JP2012205230A - Television receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a noise failure on a screen in a television receiver.SOLUTION: An AGC circuit is switchable between a scan mode with a faster operation to cope with the change of a radio wave level when a channel is switched and a tracking mode with a slower operation to cope with the change of the radio wave level when the channel is fixed. A micro-computer monitors an AGC voltage, reads an average value Va of the AGC voltage in a channel from a table (S2) when the channel is switched (YES in S1), compares the present AGC voltage with the average voltage value Va (S3), and transmits a mode switch signal so as to switch the AGC circuit into a scan mode (S5) when a change width G is larger than a predetermined value (YES in S4). When the change width is not larger than the predetermined value (NO in S4), the tracking mode is kept (S6). The AGC circuit is switched into the scan mode which copes with the large change of the radio wave level, so that the occurrence of noise is prevented.

Description

  The present invention relates to a television receiver.

  The television receiver receives a television broadcast radio wave, converts a radio wave of a channel selected by the user into an IF signal of an intermediate frequency, and receives an IF signal from the tuner and converts the IF signal from the tuner into a video signal. And a circuit for transmitting a control voltage (hereinafter referred to as AGC voltage) to the tuner to control the gain of the tuner.

  The intensity of television broadcast radio waves varies depending on the channel, and the AGC circuit controls the gain in the tuner when radio waves of different intensity are received, and the amplitude of the IF signal output from the tuner is substantially constant. To ensure that the TV screen is stable on any channel.

  On the other hand, the mode of fluctuation of television broadcast radio waves is not uniform. Specifically, when changing channels, the fluctuation range is large and the fluctuation speed is fast, but when the channel is constant, the fluctuation width is small and the fluctuation speed is slow.

  In order to deal with the above situation, the AGC circuit of a television receiver can generally be switched between a mode in which the AGC operation is fast (hereinafter referred to as a scan mode) and a mode in which the AGC operation is slow (hereinafter referred to as a tracking mode). It has become. Specifically, at the time of channel switching, the AGC circuit is switched to a scan mode with high follow-up so that the TV screen does not become unstable even if the radio field intensity is large and fluctuates quickly. On the other hand, when the channel is constant, if the AGC operation remains fast, the television screen will be less stable in response to slight fluctuations in the radio field strength, so that the tracking mode is switched to a low-tracking mode. It has become.

  In addition, when there is a channel adjacent to the channel selected by the user, there is a problem in that an image of the adjacent channel is reflected and screen noise is generated. In order to solve this problem, when it is determined from the data table that the channel selected by the user has an adjacent channel, the value of the detection output as a determination criterion for the AGC circuit to start the control operation is lower. A television set is known (see, for example, Patent Document 1). In this television, when it is determined that there is an adjacent channel in the channel selected by the user, the AGC circuit starts the control operation from the stage where the radio wave intensity is relatively low, so that generation of screen noise and the like is prevented.

  In addition, a circuit for sending the broadcast radio wave received by the antenna to the tuner after being amplified by the amplifier and a circuit for sending it to the tuner without being amplified are provided, and the two circuits are switched and used in accordance with the value of the AGC voltage. A mobile receiver for mobile reception is known (for example, see Patent Document 2).

Japanese Patent No. 4117490 JP 2006-261710 A

  By the way, near the border of Europe, where multiple broadcast radio sources from different countries are relatively close together, multiple channels with similar frequencies may coexist, and one channel is influenced by the other channel. In response, beat noise may appear on the TV screen.

  When using a tuner equipped with a high-performance bandpass filter such as a SAW filter, the occurrence of the above problems can be suppressed, but by adopting a tuner equipped with a high-performance bandpass filter, it is difficult to reduce costs accordingly. Become. In other words, in order to reduce the cost, when using a relatively inexpensive tuner that does not include a bandpass filter, the above problem is likely to occur. On the other hand, to reduce costs, there is a television receiver that does not use a tuner equipped with a bandpass filter and suppresses the influence of jamming waves in a later stage than the tuner. It was difficult to reliably solve the above-mentioned problems by itself.

  Here, the present inventor notices that, when broadcast radio waves with relatively close frequencies are mixed, the fluctuation range and speed of fluctuation of the radio field intensity are larger than usual, and conventionally, the channel is fixed to the tracking mode when the channel is constant. I came up with the intention to switch the AGC circuit operation mode to scan mode. As a result of experiments, even if an inexpensive tuner that does not have a bandpass filter is used and the function of cutting the jamming radio wave in the tuner is not sufficient, the operation mode of the AGC circuit can be controlled to After confirming that noise and other troubles can be prevented, the present invention has been invented.

  The present invention solves the above-described problem, and includes a tuner, an intermediate frequency circuit, and an AGC circuit, and the AGC circuit is a television receiver that can be switched between a scan mode and a tracking mode. An object of the present invention is to provide a television receiver capable of preventing occurrence of a failure such as beat noise on the screen by switching the operation mode of the AGC circuit when an interference wave is generated at a fixed channel.

  In order to solve the above-mentioned problems, the invention of claim 1 is a tuner that receives a television broadcast radio wave and converts a radio wave of a channel selected by a user into an IF signal of an intermediate frequency, and an IF signal from the tuner. An intermediate frequency circuit that receives and converts the signal into a video signal; and an AGC circuit that controls a gain of the tuner by transmitting a control voltage (hereinafter referred to as an AGC voltage) to the tuner. A mode in which AGC operation is fast to cope with fluctuations in radio wave level (hereinafter, scan mode), and a mode in which AGC operation is slow to deal with fluctuations in radio wave level when the channel is constant (hereinafter, tracking mode), In the television receiver which can be switched to AGC voltage monitoring means for monitoring the AGC voltage transmitted by the AGC circuit. The AGC voltage monitoring means switches the AGC circuit to the scan mode when the fluctuation range of the current AGC voltage with respect to the average AGC voltage in the channel becomes larger than a preset value when the channel is constant. It is characterized by that.

  According to a second aspect of the present invention, in the first aspect of the present invention, the AGC voltage monitoring means includes an average voltage detecting means for detecting an average value of the AGC voltage when the channel is constant, and the average voltage detecting means The average voltage storage means for storing the detected average value, the average value of the AGC voltage stored in the average voltage storage means, and the current AGC voltage value are compared, and the fluctuation range is larger than a preset value. And a switching signal transmitting means for transmitting a switching signal to the scan mode to the AGC circuit.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the AGC circuit transmits a control voltage (AGC voltage) to the intermediate frequency circuit to control the gain of the intermediate frequency circuit. The AGC voltage monitoring means monitors the AGC voltage with respect to the intermediate frequency circuit.

  According to the first aspect of the present invention, when the AGC voltage monitoring means detects that the fluctuation range of the current AGC voltage with respect to the average AGC voltage in the channel becomes large when the channel is constant, the AGC circuit is set in the scan mode. Therefore, it is possible to prevent a failure such as beat noise from appearing on the television screen even if the interference wave of the channel adjacent to the switched channel is generated.

  According to the invention of claim 2, the AGC voltage monitoring means detects the average value of the AGC voltage when the channel is constant, and the average voltage storage for storing the average value detected by the average voltage detection means. The average value of the AGC voltage stored in the means and the average voltage storage means is compared with the current AGC voltage value, and when the fluctuation range is larger than a preset value, the AGC circuit enters the scan mode. Switching signal transmitting means for transmitting the switching signal of the above-mentioned, it is possible to prevent a failure such as beat noise from appearing on the television screen even if the interference wave of the channel adjacent to the switched channel occurs.

  According to the invention of claim 3, the AGC circuit transmits a control voltage (AGC voltage) to the intermediate frequency circuit to control the gain of the intermediate frequency circuit. Since the AGC circuit is monitored and the AGC circuit is switched to the scan mode when the fluctuation range of the current AGC voltage with respect to the average AGC voltage in the channel increases when the channel is constant, the channel adjacent to the switched channel is It is possible to prevent a failure such as beat noise from appearing on the TV screen even if the disturbing radio wave is generated.

The block diagram of the television receiver which concerns on one Embodiment of this invention. The flowchart which shows the mode switching procedure of the AGC circuit in the television receiver. The figure which shows the relationship between the fluctuation | variation of the AGC voltage in the television receiver, and the operation mode of an AGC circuit.

  Hereinafter, a television receiver according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. The television receiver 1 according to the present embodiment receives a television broadcast radio wave by the antenna 2 and amplifies the radio wave (RF signal) of the channel selected by the user in synchronization with the received radio wave (RF signal). The tuner 3 that outputs the IF signal, the IF circuit 4 that converts the IF signal from the tuner 3 into a video signal, and outputs the RF / AGC voltage 5 and the IF / AGC voltage 6 to output the tuner 3 and the IF circuit 4 and an AGC circuit 7 for controlling the gain of 4.

  The video signal is input to a display 9 such as a liquid crystal panel or CRT via the image signal processing circuit 8 and displayed as a video. The tuner 3 does not include a high-performance bandpass filter such as a SAW filter and does not have a function of reliably cutting out jamming radio waves. However, a part of noise components included in the video signal is generated by the image signal processing circuit 8. Is removed softly.

  The AGC circuit 7 is connected to a microcomputer (AGC voltage monitoring means, average voltage detection means, average voltage storage means, switching signal transmission means) 11, and a channel switching signal transmitted by the user operating the remote controller 12 is received by the light receiving unit. 13 is input to the microcomputer 11 via 13, the microcomputer 11 transmits channel switching signals 14 and 15 to the tuner 3 and the AGC circuit 7, respectively. In addition, the AGC circuit 7 operates in a mode in which the AGC operation is slow (hereinafter referred to as tracking mode) to cope with a state where the fluctuation range of the radio wave level is relatively small and the fluctuation speed is relatively small when the channel is constant. When the channel is switched, it is possible to switch to a mode (hereinafter referred to as a scan mode) in which the AGC operation is fast in order to cope with a state in which the fluctuation range of the radio wave level is relatively large and the fluctuation speed is relatively large.

  The tuner 3 that has received the channel switching signal 14 changes the channel to be tuned to the channel designated by the channel switching signal 14. On the other hand, the AGC circuit 7 that has received the channel switching signal 15 switches the operation mode from the tracking mode to the scan mode once, and then switches to the tracking mode again after the channel switching by the tuner 3 is completed.

  Further, the microcomputer 11 monitors the RF / AGC voltage 5 input from the port 11a, and when the channel is constant, compares the average RF / AGC voltage in the channel with the current RF / AGC voltage 5, An AGC voltage monitoring unit 17 that transmits a mode switching signal 16 to the AGC circuit 7 when the fluctuation range of the current RF / AGC voltage 5 with respect to the average RF / AGC voltage is larger than a preset value.

  Specifically, the AGC voltage monitoring unit 17 stores an average voltage detection unit 18 that detects an average value of the RF / AGC voltage 5 when the channel is constant, and an average value Va detected by the average voltage detection unit 18. The average voltage storage unit 19, the RF / AGC voltage comparison unit 21 that compares the stored average value Va and the current RF / AGC voltage, and the difference between the two as a result of the comparison (voltage fluctuation range) 11 is provided with a mode switching signal transmission unit 22 that transmits a switching signal 16 to the AGC circuit 7 when the value is larger than a value (preset) stored in the memory 11b in the memory 11.

  The average voltage detector 18 integrates the RF / AGC voltage 5 input from the port 11a during a period in which the channel is constant, and calculates the average value Va by averaging the integrated values over time. Whether or not the channel is constant can be determined by a channel switching signal received via the light receiving unit 13. The average voltage storage unit 19 configures and stores the detected average value Va in a table corresponding to each channel. For example, 2.2 volts for one channel, 2.0 volts for two channels, 2.1 volts for three channels, and the like.

  Next, the mode switching procedure executed by the microcomputer 11 will be described with reference to the flowchart of FIG. When the microcomputer 11 receives the channel switching signal via the light receiving unit 13 (YES in S1), the microcomputer 11 reads the average value Va of the indicated channel stored in the average voltage storage unit 19 (S2), and reads the average value read out Va is compared with the current RF / AGC voltage 5 (S3). For example, if the channel is switched from the first channel to the second channel, the microcomputer 11 reads the average value Va = 2.0 volts, and then the current RF / AGC voltage 5 and the average value until the next channel is switched. Continue to compare Va. The AGC circuit 7 is in a tracking mode immediately after channel switching.

  When the fluctuation range from the average value Va of the RF / AGC voltage 5 becomes equal to or greater than the value (eg, 0.3 volts) stored in the memory 11b (YES in S4), the microcomputer 11 switches the mode. The AGC circuit 7 is temporarily switched to the scan mode by transmitting the signal 16 (S5). If the fluctuation width does not exceed the value stored in the memory 11b (NO in S4), the mode switching signal 16 is not transmitted and the tracking mode is maintained (S6).

  The timing for changing the RF / AGC voltage 5 and switching the operation mode of the AGC circuit 7 will be described with reference to FIG. Assuming that an interference wave is generated at the timing T1 after the channel is switched to the two channels, the apparent radio wave intensity is increased, so that the RF / AGC voltage 5 is lowered to lower the gain of the tuner 3. Specifically, the RF / AGC voltage 5 decreases from a stable state (a state where approximately 2.0 volts is maintained). When the fluctuation width G of the RF / AGC voltage 5 exceeds 0.3 volts (T2), the mode switching signal 16 is transmitted to the AGC circuit 7 and the AGC circuit 7 is in a constant channel state. Instead, it temporarily switches to scan mode.

  Since the tuner 3 does not include a band filter, beat noise is generated on the screen of the display 9 when the AGC circuit 7 maintains the tracking mode in the state in which the interference wave is generated as described above. Although generated, the AGC circuit 7 is switched to a scan mode having a high tracking capability that can cope with a state in which the fluctuation level of the radio wave level is large and the fluctuation speed is fast, thereby preventing beat noise from appearing on the screen.

  Thereafter, when the interfering radio wave disappears, the fluctuation range G from the average value Va of the RF / AGC voltage 5 becomes within 0.3 volts, the transmission of the mode switching signal 16 is stopped, and the AGC circuit 7 again enters the tracking mode. Switch (T3). At this time, even if the operation mode is switched to the tracking mode with a low operating speed, the jamming radio wave disappears, so that the radio wave state is stable, and it is not sensitive to a slight fluctuation of the RF signal, and is good. A screen display is obtained.

  The AGC circuit 7 is a so-called reverse control type in which the AGC voltage is increased when the gain of the tuner 3 is increased, and the AGC voltage is decreased when the gain is decreased. In the case of the forward type in which the gain has an inverse relationship, the fluctuation of the AGC voltage when the jamming wave is generated becomes a fluctuation in the direction in which the AGC voltage increases.

  In addition, the IF / AGC voltage 6 is input to the port 11a of the microcomputer 11 instead of the RF / AGC voltage 5, and the AGC voltage monitoring unit 17 monitors the IF / AGC voltage 6 to thereby generate interference radio waves. The operation mode of the AGC circuit 7 may be switched to the scan mode at the detected timing.

  Further, the average voltage detector 18 calculates an average value based on the actual RF / AGC voltage 5 output from the AGC circuit 7 while the television receiver 1 is receiving a television broadcast. However, when the place where the television receiver 1 is installed is determined in advance and the received radio wave intensity for each channel can be predicted in advance, the average voltage detector 18 is predicted in advance. The average value Va of the RF / AGC voltage for each channel may be stored.

  Furthermore, the AGC voltage monitoring unit 17 generates an interference wave when the difference (variation width) between the current RF / AGC voltage 5 and the average value Va is larger than a fixed value stored in the memory 11b. However, the occurrence of jamming radio waves may be determined based on whether the ratio of the magnitude of the fluctuation range to the average value Va is equal to or greater than a predetermined ratio set in advance.

  As described above, in the present television receiver 1, when the channel is switched, the AGC voltage monitoring unit 17 calculates the average value Va of the RF / AGC voltage of the channel and the current RF / AGC voltage 5. In comparison, when it is detected that the fluctuation range G is larger than a preset value, the mode switching signal 16 is transmitted, and the AGC circuit 7 is temporarily scanned even when the channel is constant. Since the mode is switched, it is possible to prevent a failure such as beat noise from appearing on the TV screen even if an interference radio wave occurs.

  In addition, since the microcomputer 11 has a simple configuration that only switches the operation mode of the AGC circuit 7 when it detects the occurrence of jamming waves based on the fluctuation of the RF / AGC voltage 5, hardware such as a new electronic circuit can be installed. There is no need to provide it, the configuration of the television receiver 1 is not complicated, and the cost is not increased. Furthermore, since the tuner 3 may not include a band filter such as a SAW filter, the cost of the television receiver 1 can be easily reduced.

1 Television receiver 3 Tuner 4 IF circuit (intermediate frequency circuit)
5 RF / AGC voltage (AGC voltage)
6 IF / AGC voltage (AGC voltage)
7 AGC circuit 11 Microcomputer (AGC voltage monitoring means, average voltage detection means, average voltage storage means, switching signal transmission means)
16 mode switching signal 17 AGC voltage monitoring unit 18 average voltage detecting unit 19 average voltage storage unit 22 mode switching signal transmitting unit G fluctuation range

Claims (3)

A tuner that receives a television broadcast radio wave and converts the radio wave of the channel selected by the user into an IF signal of an intermediate frequency;
An intermediate frequency circuit that receives the IF signal from the tuner and converts it into a video signal;
An AGC circuit that transmits a control voltage (hereinafter referred to as AGC voltage) to the tuner to control the gain of the tuner, and
The AGC circuit has a mode in which the AGC operation is fast (hereinafter referred to as a scan mode) to cope with fluctuations in the radio wave level when the channel is switched, and a mode in which the AGC operation is slow in order to cope with fluctuations in the radio wave level when the channel is constant ( Hereinafter, in the television receiving apparatus that can be switched to the tracking mode),
AGC voltage monitoring means for monitoring the AGC voltage transmitted by the AGC circuit,
The AGC voltage monitoring means switches the AGC circuit to a scan mode when a fluctuation range of a current AGC voltage with respect to an average AGC voltage in the channel becomes larger than a preset value when a channel is constant. A television receiving device. The AGC voltage monitoring means includes:
Average voltage detecting means for detecting an average value of the AGC voltage when the channel is constant;
Average voltage storage means for storing an average value detected by the average voltage detection means;
The average value of the AGC voltage stored in the average voltage storage means is compared with the value of the current AGC voltage. When the fluctuation range is larger than a preset value, the AGC circuit enters the scan mode. The television receiver according to claim 1, further comprising: a switching signal transmission unit that transmits a switching signal. The AGC circuit controls the gain of the intermediate frequency circuit by transmitting a control voltage (AGC voltage) also to the intermediate frequency circuit.
The television receiver according to claim 1 or 2, wherein the AGC voltage monitoring means monitors an AGC voltage with respect to the intermediate frequency circuit.

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