JP2003324321A - Audio detecting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate an audio output level difference due to a difference in frequency shift quantity when audio FM-modulated signals of a plurality of broadcasting systems, such as NTSC and PAL, which are mutually different in frequency shift quantity are detected by a common quadrature detecting circuit 22. <P>SOLUTION: In a phase shifting circuit 33 which is realized by a tank circuit composed of a parallel resonance circuit of L1, C1, and R1 and shifts the phase of the audio FM-modulated signal by 90° for the quadrature detecting circuit 22, R2 is connected to the R1 in parallel by a switch 32 when the frequency shift quantity is large; and thus the resistance value of the R1 is made small, the attenuation quantity of a resonance current of the L1 and C1 is made large, and the Q of the phase shifting circuit 33 is made small to make an audio output level low. An FM detection S curve characteristic, therefore, varies in curve gradient and then even when frequency shift quantities (modulation degree) are mutually different, audio output levels are equalized to each other. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a TV, a VTR, and a C.
The present invention relates to a circuit that is suitably mounted in a television broadcast receiving device such as a set top box for ATV and detects an FM-modulated audio signal, and particularly relates to a circuit such as NTSC and PAL, which have different frequency deviations from each other. The present invention relates to a system that uses a common quadrature detection circuit for detecting an audio signal of a broadcasting system.

[0002]

2. Description of the Related Art Currently, terrestrial television broadcasting is
There are many broadcasting systems. As a typical method, the M (NTSC) method used in Japan and the United States has 525 scanning lines and a channel bandwidth of 6M.
Hz, the frequency difference between the image carrier and the audio carrier is 4.5M
Hz and the like are specified.

On the other hand, the B (PAL) system used in the VHF band of Germany has 625 scanning lines.
The channel bandwidth is 7 MHz, and the frequency difference between the video carrier and the audio carrier is 5.5 MHz.
Even in the same Germany, the G method (PAL) used in the UHF band has 625 scanning lines, a channel bandwidth of 8 MHz, and a frequency difference between an image carrier and an audio carrier of 5.5 MHz, which is the same country. But it uses a different method.

In particular, in the European region where many countries are adjacent to each other, in addition to the above system, the I system in which the frequency difference between the image carrier and the sound carrier is 6.0 MHz, and the frequency difference between the image carrier and the sound carrier is 6 The D and K systems of 0.5 MHz are mixed.

FIG. 6 is a block diagram showing an electrical configuration of a television broadcast receiving apparatus 1 compatible with both the NTSC and PAL broadcasting systems. The received RF signal input from the antenna 2 is first extracted by the input tuning circuit 3 composed of a bandpass filter, only the desired signal component is amplified by the high frequency amplification circuit 4, and then the interstage tuning circuit 5 composed of a bandpass filter. At, further unwanted signal components are removed. This RF signal is guided to the mixing circuit 6, mixed with the LO signal generated by the local oscillation circuit 7, and frequency-converted into the IF signal.

The IF signals are SAW filters 8 and 9 adapted to the NTSC and PAL broadcasting systems, respectively.
, And the video signal component (VIF signal) and the audio signal component (SIF signal) are extracted. Separate SAW filters for video and audio may be used for these SAW filters 8 and 9, respectively. Then, the VIF signal is amplified by the amplifier circuit (VIF AMP) 10 from either of the SAW filters 8 and 9 depending on which of the NTSC broadcast and the PAL broadcast is received.
To the audio IF amplifier circuit (SI
F AMP) 11.

The VIF amplified by the amplifier circuit 10.
The signal is detected as a video signal by the video detection circuit (VideoDET) 12, and the video amplification circuit (V
It is output after being amplified in the video AMP 13). Further, the SIF signal is a voice demodulation circuit (QIF
DET) 14 performs detection (frequency conversion) to obtain a signal having a frequency difference between the video carrier and the audio carrier,
Therefore, if it is the NTSC specification, it is 4.5MH.
With the z and PAL B / G specifications, the above-mentioned signal of 5.5 MHz is obtained. The signal is an FM detection circuit (FM DET).
In 15, the signal is FM-detected by performing an inverse transform of the orthogonal transform (FM modulation), and then output as a voice signal.

FIG. 7 is a block diagram showing the electrical construction of a typical prior art FM detection circuit 21 used as the FM detection circuit (FM DET) 15 of the receiving apparatus 1 configured as described above. In the FM detection circuit 21, in order to create a signal with a 90 ° phase shift when performing the inverse transformation of the orthogonal transformation in the detection circuit 22,
A phase shift circuit 23 including a coil 11, a capacitor c1, and a resistor r1 is provided. These coils l1,
A parallel circuit of the capacitor c1 and the resistor r1 is connected to the detection circuit 22 via a DC cutting capacitor c2.

FIG. 8 is an electric circuit diagram of a quadrature detection circuit which realizes the detection circuit 22. This quadrature detection circuit includes transistors Q1, Q2; Q3, Q4; Q5, Q6 and resistors RL,
And RB. Transistors Q1, Q
The emitters of 2 are commonly connected to the collector of the transistor Q5, similarly the emitters of the transistors Q3 and Q4 are commonly connected to the collector of the transistor Q6, and the emitters of the transistors Q5 and Q6 are commonly grounded via the resistor RB. . The collectors of the transistors Q1 and Q3 are commonly connected to a predetermined high level + B power supply, and the collectors of the transistors Q2 and Q4 are commonly connected to the high level + B power supply via a load resistor RL. And
Transistor Q6; base of Q1 and Q4 becomes input,
The transistor Q6 includes the voice demodulation circuit (QIF DE
T) 14 from which the amplitude-limited audio intermediate frequency signal (square wave) e1 is input, and the audio intermediate frequency signal e1 is output to the transistors Q1 and Q4 with the 90 ° phase shifted in the phase shift circuit 23. e2 is input. The base of the transistor Q5 and the bases of the transistors Q2 and Q3 are commonly biased with a constant voltage.

Therefore, due to the parallel resonance of the coil 11 and the capacitor c1, the phase is delayed by 90 ° at the resonance frequency f0 as shown in FIG. 9, and the phase is greatly changed in the vicinity thereof. As a result, a current flows through the load resistor RL only when the audio intermediate frequency signals e1 and e2 are positive,
In the vicinity of the resonance frequency f0, the conduction angle of the load current IL changes as shown in FIG. Therefore, an audio signal can be obtained by averaging the load current IL.

[0011]

It is a well-known fact that in the FM detection circuit 21 configured as described above, the detection sensitivity changes depending on the Q of the phase shift circuit 23 and the detected sound output level changes. is there. However, the FM detection circuit has the FM detection S-curve characteristic that the audio output level changes according to the frequency shift amount (modulation degree) as shown in FIG. Circuit 21
Then, as shown in FIG. 7, Q of the phase shift circuit 23 is constant.

Therefore, the audio intermediate frequency signals e1 and e
2, the NTSC audio F with different frequency shifts
M modulation signal (with a modulation of 100%, the amount of frequency deviation is ± 2
5 kHz) and a PAL audio FM modulation signal (also having a modulation factor of 100% and a frequency deviation of ± 50 kHz) are commonly input, the audio output level is 6 dB.
PAL audio FM with large frequency deviation
When the modulated signal is received, the frequency shift amount is smaller N
There is a problem that the audio output level becomes higher than that when a TSC audio FM modulated signal is received, which gives an unpleasant feeling to the ears. The capacitor c2 is for DC cutting as described above and does not affect the detection characteristics.

An object of the present invention is to make the audio output level constant when detecting the audio FM-modulated signals of a plurality of broadcasting systems having different frequency shift amounts with each other by the common quadrature detection circuit. An object of the present invention is to provide a voice detection circuit that can improve the unpleasantness in hearing.

[0014]

SUMMARY OF THE INVENTION An audio detection circuit of the present invention is an FM detection S-curve circuit in which a common quadrature detection circuit detects audio FM modulated signals of a plurality of broadcasting systems having mutually different frequency deviations. By switching the Q of the phase shift circuit in the quadrature detection circuit that determines the characteristic, the audio output levels in the respective broadcasting systems are made to coincide with each other.

According to the above configuration, the quadrature detection circuit for obtaining the audio output by mixing the audio FM-modulated signal and the signal whose phase is shifted by 90 ° is mutually shifted in frequency. In a voice detection circuit which is commonly used for voice FM modulated signals of a plurality of different broadcasting systems, the phase is shifted and the Q of the phase shift circuit which is constant in the conventional circuit is applied to each broadcasting system. Adapt and switch.

Therefore, in the FM detection S-curve characteristic, the slope of the curve changes, and even if the frequency deviation amounts (modulation degrees) are different from each other, the sound output levels can be made to coincide with each other. it can. As a result, even if broadcasts having different frequency shift amounts are received, it is possible to improve the unpleasantness in hearing. Further, it is possible to reduce the possibility that the distortion and SN will deteriorate as compared with the case where the amplitude is limited or the amplification factor is changed in the latter-stage circuit. Furthermore, when the circuit of the present invention is sold as a unit, it is not necessary for the user of the unit to amplify the unit, and it is possible to propose a unit that is very easy to use.

The audio detection circuit of the present invention is a circuit for detecting audio FM modulated signals of a plurality of broadcasting systems having mutually different frequency deviations by a common quadrature detection circuit, from the R, L, C resonance circuits. A phase shift circuit realized by a tank circuit configured to shift the phase of the audio FM modulation signal by 90 ° for the quadrature detection circuit, and a resistance value of R in the phase shift circuit corresponding to each broadcasting system. Switching means for switching the Q of the phase shift circuit by switching so as to match the audio output levels in the respective broadcasting systems.

According to the above configuration, the quadrature detection circuit which obtains the audio output by mixing the audio FM modulated signal and the signal whose phase is shifted by 90 ° is mutually shifted in frequency. In a sound detection circuit commonly used for sound FM modulated signals of a plurality of different broadcasting systems, a phase shift circuit for shifting the phase is realized by a tank circuit composed of R, L and C resonance circuits. The Q of the phase shift circuit is switched by switching the resistance value of R by a switching means realized by a switch such as a transistor or a diode in accordance with each broadcasting system.

Therefore, in the FM detection S-curve characteristic, the slope of the curve changes, and even if the frequency deviation amounts (modulation degrees) are different from each other, the sound output levels can be made to coincide with each other. it can. As a result, even if broadcasts having different frequency shift amounts are received, it is possible to improve the unpleasantness in hearing. Further, it is possible to reduce the possibility that the distortion and SN will deteriorate as compared with the case where the amplitude is limited or the amplification factor is changed in the latter-stage circuit. Furthermore, when the circuit of the present invention is sold as a unit, it is not necessary for the user of the unit to amplify the unit, and it is possible to propose a unit that is very easy to use.

Furthermore, in the voice detection circuit of the present invention,
The broadcasting system is NTSC and PAL.

According to the above arrangement, the NTFM audio FM modulated signal has a modulation factor of 100% and the frequency deviation amount is ±.
While the frequency is 25 kHz, the PAL audio FM modulation signal has a modulation degree of 100% and a frequency deviation amount of ± 50.
kHz, and thus the difference in the amount of frequency deviation is large,
The present invention is particularly effective because the audio output level is different by 6 dB when Q of the phase shift circuit is constant.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Regarding one embodiment of the present invention,
The following is a description with reference to FIGS. 1 to 5.

FIG. 1 is a block diagram showing a schematic configuration of a voice detection circuit 31 according to an embodiment of the present invention. This voice detection circuit 31 is different from the detection circuit 22 realized by the quadrature detection circuit shown in FIG.
Two phase shift circuits 33a, 3 having different Qs from each other.
By switching and using 3b, the audio output level can be made constant even when the audio FM modulated signals of the systems having mutually different frequency deviations are received. The voice detection circuit 31 can be used as the FM detection circuit (FM DET) 15 of the reception device 1 shown in FIG.

FIG. 2 is a block diagram showing a specific configuration of the voice detection circuit 31 shown in FIG. The phase shift circuit 33 includes a coil L1, a capacitor C1, resistors R1 and R2, and the switch 32. The parallel circuit of the coil L1, the capacitor C1 and the resistors R1 and R2 is connected to the detection circuit 22 via a DC cut capacitor C2. The coil L1 and the capacitor C1
The resistor R1 and the resistor R1 are connected in parallel to each other.
The series circuit of is connected to the parallel circuit. Therefore, when the switch 32 is cut off, the resistance value in the parallel circuit is only R1, the attenuation of the resonance current of L1 and C1 is small, and the Q of the phase shift circuit 33 is high. When the switch 32 is turned on, the resistance value of the parallel circuit becomes the parallel resistance value of R1 and R2, the attenuation of the resonance current of L1 and C1 is large, and the Q of the phase shift circuit 33 is low.

FIG. 3 shows the F by changing the Q value.
It is a graph which shows the change of the M detection S curve characteristic. When the amount of frequency deviation (modulation degree) is small, for example, when detecting the above-mentioned NTSC audio FM modulated signal, the switch 32 is cut off and the Q of the phase shift circuit 33 is increased to detect the voice after detection. When the output level is set to a desired value and the frequency shift amount is large, for example, when the PAL audio FM modulation signal is detected, the switch 32 is turned on and the Q of the phase shift circuit 33 is lowered. The audio output level, which should be large, is suppressed to a low value and set to the desired value.

The switching of the switch 32 according to the frequency shift amount is performed by the voice demodulation circuit (QIF DET) 14 of the receiving apparatus 1 shown in FIG.
This can be performed by using a control voltage or the like output from a phase comparator that forms a PLL for mixing the O signal and extracting the audio FM modulated signal to a VCO (voltage controlled oscillator). More specifically, NTSC audio FM
Compared to the case of detecting the modulated signal, the PAL audio F
When detecting the M-modulated signal, the frequency of the LO signal is high and therefore the control voltage is high. By discriminating this control voltage by comparing it with a reference level, it is possible to discriminate between these different frequency shift amounts, and the switching of the switch 32 may be controlled according to the discrimination result.

In this way, by switching the switch 32 according to the frequency shift amount, the sound FM modulated signals of a plurality of broadcasting systems having mutually different frequency shift amounts are detected by the common quadrature detection circuit. At this time, the audio output level can be made constant, and thus the uncomfortable feeling in hearing can be improved.

As described above, the NTSC system and PAL
In the method, the NTSC audio FM modulated signal has a modulation degree of 100% and the frequency shift amount is ± 25 kHz, whereas the PAL audio FM modulated signal similarly has a frequency shift of 100% and a frequency shift. The amount is ± 50 kHz, and when the difference between the frequency shift amounts is large and the Q of the phase shift circuit is constant, the audio output level is 6 dB as described above.
Therefore, the present invention is particularly effective.

4 and 5 show the phase shift circuit 33 described above;
3 shows a specific configuration of the switch 32 in 33a and 33b, which is a phase shift circuit 33A and a phase shift circuit 33B, respectively. In these figures, parts corresponding to those in FIGS. 1 and 2 described above are designated by the same reference numerals.

In the phase shift circuit 33A of FIG. 4, the switch 32 is a transistor Tr1 and a bias resistor R.
3 and R4 are used. The signal for switching is divided by the bias resistors R3 and R4 and given to the base of the transistor Tr1. When the signal becomes high level, the transistor Tr1 becomes conductive, the resistor R2 is inserted, and the Q When the signal becomes low and the signal becomes low level, the transistor Tr1 is cut off, the resistor R2 is disconnected and the Q becomes high.

On the other hand, in the phase shift circuit 33B of FIG. 5, the switch 32 is the diode D1 and the bias resistor R.
5 and R6 are used. The signal for switching is applied to both terminals of the diode D1 via the bias resistors R5 and R6, and when biased so that the anode side is at a higher level than the cathode side, the diode D1 becomes conductive, and When the resistor R2 is inserted and Q is lowered and the anode side is biased to be at a lower level than the cathode side, the diode D1 is cut off and the resistor R2
2 is separated and Q becomes higher.

In this way, the switch 32 can be specifically constructed.

By the way, as a method of keeping the audio output level constant, it is conceivable to limit the amplitude or change the amplification factor in the subsequent circuit, but there is a possibility that distortion and SN will deteriorate. Further, when the circuit of the present invention is sold as a unit, that is, when the integrated circuit chip of the receiving device 1 is sold, it is not necessary for the user of the unit to amplify it, and a very convenient unit can be proposed. .

[0034]

As described above, the voice detection circuit of the present invention is a quadrature detection circuit for obtaining a voice output by mixing a voice FM modulated signal and a signal whose phase is shifted by 90 °. In a voice detection circuit which is commonly used for voice FM modulated signals of a plurality of broadcasting systems having mutually different frequency shift amounts, the phase is shifted and the phase shift circuit of the phase shift circuit which is constant in the conventional circuit is used. Q
Is switched in accordance with each of the broadcasting systems.

Therefore, in the FM detection S-curve characteristic, the slope of the curve changes, and even if the frequency deviation amounts (modulation degrees) are different from each other, the audio output levels are made to coincide with each other. You can by this,
Even if broadcasts having different frequency shift amounts are received, it is possible to improve the unpleasantness in hearing. Also, compared to limiting the amplitude or changing the amplification factor in the latter stage circuit,
It is possible to reduce the possibility that distortion and SN will deteriorate. Furthermore, when the circuit of the present invention is sold as a unit, it is not necessary for the user of the unit to amplify the unit, and it is possible to propose a unit that is very easy to use.

As described above, the voice detection circuit of the present invention is a quadrature detection circuit that obtains a voice output by mixing the voice FM modulated signal and the signal whose phase is shifted by 90 °. In a voice detection circuit which is commonly used for voice FM modulation signals of a plurality of broadcasting systems having mutually different frequency shift amounts, a phase shift circuit for shifting the phase from R, L, C resonance circuits. The phase shift circuit is realized by a tank circuit, and the resistance value of R is switched by a switching means realized by a switch such as a transistor or a diode in accordance with each broadcasting system, thereby switching Q of the phase shift circuit.

Therefore, in the FM detection S-curve characteristic, the slope of the curve changes, and the sound output levels are made to match each other even if the frequency deviation amount (modulation degree) is different from each other. You can by this,
Even if broadcasts having different frequency shift amounts are received, it is possible to improve the unpleasantness in hearing. Also, compared to limiting the amplitude or changing the amplification factor in the latter stage circuit,
It is possible to reduce the possibility that distortion and SN will deteriorate. Furthermore, when the circuit of the present invention is sold as a unit, it is not necessary for the user of the unit to amplify the unit, and it is possible to propose a unit that is very easy to use.

Furthermore, as described above, the audio detection circuit of the present invention modulates the broadcasting system in the same manner as NTSC in which the audio FM modulation signal has a modulation degree of 100% and the frequency shift amount is ± 25 kHz. The PAL has a frequency deviation of ± 50 kHz at 100%.

Therefore, the difference of the frequency shift amount is large, and when the Q of the phase shift circuit is constant, the audio output level is different by 6 dB, so that the present invention is particularly effective.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a voice detection circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a specific configuration of the voice detection circuit of FIG.

FIG. 3 is a graph showing a change in FM detection S curve characteristic due to switching of Q value according to the present invention.

FIG. 4 is an electric circuit diagram showing a specific configuration of a switch in the phase shift circuit of FIGS. 1 and 2.

5 is an electric circuit diagram showing a specific configuration of a switch in the phase shift circuit of FIGS. 1 and 2. FIG.

FIG. 6 is a block diagram showing an electrical configuration of a television broadcast receiving apparatus compatible with both NTSC and PAL broadcasting systems.

FIG. 7 is a block diagram showing an electrical configuration of a typical prior art FM detection circuit.

FIG. 8 is an electric circuit diagram of a quadrature detection circuit.

FIG. 9 is a graph showing the relationship between the input signal frequency and the input / output phase difference of the phase shift circuit.

FIG. 10 is a graph showing an FM detection S-curve characteristic of a conventional FM detection circuit.

FIG. 11 is a waveform diagram showing an operation of the quadrature detection circuit.

[Explanation of symbols]

1 receiver 2 antenna 3 input tuning circuit 4 High frequency amplifier circuit 5 interstage tuning circuit 6 mixing circuit 7 Local oscillator circuit 8,9 SAW filter 10 Amplifier circuit (VIF AMP) 11 Audio IF amplifier circuit (SIF AMP) 12 Video detection circuit (Video DET) 13 Video amplifier circuit (Video AMP) 14 Voice demodulation circuit (QIF DET) 15 FM detection circuit (FM DET) 22 Quadrature detection circuit 31 Voice detection circuit 32 switch 33; 33a, 33b; 33A, 33B Phase shift circuit C1, C2 capacitors D1 diode L1 coil Q1, Q2; Q3, Q4; Q5, Q6 Transistors R1, R2 resistance R3, R4; R5, R6 Bias resistance RB resistance RL load resistance Tr1 transistor

Claims (3)

[Claims] 1. A circuit for detecting audio FM-modulated signals of a plurality of broadcasting systems having different frequency shift amounts by a common quadrature detection circuit, wherein phase shift in the quadrature detection circuit determines FM detection S-curve characteristics. An audio detection circuit, characterized in that the audio output levels in each of the broadcasting systems are matched by switching the Q of the circuit. 2. A circuit for detecting a sound FM modulated signal of a plurality of broadcasting systems having different frequency shift amounts by a common quadrature detection circuit, which is realized by a tank circuit composed of R, L and C resonance circuits, A phase shift circuit that shifts the phase of the audio FM modulation signal by 90 ° for the quadrature detection circuit, and a resistance value of R in the phase shift circuit is switched by corresponding to each broadcasting system. An audio detection circuit comprising: switching means for switching Q to match the audio output level in each of the broadcasting systems. 3. The audio detection circuit according to claim 1, wherein the broadcasting system is NTSC and PAL.