JP2004064304A - Received signal discrimination apparatus and receiver, and received signal discrimination method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver for receiving broadcast signals adopting different systems that can quickly discriminate the systems of the received signals, e.g., as to whether the signal is a digital broadcast wave signal or an analog broadcast wave signal. <P>SOLUTION: The receiver receiving a signal being either of first and second signals includes: a first filter adapted to the spectrum of the first signal; and a second filter adapted to the spectrum of the second signal to filter the received signal. Since coincidence / dissidence of output levels of the first and second filters depends on whether the received signal is the first signal or the second signal, the receiver can quickly discriminate whether the received signal is the first signal or the second signal by taking notice of the output levels of the first and second filters. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a channel seek technology for broadcast waves.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a receiver for FM broadcasting or analog terrestrial television broadcasting, channel seek is generally performed by detecting a frequency having a high electric field level. The channel seek is a process of searching for a receivable broadcast channel by changing the frequency.
[0003]
However, in the transition period from the current analog terrestrial broadcasting to digital terrestrial broadcasting, a situation occurs in which digital broadcasting waves and analog broadcasting waves are mixed. In order to receive a digital broadcast, first, a frequency having a high electric field level is received. A broadcast wave exists at a frequency with a high electric field level, but whether it is an analog broadcast wave or a digital broadcast wave cannot be determined from the electric field level alone. For example, since a terrestrial digital broadcast wave is an OFDM (Orthogonal Frequency Division Modulation) signal, it is next determined whether or not OFDM correlation can be obtained with the received signal. If the OFDM correlation is not obtained, the received signal is a digital broadcast wave, and if the OFDM correlation is not obtained, the received signal is an analog broadcast wave. Thus, it is determined whether or not the received signal is a digital broadcast.
[0004]
[Problems to be solved by the invention]
However, compared to the process of detecting a frequency having a high electric field level, the process of obtaining the OFDM correlation requires a longer processing time. Therefore, in a situation where analog terrestrial broadcasting and terrestrial digital broadcasting coexist, if it is attempted to selectively receive only terrestrial digital broadcasting, whether or not OFDM correlation can be obtained for all frequencies having high electric field levels It is necessary to perform a determination process as to whether the channel seek time is long. An example of the problem to be solved by the present invention is such a problem.
[0005]
[Means for Solving the Problems]
According to a first aspect of the present invention, in the received signal discriminating apparatus, receiving means for receiving a first signal or a second signal having a different spectrum and outputting a received signal, and filtering the received signal to obtain a first signal. A first filter that generates a filter signal, a second filter that filters the received signal to generate a second filter signal, and sets a level of the first filter signal and a level of the second filter signal. Comparing means for determining whether the received signal is a first signal or a second signal.
[0006]
According to a sixth aspect of the present invention, in the received signal determining method, a receiving step of receiving a digital broadcast wave signal having a band of a predetermined width and an analog broadcast wave signal having a plurality of carrier frequencies and outputting a received signal; A first filtering step of filtering the reception signal by a first filter having a band of the predetermined width as a pass band to generate a first filter signal, and a step of setting the plurality of carrier frequency bands to a pass band. A second filtering step of filtering the reception signal by a second filter to generate a second filter signal, and comparing a level of the first filter signal with a level of the second filter signal to obtain the reception signal. A determining step of determining whether the signal is the digital broadcast wave signal or the analog broadcast wave signal, When the level of the first filter signal is equal to the level of the second filter signal, the received signal is determined to be the analog broadcast wave signal, and the level of the first filter signal and the second filter are determined. When the signal levels are different, the received signal is determined to be the digital broadcast wave signal.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a configuration block diagram of a reception signal discriminating apparatus and a receiver according to an embodiment of the present invention. In FIG. 1, a receiver 10 includes a received signal discriminating device 8 and a demodulating unit 7. The reception signal determination device 8 includes a first filter 1, a second filter 2, and a determination unit 5.
[0008]
The first or second signal input to the receiver 10 via an antenna or the like is supplied to the first filter 1, the second filter 2, and the demodulation unit 7. Here, the first and second signals are signals having different spectra, and preferable examples thereof include a digital broadcast wave signal and an analog broadcast wave signal, but are not limited thereto.
[0009]
The first filter 1 has a characteristic of matching the spectrum of the first signal and extracting the first signal. Further, the second filter 2 has a characteristic of matching the spectrum of the second signal and extracting the second signal. For example, when the first signal is a digital broadcast wave signal having a band of a predetermined width, the first filter 1 has a filter characteristic of making the band of the predetermined width a pass band. Further, when the second signal is an analog broadcast wave signal having a plurality of carrier frequencies, the second filter 2 has a filter characteristic of using the plurality of carrier frequency bands as pass bands.
[0010]
Therefore, when the received signal received by the receiver 10 is the first signal or the second signal, the level of the signal obtained as a result of filtering the received signal by the first filter 1 and the second filter 2 is: It differs depending on whether the received signal is the first signal or the second signal. Therefore, the discriminating means 7 determines whether the receiver 10 has received the signal based on the levels of the first filter signal output from the first filter 1 and the second filter signal output from the second filter 2. It is possible to determine whether the received signal is the first signal or the second signal.
[0011]
Preferably, one of the first filter 1 and the second filter 2 has a level of a first filter signal obtained as a result of filtering the first signal and a level of a second filter obtained as a result of filtering the second signal. It has filter characteristics such that the level of the filter signal becomes the same. On the other hand, the other of the first filter 1 or the second filter 2 has a level of a first filter signal obtained as a result of filtering the first signal and a level of a second filter obtained as a result of filtering the second signal. It has a filter characteristic such that the level of the filter signal is different. Thereby, the determination means 5 can easily determine the received signal according to the levels of the first filter signal and the second filter signal.
[0012]
When the received signal discriminating device 8 discriminates that the received signal is the first signal, the demodulating means 7 demodulates the first signal. For example, when it is determined that the received signal is a digital broadcast wave signal, the demodulation means 7 can demodulate the digital broadcast wave signal to reproduce a digital broadcast.
[0013]
As described above, the determination whether the received signal is the first signal or the second signal is performed by filtering the first signal or the second signal with a predetermined filter without actually demodulating the first signal or the second signal. Since the determination can be made based on the level of the result signal, the received signal can be determined quickly and efficiently as compared with the case where the received signal is determined by demodulating all the received signals.
[0014]
【Example】
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0015]
[Broadcast wave spectrum]
FIG. 2 illustrates the spectrum of a digital broadcast wave and an analog broadcast wave. In FIG. 2, the (A + 1) channel is a digital broadcast wave Wd, and the other channels are analog broadcast waves Wa. As shown, the digital broadcast wave Wd has a spectrum having a substantially constant level over a predetermined bandwidth. On the other hand, the analog broadcast wave Wa has a spectrum showing a high level only at a specific carrier frequency (two carrier frequencies in the example of FIG. 2). That is, the digital broadcast wave Wd and the analog broadcast wave Wa can be distinguished from each other by focusing on the difference between their spectra.
[0016]
Focusing on this point, FIG. 3 shows the principle of a method for distinguishing between digital broadcast waves and analog broadcast waves. FIG. 3 schematically shows a configuration of a discriminating portion between a digital broadcast wave and an analog broadcast wave in the receiver. In FIG. 3, a received signal received by an antenna 21 is converted into a predetermined intermediate frequency (IF) by a mixer 22 and supplied to a digital wave filter 11 and an analog wave filter 12. The digital wave filter 11 has a characteristic having a predetermined pass bandwidth so as to extract the digital broadcast wave Wd according to the spectrum of the digital broadcast wave Wd shown in FIG. On the other hand, the analog wave filter 12 has a characteristic of individually passing signals of two carrier frequencies included in the analog broadcast wave Wa shown in FIG.
[0017]
Now, it is assumed that the signal received by the antenna 21 is an analog broadcast wave. As can be understood from the spectrum of the analog broadcast wave Wa shown in FIG. 2 and the pass characteristics schematically shown in FIG. 3, both the digital wave filter 11 and the analog wave filter 12 pass through two carrier frequencies of the analog broadcast wave. Therefore, the signal level Vd of the analog broadcast wave output from the digital wave filter 11 and the signal level Va of the analog broadcast wave output from the analog wave filter 12 are substantially equal to each other, and the level There is no difference.
[0018]
On the other hand, when the signal received by the antenna 21 is a digital broadcast wave, the digital wave filter 11 allows the digital broadcast wave to pass through its entire band. The level Vd is high. However, since the analog wave filter 12 has a characteristic of passing only a specific carrier frequency portion of the analog broadcast wave, it cannot pass the digital broadcast wave over the entire band. As a result, as shown in FIG. 3, the signal level Va of the digital broadcast wave output from the analog wave filter 12 becomes lower than the signal level Vd of the digital broadcast wave output from the digital wave filter 11. There is a level difference between them.
[0019]
Therefore, by comparing the output signal level of the digital wave filter 11 with the output signal level of the analog wave filter 12, it is possible to determine whether the received signal is a digital broadcast wave or an analog broadcast wave. Can be. Specifically, when there is no level difference between the output level of the digital wave filter 11 and the output level of the analog wave filter 12, the received signal can be determined to be an analog broadcast wave. If the output level of the analog wave filter 12 is smaller than the output level of the digital wave filter 11, it can be determined that the received signal is a digital broadcast wave.
[0020]
[Receiving machine]
Next, a receiver according to an embodiment to which the above-described principle is applied will be described. FIG. 4 is a block diagram showing a schematic configuration of the receiver. As shown in FIG. 4, the receiver 100 includes a mixer 22, a local oscillator 23, a digital wave filter 11, an analog wave filter 12, level detection circuits 13 and 14, a level determination circuit 15, The circuit includes a circuit 16 and a demodulation circuit 17.
[0021]
The signal received by the antenna 21 is supplied to a mixer 22 in the receiver 100. The mixer 22 generates a predetermined intermediate frequency signal (IF signal) based on a signal of a predetermined frequency generated by the local oscillator 23 and a signal received from the antenna 21 and supplies the signal to the digital wave filter 11 and the analog wave filter 12. I do.
[0022]
The digital wave filter 11 filters the intermediate frequency signal IF and supplies the result to the level detection circuit 13 and the demodulation circuit 17. The level detection circuit 13 detects a signal level after filtering by the digital wave filter 11 and supplies the signal level to the level determination circuit 15. The analog wave filter 12 filters the intermediate frequency signal IF and supplies the result to the level detection circuit 14. The level detection circuit 14 detects a signal level after filtering by the analog wave filter 12 and supplies the signal level to the level determination circuit 15.
[0023]
The level determination circuit 15 compares the signal level from the level detection circuit 13 with the signal level from the level detection circuit 14 and supplies the result to the control circuit 16. The output of the level determination circuit 15 is a signal indicating whether the signal received by the antenna 21 is a digital broadcast wave or an analog broadcast wave. The control circuit 16 controls the oscillation frequency of the local oscillator 23 according to whether the signal received by the antenna 21 is a digital broadcast wave or an analog broadcast wave. When the signal received by the antenna 21 is a digital broadcast wave, the control circuit 16 causes the demodulation circuit 17 to execute a demodulation process of the digital broadcast wave. The demodulation circuit 17 outputs a demodulated signal of a digital broadcast wave. For example, when the digital broadcast wave is an OFDM signal, the demodulation circuit 17 performs OFMD correlation on the received signal, performs OFMD demodulation based on the correlation signal, and reproduces digital broadcast.
[0024]
FIG. 5 is a block diagram showing a main part of the receiver shown in FIG. 4. Specifically, the digital wave filter 11, the analog wave filter 12, the level detection circuits 13 and 14, and the level determination circuit 15 The part is shown. The digital wave filter 11 has a pass characteristic 11fc as shown, and the analog wave filter 12 has a mountain-shaped pass characteristic 12fc corresponding to two carrier frequencies as shown.
[0025]
The level detection circuit 13 includes a capacitor 13a and a diode 13b, and outputs the output signal level of the digital wave filter 11 to the level determination circuit 15 as a voltage level Vd. The level detection circuit 14 includes a capacitor 14a and a diode 14b, and outputs the output signal level of the analog wave filter 12 to the level determination circuit 15 as a voltage level Va.
[0026]
The level determination circuit 15 compares the voltage level Vd supplied from the level detection circuit 13 with the voltage level Va supplied from the level detection circuit 14. 6A to 6D show examples of the voltage levels Va and Vd. When the signal received by the antenna 21 is an analog broadcast wave, the voltage level Vd output from the level detection circuit 13 is as shown in FIG. 6A, and the voltage level Va output from the level detection circuit 14 Is as shown in FIG. That is, when the receiver 100 is receiving an analog broadcast wave, the voltage levels Vd and Va output from the level detection circuits 13 and 14 are substantially equal.
[0027]
On the other hand, when the signal received by the antenna 21 is a digital broadcast wave, the voltage level Vd output from the level detection circuit 13 is as shown in FIG. The level Va is as shown in FIG. That is, when the receiver 100 is receiving a digital broadcast wave, the voltage level Va output from the level detection circuit 14 is lower than the voltage level Vd output from the level detection circuit 13. This is because the analog-wave filter 12 cannot pass the digital broadcast wave over the entire band, so that the signal level after filtering is reduced.
[0028]
Therefore, the level determination circuit 15 determines that the analog broadcast wave is being received when the voltage levels Vd and Va are substantially equal, and receives the digital broadcast wave when the voltage level Va is smaller than the voltage level Vd. It is determined that there is. When it is determined that the digital broadcast wave is being received, the control circuit 16 controls the demodulation circuit 17 to demodulate the received digital broadcast wave.
[0029]
[Channel seek processing]
Next, a channel seek process performed by the receiver 100 according to the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart of the channel seek process. In this example, the receiver 100 selects and demodulates only digital broadcast waves in an environment where analog broadcasts and digital broadcasts coexist.
[0030]
In FIG. 7, the receiver 100 changes the frequency and detects the frequency at which the electric field level of the signal received from the antenna is high (step S1). When a frequency having a high electric field level is detected, the received signal is filtered by the digital wave filter 11 (step S2), and the voltage level Vd is detected based on the output signal of the digital wave filter 11 (step S3). Similarly, the received signal is filtered by the analog wave filter 12 (step S4), and the voltage level Va is detected based on the output signal of the analog wave filter 12 (step S5).
[0031]
Next, the level determination circuit 15 compares the voltage levels Vd and Va (Step S6). If the voltage levels Vd and Va are substantially equal and there is no level difference, the broadcast wave being received at that time is an analog broadcast wave, and the process returns to step S1 to search for the next frequency having the higher electric field level. On the other hand, if there is a level difference between the voltage levels Vd and Va, the broadcast wave being received at that time is a digital broadcast wave, so the level determination circuit 15 supplies a signal indicating this to the control circuit 16 and The circuit 16 controls the demodulation circuit 17 to execute the demodulation processing of the digital broadcast wave, and receives the broadcast (step S7).
[0032]
As described above, in the present embodiment, the level of the output signal of the digital wave filter and the level of the output signal of the analog wave filter are compared with each other, so that the digital broadcast wave or the analog broadcast wave is received at that time. Can be determined. Therefore, it is not necessary to determine the presence or absence of the OFDM correlation with the analog broadcast wave to determine whether or not the signal is a digital broadcast wave, so that the time required for the channel seek process can be significantly reduced.
[0033]
[Modification]
In the above embodiment, the analog broadcast wave and the digital broadcast wave are determined based on the difference between their spectra, but the application of the present invention is not limited to this. That is, it is possible to apply the present invention to a broadcast system having a spectrum different from that of an analog broadcast wave or a digital broadcast wave. In that case, two filters are prepared in accordance with the spectrums of the broadcast waves of two different broadcast systems, and one filter outputs the same signal level regardless of which of the broadcast waves of the two broadcast systems is filtered. Both filters may be designed so as to have such pass characteristics, and to have the pass characteristics such that the other filter outputs different signal levels for the broadcast waves of the two broadcast systems.
[0034]
In the example of the receiver illustrated in FIG. 4, the first intermediate frequency signal of the signal received by the antenna 21 is filtered by the digital wave filter 11 and the analog wave filter 12, but is not limited thereto. Instead, the second intermediate frequency signal and the baseband signal may be filtered by both filters to distinguish broadcast waves.
[0035]
In the above embodiment, the filter, the level detection circuit, the level comparison circuit, and the like are configured as analog circuits. However, when the present invention is applied to a system in which demodulation is performed by DSP processing or the like, a predetermined It is also possible to execute filtering, detection, level comparison processing, and the like by software processing by the above program.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a received signal discriminating apparatus according to a preferred embodiment of the present invention.
FIG. 2 is a diagram illustrating a spectrum of a digital broadcast wave and an analog broadcast wave.
FIG. 3 is a diagram illustrating a principle of a received signal determination according to an embodiment of the present invention.
FIG. 4 is a block diagram illustrating a configuration of a receiver according to an embodiment of the present invention.
5 is a block diagram showing a configuration of a main part of the receiver shown in FIG.
FIG. 6 is a diagram illustrating an example of a voltage level output from a level detection circuit.
FIG. 7 is a flowchart showing a channel seek process performed by the receiver.
[Explanation of symbols]
5 Antenna 6 Mixer 7 Local Oscillator 11 Digital Wave Filter 12 Analog Wave Filter 13, 14 Level Detection Circuit 15 Level Judgment Circuit 16 Control Circuit 17 Demodulation Circuit 100 Receiver

Claims (6)

Receiving means for receiving a first signal or a second signal having a different spectrum and outputting a received signal;
A first filter for filtering the received signal to generate a first filter signal;
A second filter for filtering the received signal to generate a second filter signal;
Determining means for comparing the level of the first filter signal and the level of the second filter signal to determine whether the received signal is the first signal or the second signal; A received signal discriminating apparatus characterized by the above-mentioned. One of the first and second filters has a characteristic of filtering so that the first filter signal and the second filter signal have the same level,
The received signal discrimination according to claim 1, wherein the other of the first and second filters has a characteristic of performing filtering such that the first filter signal and the second filter signal have different levels. apparatus. The first signal is a digital broadcast wave signal having a band of a predetermined width,
The second signal is an analog broadcast wave signal having a plurality of carrier frequencies,
The first filter has a characteristic that makes the band of the predetermined width a pass band,
The second filter has a characteristic that makes the plurality of carrier frequency bands a pass band,
The determination unit determines that the received signal is the analog broadcast wave signal when the level of the first filter signal is equal to the level of the second filter signal, and determines the level of the first filter signal and the level of the first filter signal. The received signal discriminating apparatus according to claim 1, wherein when the level of the second filter signal is different, the received signal is determined to be the digital broadcast wave signal. The first filter has a characteristic of passing both the first digital broadcast wave signal and the analog broadcast wave signal without substantially attenuating,
4. The received signal discrimination according to claim 3, wherein the second filter has a characteristic that the digital broadcast wave signal is attenuated and passed, and the analog broadcast wave signal is passed without being substantially attenuated. apparatus. A reception signal discriminating apparatus according to any one of claims 1 to 4,
Demodulating means for demodulating the first signal when the determining means determines that the received signal is a first signal;
A frequency changing unit that, when the determining unit determines that the received signal is the second signal, causes the receiving unit to receive a signal having a different frequency. A digital broadcast wave signal having a band of a predetermined width, and a receiving step of receiving an analog broadcast wave signal having a plurality of carrier frequencies and outputting a received signal,
A first filtering step of filtering the received signal with a first filter having a band of the predetermined width as a pass band to generate a first filtered signal;
A second filtering step of filtering the received signal with a second filter having the plurality of carrier frequency bands as pass bands to generate a second filtered signal;
Comparing the level of the first filter signal and the level of the second filter signal to determine whether the received signal is the digital broadcast wave signal or the analog broadcast wave signal; Have
The determination step determines that the received signal is the analog broadcast wave signal when the level of the first filter signal is equal to the level of the second filter signal, and determines the level of the first filter signal. A received signal discriminating method, wherein the received signal is determined to be the digital broadcast wave signal when the level of the second filter signal is different.

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