JPS5830289A - Sound if circuit of television set - Google Patents

Abstract

PURPOSE:To constantly maintain the frequency of the 2nd sound IF signal in the separate carrier system, by linking a local oscillator frequency for frequency conversion which is necessary to obtain the 2nd sound IF signal with the video IF. CONSTITUTION:A video IF signal from a tuner 2 is amplified by an amplifier circuit 7 and supplied to a video IF tuning amplifier circuit 8 and a video detecting circuit. The tuning amplifier circuit 8 safely removes the sound IF signal and controls the oscillation frequency of a local oscillating circuit 6. The sound IF signal from the tuner 2 is extracted and amplified at another tuning amplifier circuit 3 and converted into the 2nd sound IF at a mixing circuit 4 after it is mixed with the output signal of the local oscillating circuit 6. The 2nd sound IF is given to an FM detecting circuit after it is amplified at the 2nd sound IF amplifier circuit 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio intermediate frequency circuit in a television receiver aircraft.

Television radio waves consist of a video carrier wave and its video carrier wave4.
The bite carrier wave is 58.75 MHg due to frequency conversion in the tuner.
The g1 audio carrier wave is frequency converted to a 54.25 MHz intermediate frequency signal. There are an intercarrier method and a separate carrier method as methods for obtaining audio signals from these intermediate frequency signals.

The intercarrier method inputs the frequency-converted rain intermediate frequency signal to an amplitude detector installed near the final stage of the video intermediate frequency circuit, thereby detecting the difference (5
4,5MH of 8,75MHz -54,25MHH)
This is a method of obtaining an audio signal by extracting the audio second intermediate frequency signal of frequency g and subjecting it to FM detection. However, with this method, the 58.75 MHM Eirin intermediate frequency signal component generates noise beats (particularly when dealing with audio multiplex signals, sub-audio), and the S/N deteriorates significantly. There is a serious problem.

On the other hand, in the separate carrier method, a low Q filter circuit extracts an audio intermediate frequency signal of 54 MHz or 25 MHz from the output of the tuner, and converts this audio intermediate frequency signal into a second audio intermediate frequency signal of, for example, 10 MHz or 7 MHz. Then, the second audio intermediate frequency signal is amplified by a high-Q amplifier circuit and inputted to an FM detection circuit, thereby obtaining an audio signal. However, although this method does not have the problem of generating buzz sounds and buzz beats as compared to the intercarrier method described above, it does not have the problem of generating a buzz sound or buzz beat because the audio intermediate frequency signals of 54 and 25 MHz are processed independently to obtain the audio signal. If the frequency conversion operation in the tuner becomes unstable and it is no longer possible to obtain an accurate audio intermediate frequency signal of 54 or 25 MHz, the frequency of the second audio intermediate frequency signal obtained by further frequency conversion will shift and the sound will be returned. It may not come out. This tends to occur due to temperature changes or changes over time. Furthermore, when the vibrations of the speaker are transmitted to the tuner, the local oscillation frequency of the tuner is shifted due to the vibrations, resulting in J)/% ringing in which no sound is produced. Furthermore, in order to achieve a high S/N ratio, it is necessary for K to suppress the ripple component of the power supply voltage as much as possible.

The present invention has been made in view of the above-mentioned points, and is based on the separate carrier method, in which a local oscillation frequency for frequency conversion for obtaining a second audio intermediate frequency signal is linked to the Eirin intermediate frequency, Therefore, it is an object of the present invention to provide an audio intermediate frequency circuit that solves all of the above-mentioned problems.

Hereinafter, the present invention will be explained by examples. FIG. 1 is a block diagram showing one embodiment of the system, in which TV radio waves arriving at an antenna 1 are amplified at a tuner 2 and K
58, '75MHz Eirin intermediate frequency signal, 54, 2
The frequency is converted to a 5MH2 audio intermediate frequency signal. The audio intermediate frequency signal has a center frequency of 54 and 25M.
The H2+ low Q audio intermediate frequency tuning amplifier circuit 3 extracts and amplifies the signal from the Eirin intermediate frequency signal, and the mixing circuit 4 converts the frequency to a second audio intermediate frequency of 4.5 MHts to facilitate FM detection. , which is further amplified by the second audio intermediate frequency amplification circuit 5 and inputted into the FM detection circuit. In this case, frequency conversion is performed using a 58.75 MHz frequency signal from the local oscillation circuit 6. The above is the configuration of a normal separate carrier system.

7 is Eirin intermediate frequency amplification circuit, here 58
, 75 MHsa are amplified, and the audio intermediate frequency signal is attenuated by a trap. The output of the video intermediate frequency amplification circuit 7 reaches the video intermediate frequency tuning amplification circuit 8 and the bite detection circuit. This Eirin intermediate frequency tuned amplification circuit 8 is a circuit for completely removing the audio intermediate frequency signal, and has a center frequency of 58 and 75 MH.
It includes a tuning circuit with high DQ.The output signal from this intermediate frequency tuning amplifier circuit 8 is applied to the local oscillation circuit 6 to control its oscillation frequency.

In the above, when normal, tuner 2 outputs 54, 2
A 5 MHz audio intermediate frequency signal and a 58.75 MH1 Eirin intermediate frequency signal are output, and the output side of the mixing circuit 4 receives the 5 8 , 75 MHz oscillated by the local oscillation circuit 6 and the audio intermediate frequency signal (54, 25 MHz). ), a second audio intermediate frequency signal of 4 and 5 MHsi appears.

Here, for some reason, the local oscillation frequency of the tuner shifts by, for example, I MHts, and the audio intermediate frequency becomes 55.
, 25 MHz, and if the local oscillation frequency is fixed at 5 8 , 75 MHz, the signal output from the mixing circuit 4 will be the difference component between the two signals, 3 , 5 MHz.
2, the 4.5 MHz VC is tuned in advance and the amplification in the second audio intermediate frequency amplification circuit 5 becomes insufficient or zero and no sound is produced (conventionally), but in this embodiment, the local oscillation circuit 6 is controlled by the output from the Eirin intermediate frequency tuned amplifier circuit 8, and the output of the Eirin intermediate frequency amplifier circuit 8 becomes a 59.75 MHsi signal due to the IMHz deviation of the local oscillation frequency of the tuner. , 75MHz acts on the local oscillation circuit 6, and a signal with the same frequency as that signal is input to the mixing circuit 4, and the signal of 4.5MHz (59,75MHz
A second audio intermediate frequency signal of 55.25 MHg) can now be obtained. Therefore, there are no problems with Part 4, 5MHM.
The second audio intermediate frequency signal is transmitted to the second audio intermediate frequency amplification circuit 5.
The signal is amplified to a predetermined level and normal operation is performed.

FIG. 2 shows a specific circuit of the local oscillation circuit 6. Constants are set so that a 58.75 MHz signal oscillates internally, and the oscillation output level is the output level of the Eirin intermediate frequency tuned amplifier circuit 8. It is set to be smaller than. Therefore, when the output frequency of the Eirin intermediate frequency tuning amplifier circuit 8 deviates from 58.75 MHz, that output is dominant and is input to the mixing circuit 4.

In other words, Figure 2 shows an example of an injection type oscillation circuit.
The basic oscillation frequency formed by the transistor Q1 oscillates at 58.75 MHg, which is equal to the video intermediate frequency. The oscillation circuit 6 and the Eirin intermediate frequency tuned amplifier circuit 8 are coupled by heating the coupling capacitor C1, and the oscillation frequency of the oscillation circuit 6 is controlled and locked to the Eirin intermediate frequency.

In the above explanation, the output of the Eirin intermediate frequency tuned amplifier circuit 8 is applied directly to the local oscillation circuit 6, but it is also possible to use a Paris cap in the local oscillation circuit 6 as one of the elements that determines the oscillation frequency. , while converting the output frequency signal of the video intermediate frequency tuning amplifier circuit 8 into a DC voltage signal and applying the voltage signal to the varicap.
It is also possible to control the oscillation frequency of the local oscillation circuit 6 by this. Alternatively, it is also possible to use a PLL circuit to set the frequency signal obtained from the Eirin intermediate frequency tuned amplifier circuit 8 as a reference frequency and lock the oscillation frequency of the local oscillation circuit 6 to that frequency signal.

As described above, according to the present invention, since the beats of the video intermediate frequency signal and the audio intermediate frequency signal are not taken, there is no buzz sound or buzz beat, and the frequency of the audio intermediate frequency signal is always kept constant. Therefore, there is no need to worry about no sound being produced, and the advantages of the separate carrier method and the intercarrier method can be satisfied at the same time.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention, and FIG. 2 is a specific circuit diagram showing an example of the local oscillation circuit in FIG. 1.

Claims (6)

[Claims] (1) In the audio intermediate frequency circuit that extracts the audio intermediate frequency signal from the signal output from the tuner, converts the frequency of the signal into a lower tX2 audio intermediate frequency signal, and then sends it to the KFM detection circuit, An audio intermediate frequency circuit for a television receiver aircraft, characterized in that the local oscillation frequency is changed in conjunction with fluctuations in a video intermediate frequency. (2) The audio intermediate frequency circuit in a television receiver aircraft according to claim 1, wherein the local oscillation frequency is locked to the Eirin intermediate frequency. (3) The local oscillation frequency is changed by a pari cap, and the pari cap is controlled by a DC voltage corresponding to the video intermediate frequency. Audio intermediate frequency circuit in the television receiver set forth in Section 2. (4) The local oscillation frequency is controlled by a PLL circuit that uses the video intermediate frequency as a reference frequency.
An audio intermediate frequency circuit in a television receiver according to claim 1, characterized in that the audio intermediate frequency circuit comprises: (5) The local oscillation frequency is oscillated by a local oscillation circuit, and a video intermediate frequency signal having a signal level higher than the signal level of the local oscillation frequency is applied to the internuclear oscillation circuit. An audio intermediate frequency circuit in a television receiver aircraft according to claim 1. (6) The audio intermediate frequency circuit in a television receiver aircraft according to claim 5, wherein the local oscillation frequency is a stable video intermediate frequency.