JP3509439B2 - Signal discrimination circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal discriminating circuit effective for stereo / monaural discrimination of an input signal, and particularly to a magnetic recording / reproducing apparatus such as a HiFi VTR. It is effective when used for the commercial cut recording / reproducing function in. 2. Description of the Related Art In recent years, commercial cut recording / reproducing technology has attracted attention for magnetic recording / reproducing devices such as VTRs in terms of effective use of time. [0003] A conventional signal discriminating circuit used for commercial cut recording and reproduction will be described below. A conventional signal discriminating circuit is disclosed in Japanese Unexamined Patent Publication No.
No. 46, Japanese Unexamined Patent Publication No. 3-256253, etc., there are examples in which a stereo signal or an audio multiplex signal transmitted as a broadcast signal is discriminated, and it is known that commercial cut recording / reproduction is performed based on the information. Have been. FIG. 10 shows the signal discriminating circuit. FIG. 10 is a block diagram of a conventional signal discriminating circuit. In FIG. 10, 40 is an antenna,
41 is a tuner / demodulator unit for receiving and demodulating a broadcast signal S41 sent from the antenna 40;
Is an audio signal processing circuit for processing the audio signal demodulated by the tuner / demodulator unit 41, and 43 is a microcomputer. The operation of the conventional signal discriminating circuit configured as described above will be described below. First, the broadcast signal S 41 input to the antenna 40 is input to the tuner / demodulator unit 41. The audio signals S42 and S43 received and demodulated by the tuner / demodulator unit 41 are input to the audio signal processing circuit 42, and the output signals S44 and S44 of the audio signal processing circuit 42
45 is output to the outside from output terminals 45 and 46, respectively. On the other hand, a tuner / demodulator section 41
Outputs a stereo determination signal S46 to the microcomputer 43 when the broadcast signal S41 includes a stereo determination signal. The microcomputer 43 controls the recording / reproducing unit 44 to perform a commercial cut when the stereo determination signal S46 is input. [0009] However, in the above-described conventional configuration, the microcomputer 43 uses the stereo discrimination signal S46.
In this case, the commercial cut operation is controlled for the recording / reproducing unit 44 on the basis of the broadcast signal S41. Therefore, when the stereo discrimination signal is always superimposed on the broadcast signal S41, a normal commercial cut operation cannot be performed. Was. [0010] The present invention solves the above-mentioned conventional problems, and a signal discrimination that can perform a normal commercial cut operation regardless of the presence or absence of a stereo discrimination signal transmitted by a broadcast signal input to an antenna. It is intended to provide a circuit. In order to achieve this object, a signal discriminating circuit according to the present invention has a first input terminal for inputting a first audio signal and a second audio signal. a second input terminal, a differential amplifier for generating a difference signal of the signal level of the first input terminal and a second input terminal, the differential amplifier
A first rectifier for rectifying the output signal of the rectifier;
An inverting amplifier for inverting the polarity of the output signal of the
A second rectifier for rectifying an output signal of the amplifier;
And the output signal of the second rectifier.
An adder that adds, a detector that detects an output signal of the adder and outputs an output signal voltage, a reference voltage generator that generates a reference voltage, and an output signal of the detector and the reference voltage generator. and a comparator for comparing the reference voltage, the ratio
The comparator compares the magnitude of the output signal of the detector with the reference voltage.
Compare and determine the stereo / monaural discrimination based on the comparison result.
Is what you do. With this configuration, it is possible to obtain a signal discriminating circuit capable of performing a commercial cut recording / reproducing operation regardless of a discrimination signal of a stereo signal transmitted by a broadcast signal input to an antenna. [0013] The invention according to claim 1 of the embodiment of the present invention comprises a first input terminal for receiving a first audio signal, the second
A second input terminal for inputting the first audio signal, a differential amplifier for generating a difference signal between signal levels of the first input terminal and the second input terminal, and rectifying an output signal of the differential amplifier.
The polarity of the output signal of the first rectifier and the differential amplifier is inverted.
Inverting amplifier, and rectifying the output signal of the inverting amplifier.
A second rectifier, and an output signal of the first rectifier.
An adder for adding an output signal of the second rectifier;
A detector that detects an output signal of the adder and outputs an output signal voltage, a reference voltage generator that generates a reference voltage, and a comparison that compares an output signal of the detector with a reference voltage of the reference voltage generator. A detector, and the comparator has an output of the detector.
Compare the magnitude of the force signal and the reference voltage, and
It performs more stereo / monaural discrimination, and has an effect that a commercial cut recording / reproducing operation can be performed regardless of a discrimination signal of a stereo signal transmitted by a broadcast signal input to an antenna. Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 1 is a block diagram of a signal discriminating circuit according to the present embodiment. In FIG. 1, reference numeral 15 denotes a first input terminal to which an Lch audio signal as a first audio signal is input; Is a second input terminal to which an Rch audio signal as a second audio signal is input, 11 is a differential amplifier that takes a difference component between signals input to the first input terminal 15 and the second input terminal 16, 12 is a detector for detecting the output signal of the differential amplifier 11, 14 is a reference voltage generator for generating a reference DC voltage, 13 is the DC voltage of the output signal of the detector 12 and the DC voltage of the reference voltage generator 14. Are compared. The operation of the signal discriminating circuit of the present embodiment configured as described above will be described below. First, the audio signals S11 and S12 input to the input terminals 15 and 16 are input to the differential amplifier 11. The differential amplifier 11 generates a difference component signal S13 between the signals S11 and S12, and the signal is detected by the detector 12.
Is a DC voltage that varies according to the magnitude of the input signal, and is input to the comparator 13. The reference voltage generator 14 generates a threshold voltage for discriminating between a stereo signal and a monaural signal, and a signal S16 which is a DC voltage is input to the comparator 13. The comparator 13 compares the magnitude of the voltage between the signal S14 and the signal S16, and
When the signal 14 is larger than the signal S16, the signal is determined to be a stereo signal. When the signal S16 is larger, the signal is determined to be a monaural signal, and the comparison result is output from the output terminal 17 as a signal S15. That is, in the case of a stereo signal, the level difference between the signals S11 and S12 is large, and in the case of a monaural signal, there is almost no level difference. Therefore, by comparing the DC voltage based on this level difference with the reference DC voltage, / Monaural discrimination becomes possible. A specific circuit configuration of the signal discriminating circuit according to the present embodiment will be described with reference to FIG. The signals input to the input terminals 15 and 16 take out the difference component by the amplifier IC1 and are amplified by the amplifier IC2. The amplification factor of the amplifier IC1 is determined by the resistors R1 to R4, and the amplification factor of the amplifier IC2 is determined by the resistors R5 and R6. Although not shown in FIG. 5, a capacitor may be added in parallel with the resistor R6 of the amplifier IC2 to form an amplifier having a low-pass filter configuration, or another resistor may be added in parallel with the resistor R5 to amplify under a certain condition. A variable amplifier that changes the rate may be used and is not specifically defined. The output signal of the amplifier IC2 is a capacitor C1
The signal is envelope-detected by a diode D1 and a capacitor C2 via a high-pass filter including a resistor R7 and an amplifier IC3, and input to the amplifier IC4. The amplifier IC4 compares the input voltage with the reference voltage determined by the resistors R8 to R11, and outputs the result from the output terminal 17.
In this case, the Schmitt trigger circuit configuration is used, but is not specified. FIGS. 2 and 3 are block diagrams showing a configuration in which the signal discriminating circuit of the present embodiment is used in a video tape recorder. First, the operation will be described with reference to FIG.
The broadcast signal S21 input to the antenna 20 is input to the tuner / demodulator unit 21. Audio signal S2 received and demodulated by tuner / demodulator unit 21
2 and S23 are input to the audio signal processing circuit 22 and input to the signal determination circuit 24 as signals corresponding to the signals S11 and S12 in FIG. Output signals S24 and S25 of the audio signal processing circuit 22 are output from an output terminal 26 and an output terminal 27, respectively. On the other hand, the signal discriminating circuit 24 outputs the signal S11 input as described above.
The magnitude of the DC voltage based on the level difference between S12 and S12 is compared with the reference DC voltage, and it is determined whether the signal is a stereo signal or a monaural signal from the comparison result.
The signal S15 is input to the microcomputer 23, and the microcomputer 23 controls the recording / reproducing unit 25 to perform a commercial cut operation. Next, the operation will be described with reference to FIG. The broadcast signal S31 input to the antenna 30 is input to the tuner / demodulator unit 31. The audio signals S32 and S33 received and demodulated by the tuner / demodulator unit 31 are input to the audio signal processing circuit 32. The output signals S34 and S35 of the audio signal processing circuit 32 are 2
One of the terminals is divided into an output terminal 36 and an output terminal 37.
Is output to the outside. The other is the signal S in FIG.
11 and a signal corresponding to the signal S12 are input to the signal determination circuit 34. As described above, the signal discriminating circuit 34 uses the DC based on the level difference between the input signals S11 and S12.
The voltage and the magnitude of the reference DC voltage are compared, and it is determined from the comparison result whether the signal is a stereo signal or a monaural signal. The result of the determination is output as a signal S15, and the signal S15 is input to the microcomputer 33. The microcomputer 33 controls the recording / reproducing unit 35 to execute a commercial cut operation. As described above, according to the present embodiment, the signal discriminating circuit 34 discriminates a stereo / monaural signal from the audio signal output from the tuner / demodulator unit 31, so that a commercial signal transmitted as a stereo signal is transmitted. And program broadcast can be separated on an arbitrary basis and commercial cut recording can be performed. (Embodiment 2) Hereinafter, a second embodiment of the signal discrimination circuit of the present invention will be described. FIG. 4 is a block diagram of the signal discriminating circuit of the present embodiment. In FIG. 4, reference numeral 57 denotes a first input terminal to which an Lch audio signal is input, and 58, a second input terminal to which an Rch audio signal is input. Input terminals 55, 55 are input terminals 57 and 58
An adder 56 for adding the signal input from the input terminal 58; a branching unit 56 for branching the signal input from the input terminal 58 into two parts; and a difference 51 for outputting a difference signal between the output signal of the adder 55 and the output signal of the branching unit 56. A dynamic amplifier 52, a detector for detecting an output signal of the differential amplifier 51, a reference voltage generator 54 for generating a reference DC voltage, and a reference numeral 53, an output signal of the detector 52 and an output signal of the reference voltage generator 54. Comparator for comparing DC voltage, 5
9 is an output terminal. The operation of the signal discriminating circuit of the present embodiment configured as described above will be described below. First, the audio signal S51 input to the input terminal 57 is input to the adder 55, and the audio signal S52 input to the input terminal 58 is branched into two by the branching unit 56, and one of the signals S57 is also added to the adder 55. 55 is input. The other signal S58 of the branching unit 56 is input to the differential amplifier 51. The output signal S59 of the adder 55 is also input to the differential amplifier 51. The output signal S53 of the differential amplifier 51 is input to the detector 52, and the detector 52 outputs a signal S54 including a DC voltage that varies according to the magnitude of the input signal. The signal S54 is input to the comparator 53. The reference voltage generator 54 generates a threshold voltage when discriminating between a stereo signal and a monaural signal. The output signal S56 is a DC voltage and is input to the comparator 53.
The comparator 53 compares the magnitudes of the voltages of the signal S54 and the signal S56, and outputs the result from the output terminal 59 as a signal S55. Hereinafter, the commercial cut operation is the same as that of the first embodiment, and thus the description thereof is omitted. Next, the difference between the present embodiment and the first embodiment will be described in detail with reference to FIGS. First, when the signal levels of the input terminals 15 and 57 are L and the signal levels of the input terminals 16 and 58 are R, R = L + ΔL.
In the first embodiment, assuming that the amplification factor of the differential amplifier 11 is A1, the level of the output signal S13 is as follows: In the second embodiment, assuming that the amplification factor of the differential amplifier 51 is A2, the level of the output signal S53 is as follows: If the offset of the differential amplifier 51 is small, the level of S53 becomes 1/2 of the level of S13. As described above, according to the present embodiment, by inputting the output signals of the Lch and Rch adders 55 to the differential amplifier 51, the output level error with respect to the input level of the differential amplifier 51 is reduced by 1 /. 2 can be suppressed. (Embodiment 3) Hereinafter, a third embodiment of the signal discrimination circuit of the present invention will be described. FIG. 6 is a block diagram of a signal discriminating circuit according to the present embodiment, FIG. 7 is a waveform diagram showing a relationship between an input signal and an output signal of the adder according to the present embodiment, and FIG. FIG. 8B is a characteristic diagram of the output signal of the detector in the embodiment.
FIG. 9 is a waveform diagram of an output signal of the detector according to the first embodiment, showing an example in which the detection output level is more stable in the case of the third embodiment. In FIG. 6, reference numeral 70 denotes a first input terminal to which an Lch audio signal is input, 71 denotes a second input terminal to which an Rch audio signal is input, and 61 denotes a difference signal from the signals of the input terminals 70 and 71. A differential amplifier 66 for outputting the signal, 66 is a branching unit for branching the output signal of the differential amplifier 61 into two, and 68 is a branching unit 6
6 that outputs only the positive voltage component of the output signals of
, 67 is an inverting amplifier that outputs a signal obtained by inverting the polarity of the output signal of the branching unit 66, 69 is a second rectifier that outputs only the positive voltage component of the output signal of the inverting amplifier 67, and 65 is the first rectifier. An adder for adding the output signal of the rectifier 68 to the output signal of the second rectifier 69; 62, a detector;
4 is a reference voltage generator for generating a reference DC voltage, 6
Reference numeral 3 denotes a comparator that compares the DC voltage of the output signal of the detector 62 with the output signal of the reference voltage generator 64. The operation of the signal discriminating circuit of the present embodiment configured as described above will be described below. First, the audio signals S61 and S62 input to the input terminals 70 and 71 are input to the differential amplifier 61. The output signal S63 of the differential amplifier 61 is branched into two by the branching unit 66, and one of the signals S67 is input to the first rectifier 68 and the signal S68 having only the positive voltage component (FIG.
(A)) is input to the adder 65. The polarity of the other signal S69 of the branching unit 66 is inverted by the inverting amplifier 67, and the signal S70 is input to the second rectifier 69. In the second rectifier 69, the signal S71 having only the positive voltage component (FIG. 7)
(B)) and is input to the adder 65. Adder 65
Then, a signal S72 (FIG. 7C) obtained by adding the signals S68 and S71 is output to the detector 62. The detector 62 generates a DC voltage signal S64 that varies according to the magnitude of the input signal, and the signal S64 is input to the comparator 63. On the other hand, the reference voltage generator 64 generates a threshold voltage for discriminating between a stereo signal and a monaural signal. The output signal S66 is a DC voltage and is input to the comparator 63. Comparator 6
3 compares the magnitudes of the voltages of the signals S64 and S66, and outputs the comparison result from the output terminal 72 as a signal S65. FIG. 9 is a specific circuit diagram in the present embodiment. Hereinafter, the operation will be described. The signals input to the input terminal 70 and the input terminal 71 take out a difference component by the amplifier IC1 and are amplified by the amplifier IC2. The amplification factor of the amplifier IC1 is determined by the resistors R1 to R4, and the amplification factor of the amplifier IC2 is determined by the resistors R5 and R6. Although not shown in FIG. 9, a capacitor is added in parallel with the resistor R6 of the amplifier IC2 and L
An amplifier having a PF configuration may be used, or another variable resistor may be added in parallel with the resistor R5 to change the amplification factor under a certain condition. The output signal of the amplifier IC2 is branched into two, one of which is rectified and detected by the diode D1 and the capacitor C1.
4 is input. The other is inverted in polarity by the amplifier IC3, rectified and detected by the diode D2 and the capacitor C1, and input to the amplifier IC4. The amplifier IC4 has a resistor R
The reference voltage determined by 9 to R12 is compared with the magnitude of the input voltage, and the result is output from the output terminal 72. In this case, the Schmitt trigger circuit configuration is used, but is not specified. As described above, according to the present embodiment, Lc
When comparing the level difference between the signals of h and Rch, Lch and Rch are compared.
In order to prevent the stereo signal from being judged as a monaural signal even when the amplitude level of the signal is large and the detection level is large even if the output signal level of the channel has a difference, the in-phase of the difference signal between the Lch and the Rch By performing rectification detection processing after adding the signal and the negative-phase signal, stereo / monaural discrimination can be performed by reducing the error level in an arbitrary device at the preceding stage. As described above, according to the present invention, Lch and Rch
By providing a signal discriminating circuit that automatically discriminates between stereo sound and monaural sound by comparing the level difference between the signals, the commercial signal regardless of the stereo signal discrimination signal sent by the broadcast signal input to the antenna An excellent effect that a cut recording / reproducing operation can be performed is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a signal discriminating circuit according to the first embodiment of the present invention. FIG. 2 is a block diagram for explaining an operation of a first commercial cut recording / playback in the first embodiment. FIG. 3 is a block diagram for explaining the operation of the second commercial cut recording / playback in Embodiment 1; FIG. 4 is a block diagram of a signal discrimination circuit in Embodiment 2 of the present invention; FIG. 6 is a circuit diagram of a signal discriminating circuit according to the first embodiment; FIG. 6 is a block diagram of a signal discriminating circuit according to the third embodiment of the present invention; FIG. FIG. 9 is a characteristic diagram of the detector according to the third embodiment and the first embodiment. FIG. 9 is a circuit diagram of a signal discriminating circuit according to the third embodiment. FIG. Figure [Description of Signs] 11 Differential amplifier 12 Detector 13 Comparator 14 Reference voltage generator 24 Signal discriminating circuit

Claims (1)

(57) Claims 1. A first input terminal for inputting a first audio signal, a second input terminal for inputting a second audio signal, and the first input terminal Amplifier for generating a difference signal between the signal level of the differential amplifier and a second input terminal, a first rectifier for rectifying the output signal of the differential amplifier, and an inverting amplifier for inverting the polarity of the output signal of the differential amplifier A second rectifier for rectifying an output signal of the inverting amplifier, an adder for adding an output signal of the first rectifier and an output signal of the second rectifier, and detecting an output signal of the adder. comprising a detector for and outputting an output signal voltage, a reference voltage generator for generating a reference voltage, a comparator for comparing the reference voltage of the output signal and the reference voltage generator of the detector, the comparison The detector detects the difference between the output signal of the detector and the reference voltage.
Compare the size and determine the stereo / monaural
A signal discriminating circuit for performing discrimination.