JPH04157892A - Bs tuner - Google Patents

Abstract

PURPOSE:To normally receive the television broadcast of non-MUSE and MUSE systems by always executing automatic fine tuning control, based on a detecting voltage in a blanking section in the case of receiving the television broadcast of the MUSE system. CONSTITUTION:When the television broadcast of an NYSC system is received, a detection voltage outputted from a demodulating circuit 2 is always supplied to a microprocessor 3, and the same automatic fine tuning as a conventional BS tuner is executed. On the other hand, when the television broadcast of an MUSE system is received, if a blanking section TB of a video signal is detected by an MUSE decoder 6 and a key signal falls from 0.5V to 0V, an analog switch 101 becomes a conducting state, and a detection voltage outputted from the demodulating circuit 2 is supplied to 3. Subsequently, when the key signal rises from 0V to 0.5V, a detection voltage charged to a capacitor 103 is supplied to 3. Accordingly, normal automatic fine tuning is executed irrespective of whether a received television broadcast is the MUSE system or not.

Description

Detailed Description of the Invention "Field of Industrial Application" This invention is applicable to non-MUSE television broadcasting and MUSE
This invention relates to an S tuner that can simultaneously receive television broadcasts based on the USE system.

``Prior Art'' FIG. 3 is a block diagram showing a general configuration of a BS tuner used when receiving television broadcasting based on the NTSC system or the like. In this figure, 1 is a channel selection circuit, 2 is a demodulation circuit, and 3 is a microprocessor.

A high frequency signal received by an antenna (not shown) is input to the channel selection circuit 1 and mixed with a local oscillation signal of a frequency corresponding to the selected channel. As a result, a video intermediate frequency signal and an audio intermediate frequency signal obtained by converting the frequency of the high frequency signal of the selected channel are output. Here, the frequency of the local oscillation signal in the tuning circuit 1 is finely adjusted by an automatic fine tuning signal supplied from the microprocessor 3 according to the calculation result based on the DC voltage output from the demodulation circuit 2.

The video intermediate frequency signal and the audio intermediate frequency signal outputted from the channel selection circuit 1 are subjected to FM detection by the demodulation circuit 2, and a baseband signal consisting of the video signal and the audio signal is obtained. Furthermore, the demodulation circuit 2 integrates the baseband signal and outputs a detected voltage. Then, the microprocessor 3 captures the detected voltage at regular intervals, and supplies the automatic fine tuning signal to the tuning circuit 1 according to the difference between the temporal average value of the DC voltage and a predetermined value in the microprocessor 3. be done. In this way, the local oscillation frequency in the tuning circuit 1 is finely adjusted, and the frequencies of the video intermediate frequency signal and the audio intermediate frequency signal are controlled to be always constant.

"Problem to be Solved by the Invention" By the way, in the MUSE system for HDTV (high-definition television) broadcasting, the video signal has approximately the same maximum amplitude on the + side and on the one side around the blanking level. During broadcasting, the carrier wave is frequency-modulated by this video signal up to the maximum allowable frequency. Therefore, in order to properly receive a MUSE television signal, it is necessary to perform automatic fine tuning based on the detected voltage in the blanking interval, but no S tuner has ever been able to perform such automatic fine tuning. Ta.

This invention was made in view of the above circumstances,
B capable of receiving non-MUSE system and MUSE system television broadcasts under normal automatic fine tuning control.
The purpose is to provide an S tuner.

"Means for Solving the Problems" The present invention provides a tuning circuit whose tuning frequency is finely adjusted by an automatic fine tuning signal, selects a high frequency signal of a selected channel, and converts it into an intermediate frequency signal; a demodulation circuit that demodulates and outputs a baseband signal as well as integrates the baseband signal and outputs a detected voltage; a switch means; the detected voltage is supplied via the switch means; and a microprocessor that outputs the automatic fine tuning signal, and an MtJSE decoder to which the baseband signal is input, at a time when a synchronization signal synchronized with frame switching in MUSE television broadcasting is output, the switching means is activated. The present invention is characterized in that it includes a timing circuit that outputs a gate signal to make it conductive, and that always outputs the gate signal when the synchronization signal is not output for a predetermined period or more.

"Operation" According to the above configuration, when receiving a television signal that is not based on the MUSE system, automatic fine tuning is performed based on the detected voltage output from the demodulation circuit. Furthermore, when receiving MUSE television broadcasting, automatic fine tuning control is always performed based on the detected voltage in the blanking section.

"Example" = 5- Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a BS tuner according to an embodiment of the present invention. This BS tuner is provided with a switch circuit 4 interposed between a demodulation circuit 2 and a microprocessor 3 for transferring a detected voltage, and a timing circuit 5 for controlling this switch circuit 4. Further, the baseband signal output from the BS tuner is supplied to the NTSC video/audio reproduction section, and is also supplied via the MUSE decoder 6 to the HDTV video/audio reproduction section. The MUSE decoder 6 is
When a MUSE baseband signal is input, a key signal synchronized with the blanking section is output. The timing circuit 4 generates a timing signal T for controlling the switch circuit 4 based on this key signal.

Next, the configuration of the timing circuit 5 will be explained. 71 is MUS
This is an input terminal to which a key signal output from the E decoder 6 is input. The input terminal 71 is grounded via a resistor 72 and connected via a coupling capacitor 73 to the base of the amplifying PNP Langstaff 4. This PNP transistor 74 has an emitter connected to a positive power supply via a resistor 75 and a collector grounded via a resistor 76.

In addition, a diode 77 and resistors 78 and 79 are connected in series between the positive power supply and ground to form a base bias circuit, and the voltage at the connection point of resistors 78 and 79 is PN.
Provided to the base of P transistor 740.

A resistor 81 (resistance value R,) and a capacitor 82 (capacitance value C7) are connected in series between a positive power source and a negative power source to form a time constant circuit. Resistor 8 in this time constant circuit
The connection point between the capacitor 1 and the capacitor 82 is grounded via an analog switch 83 which is turned on or off depending on the collector voltage of the PNP transistor 74. Further, an OR gate is configured by connecting a parallel circuit consisting of analog switches 91 and 92 and a resistor 93 in series between the positive power supply and the ground line. Here, the analog switches 91 and 92 each have a resistor 81
and the voltage at the connection point of the capacitor 82 and the collector voltage of the PNP) transistor 4, which makes it conductive or non-conductive.

The voltage at the common connection point between analog switches 91 and 92 and resistor 93 is output as timing signal T.

Next, the configuration of the switch circuit 4 will be explained. The analog switch 101 has one contact inputted with a detected voltage from the demodulation circuit 2, and the other contact connected to a time constant circuit including a resistor 102 (resistance value R,) and a capacitor 103 (capacitance value C2). The output of the time constant circuit, that is, the voltage at the connection point between the resistor 102 and the capacitor 103 is taken into the microprocessor 3 via the voltage follower circuit 104.

According to such a configuration, automatic fine tuning is performed as described below. First, when receiving NTSC television broadcasting, the MUSE decoder 6 does not output a key signal. Therefore, analog switches 83 and 9
2 are both in a non-conductive state and the analog switch 91 is in a conductive state, so that the analog switch 101 is always in a conductive state. Therefore, the detected voltage output from the demodulation circuit 2 is always supplied to the microprocessor 3 via the analog switch 101, the resistor 102, and the voltage follower circuit 104, and automatic fine tuning similar to a conventional BS tuner is performed. .

On the other hand, when receiving MUSE TV broadcasts, the second
The blanking section TB of the video signal shown in figure (a) is MU
Detected by the SE decoder 6, as shown in FIG. 2(b), OV,
During other periods, a key signal of 0.5V is output from the MUSE decoder 6. When the key signal falls from 0.5V to OV, the collector voltage of the PNPI-Rangistaft 4 rises, and the analog switches 83 and 92 immediately become conductive. As a result, the charge stored in the capacitor 82 is discharged via the analog switch 88, and the analog switch 91 becomes non-conductive.

Therefore, the analog switch 101 becomes conductive, and the detected voltage output from the demodulation circuit 2 changes to the analog switch 101.
01, resistor 102 and voltage follower circuit 104
The signal is supplied to the microprocessor 3 via.

Next, when the key signal rises from OV to 0.5V, PN
P) The collector voltage of Ranjistaph 4 falls, and analog switches 83 and 92 immediately become non-conductive. At this time, charging of the capacitor 82 is started via the resistor 81, but the analog switch 91 is still in a non-conducting state until the charging voltage reaches the threshold voltage of the analog switch 9. 101
becomes non-conductive in conjunction with the analog switch 92.

The detected voltage charged in the capacitor 103 is then supplied to the microprocessor 3 via the voltage follower circuit 104. Here, the cycle of the key signal is 1/60 second, and after the key signal falls and the capacitor 82 is discharged, the next blanking section starts and the key signal falls again. The time constant R1C1 is determined so that the capacitor 82 is not charged to the threshold voltage of the analog switch 91 within 60 seconds.

Therefore, as long as the key signal is repeatedly generated at a cycle of 1/60 seconds, the analog switch 101 will be in the conductive state only during the period when the key signal is OV, and the analog switch 101 will be in the non-conducting state during the period when the key signal is 0.5 Becomes conductive.

In this manner, when receiving MUSE television broadcasting, the detected voltage of the video signal in the blanking interval is supplied to the microprocessor 3, and automatic fine tuning is performed based on this detected voltage.

"Effects of the Invention" As explained above, according to the present invention, the effect is that normal automatic fine tuning is performed and normal reception is performed regardless of whether the received television broadcast is in the MUSE format or not. is obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a BS tuner according to an embodiment of the present invention, FIG. 2 is a time chart showing video signals and key signals when receiving MUSE television broadcasting, and FIG. 3 is a conventional BS tuner. FIG. 2 is a block diagram showing the configuration of a BS tuner. 1.--.--Tuning selection circuit, 2.--.-Returning 11 circuit,
3-=・−・Microprocessor, 4・・・・・・−
-Switch circuit, 5-......timing circuit, 6......MUSE decoder.

Claims (1)

[Scope of Claims] A tuning circuit whose tuning frequency is finely adjusted by an automatic fine tuning signal, and which selects a high frequency signal of a selected channel and converts it into an intermediate frequency signal, and demodulates the intermediate frequency signal to generate a baseband signal. a demodulation circuit that outputs a detection voltage by integrating the baseband signal and outputting a detection voltage; a switch means; the detection voltage is supplied through the switch means, and the automatic fine tuning signal is output based on the detection voltage; At the time when a synchronization signal synchronized with frame switching in MUSE television broadcasting is outputted from the outputting microprocessor and the MUSE decoder to which the baseband signal is input, a gate signal is sent to make the switching means conductive. and a timing circuit that always outputs the gate signal when the synchronization signal is not output for a predetermined period or more.