VOICE SIGNAL DEMODULATION CIRCUIT

Abstract: The demodulation circuit comprises a counting circuit (11) which detects from the outputs of an error correction circuit (2) how many samples are interpolated continuously and two AND circuits (9,10) which perform AND operation of the output of the circuit (11) and a mute signal that is generated when it is out of synchronism with the output. When the samples are to be interpolated continuously more than a given number m, a voice difference signal is muted by the mute signal so that no signal is produced that seriously deteriorates the sound quality. @(20pp Dwg.No.1/6)@

Description: SPECIFICATION AUDIO SIGNAL DEMODULATION CIRCUIT TECHNICAL FIELD The present invention relates to an audio signal demodulation circuit for use in a high definition television broadcasting in the MUSE (Multiple Sub-Nyquist Sampling Encoding) transmission system. BACKGROUND ART In recent years, an audio signal demodulation circuit has been regarded as important as a circuit for demodulating PCM sound (audio signals) which is indispensable to high definition television broadcasting. Now referring to the drawings, one example of the conventional audio signal demodulation circuits will be explained. Figs. 4, 5 and 6 are a block diagram of the conventional audio signal demodulation circuit, a timing chart thereof and a waveform chart thereof, respectively. In Fig. 4, 1 is a bit de-interleave circuit; 2 is an error correction cirucit; 3 is a word de-interleave cirucit; 4 is an expansion circuit; 5 is a range detection/error correction circuit; 6 is an interpolation circuit; 7 is an integration circuit; 8 is a synchronous detection cirucit; and 9 is an AND circuit. The operation of the audio signal demodulation circuit thus constructed will be explained with reference to Figs. 5 and 6. First, an audio input signal at 1350 kb/s is detected in its synchronization pattern by the synchronous detection circuit 8 to take synchronization. The output (Fig. 5(E)) from the synchronous detection circuit 8 is at a high level if the synchronization has been taken, while it is at a low level for a muting operation if the synchronization has not been taken. Also the bit interleave of the input audio signal performed on the transmission side is de-interleaved by the bit de-interleave circuit 1. The output from the bit de-interleave circuit 1 is error-corrected by the error correction circuit 2 so that one-error correction two error detection is made in the normal mode and two-error correction three-error detection is made in the intensifying mode. The signal ((B) of Fig. 5) subjected to the two-error detection in the normal mode and the three-error detection in the intensifying mode will be used as an interpolation signal in the interpolation circuit 6. The word interleafve of the output of the error correction circuit 2 performed on the transmission side is de-interleaved by the word de-interleave circuit 3. The output from the error correction circuit 2 is also detected in its range bits and error-detected by the range detection/error correction circuit 5. The outputs from the word de-interleave circuit 3 and the range detection/error correction circuit 5 are expanded by the expansion circuit 4 using the range bits to produce a differential value. The output ((A) of Fig. 5) from the expansion circuit 4 is interpolated by the interpolation circuit 6 using the interpolation signal ((B) of Fig. 5) as follows: X (i+1) = X (i) X (i+2) = X (i) ... ... X (i+n-1) = X (i) X (i+n) = X i +X i+n-1 2 In the case where there are successive interpolation signals consisting of n (integer) samples from X (i+1) to X (i+n) for a certain channel, the n samples containing two errors in the normal mode and three errors in the intensifying mode are interpolated so that (n-l) samples are interpolated for the previous value X (i) and the last sample are interpolated for the average value of X (i) and X (i+n+1) which contain no error ((C) of Fig. 5). The output ((C) of Fig. 5) from the interpolation circuit 6 is muted by the AND circuit 9 using the mute signal ((E) of Fig. 5) output from the synchronous detection circuit so that the differential value when the synchronization has not been taken is zero ((H) of Fig. 5). This differential value (H) from the AND circuit 9 is integrated by the integration circuit 7 to be demodulated as an audio signal. The above arrangement thus constructed has the following defect. If three errors and two errors successively occur in the normal mode and the intensifying mode, respectively, the previous value is used for interpolation of the differential value. This increases distortion of the sound obtained and so greatly deteriorates the sound quality; the sound thus obtained cannot be heard as suitable sound by audiences. EP-A-0 264 986 describes apparatus for reproducing a PCM modulated signal comprising error-correcting means and a muting circuit operable when the error-correcting means are not capable of correcting errors. In the arrangement described, plural counters are employed for counting a number of error flags produced in a given time period. DISCLOSURE OF INVENTION An object of the present invention is to provide an audio signal demodulation circuit which can demodulate an audio signal as suitable sound for audiences by muting the audio signal if interpolating is to be successively made. In order to attain the above object, the present invention provides an audio signal demodulation circuit as defined by claim 1. In the arrangement of the present invention, the interpolation signal output from the error correction circuit is counted by the counter circuit, if interpolation is to be successively made for m or more samples, a mute signal is produced, and an audio differential signal is muted using the mute signal. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a block diagram of the audio signal demodulation circuit according to an embodiment of the present invention; Fig. 2 is a timing chart of the circuit of Fig. 1; Fig. 3 is a waveform chart of the circuit of Fig. 1; Fig. 4 is a block diagram of the conventional audio signal demodulation circuit; Fig. 5 is a timing chart of the circuit of Fig. 4; and Fig. 6 is a waveform chart of the circuit of Fig. 4. BEST MODE FOR CARRYING OUT THE INVENTION Now referring to the drawings, explanation will be given for the audio signal demodulation circuit according to one embodiment of the present invention. Fig. 1 is a block diagram of the audio signal demodulation circuit according to an embodiment of the present invention. Fig. 2 is a timing chart in the circuit of Fig. 1. Fig. 3 is a waveform chart in the circuit of Fig. 1. In Fig. 1, 1 is a bit de-interleave circuit; 2 is an error correction circuit; 3 is a word de-interleave circuit; 4 is an expansion circuit; 5 is a range detection/error correction circuit; 6 is an interpolation circuit; 7 is an integration cirucit; 8 is a synchronous detection circuit; and 9 is an AND circuit. These circuit units are identical to the corresponding circuit units in Fig. 4. The arrangement of Fig. 1 is different from that of Fig. 4 in provision of a counter circuit 11 for counting the interpolation signal output from the error correction circuit 2, and an AND circuit 10 for taking a logical product of the output from the counter circuit 11 and the mute signal output from the synchronous detection circuit 8, the output of the AND circuit 10 being used as one input to the AND circuit 9. The operation of the audio signal demodulation circuit thus constructed will be explained with reference to Figs. 1, 2 and 3. First, an audio input signal is detected in its synchronization pattern by the synchronous detection circuit 8 to take synchronization. The output (Fig. 1(E)) from the synchronous detection circuit 8 is used for muting so that it is at a high level if the synchronization pattern has been detected while it is at a low level if the synchronization pattern has not been detected. Also the input audio signal is cancelled in its interleave performed on the transmission side by the bit de-interleave circuit 1. The output from the bit de-interleave circuit 1 is error-corrected by the error so that one-error correction two error detection is made in the normal mode and two-error correction three-error detection is made in the intensifying mode. The signal ((B) of Fig. 1) subjected to the two-error detection in the normal mode and the three-error detection in the intensifying mode will be used as an interpolation signal in the interpolation circuit 6. The output from the error correction circuit 2 is cancelled in its word interleave performed on the transmission side by the word de-interleave circuit 3. The output from the error correction circuit 2 is also detected in its range bits and error-detected by the range detection/error correction circuit 5. The outputs from the word de-interleave circuit 3 and the range detection/error correction 5 are expanded by the expansion circuit 4 using the range bits to produce a differential value. The differential value ((A) of Fig. 1) from the expansion circuit 4 is interpolated by the interpolation circuit 6 using the interpolation signal ((B) of Fig. 2) as follows: In the case where there are successive interpolation signals consisting of n (integer) samples from X (i+1) to X (i+n) for a certain channel, the n samples containing two errors in the normal mode and three errors in the intensifying mode are interpolated so that (n-l) samples are interpolated for the previous value X (i) and the last sample are interpolated for the average value of X (i) and X (i+n+1) which contain no error ((C) of Fig. 2). X (i+1) = X (i) X (i+2) = X (i) ... ... X (i+n-1) = X (i) X (i+n) = X i +X i+n+1 2 The interpolation signal ((B) of Fig. 2) is counted by the counter circuit 11 so that the mute signal ((D) of Fig. 1) at a low level is producted if m (integer) or more successive errors occur. In (D) of Fig. 5, m = 3. The logical product of the output (D) from the counter circuit 11 and the output (E) from the synchronous detection circuit 8 is taken by the AND circuit 10 to produce a mute signal ((F) of Fig. 2). The output ((C) of Fig. 2) is muted by the AND circuit 9 using the mute signal (F) so that the differential value is zero ((G) of Fig. 2). Finally, the differential value (G) is integrated by the integration circuit 7 to be demodulated as an audio signal. INDUSTRIAL APPLICABILITY In accordance with the present invention, there are provided a counter circuit for detecting the number of samples for which interpolation is to be successively made by counting the output from an error correction circuit and an AND circuit for taking the logical product of the output from the counter circuit and the mute signal generated when synchronization has been lost, and using these circuit units, the differential value is muted if interpolation is to be successively made. Thus, the sound with large distortion and greatly deteriorated sound quality can be restricted so that an audio signal can be demodulated as suitable sound as audiences. List of reference numbers in the drawings 1 ... bit de-interleave circuit 2 ... error correction circuit 3 ... word de-interleave circuit 4 ... expansion circuit 5 ... range-detection/error correction circuit 6 ... interpolation circuit 7 ... integration circuit 8 ... synchronous detection circuit 9, 10 ... AND circuit 11 ... counter circuit

Claims: An audio signal demodulation circuit comprising: a bit de-interleave circuit (1) for canceling the bit interleave of an audio signal performed on the transmission side; an error correction circuit (2) for error-correcting the output signal from said bit de-interleave circuit (1) ; a word de-interleave circuit (3) for canceling the word interleave performed on the transmission side for a first output signal from said error correction circuit (2) ; a range-detection/error-correction circuit (5) for range-detecting and error-detecting the first output signal from said error correction circuit (2) ; an expansion circuit (4) for expanding the output from said word de-interleave circuit (3) using the range bits of an output signal from said range-detection/errorcorrection circuit (5) ; an interpolation circuit (6) for interpolating an output (A) from said expansion circuit (4) using an interpolation signal (B) which is a second output signal from said error correction circuit (2) ; a synchronous detection circuit (8) for detecting an asynchronous state of the input audio signal and generating an asynchronous detection signal (E); a first logic circuit (9) for gating an output signal (C) from said interpolation circuit (6) in response to the asynchronous detection signal (E); and an integration circuit (7) for integrating the gated output (G) from said first logic circuit (9) and producing a demodulated audio signal; wherein said audio signal demodulation circuit further comprises: a counter circuit (11) for counting and detecting a predetermined number of successive signal samples of said second output signal (B) from said error correction circuit (2) in which each signal sample possibly includes an error and, in response thereto, generating a mute enable signal (D); and a second logic circuit (10) for taking a logical product of the mute enable signal (D) and the asynchronous detection signal (E) from said synchronous detection circuit (8), thereby producing a mute signal (F) as said asynchronous detection signal to control the gating operation of said first logic circuit (9).

Inventors: IWAMOTO TAKUSHI, KAWASHIMA TADASHI, MIYOSHI TOSHIHIRO, NINOMIYA YUICHI, OKUMURA NAOJI, OTSUKA YOSHIMICHI, IWAMOTO, TAKUSHI, KAWASHIMA, TADASHI, MIYOSHI, TOSHIHIRO, NINOMIYA, YUICHI, OKUMURA, NAOJI, OTSUKA ,YOSHIMICHI, NINOMIYA, YUICHI 17-4, TAKAISHI 2-CHOME, Otsuka ,Yoshimichi 10-10, Ikuta 6-chome
Applicants: JAPAN BROADCASTING CORP, MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD., NIPPON HOSO KYOKAI
Application year: 1989
Main classification: H04B14
IPC codes: H04B1, H04B14, H04N7, H04N5