixed compression amplification modulation; Extracted from the input analog signal, it is called continuous incremental modulation; if the analog signal is integrated and then subjected to incremental modulation, it is called total incremental modulation, referred to as - modulation; if the integration circuit is integrated by two sections It is called double-integral-incremental modulation when it is connected in series.

Incremental modulation characteristics

Compared with pulse code modulation (PCM), incremental modulation has the following three characteristics: the circuit is simple, and the pulse code modulation encoder requires more logic circuits; when the data rate is less than 40 kbit / s, the voice quality ratio Pulse code modulation is good. The data rate used for incremental modulation is generally 32 kilobits / second or 16 kilobits / second. Good anti-channel error performance, can work on channels with an error rate of 10-3. Code modulation requires the channel bit error rate to be lower than 10-5 to 10-6. Therefore, incremental modulation is suitable for medium-quality communication systems such as military communications, scattered communications, and rural telephone networks. Incremental modulation technology can also be applied to the digital processing of image signals.