JP3298208B2 - Audio signal detection method and circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal detecting method and circuit suitable for use in, for example, a multi-standard television receiving a European television broadcast.

[0002]

2. Description of the Related Art In a multi-standard television receiving a European television broadcast, an amplitude-modulated audio signal (hereinafter referred to as an AM audio signal) or a frequency-modulated audio signal is received in accordance with a receiving channel. (Hereafter, the audio signal of the broadcast wave is referred to as FM audio signal)
And an AM detector and an FM detector for demodulating either of the above. In the reception mode (SYSTEM L) for AM detection of the audio intermediate frequency signal, AM audio reception is performed by the AM detector, while the reception mode (SYSTEM B / G, I,
D / K), the FM sound is received by the FM detector.

FIG. 3 is a block diagram showing a configuration of an audio signal detection circuit in such a multi-standard television. In this figure, reference numeral 6 denotes a filter which extracts and outputs only an AM intermediate frequency signal supplied from a tuner (not shown).
Reference numeral 7 denotes an AM detection circuit that detects an output signal of the filter 6 and outputs an AM audio signal. 8 is an audio switch. The audio switch 8 switches between an AM audio signal supplied to one input terminal and an FM audio signal supplied to the other input terminal in accordance with a switch signal supplied from the outside, and shifts to a subsequent stage. Output.

Reference numeral 9 denotes a band pass filter, which outputs a predetermined band component of the FM intermediate frequency signal to the next stage. Reference numeral 10 denotes an FM detection circuit that detects an output signal of the band-pass filter 9 and outputs an FM audio signal. In addition, the FM detection circuit 10 receives the reception mode (SYSTEM B / S) corresponding to the mode instruction signal supplied from the microcomputer 12.
G), the detection operation is performed in the reception mode (SYSTEM I) and the reception mode (SYSTEM D / K). 11 is
This is a mute circuit that mutes noise output from the FM detection circuit 10 in the reception mode SYSTEM L. This mute circuit 11 is used when the mute instruction signal is supplied from the microcomputer 12.
Are muted. Reference numeral 12 denotes a microcomputer that controls the entire multi-standard television, and generates the above-described switch signal, mode instruction signal, and mute instruction signal according to the reception mode.

In such a configuration, when receiving an AM sound, the microcomputer 12 supplies a switch signal for selecting the AM sound signal to the audio switch 8 and outputs a mute instruction signal for muting the FM sound signal. Supply to the mute circuit 11. Thereby, the mute circuit 11 mutes the FM audio signal,
Since the audio switch 8 outputs the AM audio signal to the next stage, the AM audio is received. On the other hand, when receiving FM sound, the audio switch 8
A switch signal for selecting the M audio signal is supplied, and a mode instruction signal for designating a reception mode is supplied to the FM detection circuit 10. As a result, the FM audio signal detected in the predetermined reception mode is output to the next stage via the audio switch 8.

[0006]

In the above-described conventional audio signal detection circuit, when the AM audio reception operation is performed without the mute circuit 11 being muted, the output of the FM detection circuit 10 is superimposed on the AM audio signal, It becomes a noise source.
Further, if the separation characteristics of the audio switch 8 that performs the signal switching operation under the control of the microcomputer 12 are poor, the output of the FM detection circuit 10 crosstalks with the AM audio signal, and this also causes noise. . Therefore, in the conventional audio signal detection circuit, the mute circuit 11 is an essential component in order to prevent the influence of such noise. If the mute circuit 11 is not provided, an audio switch 8 having good separation characteristics is required.

However, if the mute circuit 11 is provided in the audio signal detection circuit, a peripheral circuit for turning on and off the mute circuit 11 in response to the above-mentioned mute instruction signal is required, which causes an increase in cost. is there. On the other hand, when the mute circuit 11 is omitted,
Audio switch 8 with very good separation characteristics
Is required to be used, and in this case as well, this is a factor that causes an increase in cost. Therefore, the present invention has been made in view of the above circumstances, and provides an audio signal detection method and circuit that can prevent the influence of noise without providing a mute circuit and that does not lead to an increase in cost. The purpose is.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, an amplitude-modulated first intermediate frequency signal is detected to generate an AM audio signal.
An M detection process, an FM detection process for detecting a frequency-modulated second intermediate frequency signal to generate an FM audio signal, and either the AM audio signal or the FM audio signal according to an externally received signal . Select one and mode finger
A switching control step of outputting an indication signal, wherein the switching control step selects and outputs the AM audio signal,
A mode indicator corresponding to the received signal for the FM detection process
A signal is output to synchronize the FM detection process with the first intermediate frequency signal to perform a detection operation.

According to the second aspect of the present invention, there is provided an AM detecting means for detecting an amplitude-modulated first intermediate frequency signal to generate an AM audio signal, and a frequency-modulated second intermediate frequency signal. selecting a FM detection means for generating an FM audio signal by detecting a signal, either of the AM audio signal or the FM audio signal in response to receiving a signal from the outside
Switching control means for outputting a mode instruction signal together with the reception signal to the FM detection means when selecting and outputting the AM audio signal.
The FM detection means is tuned to the first intermediate frequency signal by outputting a mode instruction signal corresponding to the above-mentioned mode, and a detection operation is performed.

[0010]

According to the present invention, when an AM audio signal is output,
The switching control means controls the FM detection means for a mode corresponding to the received signal.
The FM detection means is tuned to the first intermediate frequency signal to perform a detection operation. As a result, this F
The M detection output does not crosstalk with the AM audio signal. Therefore, the influence of noise can be prevented without providing a mute circuit, and the cost is not increased.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a multi-standard television using an audio signal detection circuit according to the present invention. In this figure,
Numeral 1 designates a high frequency signal received via the antenna ANT as a video intermediate frequency signal or an AM audio intermediate frequency signal (AMS).
IF) and outputs the converted tuner. Reference numeral 2 denotes a video intermediate frequency amplifying circuit (VIF), which outputs a video intermediate frequency signal supplied from the tuner 1 to the next stage as a video signal, and uses the QPT output of this VIF as an FM audio intermediate frequency signal (FM SIF). appear.

Reference numeral 3 denotes a Y / C separation circuit, and reference numeral 4 denotes an audio signal detection circuit (SIF). The audio signal detection circuit 4 performs AM detection on the AM audio intermediate frequency signal (AM SIF) or FM audio intermediate frequency signal (FM SIF) according to an operation mode, or AM audio signal, or FM detection and FM detection.
Generate an audio signal. Reference numeral 5 denotes an amplifier, which amplifies the AM audio signal or the FM audio signal and supplies the amplified signal to the speaker SP.

FIG. 2 is a block diagram showing the configuration of the above-described audio signal detection circuit (SIF) 4. In this figure, the same parts as those shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. The configuration shown in FIG. 2 is different from the conventional example shown in FIG. 3 in that the mute circuit 11 is omitted and the influence of noise at the time of AM voice reception is prevented by the operation of the microcomputer 12. . Hereinafter, this audio signal detection circuit (S
The detection operation of IF) 4 will be described.

Operation for Receiving FM Audio Signal In this case, the above-described FM detection circuit 10 receives one of the reception modes (SYSTEM B / G, SYSTEM I, SYSTEM
EM D / K). The audio switch 8 performs a switching operation so as to select an output of the circuit 10 in accordance with an instruction from the microcomputer 12. As a result, the audio signal detection circuit (SIF) 4
FM detection of FM SIF supplied as PT output,
The resulting FM audio signal is output to the next stage via the audio switch 8.

Operation for Receiving AM Audio Signal Next, a reception mode (SYSTE) for receiving an AM audio signal is described.
In ML), the AM audio intermediate frequency signal (AM SIF) output from the tuner 1 is filtered, detected by the AM detection circuit 7, and supplied to the audio switch 8 as an AM audio signal.

At this time, an audio signal detection circuit (SIF) 4 outputs a 6.5 MHz AM signal as the QPT output of the VIF 2.
The audio intermediate frequency signal and the video signal are supplied to the FM detection circuit 10 via the band pass filter 9. The AM audio intermediate frequency signal and the video signal are
The M detection causes noise, which crosstalks with the AM audio signal in the audio switch 8.

Therefore, in order to remove such interference, the microcomputer 12 controls the FM detection circuit 10
A mode instruction signal is supplied to perform the detection operation in the reception mode (SYSTEM D / K). Thereby, the circuit 10
Is set to an operation mode for detecting a 6.5 MHz FM signal. Therefore, the FM detection circuit 10 operates at 6.5M
Since the AM signal / video signal of 6.5 Hz is detected by the FM signal of 6.5 MHz, there is no detection output. That is, F
That is, the output of the M detection circuit 10 does not become a noise source, and there is no need to mute.

As described above, according to the above-described embodiment, A
When the M intermediate frequency signal is detected to generate the AM audio signal, the reception mode is set to the FM detection circuit according to the reception signal.
The FM intermediate frequency signal is tuned to the AM intermediate frequency signal to be detected and FM detection is performed.
The detection output does not crosstalk with the AM audio signal. Therefore, the influence of noise can be prevented without providing a mute circuit, and the cost does not increase. Such a receiving operation can be handled only by changing the control program of the microcomputer 12.

[0019]

As described above, according to the present invention,
When an AM audio signal is received, the switching control means tunes the FM detection means to the first intermediate frequency signal and performs the detection operation, so that the FM detection output does not crosstalk with the AM audio signal. As a result, the influence of noise can be prevented without providing a mute circuit. Moreover, this does not lead to an increase in cost.

[Brief description of the drawings]

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

FIG. 2 is an audio signal detection circuit (SIF) in the embodiment.
FIG. 3 is a block diagram showing the configuration of FIG.

FIG. 3 is a diagram for explaining a conventional example.

[Explanation of symbols]

 6: Filter (AM detection means) 7: AM detection circuit (AM detection means) 8: Audio switch (switch control means) 9: Bandpass filter (FM detection means) 10: FM detection circuit (FM detection means) 12: Micro Computer (switch control means)

Claims (4)

(57) [Claims] 1. An AM detection process for detecting an amplitude-modulated first intermediate frequency signal to generate an AM audio signal, and detecting a frequency-modulated second intermediate frequency signal to generate an FM audio signal. FM detection process, and either one of the AM audio signal or the FM audio signal is selected according to a received signal from the outside, and the mode is selected.
And a switching control step of outputting a command signal. In the switching control step, when selecting and outputting the AM audio signal, the switching control step responds to the reception signal with respect to the FM detection step.
And outputting the same mode instruction signal to tune the FM detection process to the first intermediate frequency signal to perform a detection operation. 2. An AM detector for detecting an amplitude-modulated first intermediate frequency signal to generate an AM audio signal, and detecting a frequency-modulated second intermediate frequency signal to generate an FM audio signal. and FM detection means, mode while selecting one of the AM audio signal or the FM audio signal in response to receiving a signal from the outside
Switching control means for outputting a modulation instruction signal , wherein the switching control means responds to the FM detection means in response to the reception signal when selecting and outputting the AM audio signal.
An audio signal detection circuit which outputs the same mode instruction signal to tune the FM detection means to the first intermediate frequency signal to perform a detection operation. 3. A multi-standard television for detecting an amplitude-modulated first intermediate frequency signal and a frequency-modulated second intermediate frequency signal to generate an AM audio signal or an FM audio signal. 3. The audio signal detection circuit according to claim 2, wherein when generating the AM audio signal, the FM detection means is tuned to the first intermediate frequency signal to perform an FM detection operation. 4. A television for detecting an amplitude-modulated first intermediate frequency signal to generate an AM audio signal and detecting a frequency-modulated second intermediate frequency signal to generate an FM audio signal. Provided in the intermediate frequency block;
3. The audio signal detection circuit according to claim 2, wherein when generating the M audio signal, the FM detection means is tuned to the first intermediate frequency signal to perform an FM detection operation.