JPS6019409Y2 - television receiver - Google Patents

Description

[Detailed description of the invention] This invention relates to a television receiver, and the performance is greatly improved by focusing on the arrangement of the W amplifier, synchronous detector, and audio trap in the VIP section of the television receiver. It is an object of the present invention to provide a television receiver that can be improved in width.

Conventionally, in a configuration that uses carrier extraction type synchronous detection as the detection means, just by inserting an audio trap of about 20 dB between the IF amplifier and the tuner, it is possible to achieve the same performance as diode detection (with respect to 920K H2 beats). It was thought that it could be obtained.

However, the P/S ratio (video and sound signal strength ratio) on the image sending side
varies from about +6 to -20 dB, the degree of modulation of the sound tends to be overmodulated, and the sound also appears in areas that are away from the trap, and furthermore, with this detection method, 4.5MHz
z is output as is and has a 4.5MHz output that is higher than conventional ones (with diode detection, the depth of the audio trap is more than 5Ω), so it enters the chroma circuit without being sufficiently attenuated by the subsequent 4-5MHz) wrap. A problem has arisen in which a beat with 3.58 MHz is generated, eventually resulting in 920 KHz interference.

FIG. 1 shows a conventional configuration diagram, in which 1 is an RF amplifier, 2 is a mixer, 3 is a local oscillator, 4 is a VIP filter, 5 is a W amplifier, 6 is a VIF' filter, 7 is a detector, and terminals Audio and video signal components are extracted from a and b, respectively.

FIG. 3 shows a specific example of the circuit shown in FIG. 1, where c and d are W signal input terminals, and transistors Q3. It is connected to the base of Q and is amplified here.

Diode Q5. The AGC voltage is applied to Q6, and the gain is controlled here.

Transistor Q3. The collector output of Q passes through the emitter follower transistor Q2 and is connected to DC by the capacitor C8.
It is cut and enters the base of the emitter follower transistor Q7 again.

Here, the bias voltage is applied to the resistor r7. It is supplied through r8.

The emitter output of transistor Q7 is connected to one side of the emitter output of transistor Q9. One differential amplifier is made up of QIO, and the other is made up of transistors Q□5°Ql6.

Q8 is an emitter follower transistor, but it is a bias circuit provided symmetrically to give the same bias as transistor Q7, and C□ is a bias capacitor.

The differential amplifier of transistor Q159 Ql(3) is a tuned amplifier having Ll?C2 tuned to the video carrier wave as a load, and its collector output has a certain Q characteristic around the video carrier wave.

Q17t Ql8 are diodes that act as limiters,
This is for removing the modulation component from the collector output of the transistor Qist Ql6 to produce a pulse output.

The resistor s□q rts is the collector load of the transistor Qis*QlB, and this connection point is connected to the power supply.

Q□99 Q20 is an emitter follower transistor that connects the video carrier outputs of opposite polarities from the transistors Q□5v Ql6 to the transistor Q11? Ql□ and Q13t are supplied to the base of Ql4, respectively.

On the other hand, differential amplifier Q9. The collector of Qlo is connected to the emitters of transistors Q□□, Q□2 and transistor Qi3.
The amplified outputs are connected to the emitters of transistors Q□1. Q1゜v Ql3. Q
This is a circuit that performs switching operation and detection using l4.

In other words, transistor Q□1゜Q1□v Q13t Q□
The signal coming from the 4 emitters is subjected to switching detection using pulses at the video carrier frequency at the base.

This is a detection circuit using a double-balanced differential amplifier.

This is multiplicative detection, and although the video carrier frequency and the color and sound carrier beats are obtained, the color and sound carrier beats, that is, 920 KHz, are essentially not detected.

Therefore, like diode detection, 50
It was thought to have an advantage in that there was no need to attenuate the sound carrier by more than dB.

However, since the Q of the tuned circuit of Ll and C2 is finite,
In reality, this tuning circuit has a 54.25M color carrier wave of 55.17MHz in addition to a 58.75MHz video carrier wave.
A sound carrier wave of Hz is generated.

As a result, even with the double-balanced synchronous detector, 92
A beat signal of 0 KHz will be generated.

The present invention aims to prevent such 920 KHz beats from appearing, and one embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, 1 to 5 indicate the same blocks as in FIG.

6' is a W filter, but this is not necessary if the VIP filter 4 can be a satisfactory bandpass filter.

The features here are that there is an audio trap circuit 6# between the IP amplifier 5 and the video detector 7'', and that the audio detector 7' is connected from the front stage of the audio trap circuit 6'' to the detector 7''. This is a separate matter.

FIG. 4 shows a specific example of the circuit shown in FIG. 2, in which a voice trap circuit 6'' consisting of r2□, C3, C1, C5, L, 2 is connected in place of co in FIG. The audio carrier wave is attenuated by at least 1 QdB here, and the interference of audio in the video can be greatly improved.

Although not shown here, sound detection is performed through a separate detector 7' from the front stage of the audio trap circuit 6'' as shown in FIG.

As described above, according to the present invention, the interference of sound in images can be greatly improved compared to conventional synchronous detection, and since sound detection is performed in a separate system, the S/N ratio of sound can be improved, especially in weak electric fields. S/
This made it possible to improve the N ratio.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional example, Fig. 2 is a block diagram showing an embodiment of the present invention, Fig. 3 is an example of a specific circuit of Fig. 1, and Fig. 4 is a specific circuit of Fig. 2. This is an example diagram. 5...IF amplifier, 6'...Audio trap circuit, 7'...Audio detector, 7''...
...Video detector, a...Audio signal terminal, b...
...Video signal terminal, (4, Q4...IF amplifier, Q□51 Ql6...Tuning amplifier, Q,
□～Q□,... Multiplying detector.

Claims (1)

[Scope of utility model registration request] A means for amplifying the oscilloscope containing a video carrier wave, a color carrier wave, and a sound carrier wave is provided, the video carrier wave is extracted by a tuned amplifier having a finite value of Q, and a double-balanced differential amplifier mainly composed of four transistors is installed. the output of the tuned amplifier is added to the base of the transistor making up the differential amplifier, the IF signal is added to the emitter of the transistor making up the differential amplifier, and the output of the tuned amplifier and the IF signal are combined. A video detection means that performs multiplication detection is constructed, and an audio carrier trap circuit means capable of attenuating the audio carrier wave by 10 dB or more is interposed between the two means, and the audio detector is connected from the front stage of the audio carrier trap circuit means. 1. A television receiver, characterized in that an input signal is supplied to remove interference caused by a sound carrier wave from a video detection output.