JP2000165269A - Multiple broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a reception characteristic of a multiple broadcast receiver. SOLUTION: The receiver is provided with a front end circuit 12 that applies frequency conversion to a received broadcast wave signal into an intermediate frequency signal and a demodulation circuit 17 that demodulates a multiplexed signal from the intermediate frequency signal. Intermediate frequency filters 15A-15D are provided to an intermediate frequency signal line between the front end circuit 12 and the demodulation circuit 17. The receiver is also provided with a decoder circuit 31 that decodes data of a teletext from the multiplexed signal outputted from the demodulation circuit 17, a detection circuit 40 that detects a signal component of a noise and an adjacent disturbing signal included in the intermediate frequency signal and a detection circuit 32 that detects presence of the teletext data. According to the detection result by the detection circuits 40, 32, the intermediate frequency filters 15A-15D are selected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multiplex broadcasting receiver.

[0002]

2. Description of the Related Art In FM broadcasting, most programs are stereophonic, but the signal to be transmitted (modulated signal) is shown in FIG.
As shown in FIG. 5, a sum signal (L + R) of the left and right channel audio signals L and R, a modulated signal S (LR) carrier-amplitude-modulated by a difference signal (LR), a pilot signal SPLT Is a frequency multiplexed signal. The occupied frequency band of each signal is such that the sum signal (L + R) is 50
Hz to 15 kHz, pilot signal SPLT 19 kHz, modulated signal S (LR) 23 kHz to 53 kHz (subcarrier frequency 38 kHz)
It has been.

In FM broadcasting, a technique of broadcasting a program such as text information together with an audio program by frequency multiplexing has been put to practical use. In Japan, FM text multiplex broadcasting is based on the DARC system. Digital data such as text information is called. Subcarrier frequency: 76 kHz Transmission rate: 16 kbit / s Modulation method: LMSK (72 kHz when "0", "1"
Error correction method: (272,190) The LMSK signal SLMSK of the product code of the shortened difference set cyclic code is used as the LMSK signal SLMSK.
However, as shown in FIG. 3B, the signal is frequency-multiplexed with the signal of the original audio broadcast program and transmitted.

[0004]

However, if broadcast waves having different frequency spectra are mixed in one broadcast wave band as described above, the broadcast may not be received in the best condition.

That is, if the pass band width of the intermediate frequency filter of the receiver is made to correspond to the frequency spectrum shown in FIG. 3A, it is impossible to properly receive the teletext broadcast having the frequency spectrum shown in FIG. 3B. Can not.
However, if the pass band width of the intermediate frequency filter is made to correspond to the frequency spectrum of FIG. 3B, the noise level increases when receiving a non-text multiplex broadcast, or interference from adjacent stations is reduced. It becomes easy to receive.

When the pass band width of the intermediate frequency filter is made to correspond to the frequency spectrum shown in FIG. 3B, scanning reception of text multiplex broadcasting (scanning FM broadcasting band, and when text multiplex broadcasting is detected, Stop scanning,
After that, if there is noise or adjacent interference when performing the function of continuing to receive the text multiplex broadcasting, the scanning stops once, it is determined that it is not the text multiplex broadcasting, and the scanning is restarted. It takes a long time to receive text multiplex broadcasting.

[0007] The present invention is to solve the above problems.

[0008]

Therefore, according to the present invention, in a receiver for multiplexing data such as a text program to an audio program signal and receiving a multiplex broadcast for broadcasting the multiplex signal, A front-end circuit that converts a received broadcast wave signal into an intermediate frequency signal and outputs the converted signal; a demodulation circuit that demodulates the multiplexed signal from the intermediate frequency signal; and an intermediate circuit between the front-end circuit and the demodulation circuit. An intermediate frequency filter provided in a frequency signal line, a decoder circuit for decoding the text program data from the multiplexed signal output from the demodulation circuit, and a signal included in the intermediate frequency signal due to noise or adjacent interference A first detection circuit for detecting a component, and a second detection circuit for detecting the presence or absence of the text program data, wherein the first and second detection circuits are provided. In accordance with the detection result of the circuit, it is an receiver of the multiplex broadcasting to change the pass bandwidth of the intermediate frequency filter. Therefore, the pass bandwidth of the intermediate frequency filter is changed to an appropriate value according to the reception state of the audio program or the text program.

[0009]

FIG. 1 shows a case where the pass band width of an intermediate frequency filter of an FM receiver can be changed in four stages in order to properly receive FM broadcasts.

That is, a broadcast wave signal received by the antenna 11 is supplied to a front-end circuit 12 configured in a PLL synthesizer system, and a broadcast wave signal of a target frequency is converted into an intermediate frequency signal S12 and output. You. Then, the intermediate frequency signal S12 is passed through an amplifier 13 for intermediate frequency amplification, and further through a switch circuit 14 to bandpass filters 15A to 15A for intermediate frequency filters.
15D.

In this case, the switch circuit 14 and the subsequent switch circuit 16 are switched in accordance with the reception state of the FM broadcast, as will be described later.
A to 15D are constituted by, for example, ceramic filters.

The filter 15A has a pass band having a sufficiently wide pass band, for example, an intermediate frequency ± 280 kHz, and an intermediate frequency signal S12 of a broadcast wave signal having the contents shown in FIG. 3B.
Can be passed in an optimal state. The filter 15D has a narrow pass band width, for example, an intermediate frequency of ± 160 kHz, and passes the intermediate frequency signal S12 of the broadcast wave signal shown in FIG. 3A with minimum noise and adjacent interference. Have been able to. Further, the remaining filters 15B and 15C are each made to have a pass bandwidth intermediate between the filters 15A and 15D.

The switch circuit 16 is switched corresponding to the switch circuit 14, and the filters 15A to 15D
The intermediate frequency signal S12 supplied to any one of the above is extracted through the switch circuit 16, and the extracted intermediate frequency signal S12 is supplied to the FM demodulation circuit 17 to demodulate the signal S17 shown in FIG. 3A or 3B. It is taken out.

The demodulated signal S17 is supplied to a stereo demodulation circuit 18 to demodulate the left and right channel audio signals L and R. These signals L and R are used as glitch noise removal hold circuits 19L described later. , 19
It is supplied to speakers 22L and 22R through R and low frequency amplifiers 21L and 21R.

When the demodulated signal S17 has the contents shown in FIG. 3B, the signal S17 is supplied to the decoder circuit 31 to
Text program data is decoded and error-corrected and extracted from the MSK signal SLMSK, and this data is supplied to the microcomputer 32.

The microcomputer 32 uses the F
This is for controlling system control such as channel selection of the M receiver and display of a text program by FM text multiplex broadcasting. Therefore, a control signal of the reception frequency is supplied from the microcomputer 32 to the front end circuit 12.
Further, various operation keys 33 and a display for displaying a text program, for example, an LCD 34 are connected to the microcomputer 32 as a user interface.

The ROM of the microcomputer 32
Various programs executed by the CPU of the microcomputer 32 are prepared, and a routine 100 shown in FIG. 2 is prepared as a part of the programs.

Further, the output signal S17 of the demodulation circuit 17 is supplied to the noise detection circuit 40, and the level of the noise included in the signal S17 is detected. That is, the output signal S17 of the demodulation circuit 17 is supplied to a band-pass filter 41 having a pass band of, for example, 70 kHz to 120 kHz, and a noise component S41 included in the signal S17 is extracted. Then, the noise component S41 is supplied to the detection circuit 43 through the amplifier 42, and a DC voltage V43 having a level corresponding to the level of the noise component S41 is taken out. The voltage V43 is supplied to the analog input port A / D of the microcomputer 32. Is done.

A switching control signal is supplied from the microcomputer 32 to the switch circuits 14 and 16, and a control signal is supplied to the hold circuits 19L and 19R.

In such a configuration, processing for selecting a channel and displaying a text program is executed in the same manner as a general PLL synthesizer type text multiplex broadcast receiver. Then, at that time, in the microcomputer 32, the processing of the routine 100 starts from step 101,
Next, at step 102, it is determined whether or not the mode for receiving teletext broadcasting has been set.

If the mode is set to receive teletext broadcasting, the process proceeds from step 102 to step 103. In this step 103, the output signal of the decoder circuit 31 is checked to check the output of the text program. It is determined whether or not data can be obtained, and if so, the processing proceeds from step 103 to step 104.
In step 104, the output voltage V43 of the detection circuit 43 is compared with the first specified value VA.

When V43 <VA, since the noise component contained in the demodulated signal S17 is sufficiently small,
The process proceeds from step 104 to step 121. In this step 121, the switch circuits 14 and 16 are controlled to enable the filter 15A, and when the filters are switched, the hold circuits 19L and 19R output the audio signals L and R. The level is temporarily held and glitch noise is removed. Then, the routine 100 ends in step 125.

In step 104, V43 ≧ V
In the case of A, the processing is performed from step 104 to step 11
1 and in this step 111, the output voltage V43
Is compared with a second specified value VB (VB> VA).

When V43 <VB, the process proceeds from step 104 to step 122. In this step 122, the switch circuits 14 and 16 are controlled to make the filter 15B effective, and when the filter is switched, the hold is performed. The circuits 19L and 19R temporarily hold the levels of the audio signals L and R to remove glitch noise. And then, step 12
5 ends this routine 100.

In step 111, V43 ≧ V
In the case of B, the processing proceeds from step 111 to step 12
In this step 123, the switch circuits 14 and 16 are controlled to enable the filter 15C, and when the filter is switched, the hold circuit 1
The levels of the audio signals L and R are temporarily held by 9L and 19R to remove glitch noise. Then, at step 125, the routine 100 is executed.
To end.

Further, if it is determined in step 102 that the mode for receiving teletext broadcasting is not set, and if it is not possible to obtain text program data in step 103, the process proceeds from step 102 or 103 to step 112. In step 112, the output voltage V43 is compared with the first specified value VA.

When V43 <VA, the process proceeds from step 112 to step 122. In this step 122, the filter 15B is validated, and thereafter, the routine 100 is terminated in step 125.

In step 112, V43 ≧ V
In the case of A, the processing is performed from step 112 to step 11
3 and in this step 113, the output voltage V43
Is compared with a second specified value VB.

When V43 <VB, the process proceeds from step 104 to step 123. In this step 123, the filter 15C is made effective, and thereafter, the routine 100 is terminated in step 125.

Further, in step 113, V43 ≧
In the case of VB, the processing proceeds from step 113 to step 1
Proceeding to 24, in this step 124, the switch circuits 14 and 16 are controlled to enable the filter 15D, and when the filters are switched, the levels of the audio signals L and R are temporarily held by the hold circuits 19L and 19R. To remove glitch noise. Then, at step 125, the routine 100 is executed.
To end.

As described above, this FM receiver is for the case of receiving a text multiplex broadcast, in which the intermediate frequency signal S12
Is sufficiently small, the pass band width for the intermediate frequency signal S12 is maximized by the filter 15A, so that the LMSK signal SLMSK in the teletext broadcasting can be appropriately obtained. Information can be displayed on the LCD 34.

When the teletext is not received, the filter is switched to the filters 15B to 15D in accordance with the noise level included in the intermediate frequency signal S12, so that the influence of noise and adjacent interference can be reduced.

Further, when performing scanning reception of teletext broadcasting, during the scanning, by selecting a filter having a narrow pass band width from among the filters 15A to 15D,
It is possible to prevent the scanning from being stopped due to noise, adjacent interference, or the like, and it is possible to significantly reduce the search time for the station that implements the teletext broadcasting. Then, when receiving text multiplex broadcasting and displaying text information, by selecting a filter having a wide pass bandwidth, the text information can be reliably displayed.

As described above, the FM receiver shown in FIG. 1 detects noise and adjacent interference, detects the presence or absence of text program data, and, based on the detection results, passes the pass band for the intermediate frequency signal S12. Since the width is changed, audio programs and text programs can be properly received.

In the above description, the pass bandwidth for the intermediate frequency signal S12 is changed depending on the noise level and the presence / absence of text program data. Can also control the pass bandwidth for the intermediate frequency signal S12.

[0036]

According to the present invention, it is possible to optimize the respective reception characteristics when receiving an audio program or teletext broadcasting. In addition, since it is possible to cope with various situations only when receiving an audio program, it is possible to improve the reception performance. Furthermore, when receiving a text multiplex broadcast by scanning a broadcast wave band, it is possible to reduce the time required before the text multiplex broadcast can be actually received.

[Brief description of the drawings]

FIG. 1 is a system diagram illustrating one embodiment of the present invention.

FIG. 2 is a flowchart illustrating one embodiment of the present invention.

FIG. 3 is a frequency spectrum diagram for explaining the present invention.

[Description of Signs] 12: Front-end circuit, 14: Switch circuit, 15
A to 15D: band pass filter, 16: switch circuit, 17: FM demodulation circuit, 18: stereo demodulation circuit, 1
8L and 18R: Hold circuit, 22L and 22R
... Speaker, 31 ... Decoder circuit, 32 ... Microcomputer, 33 ... Operation keys, 34 ... LCD, 40 ... Noise detection circuit, 41 ... Band pass filter, 43 ... Detection circuit

Claims (4)

[Claims] 1. A receiver for multiplexing data of a text program or the like with an audio program signal and receiving a multiplex broadcast in which the multiplex signal is broadcast, the receiver converts a received broadcast wave signal into an intermediate frequency signal. A front-end circuit that outputs the output signal; a demodulation circuit that demodulates the multiplexed signal from the intermediate-frequency signal; an intermediate-frequency filter provided on an intermediate-frequency signal line between the front-end circuit and the demodulation circuit; A decoder circuit for decoding the data of the text program from the multiplexed signal output from the demodulation circuit, a first detection circuit for detecting a signal component included in the intermediate frequency signal due to noise or adjacent interference, A second detection circuit for detecting the presence / absence of data of the text program, wherein the intermediate frequency is determined according to the detection results of the first and second detection circuits. A multiplex broadcasting receiver that changes the pass bandwidth of the filter. 2. The receiver for multiplex broadcasting according to claim 1, wherein said intermediate frequency filter is composed of a plurality of bandpass filters having different passbands from each other. A multiplex broadcast receiver that changes the pass bandwidth of a frequency filter. 3. The receiver for multiplex broadcasting according to claim 2, wherein when the character program is received and displayed, a band-pass filter having a wide pass band is selected from the plurality of band-pass filters. When receiving and reproducing the audio program, a multiplex broadcast receiver that selects a band-pass filter having a narrow pass-band width from among the plurality of band-pass filters. 4. The multiplex broadcast receiver according to claim 2, wherein, when the band-pass filter is switched, a hold circuit that holds a level of an audio signal immediately before the switch is received. Machine.