JPS5841693B2 - TV show - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise removal device for a television receiver.

In recent television receivers, each circuit is integrated into an integrated circuit, and the video intermediate frequency amplification circuit and the video detection circuit following it are directly connected within the integrated circuit.

However, in such a circuit configuration, the noise generated in the video intermediate frequency amplification circuit (frequency components lower than the video intermediate frequency) is directly transmitted to the video detection circuit, and the SN after detection is
The ratio becomes significantly worse.

Furthermore, if a filter is inserted and connected between both circuits instead of directly connecting them, two pins must be provided, one for the output of the video intermediate frequency amplification circuit and the other for the detection input.

This invention was made in view of the above circumstances, and is a noise remover for television receivers that can sufficiently remove noise (frequency components lower than the video intermediate frequency) even with an integrated circuit, and significantly improves the S/N ratio after detection. The purpose is to provide equipment.

The present invention will be described in detail below with reference to one drawing.

First, a block diagram is shown in Fig. 1, in which a video detection circuit 2 is connected to the output side of a video intermediate frequency amplification circuit 1 in a television receiver, and is connected in parallel to this video detection circuit 2. An I-cut filter 3 and a circuit 4 equivalent in low frequency to the video detection circuit 3 are provided in series, and each output of each circuit 2, 4 is applied to a differential amplifier 5, respectively.

Noise (frequency components lower than the video intermediate frequency) is canceled out and removed by the differential amplifier 5, and only the signal is output to the video amplification circuit 6.
supplied to

Note that a comparison and loop bias circuit 7 is connected between the circuit 4 and the video intermediate frequency amplification circuit 10.

A specific circuit example of such a noise removal device is shown in FIG. 2, and the same parts as in FIG. 1 are indicated by the same symbols.

That is, the input terminal 8 is grounded through the coil L and the capacitor C5 in series, and is also connected to the base of the transistor Q1.

The collector of this transistor Q is connected to +
It is connected to the V DC power supply, and its emitter is grounded via a resistor R2 and connected to the base of a transistor Q2.

The emitter of this transistor Q2 is grounded via a resistor R4, and the collector is connected to the +V DC power supply via a resistor R3, and is also grounded via a resistor R5 and a capacitor C4, which form a high-cut filter 3, in series. , and further connected to the base of transistor Q3.

The collector of this transistor Q3 is connected to the +V DC power supply, and the emitter is grounded through a resistor R6 and a capacitor C1 in parallel, and is connected to the base of a transistor Q4 through a resistor R7.

The base of this transistor Q4 is grounded via a capacitor C2, the collector is connected to a DC power supply via a resistor R8, and the emitter is grounded via a resistor R9. connected to the base.

The collector of this transistor Q5 is connected to the +V DC power supply, and the emitter is connected to the emitter of a transistor Q6 via resistors R2o and R11 in series.

The connection point between the resistors RIO and R11 is connected to the respective collectors of transistors Q7 and Q8.
The emitter of the transistor Q8 is grounded through the resistor R12, and the base is connected to the emitter of the transistor Q7.

The base of transistor Q7 is connected to the +V DC power supply via resistor R14, and is also connected to the collector and base of transistor Q via resistor R15, and the emitter of transistor Q9 is connected to transistor Q.

This transistor Q1 is connected to the base and collector of
The emitter of o is grounded.

On the other hand, the collector of the transistor Q6 is connected to the 10V DC power supply via a resistor R13, and is also connected to the base of the transistor Q11.
The emitter of is connected to the +V DC power supply through a capacitor C3, and is also connected to a variable resistor R18 through a resistor R17.
The other end of this variable resistor R18 is connected to the emitters of the transistors Q and t, and also to the collector of the transistor Q12.

The base of this transistor Q12 is the transistor Q12.
1. It is connected to the collector of transistor Q13 and to its emitter via resistor R36, and this emitter is grounded via resistor R19 and connected to the base of transistor Q13.

The collector of this transistor Qss is connected to the +V DC power supply via the resistor R20, and the emitter is connected to the resistor R2,
It is grounded through the terminal and connected to the output terminal 9.

Now, during operation, a signal from input terminal 8 or transistor Q
1 to the base of transistor Q1. It is amplified by Q2.

The amplified signal is transferred to transistor Q3, resistor R6,
The wave is detected by capacitor C1.

Furthermore, the IF signal component is removed by an ikat filter consisting of a resistor R7 and a capacitor C2, and then passed through an emitter follower transistor Q4 to a differential amplifier transistor Q5.
supplied to the base of

On the other hand, as mentioned above, transistor Q1. A part of the signal amplified by Q2 is applied to a high-cut filter 3 consisting of a resistor R5 and a capacitor C4, and the signal components are removed, leaving only frequency components lower than the video intermediate frequency, which are sent to the base of the transistor Qa'.

And transistors Q3', Q4', resistors R6/~R9
In terms of low frequencies, the circuit 4 consisting of / is equivalent to the video detection circuit 2 consisting of transistor Q3=Q, resistors R6-R9, etc.

Now, the noise generated in the video intermediate frequency amplification circuit 1, that is, the noise appearing at the collector of the transistor Q2, passes through the video detection circuit 2 and the circuit 4 which is equivalent to this circuit 2 in terms of low frequency.

Therefore, the emitter of transistor Q4 and transistor Q4
' emitter appears as the same output.

Then, at the emitter of transistor Q4, the sum of the detection output and noise becomes the output (see Figure 3C), and transistor Q4
', only noise appears as an output (see Figure 3).

Of course, the emitter of transistor Q4 and the emitter of transistor Q4' when there is no signal are at the same potential because they are symmetrical circuits.

Now, when the output of the emitter of transistor Q4 and the output of the emitter of transistor Q4' enter the bases of transistors Q5 and Qa, which constitute a differential amplifier, noise appears on the output side, that is, the collector of transistor Q6, because it is a common mode input. do not have.

On the other hand, the detected output is applied as a differential input and appears as an output at the collector of transistor Q6 (see Figure 3C).

This output is amplified by the transistor Qlls Q12 and taken out from the output terminal 9 via the emitter follower transistor Q13.

Note that the variable resistor R18 is a variable resistor for adjusting the no-signal level.

In addition, transistors Q14s and Q15 are comparator circuits that amplify the difference voltage between the bias voltage at the midpoint of resistors R26S and R27 and the voltage of transistor Q4', and the transistors Q and 6°Q17 amplify and level shift the voltage to the base of transistor Q1. has given negative feedback.

Therefore, the voltage across transistor Q4' is equal to resistor R269R27.
The voltage of the transistor Q4 when there is no signal is also kept equal to this voltage.

Since the noise removal device of the present invention is constructed as described above and shown in the drawings, noise is removed and as a result, the S after detection is
The N ratio is significantly improved.

Another advantage is that a stable loop bias can be applied by the comparison and loop bias circuit T.

As described above, according to the present invention, it is possible to provide a noise removal device for a television receiver that has great practical value.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a noise removal device for a television receiver according to the present invention, FIG. 2 is a circuit configuration diagram showing a specific circuit, and FIG. 3 shows signals of each part in the device of the present invention. FIG. 1... Chivalry intermediate frequency amplification circuit, 2... Chivalry detection circuit, 3... High-cut filter, 4...
...Circuit equivalent in low frequency to iron image detection circuit, 5...
・−・Differential amplifier.

Claims (1)

[Claims] 1. A video detection circuit is connected to the output side of the video intermediate frequency amplification circuit, and in parallel with this video detection circuit, an Igat filter and a circuit equivalent to the video detection circuit in terms of low frequency are provided in series. A noise removal device for a television receiver, characterized in that each output of the video detection circuit is applied to a differential amplifier to cancel and remove noise.