JPS643391B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement of a multi-system color television receiver capable of receiving color television broadcasts of different systems such as the PAL system and the NTST system.

(Prior Art) As is well known, a multi-system color television receiver has a circuit configuration as shown in FIG. Therefore, the audio trap and SIF input bandpass filter corresponding to each broadcasting system are switched. This audio carrier frequency detection circuit m has a circuit configuration as shown in FIG. Currently known broadcasting systems have audio carrier frequencies of 4.5MHz, 5.5MHz, 6.0MHz and
There are four of 6.5MHz. Here, the NTSC system (audio carrier frequency 4.5MHz, color subcarrier frequency
3.58MHz) and the PAL/SECAM method (audio carrier frequency 5.5MHz, color subcarrier frequency 4.43MHz) will be described.

The detection output signal from the VIF detection output circuit C is passed through an audio carrier bandpass filter (hereinafter referred to as audio BPF).
) is added to 1. For this audio BPF1, the audio carrier frequency of NTSC system is 4.5MHz.
The color subcarrier frequency of PAL/SECAM system is 4.43M
A bandpass filter with a center frequency of 5.5MHz is used because the frequency is very close to Hz and misjudgment is likely to occur.
Therefore, only the 5.5MHz audio carrier
Passes BPF1. Next, the signal that has passed through this audio BPF 1 is amplified by a linear amplifier 2 and applied to a peak detection circuit 3. If the input signal is a carrier with an audio carrier frequency of 5.5MHz, a peak detection output will be generated when peak detection is performed, but if the input signal is a 4.5MHz audio carrier, that is, an NTST input signal, the VIF detection output will be: audio
It cannot pass through BPF1, and no peak detection output is generated even if peak detection is performed. Therefore, by inputting the output of this peak detection circuit 3 to a comparator 4 and setting a certain threshold level, the detection output circuit 5 can determine whether it is a 5.5MHz audio carrier or not.
In other words, a 4.5MHz detection output is obtained here.

Now, the multi-system color television receiver shown in FIG. 1 will be explained. A tuner a selects a television signal of a necessary channel from among the television signals received by the antenna. This selected television signal is input to filter b, which imparts the necessary selectivity to the frequency characteristics of the signal. Looking at the relationship between the frequency characteristics of this television signal and the color subcarrier and video carrier, the color subcarrier frequency and the video carrier frequency are set at a frequency -6 dB from the maximum gain level of the frequency characteristics. The difference between the color subcarrier frequency and the video carrier frequency is 3.58MHz for the NTSC system and 4.43MHz for the PAL/SECAM system.
The NTSC format is narrower, so when the input television signal is an NTSC format signal, a trap circuit h is inserted to change the filter characteristics to PAL.
It has a narrower band than the input signal of the SECAM method. The signal passed through filter b is
The signal is input to the VIF circuit c, where video detection is performed and an audio carrier is also obtained as an intercarrier beat.

The VIF output is input to the audio carrier frequency detection circuit m, and the audio carrier frequency of the input signal is 4.5M.
Hz or 5.5MHz is detected.
Here, as mentioned above, a center frequency of 5.5 MHz is used as the audio BPF 1 of the detection circuit m, and when the comparator 4 output is obtained, the detection circuit m output is high level, and when the comparator 4 output is not obtained, the detection circuit m output becomes low level. Depending on the output of the audio carrier frequency detection circuit m, the switch connections at the front stage of the bandpass filters d and e are changed over. In other words, when the detection circuit m output is high level, 5.5MHz bandpass filter d is selected, and when it is low level, 4.5MHz bandpass filter d is selected.
Hz bandpass filter e is selected. Therefore, one of the bandpass filters d and e is selected according to each input television signal, and the outputs of the bandpass filters d and e are input to the SIF circuit f. Then, the SIF circuit f performs audio detection, and this audio signal is amplified by the low frequency amplification circuit g to drive the speaker. The output of the audio carrier frequency detection circuit m is also used as a control signal for the switches at the front stage of the audio traps i and j, and when the output of the detection circuit m is at a high level, the frequency is 5.5M.
Hz audio trap i, 4.5MHz when low level
Audio trap j is selected. As a result, VIFC
A composite video signal with the audio carrier component attenuated from the output is obtained as the audio trap i, j output.
The outputs of the audio traps i and j are input to a video amplification circuit k, a SECAM decoder q, bandpass filters o and p, a color subcarrier frequency detection circuit n, and a sync separation circuit w, respectively.

The frequency of the color subcarrier of the composite video signal inputted to the color subcarrier frequency detection circuit n is detected, and when the color subcarrier of 3.58 MHz is detected, the trap circuit h is set to the ON state.

The composite video signal input to the synchronization separation circuit w is
Vertical synchronization signal is separated and vertical frequency detection circuit x
The vertical frequency is detected at . This vertical frequency is 50Hz for PAL/SECAM format and 50Hz for NTSC format.
It is 60Hz.

Based on the output of this vertical frequency detection circuit
1 and deflects the electron beam in the CRT.

The composite video signal is also input to the SECAM decoder q, which provides a color difference output and determines whether the input television signal is a SECAM format signal.

The outputs of the color subcarrier frequency detection circuit n, SECAM decoder q, and vertical frequency detection circuit x are input to a gate circuit v, and gate outputs that realize four types of control are output according to the outputs of these three circuits. Ru.

First, when the vertical frequency is 50Hz and the SECAM decoder q output is a signal indicating the SECAM method, the color difference output signal of the SECAM decoder q is supplied with the video signal amplified by the video amplification circuit k. is supplied to the matrix circuit.

Second, when the vertical frequency is 50Hz and the SECAM decoder q output is a signal indicating that the SECAM method is not used, the 4.43MHz bandpass filter o and
The PAL color difference output obtained via the PAL decoder r is supplied to the matrix circuit.

Third, when the vertical frequency is 60Hz and the color subcarrier frequency is 4.43MHz, the output of the 4.43MHz bandpass filter o is supplied to the NTSC decoder s, and the oscillation signal of the 4.43MHz crystal oscillator t is sent to the NTSC decoder. The output of this NTSC decoder s is supplied to the matrix circuit as a color difference output.

And finally, when the vertical frequency is 60Hz and the color subcarrier frequency is 3.58MHz, the output of the 3.58MHz bandpass filter p is supplied to the NTSC decoder s, and the output of the 3.58MHz crystal oscillator u is used as the color difference output. Supplied to the matrix circuit.

Primary color signals are formed from the color difference outputs in the matrix circuit and displayed on the CRT.

(Problems to be Solved by the Invention) In the above-mentioned conventional configuration, the trap circuit h coupled to the filter b has a color subcarrier frequency detection circuit n whose input color subcarrier frequency is 3.58MHz. When it is determined that this is the case, the filter is turned on, and the frequency characteristics of filter b are made to have a narrow band. Therefore, in the initial state, filter b has wideband characteristics that allow it to pass signals of any broadcasting system. Then, the output of filter b is an NTSC television signal (color subcarrier frequency: 3.58MHz, audio carrier frequency: 4.5M), which provides a relatively high level signal.
Hz) 920KHz beat component should also be at a high level. One frequency at which this 920KHz beat component is generated is 5.42MHz. This 5.42M
The Hz beat component is the audio signal with a center frequency of 5.5MHz that constitutes the audio carrier frequency detection circuit m.
The signal passes through BPF1, and a detection output is obtained as the output of comparator 4. In other words, although the input television signal is an NTSC television signal (color subcarrier frequency 3.58MHz, audio carrier frequency 4.5MHz), it is a PAL/SECAM television signal (color subcarrier frequency 4.43MHz,
Based on this false detection, bandpass filters d, e and audio trap circuits i, j are selectively switched, and as a result, normal audio and images cannot be obtained. become.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a multi-system color television receiver that does not misjudge the broadcast system.

(Means for Solving the Problems) In order to achieve the above object, the multi-system color television receiver of the present invention includes an audio BPF that passes only the first audio carrier frequency component from the VIF detection output, and an audio BPF that passes only the first audio carrier frequency component from the VIF detection output. A peak detection circuit that performs peak detection to which the BPF output signal is applied; a sync separation circuit that separates and outputs a sync signal from the input television signal; and a sync signal that forms a sync signal partial extraction pulse in synchronization with the output of this sync separation circuit. Equipped with a constant current source that supplies a constant current for driving to a partial sampling pulse generation circuit and a peak detection circuit, the constant current source is activated only during the period of the synchronous signal portion by the synchronous signal partial sampling pulse
This is the ON state.

(Function) With the above configuration, the frequency discrimination of the audio carrier frequency is performed on the color subcarrier and, in turn, on the synchronization signal portion without a beat component due to the audio carrier and color subcarrier. As a result, erroneous discrimination of the audio carrier frequency due to the beat component does not occur, and the broadcast system can be accurately discriminated.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram showing the configuration of a multi-system color television receiver according to an embodiment of the present invention, and FIG. 4 is a circuit diagram of the main parts thereof. In FIG. 3, the same components as those shown in FIG. 2 are given the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 3, w is the synchronization separation circuit shown in FIG. A synchronizing signal partial sampling pulse is created in which a pulse is output only for a portion of the signal. This pulse generation circuit 6
A synchronizing signal partial extraction pulse from the synchronous signal is applied to the switch 7, and the constant current source 8 of the peak detection circuit 3 is controlled to be on/off. As a result, this peak detection circuit 3 is set to operate in the ON state only for the synchronization signal portion and performs peak detection.

On the other hand, the peak detection circuit 3 is set to an OFF state for a portion of the color burst signal and the color signal, and the beat component of the audio carrier and color subcarrier causes erroneous discrimination of the audio carrier frequency during the initial operation of the television receiver. will no longer occur.

Next, a specific circuit example of the audio carrier frequency detection circuit shown in FIG. 3 will be explained with reference to FIG. 4.

First, in order to improve the detection accuracy of the audio carrier frequency detection circuit, the output of VIF circuit c is set at the center frequency.
The signal is input to a trap circuit 9 with a frequency of 4.5 MHz, and then to a band pass filter 10 with a center frequency of 5.5 MHz. Therefore, as the output of the audio BPF 1, the 4.5 MHz frequency component, that is, the audio carrier component of the NTSC television signal, is attenuated compared to that shown in FIG. In the initial operating state of the television receiver, as mentioned above, the frequency characteristics of filter b are broadband, and this 4.5MHz
Without the trap circuit 9, the beat component (5.42 MHz component) of the NTSC television signal would also be obtained at a relatively high level as the output of the audio BPF 1.
Therefore, by inserting this 4.5MHz trap circuit 9, it is possible to improve the accuracy of determining the audio carrier frequency.

The output of the audio BPF 1 is input to the base of a transistor Q ₇ of a differential amplifier composed of transistors Q 7 and Q ₈ that constitute _a linear amplifier 2 . The 5.5MHz audio carrier component amplified by this linear amplifier 2 is transmitted through the emitter follower transistor Q ₁₁ ,
It is input to the bases of transistors Q ₂₁ and Q ₂₄ and the bases of transistors _{Q 22 and} Q ₂₃ through Q 12, respectively. On the other hand, this 5.5MHz audio carrier component is
It is input to the bases of transistors Q 25 _and Q ₂₆ through a level shift diode inserted between the emitters of transistors Q ₁₁ and Q ₁₂ and the collectors of transistors Q ₁₄ and Q ₁₅ forming a constant current source. Note that the operation will be described here assuming that the transistors Q ₁₄ , Q ₁₅ , and Q ₁₆ that constitute the constant current source are in the on state. Transistors Q ₂₁ , Q ₂₂ ,
Q ₂₃ , Q ₂₄ and transistors Q ₂₅ , Q ₂₆ constitute a multiplier. This multiplier performs a square operation on the input signal. When the input signal to this multiplier becomes large, the collector currents of transistors Q ₂₁ and Q ₂₄ become large, while the collector currents of transistors Q ₂₂ and Q ₂₃ become small. Transistor Q ₂₁ ,
The collector currents of the transistors Q ₂₁ and Q ₂₃ are current mirrored to the transistor Q _{19 by the transistor Q 18 whose} collector is coupled to the collector of Q ₂₃ , and the collector currents of the transistors Q ₂₂ and Q ₂₄ are reduced. A capacitor is connected to the connection point between the collector of transistor Q ₁₉ and the base of transistor Q ₂₈ . When the charging potential of this capacitor, that is, the base potential of transistor Q ₂₈ rises and becomes higher than the base potential of transistor Q ₂₉ , transistor Q ₂₉ is turned on. Transistor Q ₂₉
When Q30 turns on, transistor _Q30 also turns on. A low level signal indicating that the input signal is a 5.5MHz audio carrier component is output from the collector of transistor _Q30 . That is, the detection output is obtained using the base potential of the transistor _Q29 as a reference level.

Next, the transistors constituting the peak detection circuit 3
The current source of the multiplier consisting of Q ₂₁ to _{Q 26} and the configuration for driving it will be explained.

The horizontal synchronization signal obtained by the synchronization separation circuit w shown in FIG. 1 is input to the base of the transistor _Q1 constituting the sampling pulse generation circuit 6, and the transistor _Q1 is turned on during the horizontal synchronization signal period. Note that transistor Q ₂ constitutes a differential amplifier circuit with transistor Q ₁ , and transistors Q ₃ , Q ₄ ,
Q ₅ constitutes its current source. transistor
When Q ₁ is turned on, collector current flows and a voltage is generated in the load connected to the collector of transistor Q ₁ . The voltage developed across the load turns on transistor _Q17 during the horizontal synchronization signal period. At this time, transistor _Q1 to transistor
The signal applied to _Q17 is a pulse signal at H level during the horizontal synchronization signal period, and this is called a synchronization signal partial sampling pulse. Now, when the horizontal synchronizing signal period transistor _Q17 is turned on by the synchronizing signal partial sampling pulse, the transistor Q17 is turned on in conjunction with this.
The constant current source 8 consisting of Q ₁₆ is also turned on, and for the first time, the transistors Q ₂₁ to _{Q 26} become operable as multipliers. As described above, this audio carrier frequency detection circuit discriminates the frequency of the audio carrier only during the horizontal synchronization signal period.

As described above, according to this embodiment, the constant current source 8 of the peak detection circuit 3 is controlled to turn on and off without providing a switch function for separating and coupling the transmission path in the signal transmission path for voice carrier frequency discrimination. By performing peak detection only during the horizontal synchronization signal period,
Even in the initial operating state of the television receiver,
Misjudgment of the audio carrier frequency due to beat components of the audio carrier and color subcarrier does not occur. Furthermore, since noise associated with switching does not enter the peak detection circuit, malfunctions do not occur. As a result, the audio carrier frequency can be accurately determined.

(Effects of the Invention) According to the present invention, the constant current source that supplies the drive current to the peak detection circuit is controlled on/off, and peak detection is performed only during the synchronization signal period, without providing a switching means before the peak detection circuit. As a result, the audio carrier frequency can be accurately determined without noise contamination due to switching and malfunctions caused by the beat component of the audio carrier in the burst signal or color subcarrier.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a multi-system color television receiver, FIG. 2 is a block diagram of a conventional audio carrier frequency detection circuit, and FIG. 3 is a block diagram of an audio carrier frequency detection circuit according to the present invention. , FIG. 4 is a circuit diagram showing a specific example of the audio carrier frequency detection circuit shown in FIG. 3. 1...Audio carrier band pass filter, 2...
...Linear amplifier, 3...Peak detection circuit, 4...
Comparator, 5...detection output circuit, 6...synchronous signal partial extraction pulse generation circuit, 8...constant current source.

Claims (1)

[Claims] 1. A multi-system television receiver that switches circuits within the receiver in response to multiple broadcasting systems,
An audio carrier bandpass filter that passes only the first audio carrier frequency component from the VIF detection output, a peak detection circuit that performs peak detection to which the output signal of the audio carrier bandpass filter is applied, and a synchronization signal from the input television signal. a synchronous signal separation circuit that separates output; a synchronous signal partial sampling pulse generation circuit that forms a synchronous signal partial sampling pulse in synchronization with the output of the synchronous separation circuit; and a constant current source that supplies a driving constant current to the peak detection circuit. A multi-system color television receiver, characterized in that the constant current source is turned on only during the period of the synchronizing signal portion by the synchronizing signal partial sampling pulse.