JPH10112826A - Channel selecting system of television receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a channel selecting system of a television receiver which can detect broadcast waves that are practically receivable regardless of electric field intensity of each area. SOLUTION: A television receiver 100 comprises a channel select controlling part 4 comprising a search controlling part 40, a frequency sweeping part 42 and a broadcast wave deciding part 44, a broadcast wave detecting circuit 66 which outputs a broadcast wave detection signal based on a noise level that is included in sound after demodulation, an AGC(automatic gain control) detecting circuit 70, an AGC amplifier circuit 72 and an RF-AGC circuit 18 which perform automatic gain control, based on a video output. After the part 42 starts frequency sweep, the part 44 decides that broadcast waves exist when it detects that a noise level which is included in a sound signal becomes low based on a broadcast wave detection signal that is outputted from the circuit 66 or when it detects that AGC voltage which is applied on the circuit 18 by the circuit 72 becomes low.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel selection system for a television receiver which automatically detects a receivable broadcast wave by sweeping a frequency.

[0002]

2. Description of the Related Art Some in-vehicle or portable television receivers have a so-called search function of automatically detecting a receivable broadcast wave by sweeping the frequency in one direction. As a broadcast wave detection method, for example, a method is known in which a noise component included in an audio signal transmitted together with a video signal is extracted, and when this noise level is reduced, it is determined that a broadcast wave exists. I have.

[0003]

By the way, in the conventional broadcast wave detection system in which it is determined that a broadcast wave is present when the noise level becomes low, the television is located in an extremely strong electric field region where the intensity of the received radio wave is extremely large. When the receiver is placed, inconvenience may occur. For example, when receiving a broadcast wave by placing a television receiver directly below an antenna of a broadcast station, the received radio wave may be too strong and the audio signal may be saturated to cause distortion. Therefore, the search function may not operate effectively because the originally existing broadcast wave cannot be detected.

[0004] Such a phenomenon also occurs when a booster is provided not only for an extremely strong electric field region but also for a weak electric field region. Generally, a booster connected to a television receiver amplifies a radio wave received by an antenna in a weak electric field area by about 10 to 20 dB over the entire band. Since a broadcast wave from which a good image can be obtained when amplified by the booster needs to be searched, the search operation is usually performed with the booster operated.
For this reason, in the case of performing a search operation in a strong electric field region, etc., amplification is further performed by a booster even though a sufficient received radio wave intensity is obtained. In some cases, the amplified radio waves are too strong, so that the audio signal is saturated and distortion occurs, and the distortion becomes noise and the search function may not operate effectively.

[0005] The present invention has been made in view of the above points, and a purpose thereof is to provide a television receiver capable of detecting a broadcast wave which can be actually received irrespective of the electric field strength for each area. In providing a channel selection method.

[0006]

In order to solve the above-mentioned problems, a tuning method for a television receiver according to the present invention comprises a tuner section for selecting a component having a predetermined tuning frequency from a received signal, A frequency sweep unit that sweeps a tuning frequency of a tuner unit in a predetermined direction, a broadcast wave determination unit that determines the presence or absence of a broadcast wave by monitoring a noise level and received radio wave intensity included in the demodulated audio signal, A search control unit that starts frequency sweeping by the frequency sweeping unit when a sweep start instruction is issued, and stops frequency sweeping by the frequency sweeping unit when a broadcast wave is detected by the broadcast wave determination unit. Further, the above-described broadcast wave determination unit determines that a broadcast wave is present when at least one of the following conditions is satisfied: when the noise level included in the demodulated audio is low, and when the received radio wave intensity is high. judge.
According to the present invention, the presence / absence of a broadcast wave is determined in accordance with the noise level included in the audio signal, and the presence / absence of the broadcast wave is determined by monitoring the received radio wave intensity. Therefore, even if the broadcast wave cannot be detected based on the noise level included in the audio signal, the broadcast wave can be reliably detected.

[0007] More specifically, the tuning method of the television receiver according to the present invention provides a broadcast wave that outputs a broadcast wave detection signal indicating the presence of a broadcast wave when the noise level contained in the demodulated audio signal is low. The broadcast wave determination unit further includes a detection circuit, and the broadcast wave determination unit can easily determine the presence or absence of a broadcast wave according to a noise level included in audio based on the broadcast wave detection signal.

[0008] Further, the channel selection system for a television receiver according to the present invention further comprises a gain control section for generating a gain control voltage for controlling the degree of amplification of the tuner section based on the demodulated video signal. The wave determination unit can easily determine the presence or absence of a broadcast wave according to the received radio wave intensity based on the gain control voltage.

Further, a search operation may be performed by operating a booster provided in a preceding stage of the tuner section. In a weak electric field area, by amplifying the broadcast wave received by the booster, the broadcast wave can be detected with a weak broadcast wave as a search target. Conversely, in a strong electric field area, a broadcast wave having a good reception strength may be amplified and a sound signal may be distorted.However, even in such a case, according to the received radio wave strength amplified by the booster. Thus, broadcast wave detection can be performed reliably.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The channel selection method of a television receiver according to the present invention is based on detection of a broadcast wave according to the level of noise included in an audio signal, and AGC (automatic control) which changes in accordance with the intensity of a received radio wave. It is characterized in that the broadcast wave detection according to the voltage is also used in conjunction with the detection of the broadcast wave without fail during the search operation. Hereinafter, a television receiver according to an embodiment of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a television receiver according to one embodiment to which the present invention is applied. The television receiver 100 of the present embodiment shown in FIG.
0, a tuner unit 1 for extracting a desired tuning frequency component from the signal received through the frequency converter 0 and performing frequency conversion on the extracted signal, and a PLL control for performing PLL control on the tuning frequency of the tuner unit 1. The tuning control section 4 is configured to sweep the tuning frequency of the tuner section 1 in one direction and stop the frequency sweep when a broadcast wave is detected.

The above-described tuner 1 includes an input circuit 10,
High frequency amplifier circuit 12, mixing circuit 14, local oscillation circuit 16
And an RF-AGC circuit 18. Input circuit 1
0 is for matching the impedance of the connection line for drawing the received signal from the antenna 20 with the input impedance of the high-frequency amplifier circuit 12. High frequency amplifier circuit 12
Performs a tuning operation of selecting and outputting a predetermined frequency component from a received signal input via the input circuit 10 while securing a predetermined bandwidth (6 MHz), and performs a tuning operation on the tuned output. Perform high frequency amplification. Mixing circuit 14
Mixes the signal output from the high-frequency amplifier circuit 12 with the signal output from the local oscillation circuit 16 and outputs an intermediate frequency signal having a frequency equal to the difference between these two signals. The frequency of this intermediate frequency signal is 5 for the video carrier.
8.75MHz, 54.25M for voice carrier
Hz. The local oscillation circuit 16
This is a voltage-controlled oscillation circuit whose oscillation frequency can be set according to the applied control voltage. The control voltage is applied from the PLL control unit 3. The RF-AGC circuit 18 changes the amplification degree of the high-frequency amplifier circuit 12 according to the strength of the received radio wave. When the electric field strength of the received radio wave is small, the amplification degree is increased, and conversely, the electric field strength of the received radio wave is increased. Is large, the amplification degree is set small.

The above-described tuner 1 and antenna 2
Between 0 and 0, a booster 22 that amplifies radio waves received by the antenna 20 by about 10 to 20 dB over the entire band is connected. On / off control of the amplification operation by the booster 22 is performed by the booster switching control unit 24. .

The above-described PLL control unit 3 includes a frequency divider 30,
34, a phase comparator 32 and a reference frequency oscillator (reference O
SC) 36, and each of these components forms a phase-locked loop together with the local oscillation circuit 16 in the tuner unit 1 described above, and sets the frequency of the local oscillation circuit 16. The reference frequency oscillator 36 is a fixed frequency oscillator having a high frequency stability using a crystal oscillator or the like, and its oscillation output is frequency-divided by one frequency divider 34 having a fixed frequency division ratio. It is input to one input terminal. The other frequency divider 30 is a variable frequency divider whose frequency division ratio N can be set arbitrarily. A signal obtained by dividing the output of the local oscillation circuit 16 by the frequency division ratio N is output from the phase comparator 32. It is input to the other input terminal. The phase comparator 32 includes two frequency dividers 30 and 34
And a control voltage for reducing the phase difference is applied to the local oscillation circuit 16, and the oscillation frequency of the local oscillation circuit 16 is set at the above-mentioned variable frequency division ratio N. It is controlled to a predetermined value determined.

The above-mentioned tuning control unit 4 includes a search control unit 4
0, a frequency sweep unit 42 and a broadcast wave determination unit 44. The broadcast wave determination unit 44 includes a broadcast wave detection circuit 6 described later.
6 and each output of the AGC amplifier circuit 72, it is determined whether or not a signal of the current reception frequency includes a broadcast wave. The search control unit 40 instructs the frequency sweeping unit 42 to start a sweep operation in response to an instruction from the key input unit 50. The key input unit 50 is used by the user to perform various operation instructions. Various operation keys such as a “search” key for instructing a search operation for searching for receivable broadcast waves by performing frequency sweep in one direction are provided. Have. The frequency sweep unit 42 sweeps the tuning frequency of the tuner unit 1 in one direction by sequentially increasing or decreasing the variable frequency division ratio N of the frequency divider 30 in the PLL control unit 3.

Also, the television receiver 1 of the present embodiment
Reference numeral 00 denotes a video intermediate frequency amplification circuit 52, a video detection circuit 54, a video amplification circuit 56, an AGC detection circuit 70, and A
The GC amplification circuit 72 includes an audio intermediate frequency detection circuit 58, an FM detection circuit 60, and a low frequency amplification circuit 62 for extracting and reproducing an audio signal from a received signal.

The video intermediate frequency amplifying circuit 52 amplifies an intermediate frequency signal including a video signal and an audio signal output from the mixing circuit 14 of the tuner unit 1, and passes only components in a necessary frequency band. Have a predetermined selectivity characteristic. The amplified intermediate frequency signal is supplied to a video detection circuit 5.
4 and the audio intermediate frequency detection circuit 58. The video detection circuit 54 detects the video intermediate frequency signal amplified by the video intermediate frequency amplification circuit 52 and extracts a composite video signal. In general, in order to faithfully reproduce the video signal, a diode detection circuit having a small distortion is used. And low-level video detection (LLD). The video signal detected in this way further passes through a video amplification circuit 56,
After being separated into a luminance signal and a carrier chrominance signal, the carrier chrominance signal is color-demodulated and combined again with the luminance signal, and then a video display from a liquid crystal display device or the like (not shown) is performed.

The audio intermediate frequency detection circuit 58 extracts a 4.5 MHz SIF signal (beat signal) from the 54.25 MHz audio intermediate frequency signal included in the output of the video intermediate frequency amplification circuit 52. Representative methods for extracting the SIF signal include an intercarrier method and a separate carrier method. The FM detection circuit 60 is connected to the 4.5 MHz SIF output from the audio intermediate frequency detection circuit 58.
The signal is subjected to FM detection, and the detected audio signal is amplified by the low-frequency amplifier 62 and then output from the speaker 64. The signal output from the FM detection circuit 60 is also input to the broadcast wave detection circuit 66.

The AGC detection circuit 70 includes a video amplification circuit 56
Generates a voltage waveform corresponding to the strength of the received radio wave based on the detected video signal output from the
Automatic gain control for the video intermediate frequency amplification circuit 52 is performed by the AGC voltage amplified by the C amplification circuit 72. The AGC voltage output from the AGC amplifier circuit 72 is output to the RF-AGC circuit 18 in the tuner 1.
The automatic gain control for the high-frequency amplifier circuit 12 is performed by the RF-AGC circuit 18. As described above, the gain of the video intermediate frequency amplification circuit 52 and the gain of the high frequency amplification circuit 12 in the tuner unit 1 are controlled by the AGC detection circuit 70, the AGC amplification circuit 72, and the RF-AGC circuit 18 according to the strength of the received radio wave. You. For example, when the received radio wave intensity is weak, the high frequency amplifier circuit 12 in the tuner unit 1 is operated at the maximum gain so that the SN ratio does not decrease, and only the gain of the video intermediate frequency amplifier circuit 52 is controlled. When the received radio wave intensity is strong, the gain of the video intermediate frequency amplification circuit 52 is set to a small value to some extent, and the gain of the high frequency amplification circuit 12 is controlled to suppress the occurrence of cross-modulation interference and the like.

In the above-described configuration of the television receiver 100 of the present embodiment, the RF-AGC circuit 18
The AGC detection circuit 70 and the AGC amplification circuit 72 correspond to a gain control unit.

FIG. 2 is a diagram showing a detailed configuration of the broadcast wave detection circuit 66. The broadcast wave detection circuit 66 shown in FIG.
A noise detection circuit 80 for extracting a noise component from the audio signal output from the M detection circuit 60;
D that converts the noise component extracted by
It is configured to include a C conversion circuit 82 and a switching transistor 84 having a collector connected to a resistor. The noise detection circuit 80 is constituted by, for example, a high-pass filter whose cutoff frequency is set to a frequency higher than the audio band, and allows only a noise component higher than the audio signal to pass. The DC conversion circuit 82 includes, for example, an amplifier, a rectifier circuit, and a smoothing circuit. The DC converter 82 amplifies a noise component, rectifies the noise component, and removes an AC component to thereby reduce the DC component proportional to the noise level included in the audio signal. A voltage is applied to the base of the switching transistor 84.

In a frequency region where no broadcast wave exists, noise components included in the audio output of the FM detection circuit 60 increase, so that the output voltage of the DC conversion circuit 82 increases, the switching transistor 84 is turned on, and the output from the collector is output. The detected broadcast wave detection signal becomes low level. Conversely, in the frequency domain where the broadcast wave exists, the FM detection circuit 60
Noise component contained in the audio output of
The output voltage of the C conversion circuit 82 decreases, the switching transistor 84 turns off, and the broadcast wave detection signal output from the collector goes high.

The television receiver 100 of the present embodiment has such a configuration, and its operation will be described next. FIG. 3 shows the AG applied from the AGC amplifier circuit 72 to the video intermediate frequency amplifier circuit 52 and the RF-AGC circuit 18.
It is a figure which shows the relationship between C voltage and received radio wave intensity (electric field intensity of received radio wave). As shown in the figure, the AGC voltage increases as the intensity of the received radio wave decreases, and conversely, the AGC voltage decreases as the intensity of the received radio wave increases. in this way,
Since the AGC voltage changes according to the received radio wave intensity, it can be determined by monitoring the AGC voltage whether the electric field intensity is strong enough to cause distortion in the sound signal of the existing broadcast wave.

FIG. 4 is a flowchart showing an operation procedure of the television receiver of the present embodiment, and mainly shows an operation procedure focusing on a search operation of a broadcast wave under the control of the tuning control unit 4. For example, it is assumed that a predetermined search operation is started when any broadcast wave is currently received and the “search” key of the key input unit 50 is pressed thereafter.

The search control unit 40 constantly monitors whether the "search" key of the key input unit 50 has been pressed (step 400). When the "Search" key is pressed,
Next, the search control unit 40 sends a frequency sweeping instruction to the frequency sweeping unit 42, and upon receiving the instruction, the frequency sweeping unit 42 sets the frequency of the currently received broadcast wave as the search start frequency and sets the frequency in the frequency increasing direction. Alternatively, the frequency sweep is started in the frequency decreasing direction (step 401). Specifically, the oscillation frequency of the local oscillation circuit 16 is changed to a higher value by gradually changing the variable frequency dividing ratio N of the frequency divider 30 in the PLL control unit 3 by the frequency sweeping unit 42, or By gradually changing the variable frequency dividing ratio N of the frequency divider 30 to a smaller value, the oscillation frequency of the local oscillation circuit 16 is changed to a lower value.

In parallel with the above-described frequency sweeping operation, the broadcast wave determination section 44 checks whether or not the broadcast wave detection signal output from the broadcast wave detection circuit 66 is at a high level (step 402). As described above, the broadcast wave detection signal output from the broadcast wave detection circuit 66 is at a high level when there is a broadcast wave of the frequency being swept, and at a low level when there is no broadcast wave. Becomes Therefore, when the frequency is swept and reaches one of the broadcast wave frequencies, the broadcast wave detection signal changes from a low level to a high level. The broadcast wave determination unit 44 monitors the state of the broadcast wave detection signal, and determines that there is a broadcast wave by detecting a change to a high level. When the broadcast wave detection signal changes to the high level and it is determined that the broadcast wave exists, the search control unit 40 stops the frequency sweeping operation by the frequency sweeping unit 42 (Step 403), and thereafter, the search operation is performed by the search operation. Video and audio reproduction of the broadcast wave is performed.

The broadcast wave determination unit 44 includes a broadcast wave detection circuit 66
If the broadcast wave detection signal output from is not high level (low level state is maintained), RF
Check whether the AGC voltage applied to the AGC circuit 18 is equal to or lower than a predetermined value (step 404). As described above, when the received radio wave intensity is so strong that the audio signal is distorted, noise due to the distortion is generated, so that the broadcast wave that should originally exist may not be detected in some cases.
Therefore, the broadcast wave determination unit 44 determines whether or not the intensity of the received radio wave is higher than a certain level by determining whether the AGC voltage is higher than the VGC shown in FIG.
a by checking whether it is less than or equal to
If the received radio wave intensity has increased to a certain degree or more, it is determined that there is a broadcast wave. When it is determined that there is a broadcast wave, the search control unit 40 stops the frequency sweeping operation by the frequency sweeping unit 42 (Step 403), and the video and audio of the broadcast wave are reproduced.

The broadcast wave detection signal output from the broadcast wave detection circuit 66 is at a low level and the RF-AGC circuit 1
8 is higher than a predetermined value,
The search control unit 40 monitors whether the frequency sweep has completed one cycle (step 405). If not,
Returning to step 401, the frequency sweep operation is continued.
If no broadcast wave other than the currently received broadcast wave can be detected even after one round of frequency sweeping, in order to notify the person who pressed the "search" key that there is no other receivable broadcast wave, For example, a predetermined alarm sound is output from the speaker 64 (step 406).

As described above, in the television receiver 100 of the present embodiment, after the frequency sweeping unit 42 starts the frequency sweeping, the broadcast wave determining unit 44 determines whether or not there is a broadcast wave of the frequency being swept. If a broadcast wave exists, the search control unit 40 is notified of the fact and the search operation is stopped, and the video and audio of the searched broadcast wave are reproduced. The determination of the presence / absence of a broadcast wave by the broadcast wave determination unit 44 uses both the determination based on the magnitude of the noise level included in the audio signal and the determination based on the magnitude of the received radio wave intensity. In such a case, the search operation is stopped.

Therefore, when used in a normal environment, when the noise level included in the audio signal decreases, the broadcast wave determination unit 44 determines that a broadcast wave is present, and the frequency is swept under the control of the search control unit 40. The frequency sweeping operation by the unit 42 can be stopped. In addition, for example, in a case where an audio signal tends to be saturated and causes distortion as in an extremely strong electric field area near a broadcast antenna, the AGC is used.
A applied from the amplification circuit 72 to the RF-AGC circuit 18
When the GC voltage becomes low, the broadcast wave determining unit 44 determines that there is a broadcast wave, and the frequency sweeping unit 42 can stop the frequency sweeping operation under the control of the search control unit 40.

As described above, it is possible to determine the presence of a broadcast wave even in an ultra-high electric field area where the audio signal may be distorted. Therefore, regardless of the electric field strength for each area, that is, the electric field strength for each area Thus, the search accuracy can be improved by reliably detecting the broadcast waves that can be actually received without taking into account the above.

Since the above-mentioned broadcast wave determination section 44 determines the presence or absence of a broadcast wave according to the AGC voltage applied to the tuner section 1, it is possible to use the existing tuner section 1 without changing hardware. There is also an advantage that the design change for the current product can be minimized.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, in the television receiver 100 of the above-described embodiment, in consideration of a case where a broadcast wave is received in a weak electric field area, the television receiver 100 is connected between the antenna 20 and the input circuit 10 in the tuner 1 during a search operation. Booster 2
2 may always be operated.

FIG. 5 is a flowchart showing an operation procedure of the television receiver in which the booster 22 is always operated during the search operation. The operation procedure shown in the figure is almost the same as the operation procedure shown in FIG.
00 (determination of whether or not the search key is pressed) and step 401
During the (frequency sweeping operation), the process of step 400a for starting the booster 22 is inserted. When the "search" key of the key input unit 50 is pressed, the search control unit 40 sends an instruction to the booster switching control unit 24 to activate the booster 22 (step 400a). Therefore, since the search operation after step 401 is performed while the booster 22 is always operated, if the received radio wave intensity of the broadcast wave is strong, for example, when the television receiver 100 is placed in a strong electric field area, the sound is not transmitted. Although the signal may be distorted, the broadcast wave determination unit 44
Since the determination of the presence or absence of the broadcast wave based on the GC voltage is also used, the broadcast wave can be reliably detected.

[0035]

As described above, according to the present invention, the presence / absence of a broadcast wave is determined according to the noise level included in the audio signal, and the presence / absence of the broadcast wave is determined by monitoring the received radio wave intensity. Therefore, even when the received radio wave intensity is very strong and the broadcast wave cannot be detected based on the noise level included in the audio signal, the broadcast wave can be reliably detected.

Further, by performing a search operation by operating a booster provided in a preceding stage of the tuner section, it is possible to detect broadcast waves in a weak electric field area, and an audio signal is generated when a broadcast wave is detected in a strong electric field area. Even if the noise level rises due to saturation, the broadcast wave can be reliably detected.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a television receiver according to an embodiment to which the present invention has been applied.

FIG. 2 is a diagram illustrating a detailed configuration of a broadcast wave detection circuit.

FIG. 3 is a diagram illustrating a relationship between a received radio wave intensity and an AGC voltage.

FIG. 4 is a flowchart showing an operation procedure of the television receiver of the embodiment.

FIG. 5 is a flowchart showing a modification of the operation procedure of the television receiver of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tuner part 3 PLL control part 4 Tuning control part 18 RF-AGC circuit 22 Booster 24 Booster switching control part 40 Search control part 42 Frequency sweep part 44 Broadcast wave judgment part 50 Key input part 52 Video intermediate frequency amplification circuit 54 Video detection Circuit 56 Video amplification circuit 58 Audio intermediate frequency detection circuit 60 FM detection circuit 66 Broadcast wave detection circuit 70 AGC detection circuit 72 AGC amplification circuit

Claims (5)

[Claims] 1. A tuner section for selecting a component having a predetermined tuning frequency from a received signal, a frequency sweeping section for sweeping a tuning frequency of the tuner section in a predetermined direction, and a noise included in a demodulated audio signal. A broadcast wave determination unit that determines the presence or absence of a broadcast wave by monitoring a level and a received radio wave intensity, and when a predetermined sweep start instruction is issued, starts a frequency sweep by the frequency sweep unit, and the broadcast wave determination unit A search control unit that stops frequency sweeping by the frequency sweeping unit when a broadcast wave is detected, and a tuning method for a television receiver. 2. The broadcast wave determination unit according to claim 1, wherein the broadcast wave determination unit is configured to satisfy at least one of a case where a noise level included in demodulated audio is low and a case where received radio wave intensity is high. A method for selecting a television receiver, which determines that a broadcast wave exists. 3. The broadcast wave detection circuit according to claim 1, further comprising a broadcast wave detection circuit that outputs a broadcast wave detection signal indicating the presence of a broadcast wave when a noise level included in the demodulated audio signal is low. A method of selecting a television receiver, wherein the broadcast wave determination unit determines the presence or absence of a broadcast wave based on a noise level based on a broadcast wave detection signal. 4. The gain control unit according to claim 1, further comprising: a gain control unit that generates a gain control voltage for controlling an amplification degree of the tuner unit based on the demodulated video signal. A method of selecting a television receiver, wherein the presence / absence of a broadcast wave is determined by the broadcast wave determination unit based on a voltage based on a received radio wave intensity. 5. The booster according to claim 1, further comprising a booster for amplifying a radio wave received from an antenna at a stage preceding the tuner unit, wherein the booster is operated at the time of frequency sweeping by the frequency sweeping unit. A method for selecting a television receiver, characterized in that: