JPS6337545B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital signal transmission device, such as a digital mobile radio, that transmits digital data using a wired or wireless transmission path for transmitting audio digital signals. It is something.

Configuration of a conventional example and its problems FIG. 1 shows an outline of a transmitting section and a receiving section of a conventional digital mobile radio.

In FIG. 1, 1 is an adaptive delta code circuit that converts an audio signal from a microphone 2 into an audio digital signal; 3 is a data conversion circuit that adds redundant bits to digital data applied to an input terminal 4 and converts the rate; 5 is a changeover switch, and the audio digital signal or digital data selected by this changeover switch 5 is transmitted to the modulation circuit 6.
is input. 7 is a wired or wireless transmission path; 8 is a demodulation circuit; the output of the demodulation circuit 8 is applied to an adaptive delta decoding circuit 9 and an error correction circuit 10; 11 is a switch connected between the adaptive delta decoding circuit 9 and the speaker 12; 13 is a digital data output terminal.

Next, the operation of the above conventional example will be explained. The audio signal applied to the input terminal of the adaptive delta code circuit 1 is converted into a digital signal and applied to the modulation circuit 6 through the changeover switch 5. The signal input to the modulation circuit 6 modulates the carrier signal, which is the other input of the modulation circuit 6, and then sends it out to a wired or wireless transmission path 7.

On the other hand, digital data, which has a lower transmission rate than the audio digital signal but is more reliable, is applied to the input terminal 4 of the data conversion circuit 3, where redundant bits are added and the rate is converted. Similarly, it is added to the modulation circuit 3.

On the other hand, a signal that has passed through a wired or wireless transmission path 7 is demodulated into a digital signal by a demodulation circuit 8. If the demodulated signal corresponds to an audio signal, the demodulated signal is decoded into an audio signal by the adaptive delta decoding circuit 9 and connected to the speaker 12 via the switch 11.

On the other hand, if the digital signal demodulated by the demodulation circuit 8 corresponds to the digital data input,
This digital signal is received as a digital data output by error correction circuit 10 which corrects any erroneous bits occurring on the line.

However, in the conventional example described above, large noise is generated at the output terminal of the adaptive delta demodulation circuit 9 during digital data transmission, so in this case, it is necessary to take the trouble to disconnect the signal using the switch 11.
In other words, the adaptive delta code/decoding circuit outputs a repeating signal of 101010... when there is no audio signal, and when there is an audio signal and bits of the same code occur consecutively, the output level of the decoding circuit increases. Therefore, it had the disadvantage of producing a large amount of noise.

OBJECTS OF THE INVENTION The present invention eliminates the drawbacks of the above-mentioned conventional example, and aims to eliminate the need for a switch for cutting off audio and eliminate unnecessary noise signals during digital data transmission.

Structure of the Invention In order to achieve the above object, the present invention automatically eliminates noise generated at the output end of an audio decoding circuit during digital data transmission by converting digital data "1" and "0" into a predetermined repetitive signal. This has the effect of suppressing the situation.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below. This embodiment is based on the switch 1 in the conventional example shown in FIG.
1 is removed, and the data conversion circuit 3 performs specific data conversion.

Next, the operation of the above embodiment will be explained with reference to the timing chart shown in FIG.

The low-speed digital data applied to the input terminal 4 of the data conversion circuit 3 of the transmitting section is converted by the data conversion circuit 3 into data ``1010101'' for digital data ``0'' and ``0101010'' for digital data ``1.'' is converted and output. This waveform is shown in FIG. 2b. The digital data converted by the data conversion circuit 3 or the audio digital signal encoded by the adaptive delta code circuit 1 is selected by the changeover switch 5. Next, this digital signal is transmitted through a modulation circuit 6, a wired or wireless transmission line 7, and a demodulation circuit 8 to restore the original digital signal.

Furthermore, if this corresponds to a digital data signal, the original digital data is restored after the line error is corrected by the error correction circuit 10. Here, the timing when majority logic is used in this error correction circuit is shown in FIGS. 2b to 2e. The error correction circuit 10 performs an exclusive OR of the internally generated waveform c and the input waveform b (this waveform is shown in d in the same figure) and determines whether it is "0" or "1" per subframe. 00 or 1 is determined depending on the number of . This waveform is shown in figure e. Note that the shaded portions in FIGS. 2b and 2d show waveforms when a line error occurs.

On the other hand, when digital data input is transmitted, the waveform shown in FIG. 2b is applied to the adaptive delta decoding circuit 9. In this case, the decoded signal (in this case, noise) level will be suppressed to a very low level for the following two reasons.

(a) In most cases, the adaptive logic of the adaptive delta code/decoder circuits 1 and 9 is a series of encoded “1” and “0” signals (for example, three consecutive bits of “1” or “0”) The quantization step is determined in proportion to the frequency of occurrence of the state in which Therefore, in a waveform with almost no identical codes as shown in FIG. 2b, the quantization step becomes very small and the decoded signal level becomes small.

(b) If the digital signal applied to the adaptive delta code circuit is an alternating signal of “1” and “0”, then
The decoded signal falls outside the band required for transmission (3kHz for audio) and can be removed by a filter. Therefore, even if the waveform shown in FIG. 2b is applied to the adaptive delta decoding circuit, most of the components become out-of-band signals and can be removed.

In this embodiment, the output signal (noise) of the adaptive delta decoding circuit can be automatically suppressed during digital data transmission, so the noise can be manually cut off using the switch 11 as in the conventional example. Furthermore, it is no longer necessary to distinguish between an audio signal and a digital signal in the receiving section (in this case, the discrimination takes time and noise is generated during that time).

Effects of the Invention The present invention has the above-described configuration, and since the digital data "1" corresponds to the opposite polarity to the alternating signal "0" such as 1010...1, etc., the adapter can be easily used during digital data transmission. The noise generated in the tabe-delta encoder is suppressed. This has the advantage that it becomes unnecessary to install a switch to cut off that noise, or to add a circuit that automatically distinguishes between voice transmission and digital data transmission to cut off noise during digital data transmission. has.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional digital signal transmission device, and FIG. 2 is a timing chart of a digital signal transmission device according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Adaptive delta code circuit, 2...Microphone, 3...Data conversion circuit, 4...Digital data input terminal, 5...Select switch, 6...Modulation circuit, 7...Transmission line, 8...Demodulation circuit, 9...Adapter Eve delta decoding circuit, 10...Error correction circuit, 11...
Switch, 12...Speaker, 13...Digital data output terminal.

Claims (1)

[Claims] 1. An adaptive delta code means for converting an audio signal into an audio digital signal, a data conversion means for converting "1" and "0" of input digital data into a repeating signal of multiple bits each having a different polarity, A modulation means for modulating an audio digital signal or digital data, a wired or wireless transmission path for transmitting the output of this modulation means, a demodulation means for demodulating the modulated signal transmitted via this transmission path, and this demodulation means A digital signal transmission device comprising: adaptive delta decoding means for decoding the output of the demodulating means into an audio signal; and digital data restoring means for restoring the output of the demodulating means into digital data.