JP2007037023A - Analog tv receiver having analog broadcast/digital broadcast discriminating function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an analog TV receiver which surely automatically tunes only to analog TV broadcasting without erroneous detection, in hardware configuration with no remarkable difference from the prior art, when digital TV broadcasting coexists with analog TV broadcasting. <P>SOLUTION: The present invention relates to an analog TV receiver which comprises an automatic tuning means comprised of PLL frequency synthesizers (104-105) and independently processes a video signal system and an audio signal system, wherein a level detection means 112 and a control means 113 are provided for generating a receiving level, for stopping the automatic tuning means in a specific frequency, from the audio signal system through level detection. If the receiving level exceeds a first threshold value, the control means changes a tuning frequency of the automatic tuning means toward a video carrier wave to stop the automatic tuning means and if the receiving level does not exceed a second threshold value at such a time, presence of analog TV broadcasting waves is discriminated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an analog TV receiver having a function of discriminating between analog broadcasting and digital broadcasting.

  Currently, terrestrial digital television broadcasting (hereinafter referred to as “digital TV broadcasting”) and terrestrial analog television broadcasting (hereinafter referred to as “analog TV broadcasting”) coexist and are assigned to each channel. It is known that the frequency bands are adjacent (see, for example, Patent Document 1). Further, the signal component of the digital TV broadcast wave has a bandwidth of 5.7 MHz close to the TV signal transmission band (6 MHz), and is uniformly distributed at a constant carrier interval (1 KHz, etc.).

  Conventionally, a method of obtaining an audio signal carrier by level detection is used as a stop signal (trigger) for automatic tuning of analog TV broadcasting. When attempting to automatically tune to analog TV broadcasting using this method, there has been a problem in that a false detection that automatically tunes to digital TV broadcasting occurs due to the trigger of digital broadcasting waves distributed near the audio carrier.

JP 2000-350107 A

  Therefore, the present invention provides an analog TV receiver that automatically tunes to only analog TV broadcasts without erroneous detection, with a hardware configuration that is not much different from that of the prior art even when digital TV broadcasts and analog TV broadcasts coexist The purpose is to do.

  An analog TV broadcast receiver according to the present invention is an analog TV broadcast receiver, and includes tuning means for extracting a radio wave of a desired frequency from received radio waves, and a reception level of the radio wave extracted by the tuning means as an audio signal. When the reception level exceeds the first threshold, the tuning level of the tuning means is changed in the direction of the video carrier and stopped when the reception level exceeds the first threshold. Control means for discriminating that there is an analog TV broadcast wave when the threshold value is not exceeded.

  An analog TV broadcast receiver according to the present invention is an analog TV broadcast receiver, and includes tuning means for taking out a radio wave of a desired frequency from received radio waves, and a reception level of the radio wave taken out by the tuning means. Video system reception level detection means for detecting from the video signal system, audio system reception level detection means for detecting the reception level of the radio wave extracted by the tuning means from the audio signal system, and the video system reception level exceeds a first threshold value Control means for determining that there is an analog TV broadcast wave if the audio system reception level does not exceed the second threshold at this time, the tuning frequency of the tuning means is changed in the direction of the audio carrier wave and stopped. It is characterized by providing.

  The analog TV broadcast receiver according to the present invention further comprises vertical synchronization detection means for detecting a vertical blanking period from the video signal system, and the control means has a reception level detected from the audio signal system as a first level. When the threshold value is exceeded, the tuning frequency of the tuning means is changed in the direction of the video carrier and stopped, and the reception level detected from the audio signal system in the vertical blanking period does not exceed the second threshold value. It is characterized that an analog TV broadcast wave is present.

  When the reception level received from the audio signal system exceeds the first threshold, the control means changes the tuning frequency of the tuning means in the direction of the video carrier and stops it, and detects from the audio signal system. The received level is detected (2n-1) times within the field travel period (n is an integer of 2 or more), and the number of times the received level received from the audio signal system exceeds the second threshold is less than n times. In the case, it is determined that there is an analog TV broadcast wave.

  The control means sets the tuning frequency of the video carrier so that when the reception level received from the audio signal system exceeds the first threshold, the tuning frequency of the tuning means is set at the upper end of the video band. When the reception level detected from the audio signal system does not exceed the second threshold, it is determined that there is an analog TV broadcast wave.

  The first threshold value is a value that can reliably detect reception of an analog TV broadcast, and the second threshold value is a value that can reliably detect only reception of a digital broadcast.

  According to the present invention, analog / digital broadcasting is discriminated by detecting a signal level closer to the video band than the audio carrier wave. Thereby, it is possible to realize an analog TV broadcast receiver having an auto-tuning function with few false detections of digital broadcast waves by using a hardware configuration that is not significantly different from the conventional one.

1 is an analog TV receiver according to a first embodiment of the present invention.
The configuration of this receiver will be described with reference to FIG.

  A signal received by the antenna 101 is amplified by the radio frequency amplifier 102 and sent to the first mixer 103. The mixer 103 mixes the output signal of the radio frequency amplifier 102 and the output signal of the first oscillator 104 to generate an intermediate frequency signal. This signal is sent to the video IF filter 106 and the audio IF filter 109, and is respectively filtered to extract a video band signal and an audio band signal.

  The output signal of the video IF filter 106 is amplified by the video IF amplification unit 107 and further demodulated by the video demodulation unit 108 to obtain a video signal. The output signal of the audio IF filter 109 is amplified by the audio IF amplification unit 110 and further demodulated by the audio demodulation unit 111 to obtain an audio signal.

  The output signal of the audio IF amplification unit 110 is also sent to the level detection unit 112, where reception level information is detected, and the reception level information is sent to the control unit 113. The control unit 113 controls the frequency division ratio N given to the PLL 105 based on a flow described later. The PLL 105 is paired with the first oscillator 104 to constitute a frequency synthesizer.

FIG. 2 is a principle diagram of a PLL frequency synthesizer.
2, the output signal (frequency f _o ) of the voltage controlled oscillator 25 corresponding to the first oscillator 104 in FIG. 1 is divided by the programmable divider 26 according to the division ratio N given from the control unit 113 in FIG. As a result, a signal of frequency f _o / N is input to the phase comparator 23. This signal and the output signal (frequency f _i ) of the crystal oscillator 22 are compared by the phase comparator 23, and the resulting error signal is filtered by the low-pass filter 24 and applied to the voltage controlled oscillator 25.

Since the oscillation frequency of the voltage controlled oscillator 25 is controlled so that the error signal becomes 0,
f _o / N = f _i
That is,
f _o = Nf _i
Holds.
That is, the first oscillator 104 in FIG. 1 outputs a signal having a frequency proportional to the frequency division ratio N given from the control unit 113 in FIG.

FIG. 3 is a control flow of the control unit 113 in FIG. 1 at the time of search-up channel selection.
The analog broadcast / digital broadcast discrimination function according to the first embodiment of the present invention will be described with reference to FIG.

  First, the frequency division ratio N given by the control unit 113 shown in FIG. 1 is increased by the frequency division ratio K corresponding to the channel interval (for example, 6 MHz) (S301). This is intended to select a channel one level above. The initial value of N is a value corresponding to the frequency of the audio carrier of the lowest channel.

Next, the reception level is detected based on the reception level information input from the level detection unit 112 to the control unit 113 (S302). Then, it is determined whether or not the detected reception level exceeds a predetermined first threshold (S303). If the reception level exceeds the predetermined first threshold (Yes), it is determined that there is an analog TV broadcast or digital TV broadcast reception level, and the process proceeds to S304. If not (No), the process proceeds to S301. . The first threshold value is set to a value that can reliably detect reception when an analog TV broadcast is received.
By the loop of S301 to S303, the tuning frequency is shifted one channel at a time until it is determined that there is a reception level in S303.

  If it is determined that there is a reception level in S303 (Yes), the frequency division ratio N provided by the control unit 113 is decreased by the frequency division ratio D (> 0) corresponding to the frequency shift amount Δf (<0) (S304). The reception level is detected based on the reception level information input from the level detection unit 112 to the control unit 113 (S305). Thereby, a signal energy level in the vicinity of a frequency lower than the audio carrier by | Δf | (close to the video carrier frequency) is detected.

  In the case of digital TV broadcasting, due to the characteristics of uniform energy distribution on the frequency axis, the first reception level detected in S302 and the second reception level detected in S305 are substantially the same.

  On the other hand, in the case of analog TV broadcasting, Δf so that the second level detection detected in S305 is performed near the middle of the video carrier frequency and the color subcarrier frequency due to non-uniform energy distribution (concentration near the carrier). If (that is, D) is appropriately selected, the second reception level detected in S305 is clearly lower than the first reception level detected in S302.

  Therefore, when the broadcast of the reception level determined to have a level in S303 is a digital TV broadcast, a second threshold is set to detect this. Therefore, the second threshold is set to a value that can reliably detect only reception of digital TV broadcasts. It should be noted that the reception level of digital broadcasting has a certain width and may be smaller than a value (first threshold in S302) that can reliably detect reception of analog broadcasting. It is preferable to set it slightly smaller than the threshold value.

  Next, it is determined whether or not the second reception level detected in S305 exceeds a predetermined second threshold (S306). If it exceeds (Yes), it is determined that there is a digital TV broadcast reception level, and the process proceeds to S309. Otherwise (No), since the second reception level is clearly lower than the first reception level, it is determined that the reception is analog TV broadcast, and the process proceeds to S307.

  If it is determined that the received channel is a digital TV broadcast, the division ratio given by the control unit 113 is equal to the sum of the division ratio K corresponding to the channel interval and the division ratio D corresponding to the frequency shift amount Δf. N is increased (S309), and the process proceeds to reception level detection in S302. As a result, the signal energy level near the audio carrier frequency of the channel one level above is detected.

  If it is determined that the received channel is an analog TV broadcast, the frequency division ratio N provided by the control unit 113 is increased by the frequency division ratio D corresponding to the frequency shift amount Δf (S307), and the analog TV broadcast is performed. Is received (S308).

  In S306, the branch destination is determined by comparing the predetermined second threshold value with the reception level obtained in S305, but the difference between the reception level obtained in S302 and the reception level obtained in S305 is calculated. If this difference is larger than the predetermined third threshold, the process may proceed to S307, and if not, the process may proceed to S309.

  According to the present embodiment, it is possible to realize an analog TV broadcast receiver having an automatic tuning function with few digital wave false detections using the same hardware configuration as that of the prior art.

  FIG. 4 shows an analog TV receiver according to the second embodiment of the present invention. The same reference numerals are given to the same components in the first embodiment and the second embodiment.

  The configuration of the receiver of the present embodiment is almost the same as that of the receiver of the first embodiment, but the output signal of the video IF amplifier 107 is input to the video system level detector 401, where the video signal The difference is that a configuration for detecting reception level information and inputting it to the control unit 113 is added.

  The control flow of the control unit is common to the first and second embodiments, but the reception level detection in S302 is performed using reception level information obtained from the video system level detection unit instead of the audio system level detection unit. The difference is that it is executed, and Δf> 0 and D <0. Note that the initial value of N at the time of search-up channel selection is a value corresponding to the frequency of the video carrier of the lowest channel. The threshold value is set in the same manner as in the first embodiment.

  That is, the reception level detection of S302 in FIG. 3 is performed using reception level information obtained from the video system level detection unit, and the level detection of S305 is performed using reception level information obtained from the audio system level detection unit, The level detection in S302 is performed in a state in which the frequency is shifted in the direction of the audio carrier wave.

  According to the present embodiment, automatic tuning is performed by performing the first level detection (S302) using the video carrier, and then the second level detection (S305) is performed at the frequency shifted by Δf (> 0). Analog / digital broadcasting is discriminated by using the audio system signal. As a result, it is possible to realize an analog TV broadcast receiver having an automatic tuning function with few false detections of digital waves when performing automatic tuning operation with emphasis on video signals.

  FIG. 5 shows an analog TV receiver according to Embodiment 3 of the present invention. The same reference numerals are given to the same components in the first embodiment and the third embodiment.

  The configuration of the receiver of the present embodiment is almost the same as the receiver configuration of the first embodiment, but the video signal output from the video demodulator 108 is input to the vertical synchronization detector 501 where the vertical blanking period The point which added the structure which detects this and inputs it into the control part 113 differs. Further, Δf, D, and the threshold value are set in the same manner as in the first embodiment.

FIG. 6 is a control flow of the control unit 113 of the analog TV receiver shown in FIG. 5 at the time of search-up channel selection.
The analog broadcast / digital broadcast discrimination function of the third embodiment of the present invention will be described with reference to FIG.

  First, the frequency division ratio N given by the control unit 113 is increased by the frequency division ratio K corresponding to the channel interval (for example, 6 MHz) (S601). This is intended to select a channel one level above. The initial value of N is a value corresponding to the frequency of the audio carrier of the lowest channel.

Next, the reception level is detected based on the reception level information input from the voice system level detection unit 112 to the control unit 113 (S602). Then, it is determined whether or not the detected reception level exceeds a predetermined first threshold (S603). If the reception level exceeds the predetermined first threshold (Yes), it is determined that there is an analog TV broadcast or digital TV broadcast reception level, and the process proceeds to S604. If not (No), the process proceeds to S601. .
By the loop of S601 to S603, the tuning frequency is shifted to the upper channel one by one until it is determined in S603 that there is a reception level.

  If it is determined in S603 that the reception level is present (Yes), the frequency division ratio N provided by the control unit 113 is decreased by the frequency division ratio D (> 0) corresponding to the frequency shift amount Δf (<0) (S604). . Next, the output signal of the vertical synchronization detection unit 501 is repeatedly measured and waits until the vertical blanking period is reached (S605, S606). Based on the reception level information input from the level detection unit 112 to the control unit 113 The reception level is detected (S607). As a result, in the vertical blanking period, a signal energy level in the vicinity of a frequency lower than the audio carrier by | Δf | (close to the video carrier frequency) is detected.

  Next, it is determined whether or not the second reception level detected in S607 exceeds a predetermined second threshold (S608). If it exceeds (Yes), it is determined that there is a digital TV broadcast reception level, and the process proceeds to S611. Otherwise (No), since the second reception level is clearly lower than the first reception level, it is determined that the reception is analog TV broadcast, and the process proceeds to S609.

  If it is determined that the received channel is a digital TV broadcast, the division ratio given by the control unit 113 is equal to the sum of the division ratio K corresponding to the channel interval and the division ratio D corresponding to the frequency shift amount Δf. N is increased (S611), and the process proceeds to reception level detection in S602. As a result, the signal energy level near the audio carrier frequency of the channel one level above is detected.

  If it is determined that the received channel is an analog TV broadcast, the frequency division ratio N provided by the control unit 113 is increased by the frequency division ratio D corresponding to the frequency shift amount Δf (S609), and the analog TV broadcast is performed. Is received (S610).

  In S608, the branch destination is determined by comparing the predetermined second threshold value with the reception level obtained in S607, but the difference between the reception level obtained in S602 and the reception level obtained in S607 is calculated. If this difference is larger than the predetermined third threshold value, the process may proceed to S609, and if not, the process may proceed to S611.

  According to the present embodiment, since the second reception level detection is performed during the vertical blanking period in which no chroma or video signal is included, erroneous detection can be further reduced.

The configuration of the analog TV receiver according to the fourth embodiment of the present invention is the same as that shown in FIG. Further, Δf, D, and the threshold value are set in the same manner as in the first embodiment.
FIG. 7 is a control flow of the control unit 113 in FIG. 1 at the time of search-up channel selection according to the fourth embodiment.
With reference to the figure, an analog broadcast / digital broadcast discrimination function according to the fourth embodiment of the present invention will be described.

  First, the frequency division ratio N given by the control unit 113 is increased by the frequency division ratio K corresponding to the channel interval (for example, 6 MHz) (S701). This is intended to select a channel one level above. The initial value of N is a value corresponding to the frequency of the audio carrier of the lowest channel.

Next, the reception level is detected based on the reception level information input from the level detection unit 112 to the control unit 113 (S702). Then, it is determined whether or not the detected reception level exceeds a predetermined first threshold (S703). If the reception level exceeds the predetermined first threshold (Yes), it is determined that there is an analog TV broadcast or digital TV broadcast reception level, and the process proceeds to S704. If not (No), the process proceeds to S701. .
By the loop of S701 to S703, the tuning frequency is shifted one channel at a time until it is determined in S703 that there is a reception level.

  If it is determined that there is a reception level in S703 (Yes), the frequency division ratio N provided by the control unit 113 is decreased by the frequency division ratio D (> 0) corresponding to the frequency shift amount Δf (<0) (S704). .

Based on the reception level information input from the level detection unit 112 to the control unit 113, detection of the reception level is performed at an odd number every time Δt within a field scanning period (for example, about 16.7 msec) (3 every 5 msec). Etc.) (S705 to S709).
M is a variable for rotating this detection loop, and the number of times the loop is rotated can be determined by the value of M determined in S707.
In the example shown in FIG. 7, this detection loop rotates only three times.

  In S706, the reception level is detected, it is determined whether or not it exceeds a predetermined second threshold, and the number of times that the second threshold is exceeded during the loop is counted as the number of detections. As a result, the number of times that the signal energy level near the frequency lower than the audio carrier by | Δf | (close to the video carrier frequency) exceeds a certain level is counted.

  Next, it is determined whether or not the number of times of detection described above is equal to or more than a majority (two times in this example) of turning the loop (S710). If it is greater than the majority (Yes), it is determined that there is a digital TV broadcast reception level, and the process proceeds to S713. If not (No), it is determined that analog TV broadcast is received, and the process proceeds to S711.

  If it is determined that the received channel is a digital TV broadcast, the division ratio given by the control unit 113 is equal to the sum of the division ratio K corresponding to the channel interval and the division ratio D corresponding to the frequency shift amount Δf. N is increased (S713), and the process proceeds to reception level detection in S702. As a result, the signal energy level near the audio carrier frequency of the channel one level above is detected.

  If it is determined that the received channel is an analog TV broadcast, the frequency division ratio N provided by the control unit 113 is increased by the frequency division ratio D corresponding to the frequency shift amount Δf (S711), and the analog TV broadcast is performed. Is received (S712).

  According to the present embodiment, erroneous detection can be reduced by detecting the reception level a plurality of times in one field.

FIG. 8 is an example of a waveform obtained by observing the IF signal, which is the output signal of the first mixer 103 in FIG. 1, with a spectrum analyzer.
Note that the IF signal is observed with the frequency axis inverted relative to the RF signal.
For example, a spectrum of 15 channels appears in a frequency band higher than 14 channels in the RF signal, but a spectrum of 15 channels appears in a frequency band lower than 14 channels in the IF signal.

  When a strong digital TV broadcast signal is received in 15 channels and no signal is received in 14 channels with an analog TV broadcast receiver, waveform distortion occurs due to reasons such as non-optimal AGC, as shown in FIG. As shown, energy appears in 14 channels.

  When the first embodiment is applied to such a signal, the first reception level detection is performed at the frequency A, and the second reception level detection is performed at the frequency B where the frequency is shifted by Δf. However, since the reception level at the frequency B is considerably lower than the reception level at the frequency A, it is erroneously detected that there is an analog TV broadcast on the 14th channel, and the tuning stops at the 14th channel.

In order to prevent this, it is conceivable to reduce the influence of distortion by setting the frequency shift amount | Δf | to the minimum amount necessary for the detection operation.
The bandwidth of the audio system filter that performs audio system level detection is, for example, 500 KHz, but the amount of shift is such that this filter is shifted in the video band direction (downward) on the frequency axis so that it is covered by the video band. , The minimum amount.

Since the difference between the upper end frequency (video carrier frequency + 4.2 MHz) of the analog TV broadcast video band and the center frequency of the audio system filter is 300 KHz,
300 + 500/2 = 550KHz
If the audio system filter is shifted only in the video band direction (downward), the audio system filter is just covered with the video band.

  Therefore, by using the configuration, the flow, and the threshold value of the first embodiment as they are and setting Δf = −550 KHz, the tuning frequency for the second reception level detection is set at the upper end of the video band. Therefore, the frequency A and the frequency B are close to each other, and it is possible to prevent the second reception level from becoming excessively low, thereby causing a malfunction that stops one channel before the powerful digital TV broadcast. Can be avoided.

  According to the present embodiment, it is possible to determine a TV broadcasting system with few malfunctions even under strong input near the broadcasting station.

  In the above-described embodiment, the search-up channel selection has been described as an example of the automatic channel selection. However, in the case of the search-down channel selection, all the configuration diagrams and flows can be used in exactly the same manner. It will be understood that the sign of the constant K appearing in the above need only be inverted.

It is a figure which shows the structure of the analog TV receiver by Example 1 of this invention. It is a principle diagram of a PLL frequency synthesizer. It is a control flow of the control part at the time of search-up channel selection. It is a figure which shows the structure of the analog TV receiver by Example 2 of this invention. It is a figure which shows the structure of the analog TV receiver by Example 3 of this invention. It is a control flow of the control part at the time of search-up channel selection. It is a control flow of the control part at the time of search-up channel selection. It is an example of the waveform which observed IF signal with the spectrum analyzer.

Explanation of symbols

101 Antenna 102 Radio Frequency Amplifier 103 First Mixer 104 First Oscillator 105 PLL
106 video IF filter 107 video IF amplifier 108 video demodulator 109 audio IF filter 110 audio IF amplifier 111 audio demodulator 112 level detector 113 controller

Claims (6)

An analog TV broadcast receiver,
A tuning means for extracting a radio wave of a desired frequency from the received radio waves;
Reception level detection means for detecting the reception level of the radio wave extracted by the tuning means from the audio signal system;
When the reception level exceeds the first threshold, the tuning frequency of the tuning means is changed in the direction of the video carrier and stopped, and when the reception level does not exceed the second threshold, analog TV broadcasting An analog TV broadcast receiver comprising control means for determining that there is a wave. An analog TV broadcast receiver,
A tuning means for extracting a radio wave of a desired frequency from the received radio waves;
Video system reception level detection means for detecting the reception level of the radio wave extracted by the tuning means from the video signal system;
Audio system reception level detection means for detecting the reception level of the radio wave extracted by the tuning means from the audio signal system;
When the video reception level exceeds the first threshold, the tuning frequency of the tuning means is changed in the direction of the audio carrier and stopped. At this time, the audio reception level does not exceed the second threshold And an analog TV broadcast receiver characterized by comprising control means for determining that there is an analog TV broadcast wave. Furthermore, a vertical synchronization detecting means for detecting a vertical blanking period from the video signal system is provided,
When the reception level detected from the audio signal system exceeds a first threshold value, the control means changes the tuning frequency of the tuning means in the direction of the video carrier and stops, and in the vertical blanking period, 2. The analog TV broadcast receiver according to claim 1, wherein it is determined that an analog TV broadcast wave is present when the reception level detected from the audio signal system does not exceed the second threshold.   When the reception level received from the audio signal system exceeds the first threshold, the control means changes the tuning frequency of the tuning means in the direction of the video carrier and stops it, and detects from the audio signal system. The received level is detected (2n-1) times within the field travel period (n is an integer of 2 or more), and the number of times the received level received from the audio signal system exceeds the second threshold is less than n times. The analog TV broadcast receiver according to claim 1, wherein it is determined that there is an analog TV broadcast wave.   The control means sets the tuning frequency of the video carrier so that when the reception level received from the audio signal system exceeds the first threshold, the tuning frequency of the tuning means is set at the upper end of the video band. 2. The method according to claim 1, wherein when the reception level detected from the audio signal system does not exceed the second threshold, it is determined that there is an analog TV broadcast wave. Analog TV broadcast receiver.   The first threshold value is a value that can reliably detect reception of an analog TV broadcast, and the second threshold value is a value that can reliably detect only reception of a digital broadcast. The analog TV broadcast receiver according to the item.

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