JPH0640667B2 - Television receiver - Google Patents

Description

TECHNICAL FIELD The present invention relates to a television receiver capable of receiving several kinds of television signals having different frequencies of audio intercarrier signals.

(B) Conventional technology Currently, the audio inter-carrier frequencies (hereinafter, abbreviated as SIF) of the television system of each country are 4.5MHz, 5.5MHz, 6.0M.
There are four types, Hz and 6.5 MHz, and in order to be able to automatically reproduce each of these SIF signals by the television receiver as described above, the above SIF signals are identified and detected, and the detected SIF signals are detected. The audio reproduction circuit system in the receiver must be switched so as to be compatible with the reproduction of. That is, the operation or non-operation of the SIF frequency conversion circuit provided in the reproduction system is switched or the detection characteristic of the audio detection circuit in the reproduction system is switched according to the detection output.

As a result, the SIF signal identification / detection circuit has a conventional AM
A detection type is used, and in particular, as an example of an identification and detection circuit of this type, Japanese Patent Application Laid-Open No. Sho 5 has been proposed by the applicant.
There is one disclosed in Japanese Unexamined Patent Publication No. 6-101265. That is,
In the identification circuit of this publication, each SIF signal derived by reception is gated and extracted only in the horizontal flyback pulse period,
Since the extracted SIF signal is detected by AM detection, there is an advantage that malfunction due to noise or the like is relatively unlikely to occur.

However, even the above-mentioned discrimination circuit is vulnerable to noise generated during the horizontal flyback pulse period, and in particular, when the electric field is weak, the discrimination circuit may malfunction. Also, for example, three types of SI of 5.5MHz, 6.0MHz, 6.5MHz
To obtain the discrimination output (S ₁ ) (S ₂ ) (S ₃ ) of the F signal,
As shown in FIG. 1, at least two identification circuits (A)
Since (B) must be provided, there is also a drawback that the cost becomes high.

(C) Object of the invention The present invention has been made in view of the above points, and has a simple configuration of a television receiver capable of accurately demodulating and reproducing each SIF signal with almost no fear of malfunction due to noise. The purpose is to make it possible to realize more inexpensively.

(D) Configuration of the invention The television receiver of the present invention discriminates and detects the derived audio intercarrier signal by the FM detection circuit, and reproduces the intercarrier signal by the detection output. The configuration is characterized in that the audio reproduction circuit system is switched so as to comply with.

(E) Embodiment In the embodiment of the present invention shown in FIG. 2, (1) is VIF
(Video intermediate frequency) -The inter-carrier detection circuit provided in the SIF signal processing IC (2), (3) the 5.5MHz, 6.0MHz, 6.5MHz SIF signals derived from this detection circuit Ceramic filter (4a) (4b) for extraction
A switching circuit for selectively leading to (4c), (5) a mixing circuit that receives the output signal of each filter and the output of the local oscillation circuit (6) as input, (7) a ceramic filter for 5.5 MHz,
(8) and (9) are a limiter amplifier and a voice detection (FM detection) circuit provided in the IC (2), and each of the above circuits constitutes a so-called voice reproduction circuit system (10) of the present invention. There is.

On the other hand, (11a) and (11c) are ceramic filters similar to the filters (4a) and (4c), and (12) is an FM detection IC having a limiter amplifier (13) and a quadrature type FM detection circuit (14). , (15) is the carrier tuning and 90 ° phase shift circuit, (16) is the capacitor for smoothing the FM detection output, (17) is 5.5MHz, 6.0MHz, 6.5MHz by judging the output voltage after the smoothing. A switching signal generation circuit that outputs three switching signals (Sa) (Sb) (Sc) corresponding to each SIF signal of MHz.
An IF signal identification and detection circuit system (20) is configured.

Here, the FM detection IC (12) may be, for example, a television sound demodulation device such as μpc1391H manufactured by NEC Corporation, but in this embodiment, the detection characteristic is particularly third.
As shown by the solid line in Fig. (A), the carrier tuning and 90 °
A major feature is that the phase shift circuit (15) is selected.

Therefore, in the real image machine of FIG. 2, when the 6.5 MHz SIF signal is derived from the intercarrier detection circuit (1), the SIF signal is output from the ceramic filter (11).
It is input to the FM detection IC (12) through (a) and detected, and the detected output is smoothed by the capacitor (16), so that the output corresponding to approximately Va in FIG. The voltage is obtained. Similarly, when a 6.0 MHz SIF signal is input, an output voltage of approximately Vc is obtained at point P. Also 5.5M
When the SIF signal of Hz is output from the intercarrier detection circuit (1), the SIF signal is not input to the IC (12), so that the substantial detection operation is not performed, and the output of about Vb is output to the point P. The voltage is obtained.

Here, 5.5 MHz is the linear detection range (Va-V) of FIG. 3 (a).
It is set to be outside (between c) with the SI of the main television broadcasting in the television receiver of the present embodiment.
Since F is 5.5MHz, its main 5.5M even in a weak electric field.
This is so that the SIF signal of Hz can be accurately demodulated and reproduced. That is, the FM detection characteristic of the IC (12) may be set as shown by the solid line in FIG. 3 (b), but in that case, if the detection characteristic deteriorates as shown by the broken line in the same figure in a weak electric field, 5.5 This is because the output voltage at MHz becomes Vc '(Vc at normal time), which cannot be accurately identified. On the other hand, the above-mentioned third
When set as shown by the solid line in Fig. (A), even if this detection characteristic deteriorates as shown by the broken line in the same figure when the electric field is weak, the output voltage at 5.5 MHz is still Vb or less, and it can be accurately identified. Because you can. Further, in the case of FIG. 3 (a), since the linear detection range can be narrowed, the deterioration itself of the detection characteristics as described above can be improved.

If a filter for 5.5 MHz is further connected in parallel to the filters (11a) and (11b), the reliability of the identification operation for the 5.5 MHz SIF signal can be further improved.

Next, the switching signal generation circuit (17) operates as shown in FIG.
In order to discriminate between b and Vc with a margin, a switching signal Sa which becomes “low” only when the output at the point P is equal to or higher than the third (a) Vs ₂ (at 6.5 MHz) and Vs _{2 to} Vs ₁ Hour (at 5.5 MHz)
Only the switching signal Sb that becomes "low" and the switching signal Sc that becomes "low" only when Vs ₁ or less (at 6.0 MHz) are output. Then, the switching circuit (3) corresponds to each of the switching signals Sa, Sb, Sc and a, b,
Switch to position c. The oscillation circuit (6) stops the oscillation operation when Sb of the switching signal is “low”,
Oscillates at 1 MHz when is low, and oscillates at 0.5 MHz when both Sa and Sb are high.

Therefore, 6.5MHz from the intercarrier detection circuit (1)
SIF signal passes through the filter (4a) to the mixing circuit (5)
Is mixed with the 1 MHz oscillation signal to be converted into a 5.5 MHz SIF signal. Similarly, the 6.0 MHz SIF signal is mixed with the 0.5 MHz oscillation signal in the mixing circuit (5) and converted into a 5.5 MHz SIF signal. In addition, the 5.5 MHz SIF signal is led out as it is through the mixing circuit (5) which acts as a mere amplifying circuit at this time. Then, each 5.5 MHz SIF signal passes through the ceramic filter (7) and is input to the IC (2) for voice detection.

FIG. 4 shows the details of the switching signal generating circuit (17). Each of the transistors (Q ₁ ) to (Q ₈ ) in the drawing is designed to perform a switching operation. And
The base resistances (R ₁ ) to (R ₄ ) of Q ₁ and Q ₂ are the third
Vs ₁ × R ₂ / (R ₁ +) where Vbe is the rising voltage between the base and emitter with respect to Vs ₁ and Vs _{2 in} FIG.
R ₂ ) = Vbe, Vs ₂ × R ₄ / (R ₃ + R ₄ ) = Vb
Selected as e. Therefore, the third input terminal (Si)
When Vc in the figure (a) is input, Q ₁ , Q ₂ , Q ₅ ,
When Q ₆ and Q ₈ are off and Q ₃ , Q ₄ and Q ₇ are on, only the switching signal Sc is “low” and the other switching signals Sa,
Sb goes "high". Similarly, when Vb is input, only Sb is "low", and when Va is input, only Sa is "low".

On the other hand, FIG. 5 shows the details of the oscillator circuit (6). This circuit basically comprises a grounded Colpitts oscillator and switching transistors (Q ₁ ) (Q ₂ ), and a switching signal S from the circuit of FIG. 4 is applied to a terminal (Sa).
a is applied, and the switching signal Sb is applied to the terminal (Sb). And when S1b is "low" (at 5.5 MHz), the switching transistor (Q ₁₎ a Sa is "high" even because turned on, is supplied at all power to the oscillation transistor (Q ₃₎ Without oscillation. Also, when Sc is “low” (at 6.0 MHz),
Since Sa and Sb are both “high”, the transistor (Q ₁ ) is on and the transistor (Q ₂ ) is off, the high level Sb is supplied as the power source of the oscillation transistor (Q ₃ ). It operates and oscillates at 0.5 MHz by the coils (L ₁ ) (L ₂ ) and capacitors (C ₆ ) (C ₇ ). Furthermore, when Sa is "low" (6.
Even at 5 MHz), Sb is "high". At this time, since the transistor (Q ₁ ) is off and the transistor (Q ₂ ) is on, the coil (L ₁ ) is substantially disconnected, and thus 1 MHz
It oscillates at z. At that time, at the time of this 1 MHz oscillation, the base potential of the oscillation transistor (Q ₃ ) is oscillated by 0.5 MHz because the power supply voltage (+ Vcc) is applied through the resistor (R ₂₁ ) and the diode (D ₁ ). This is higher than the time, thereby making the oscillation signal intensities during both oscillations substantially equal.

In the embodiment described above, each SI having a different frequency is
Although the F signal is frequency-converted to 5.5 MHz for voice detection, the detection characteristic of the voice detection circuit can be switched for each SIF signal to perform linear detection.
In this case, the detection characteristics may be switched by the above-mentioned switching signals Sa, Sb, Sc.

(F) Effect of the Invention According to the television receiver of the present invention, when SIF signals having different frequencies are demodulated and reproduced, the SIF signals are discriminated and detected by FM detection. Compared with the method using AM detection, malfunction due to the influence of noise is extremely unlikely to occur. Moreover, since a large number of SIF signals can be discriminated and detected by a single FM detection circuit, there is an advantage that the number of constituent components of the discrimination circuit is small and the circuit can be realized at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conventional intercarrier signal identification and detection circuit, FIG. 2 is a block diagram showing a schematic configuration of a main part of an embodiment of a television receiver according to the present invention, and FIG.
(a) and (b) are characteristic diagrams for explaining the operation, and FIGS. 4 and 5 are circuit diagrams showing details of the main part of the above embodiment. (10) ...... Voice reproduction circuit system, (20) …… Identification detection circuit system.

Claims (2)

[Claims] 1. A television receiver capable of receiving three or more types of television signals having different frequencies of the voice intercarrier signal, the received voice intercarrier signal being detected by an FM detection circuit. In a television receiver configured to identify and detect a carrier signal and switch the audio reproduction circuit system to match the reproduction of the intercarrier signal by the detection output, the detection characteristic of the FM detection circuit is the center of the characteristic. Has a linear detection range with a linear detection characteristic that is symmetric with respect to the output point of
Outside the linear detection range, the output is the same as that of the central output point, and further, the FM detection circuit outputs the signal having the highest (minimum) frequency and the intermediate frequency among the three or more types of the intercarrier signals to the linear detection. A television receiver set such that a main signal having the lowest (highest) frequency falls within the range and is outside the linear detection range. 2. The detection circuit is configured so that only signals other than the highest or lowest frequencies of the voice intercarrier signal are input through respective dedicated filters. The television receiver according to item 1.