JP3207283B2 - Data erroneous recognition prevention circuit for FM multiplex receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for preventing data erroneous recognition of an FM multiplex receiver, and more particularly to a data erroneous recognition of an FM multiplex receiver capable of enhancing the resistance of a data channel to interference signals such as multipath. It relates to a prevention circuit.

[0002]

2. Description of the Related Art Conventionally, a car radio as a mobile receiver has been required to provide other useful data information in addition to easily obtaining data information such as traffic information. At present, in Europe, EBU
(Radio Data System) has been put to practical use by the European Broadcasting Union. On the other hand, in Japan, the Telecommunications Technology Council has proposed FM multiplex broadcasting for effectively utilizing existing FM broadcasting radio waves and facilities and providing additional information as much as possible, and is being put to practical use.

[0003] This FM multiplex broadcasting is a system in which various digital data information is superimposed on an FM broadcasting signal and transmitted.
The transmission contents include (1) characters and graphics and (2) receiver control signals (additional information).

[0004] The encoding system is shared with TV multiplex teletext currently in practical use and is simplified. That is, it is for facilitating the exchange of programs in the production of TV multiplex text broadcasting and FM multiplex text / graphic broadcasting. The outline of the encoded and transmitted character and graphic sets and their control are shown below. The contents of additional information that are currently considered are shown below. (1) Character set Kanji, hiragana, katakana, alphanumeric characters, dynamically redefined character set, mosaic, geometric, etc. (2) Graphic A photographic graphic transmitted by a pixel, a mosaic graphic / dynamically redefined character set graphic transmitted by a character code, and a geometric graphic transmitted by a graphic description instruction code. (3) Character control Character size control, color control, flushing, concealment, etc. (4) Additional information Broadcast station name, program category, time, program identification, traffic information flag, broadcast station identification, alternative frequency list, etc.

[0005] As described above, in the FM multiplex broadcasting, various messages are multiplexed and transmitted to the FM broadcasting being received, so that it is possible to obtain new information. In addition, FM multiplex broadcasting for mobile reception multiplexes a digital data signal (multiplexed data signal) on a subcarrier of 76 kHz on the base band of the FM broadcast signal, and is an L-MSK that varies the multiplex level according to the stereo sub signal level. (Level controlled modulation shift keying)
A modulation method is used. The bit rate of the multiplexed data signal is 16 kbps, and the modulation degree is 4 kbps.
-10%.

FIG. 4 is an explanatory diagram showing an example of a multiplex data signal modulation degree control curve for the L-MSK modulation method. Referring to FIG. 4, the vertical axis indicates the multiplexed data signal modulation degree, and the horizontal axis indicates the stereo sub-signal modulation degree. That is, in this figure, the multiplexed data signal modulation degree is constant at 4% when the stereo sub-signal modulation degree is up to 2.5%, and the multiplexed data signal modulation degree is up to 2.5% to 5%. Varies from 4% up to 10%. When the degree of modulation exceeds 5%, the multiplex data modulation degree is up to 10%.
It shows that it is constant. Thus, the modulation scheme is such that the modulation degree of the multiplexed data signal changes according to the modulation degree of the stereo sub-signal.

[0007]

However, LM
A conventional F that superimposes a multiplexed data signal by the SK modulation method
In the M multiplex receiver, the purpose of changing the modulation degree of the multiplexed data signal in this way is to eliminate the interference of the stereo sub-signal to the data channel. Since there is no effect, there is a problem that multiplexed data is erroneously recognized when affected by a multipath interference signal. In view of the above, an object of the present invention is to provide an FM multiplex receiver capable of preventing erroneous recognition and erroneous display of multiplexed data when receiving an influence of an interference signal such as a multipath interference signal during reception. An object of the present invention is to provide a data erroneous recognition prevention circuit.

[0008]

SUMMARY OF THE INVENTION According to the present invention, there is provided an FM multiplex receiver for demodulating and utilizing a multiplex data signal superimposed on a subcarrier in an FM multiplex broadcast signal. Noise detecting means for detecting noise generated by the interference signal, etc .; reference level setting means for setting a predetermined reference level based on the noise level detected by the noise detecting means; and setting by the reference level setting means. A comparator for comparing the reference level with the level of the multiplexed data signal superimposed on the subcarrier and outputting a result, and removing noise included in the multiplexed data signal when noise is detected by the noise detection means. It is achieved by doing so.

[0009]

In the FM multiplex receiver having the above configuration, the noise detecting means detects noise generated by an interference signal such as a multipath interference signal. Then, the reference level setting means sets a predetermined reference level based on the noise level detected by the noise detection means. Therefore, the comparator compares the reference level with the level of the multiplexed data signal superimposed on the subcarrier, and removes noise included in the multiplexed data signal.

[0010]

FIG. 1 is a block diagram showing a main part of an FM multiplex receiver having a data erroneous recognition circuit according to the present invention. First, the configuration will be described. Reference numeral 1 denotes a PLL circuit which outputs a predetermined voltage signal corresponding to a station to be received to the FM front end 2. The FM front end 2 receives a broadcast station input from the antenna ANT based on the voltage signal, and generates a predetermined intermediate frequency signal (IF). Reference numeral 3 denotes an intermediate frequency detection amplifier that amplifies the intermediate frequency signal converted by the FM front end 2 to a predetermined level and detects the signal.

Reference numeral 4 denotes an NC + MPX (noise killer control circuit + multiplex circuit), which receives a detection signal from the intermediate frequency detection amplifier 3 and removes pulse-like vehicle noise such as ignition noise included in the detection signal. At the same time, the detected signal is demodulated into a stereo signal. 5
Is an AMP (amplifier), which amplifies a stereo signal according to a volume setting value (not shown). Reference numeral 6 denotes a speaker which is driven by the AMP 5 and outputs an audio signal.
7 is a 76 kHz sub-carrier containing a multiplexed data signal
(BPF) for taking out the light.

Reference numeral 8 denotes a disturbance signal such as a multipath disturbance signal.
A noise generated when the detection signal is subjected to phase modulation is detected from the NC + MPX4, and a reference level of a comparator described later is set based on the noise level.
This is a reference level setting section. Reference numeral 9 denotes a comparator, which compares the reference level set by the noise detection / reference level setting unit 8 with the level of the multiplexed data signal superimposed on the subcarrier, and outputs the result. That is, when the noise level detected by the noise detection / reference level setting unit 8 is high, the reference level of the comparator 8 is lowered to relatively increase the multiplexed signal level so as to eliminate the interference to the data channel due to the interference signal. I have to.

Here, the operation of the comparator 9 will be described in detail. FIG. 2 is a first explanatory diagram showing the operation of the comparator 9 according to the present invention. Referring to FIG. 2, the comparator input (+ input of the comparator) shows a state where the level of the multiplexed data signal changes according to the level of the stereo sub-signal. The reference level Vref. A is set to a voltage level corresponding to the minimum of 4% of the multiplex level, and a comparator output as shown in FIG.
This is the basic form of the operation of the comparator 9.

FIG. 3 is a second explanatory diagram showing the operation of the comparator 9 according to the present invention. Referring to FIG. 3, the comparator input shows a state in which noise is superimposed on a multiplexed data signal whose level is changed according to the stereo sub-signal,
The conventional reference voltage is Vref. Since the signal is fixed at A, the signal becomes an intermittent signal as shown in FIG. In the present invention, since the reference level is set based on the noise level from the noise detection / reference level setting unit 8, when the noise level is large, the reference level is Vref. Vre lower than A
f. B. Therefore, a constant comparator output without data loss as shown in FIG.

Reference numeral 10 denotes an FM multiplex decoder circuit for demodulating a multiplexed data signal transmitted at a predetermined transmission timing and modulated by the L-MSK method. An error correction circuit 11 detects an error of the FM multiplexed data demodulated by the FM multiplexing decoder circuit 10 while synchronizing each group, and corrects the error.

Reference numeral 12 denotes a signal meter circuit, which detects the level of the reception state of the receiving station by monitoring the signal strength (eg, electric field strength) of the intermediate frequency signal output from the intermediate frequency detection amplifier 3.

Reference numeral 13 denotes a display unit for displaying characters, figures, and the like from the FM multiplex data. A control unit 14 controls the overall operation of the FM multiplex receiver, and causes the display unit 13 to display characters, graphics, and the like based on the multiplexed data.

Hereinafter, the operation of the FM multiplex receiver having the data erroneous recognition circuit of FIG. 1 will be described in detail. By operating an operation unit (not shown) of the FM multiplex receiver, a broadcast wave on which a multiplex data signal is superimposed based on a voltage signal output from the PLL circuit 1 and corresponding to a frequency of a predetermined broadcast station is transmitted to the antenna ANT. The FM front end 2 receives the signal, converts it to an intermediate frequency, and outputs the intermediate frequency.

The intermediate frequency detection circuit 3 receives the intermediate frequency, detects it, and outputs it as a detection signal. The detection signal is input to NC + MPX 4, while a 76 kHz subcarrier on which the multiplexed data signal is superimposed is extracted by the BPF 7 and input to the comparator 9. At the same time, the noise detection / reference level setting unit 8 detects noise caused by an interference signal such as a multipath interference signal from the NC + MPX 4 and sets a reference level corresponding to the noise level in the comparator 9. The comparator 9 compares the reference level with the level of the multiplexed signal superimposed on the subcarrier, removes the noise, and outputs a comparator output having a constant amplitude without data loss.

The output of the comparator is input to the FM multiplex decoder circuit 10, demodulated into a multiplexed data signal, and the error correction circuit 11 corrects the data error.
4 is input. The control unit 1 to which the multiplex data signal has been input
Reference numeral 4 causes the display unit 13 to display characters, graphics, and the like based on the multiplexed data signal.

[0021]

As described above, according to the present invention, an FM multiplex receiver for demodulating and utilizing a multiplex data signal superimposed on a subcarrier in an FM multiplex broadcast signal has a multipath interference. A noise detection unit that detects noise generated by a disturbing signal such as a signal; a reference level setting unit that sets a predetermined reference level based on the noise level detected by the noise detection unit; A comparator that compares the reference level and a multiplexed data signal level superimposed on a subcarrier and outputs a result.When noise is detected by the noise detection unit, noise included in the multiplexed data signal is detected. Since it is removed, erroneous recognition of multiplexed data due to interfering signals such as multipath interfering signals does not occur,
This has the effect of providing accurate display.

[Brief description of the drawings]

FIG. 1 is an FM including a data erroneous recognition circuit according to the present invention.
It is a principal part block diagram of a multiplex receiver.

FIG. 2 is a first explanatory diagram showing an operation of a comparator 9 according to the present invention.

FIG. 3 is a second explanatory diagram showing the operation of the comparator 9 according to the present invention.

FIG. 4 is an explanatory diagram showing an example of a multiplexed data signal modulation factor control curve for an L-MSK modulation scheme.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 PLL circuit 2 FM front end 3 Intermediate frequency detection amplifier 4 NC + MPX (noise killer control circuit + multiplex circuit) 7 BPF (bandpass filter) 8 noise detection / reference level setting section 9 comparator 10 FM multiplex decoder circuit 11 error correction Circuit 13 Display unit 14 Control unit

Claims (1)

(57) [Claims] 1. A noise detecting means for demodulating a multiplex data signal superimposed on a subcarrier in an FM multiplex broadcast signal and detecting noise generated by an interference signal such as a multipath interference signal in an FM multiplex receiver to be used. Detecting means; reference level setting means for setting a predetermined reference level based on the noise level detected by the noise detecting means; multiplexed data superimposed on the sub-carrier and the reference level set by the reference level setting means A comparator for comparing the signal level with a signal level and outputting a result, wherein when noise is detected by the noise detecting means, noise included in the multiplexed data signal is removed. Circuit for preventing incorrect recognition of data by the receiver.