JPH04110031U - Multi-system monaural audio receiver - Google Patents

Abstract

(57) [Summary] [Purpose] BG, I, DK in Europe, etc.
This prevents noise interference caused by the NICAM second audio signal in a multi-system monaural audio receiver such as the following. [Structure] When receiving BG, the transistor switches 9 and 16 are turned on by the control signal from the terminal 18, and the tuning frequency of the tuning circuit 19 is set to 5.5 MHz.
As a result, the BG-NICAM first audio intermediate frequency signal (5.5 MHz) passes through the transmission line and is demodulated, but the BG-NICAM second audio intermediate frequency signal (5.85 MHz) passes through the transmission line and is demodulated.
MHz) are greatly attenuated. When receiving I, terminal 17
A control signal from the transistor switch 48,1
5 is turned ON, and the tuning frequency of the tuning circuit 19 is 6.0M.
Can be switched to Hz. As a result, I-NICAM 1st
The audio intermediate frequency signal (6.0MHz) is demodulated,
I-NICAM second audio intermediate frequency signal (6.552MH
z) is greatly attenuated.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention applies to locations where BG-NICAM broadcasting or I-NICAM broadcasting is performed. The present invention relates to a multi-system monaural audio receiver suitable for use in the area.

0002

[Conventional technology]

In Europe and other regions, TV broadcasting mainly uses BG, I, DK, etc. Ru. In these systems, the difference between the audio carrier frequency and the video carrier frequency is The audio intermediate frequency is different, 5.5 and 6.0 for BG, I, and DK systems, respectively. , 6.5MHz.

0003 By the way, in NICAM broadcasting in the BG, I system that has been started in recent years, It has a first audio carrier wave and a second audio carrier wave, and the first audio carrier wave is a monaural audio signal. The audio intermediate frequency is 5.5, 6.0M for each BG and I system. Hz, but the second audio carrier wave is a stereo audio etc. subjected to pulse code modulation, The audio intermediate frequency is 5.85 and 6.552 MHz for each BG and I system. Ru.

0004 Figure 3 shows a multi-system monophonic system for receiving monaural audio of the BG, I, and DK three systems. This is a conventional example of a digital audio receiving circuit. Center frequencies of audio intermediate frequency band pass filters (hereinafter abbreviated as BPF) 5, 6, and 7 The numbers are 5.5, 6.0, and 6.5 MHz, respectively. The first input from input terminal 1 In the case of the BG method, the audio intermediate frequency signal passes through the tuning capacitor 2 and BPF 5, and is sent to the I direction. In the case of the formula, it passes through the tuning capacitor 3 and BPF6, and in the case of the DK method, it passes through the tuning capacitor 4 and Passes BPF7.

[0005] On the other hand, the second audio intermediate frequency signal present during NICAM broadcasting is monaural audio. When receiving a message, it is unnecessary and it is desirable not to pass through the BPF. Yes. However, in the case of BG method reception, the second audio intermediate frequency signal 5.85MH z is greatly attenuated in BPFs 5 and 7, but in BPF 6, the center frequency is 6. ．． Since it is close to 0MHz, it does not receive much attenuation. Similarly, in the case of I method, 6.55 The 2MHz second audio intermediate frequency signal is greatly attenuated by BPFs 5 and 6, but BPF7 does not receive much attenuation because the center frequency is close to 6.5 MHz.

[0006] Therefore, in the case of BG method reception, the control signal from the control signal input terminal 18 By turning on the switching transistor 9, the 5.85MHz The second audio intermediate frequency signal is greatly attenuated, and in the case of I method, the control signal input terminal 1 The switching transistor 8 is turned on by the control signal from 7. Thus, the second audio intermediate frequency signal of 6.552 MHz is greatly attenuated.

[0007] The local oscillator 22 outputs an oscillation frequency signal of 0.5MHz, and the mixer 21 outputs an oscillation frequency signal of 0.5MHz. The mixer 21 receives the 0.5 MHz oscillation frequency signal and enables frequency conversion operation. The first audio intermediate frequency signal input to the mixer 21 is all converted to 6.0 MHz. It passes through the next stage BPF 23 with a center frequency of 6.0 MHz, and is output by the audio demodulation circuit 10. The demodulated monaural audio signal is output from the output terminal 20.

[0008] Here, the tuning circuit 19 used for demodulation in the audio demodulation circuit 10 has a tuning input. It consists of an inductance 11 and a tuning capacitor 12, and the tuning frequency is 6.0 MHz.

[0009]

[Problem that the idea aims to solve]

However, when receiving the BG method, the switching transistor 9 is turned off. Even if it is N, the stray impedance component of the switching circuit and BPF5, Due to the variation in the amount of attenuation, the second audio intermediate frequency signal of 5.85 MHz is It does not necessarily mean that it will be attenuated. Therefore, the 5.85MHz signal that was not sufficiently attenuated The second audio intermediate frequency signal passes through the mixer 21, also passes through the BPF 23, and is audio demodulated. As shown in FIG. 4(A), the input to the circuit 10 is the BPF 23 and the tuning circuit 19. Since it is only 150KHz away from the center frequency of do not have. Therefore, the second audio intermediate frequency signal of 5.85 MHz is transmitted within the audio demodulation circuit 10. The ratio of the audio signal level to the noise level at the output terminal 20 (hereinafter referred to as S /N ratio) deteriorates.

0010 Similarly, in I method reception, switching transistor 8 is turned on. However, the stray impedance components of the switching circuit and the attenuation of BPF5 and 6 Due to the variation in the amount, the second audio intermediate frequency signal of 6.552 MHz may be sufficiently reduced. It doesn't necessarily mean it will weaken. Therefore, the 6.552MHz frequency that was not sufficiently attenuated The two audio intermediate frequency signals pass through the mixer 21, the BPF 23, and the audio demodulation circuit. However, as shown in FIG. 4(B), the BPF 23 and the tuning circuit 19 Since it is only 52KHz away from the center frequency, it does not receive much attenuation. . Therefore, the second audio intermediate frequency signal of 6.552 MHz is affected by noise within the audio demodulation circuit. Therefore, there was a problem that the S/N ratio at the output terminal 20 deteriorated as described above. .

[0011]

[Means to solve the problem]

In order to solve this problem, the multi-system monaural audio receiver of the present invention has A plurality of audio intermediate frequency signals including a first audio intermediate frequency signal and a second audio intermediate frequency signal having different frequency bands. In a multi-system monaural audio receiver for receiving system audio signals, connect in parallel. a plurality of audio intermediate frequency signals each having a different passing frequency band; a first audio intermediate frequency bandpass filter; and the first audio intermediate frequency bandpass filter. monaural sound under the tuned frequency from the first audio intermediate frequency signal of each frequency band that has passed through the an audio demodulation circuit that demodulates voices; and a tuning circuit that sets a tuning frequency of the audio demodulation circuit. a second audio intermediate frequency signal having a pass frequency band close to the frequency band of the second audio intermediate frequency signal; 1 Audio intermediate frequency band pass filter, and the corresponding filter is connected to the audio intermediate frequency band pass filter. A step for blocking input of the second audio intermediate frequency signal to the first audio intermediate frequency band-pass filter. and a switch circuit, wherein the tuning circuit operates to adjust the tuning frequency in conjunction with the switch circuit. is the frequency of the first audio intermediate frequency signal passing through the first audio intermediate frequency bandpass filter. It is characterized by comprising a switch circuit that switches to a value corresponding to the number.

0012

[Effect]

During audio of any method including a first audio intermediate frequency signal and a second audio intermediate frequency signal When the intermediate frequency signal is input from the input terminal, the first audio intermediate frequency signal is inputted from the first audio intermediate frequency signal. Passing through a first audio intermediate frequency band-pass filter tuned to the audio intermediate frequency signal frequency. Ru.

[0013] When a control signal is input to the control signal input terminal corresponding to the above method, the first audio A switch circuit that cuts off input of the second audio intermediate frequency signal to the intermediate frequency band pass filter. the second audio intermediate frequency signal is blocked by the switch circuit; The first audio intermediate frequency band pass filter cannot be passed through.

[0014] On the other hand, the control signal is also transmitted to the tuning circuit that sets the tuning frequency of the audio demodulation circuit. and setting the tuning frequency of the tuning circuit to the first audio intermediate frequency signal frequency. , the first audio intermediate frequency signal passed through the first audio intermediate frequency bandpass filter. is input to the audio demodulation circuit, demodulated by the audio circuit, and a monaural audio signal is output. Output from the terminal.

[0015]

【Example】

An embodiment of the present invention will be described below with reference to FIG. Control when receiving BG When a control signal is applied to the signal input terminal 18, the switching transistors 9, 16 is conductive, and the tuning circuit 19 includes the tuning inductance 11 and the tuning capacitance 12, 14 to tune to 5.5MHz. 5.5MHz first input from input terminal 1 The audio intermediate frequency signal passes through the tuning capacitor 2 and BPF 5, and is demodulated by the audio demodulation circuit 10. The demodulated monaural audio signal is output from the output terminal 20. On the other hand5. The second audio intermediate frequency signal of 85 MHz is transmitted through the switching transistor 9 and the BPF. 5 and 7 and is selectively received by the tuning circuit 19. The demodulation circuit output for the two audio signals becomes extremely small.

[0016] Similarly, when receiving the I method, a control signal is applied to the control signal input terminal 17. , the switching transistors 8 and 15 become conductive, and the tuning circuit 19 becomes a tuning input. It is tuned to 6.0 MHz with the inductance 11 and the tuning capacitors 12 and 13. input end The first audio intermediate frequency signal of 6.0 MHz input from child 1 is transmitted through tuning capacitor 3 and BPF. 6 and is demodulated by the audio demodulation circuit 10. On the other hand, the second tone of 6.552MHz The voice intermediate frequency signal is increased by the switching transistor 8 and the BPFs 5 and 6. Since the second audio signal is attenuated and selectively received by the tuning circuit 19, the second audio signal is The output of the regulator circuit becomes extremely small.

[0017] In the case of DK method reception, no signals are input to the control signal input terminals 17 and 18. Therefore, switching transistors 8, 9, 15, and 16 are all non-conductive. Therefore, the tuning circuit 19 has a tuning inductance 11 and a tuning capacitance 12, and has a power of 6.5 Tune to MHz. 6.5MHz first audio intermediate frequency signal input from input terminal 1 The signal passes through the tuning capacitor 4 and BPF 7, and is demodulated by the audio demodulation circuit 10.

[0018] As described above, in the case of BG method reception, the switching circuit before the BPF and the BP The second audio intermediate frequency signal of 5.85 MHz that was not sufficiently attenuated by F is the audio As shown in Fig. 2(A), the tuning frequency of the tuning circuit is 35 Because they are 0KHz apart, the frequency is larger than the 150KHz of the conventional example shown in Figure 4(A). As a result, the level of noise output from the audio demodulation circuit becomes smaller. This improves the S/N ratio.

[0019] The same applies to I method reception, but in this case, as shown in FIG. 2(B), 6. The second audio intermediate frequency of 552MHz is the tuning frequency of the tuning circuit, which is 552KH. 52 KHz in the conventional example shown in Fig. 4(B). This reduces the level of noise output from the audio demodulation circuit. , the S/N ratio is improved. Furthermore, the local oscillator, mixer, and BPF next to the mixer, which were in the conventional example, are removed. This makes it possible to greatly simplify the circuit.

[0020]

[Effect of the idea]

a switch circuit connected to a first audio intermediate frequency bandpass filter; The second audio intermediate frequency signal that was not sufficiently attenuated by the audio intermediate frequency bandpass filter. is input to the audio demodulation circuit, and the second audio intermediate frequency signal frequency is input to the audio demodulation circuit. Since the tuning frequency of the tuning circuit that sets the tuning frequency of the circuit is far enough away, 2 The demodulation circuit output for the audio intermediate frequency signal becomes extremely small, improving the S/N ratio. let

[0021] In addition, local oscillators, mixers and The first audio intermediate frequency band-pass filter in the next stage of the combiner is removed, greatly simplifying the circuit. come.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a multi-system monaural audio receiver that is an embodiment of the present invention.

[Figure 2] Characteristic diagram for explaining the noise reduction effect of the embodiment of the present invention

FIG. 3 is a block diagram showing the configuration of a conventional multi-system monaural audio receiver.

[Figure 4] Characteristic diagram for explaining noise generation in conventional embodiments

[Explanation of symbols]

5 BPF (center frequency 5.5MH
z) 6 BPF (center frequency 6.0MH
z) 7 BPF (center frequency 6.5MH
z) 23 BPF (center frequency 6.0MH
z) 8, 9, 15, 16 Transistor switch 10 Audio demodulation circuit 19 Tuning circuit 21 Mixer 22 Local oscillator

Claims (1)

[Scope of utility model registration request] Claim 1: A multi-system monaural audio receiver for receiving a multi-system audio signal including a first audio intermediate frequency signal and a second audio intermediate frequency signal each having a different frequency band, wherein each of the multiple audio intermediate frequency signals connected in parallel has a different passing frequency. a plurality of first audio intermediate frequency band-pass filters that pass a first audio intermediate frequency signal in a frequency band; and a tuning frequency from the first audio intermediate frequency signal in each frequency band that has passed through the first audio intermediate frequency band-pass filter. an audio demodulation circuit for demodulating monaural audio; a tuning circuit for setting a tuning frequency of the audio demodulation circuit; and a first audio intermediate frequency band pass having a pass frequency band close to the frequency band of the second audio intermediate frequency signal. connected to the filter, and the first
a switch circuit that blocks input of the second audio intermediate frequency signal to the audio intermediate frequency band-pass filter, the tuning circuit interlocking with the switching circuit to change the tuning frequency to the first
A multi-system monaural audio receiver comprising a switch circuit that switches to a value corresponding to the frequency of a first audio intermediate frequency signal passing through an audio intermediate frequency band-pass filter.