The basic principle of delta modulation is proposed in 1946, it is one of the simplest differential pulse code. Early language delta modulation encoder is composed of discrete components. With the development of analog integrated circuits technology, in the late 1970s there has been amplification of syllabic modulator monolithically integrated amount, 80s instantaneous companding monolithically integrated, single-chip comprising the switched capacitor filter and a switched capacitor integrator, continuously improve the degree of integration, the volume of the delta modulation encoder is reduced, reducing power consumption.
Simple delta modulation (DM) of the principle shown in FIG. FIG: x ( n ) denotes analog signal n sampled values; Min ( n ) denotes x ( n ) of the predicted value; Benjamin ( n ) represents an approximation of the n th sample values, Min ( n ) = Benjamin ( n -1); d ( n ) samples representing x difference ( n ) and its predicted value Min ( n ) of, d ( n ) = x ( n ) - Min ( n ); Lu ( n ) denotes the quantizer output value , if the difference d ( n ) is positive, Lu ( n ) = Jian, Jian called the order of magnitude; if d ( n ) is negative, Lu ( n ) = - Jian.
delta modulation delta modulation systems transmit digital form end rule: If the quantizer output Lu ( n ) = Jian, the digital c ( n ) = 1, also known as "1" code; otherwise Lu ( n ) = - Jian, the digital c ( n ) = 0, also known as "0" code. In the receiving side, an order of magnitude from a digital solution Lu '( n ), which decoding rule is: the received "1" code, c ' ( n ) = 1, gives the order of magnitude Lu '( n ) = Jian; received "0" code, c ' ( n ) = 0, gives the order of magnitude Lu '( n ) = - Jian. Xun output signal samples ( n ) = Lu '( n ) + Lu' ( n -1). If the transmission channel without error i.e. c ( n ) = c '( n ), the receive end Xun (n) same as ( n ) and Benjamin transmit end, and the holding circuit after a low pass filter to restore the original sampled analog signal. An actual circuit, the integrator can be used to implement the functions of adding and delay units; available amount and polarity switch to the generator stage quantizer composition; and sampling, the digital portion may be formed to constitute a shift register.
Early simple delta modulation is the dynamic range is narrow, can not meet the practical requirements of the telephone system, therefore, there have been many improvements of different types of delta modulation form. Wherein a wider class of applications is an adaptive delta modulation, which is characterized by the order of magnitude quantizer can automatically follow changes in the signal amplitude, thereby expanding the dynamic range. If the order of magnitude of the mean slope information size (average value of 10 ms in the syllable) directly detects the output of the digital controlled, it is called digital modulation detection syllabic amplification amount; if the amount of control depending on adjacent bands two digital, the amount of amplification is called the instantaneous pressure modulation; if large syllable companded signal segment, and in the small-signal segment instantaneous companding, known as the mixing amount of the amplified modulated pressure; if the order of magnitude of control information directly extracted from the input analog signal, is called a continuous delta modulation; if the analog signal is then carried through the integration delta modulator is called a sigma delta modulator, modulation referred Jian -Σ; if integration circuit section is composed of two integral series consisting of double integral is called delta modulation.
delta modulation and pulse code modulation (PCM) compared with the following three characteristics: ① simple circuit, and pulse code modulation encoder requires more logic circuit; ② when a data rate lower than 40 kbit / s data pulse code modulation voice quality is good, generally using delta modulation rate of 32 kbit / s or 16 kbit / s; ③ good anti-channel error performance, can work in the channel bit error rate is 10-3, while pulse code modulation is lower than the required channel error rate of 10-5 ~ 10-6. Therefore, the delta modulation for medium-quality military communications, scatter communications and rural telephone network communication systems. Delta modulation technique is also applicable to digital processing of the image signal.