SU771870A1 - Digital-analogue of differential pulse-cose modulation signal - Google Patents

Description

Transmitter code 1 signal, which is a sequence of code groups, a; b, c, d .... i, J .... These code groups are fed to the input of a digital adder 2 and are sequentially recorded in cell 1 of delay element 5 .. Digital adder 2 generates pulse code modulation (PCM) code groups a; l; with ; i,. . (Fig.2.2), carrying information about the value of a copy of the signal from the sampling points. Each of the code groups a; B; . . . . i. . . is the result of the digital summation of the corresponding code group from the sequence a, b, c, d ..., ... with the preceding code groups, for example group a is the result of the sum of code group a, which appeared at the output of code converter 1, with the previous code groups (not shown in Fig. 2.1). The code group b is the result of the summation of the code group b with group a and the previous code groups.

The output digital stream of the digital adder 2 is fed to the delay element 4 and is recorded in the cell 1. The code groups are promoted to the delay element 4.5 as the following code combinations arrive.

The signals generated in each of the cells of the delay element 4 are shown in the diagrams of FIG. 2. The diagram of FIG. 2.2 corresponds to a digital signal generated in the cell 1 of the delay element 4. The code combination in the specified cell occurs simultaneously with the formation of the output signal of the digital adder 2. Timing diagrams signals in cells 2, 4 elements, delay 4 are presented in the diagrams of FIG. 2.3,4,5, respectively.

For the case in question, the delay time of the delay elements 4.5 is 4 sample periods. Those. it is equal to the transmission time of the four code groups in the sequences a, b, c, d, ..., ... or a; B;

c; ... By the time t

(FIG. 2) in cell 4 of the delay element 4, the code combination a is recorded (FIG. 2.5), in cell 3 of this cross of the delay element the code combination (FIG. 2.4), in cells 2 and 1 of the combination c, d, respectively (FIG. .2.3,2). At the same time t, in the delay element 5, the code combinations are distributed as follows: cell 4 is a combination (Fig. 2.6), cells 3,2,1 combinations of b, c, d, respectively.

If the code combination corresponds to a front edge in the original analog signal, i.e. carries information about the large quantization step, then a control signal is generated at the output of the decoder 7 (Fig. 2.7), which arrives at the input of the control unit B. The latter replaces the code groups a, b, c recorded in cell 1 of the same delay element. Thus, the correction of the digital signal is performed by erasing 4,3,2 delay elements 4 of code groups a, b, c in cells and inserting code groups d similar to the code group recorded in cell 1 of delay element 4 into the indicated cells The arrival of subsequent code combinations e, f to the input of delay element 4 leads to the advancement of combinations in its cells and forming it at the output of delay element 4 of the digital stream with corrected code groups (Fig. 2.8). In the absence of a digital stream a; B; with; d code groups corresponding to large quantization levels are not replaced, and the digital signal at the output of delay element 4 (Fig. 2.9) is the input signal (Fig. 2.3), delayed by time. 4To.

 The process of forming code groups and their promotion can also be carried out in parallel code. The principle of operation of the proposed device in this case is similar to that described above.

Delay elements 4.5 delay the digital signals at the same time. In the case of the identical bitness of the code groups a, b, c ... and a, b, c. .. delay elements 4,5 can be identical. If in the process of forming the sequence a,, ... there occurs a change in the code group size, then the delay elements 4.5 will not be identical from the point of view of the circuit diagram, but in this case they must have the same delay time.

The process of shifting code groups in delay elements 4.5 is carried out either by a clock frequency, with consecutive arrival of bits of code groups, or, when advancing a parallel code, by sampling frequency FJJ. In both cases, the pushing (shifting) signals come from the code converter 1 of the DPCM code groups to the code groups of the natural code. The same signals synchronize the operation of the digital code group adder.

The use of new elements - two delay elements, a control unit and a decoder favorably distinguishes the proposed digital-to-analog converter of the differential pulse-code modulation signal from the specified prototype, since the error of quantization of the edges of the transmitted signal is reduced without increasing the size of the DICH code. When using the proposed device, it is possible to reduce the DPM code bit size and, consequently, decrease the required bandwidth of the communication channel. This makes it possible to simplify either the compaction equipment or the communication line itself.

The use of the proposed device also makes it possible to transmit half-tone images using the DPCM method with an eight-level quantization scale. At the same time, the quality of the received reproduction is not worse than in the case of the use of the 16-level DMC. A 25% reduction in the amount of transmitted binary information allows an increase in the transmission rate and, consequently, a decrease in the occupancy time.

communication channel. For example, the transmission time of a black-and-white halftone original of the () mm format, with resolution, using 16-level DPCM and J at a clock frequency of the digital communication channel of 4.8 К1ц is 25 minutes. The use of the proposed device allows, with the same parameters, to transmit the original for

0 minutes As an example, the table calculates the expected economic effect by reducing the cost of renting a channel of a digital communication system for some characteristic photo-telegraph lines. (The calculation was carried out subject to the daily transfer of 10 images of the specified format). In practice, the network of phototelegraphic communications covers all the major administrative and industrial centers of the Soviet Union.

0.20 5.00

Claims (1)

0.35 8.75 0.50 12.50 Claims of the invention A digital-to-analog converter of a differential pulse-code modulation signal containing a code converter whose output is connected to the input of a digital adder, and a digital-to-analog converter, characterized in that, in order to improve the accuracy of the conversion, two multi-tap delay elements and a serially connected decoder and a control unit, the outputs of which are connected to the taps of the first delay element. the input of which is connected to the output of digit 3.75 4550 6.56 7972 9.38 11357 of an adder, whose input is connected to the second delay input, the output of which is connected to the input of the decoder, while the second input of the control unit is connected to the corresponding tap of the first delay element, the output of which is connected to the input of the digital-to-analog converter. Sources of information taken into account in the examination 1. 3 .L.Hul let.Wa .Lavery., A, Coding, ATR, vo |, 5, № 2, November, 1971 ( prototype),.