JPS5925425B2 - Noise removal device for television receivers - 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 corresponding video detection circuit are directly connected within the integrated circuit.

The video intermediate frequency amplification circuit is, for example, a high frequency 58.7
Amplify the 5MH2 video intermediate frequency signal and convert it to approximately 4MH
The video signal of the second band is detected. In addition to the 58.75 MH2 video intermediate frequency signal supplied from the tuner, the signals input to this video intermediate frequency amplification circuit include low frequency noise whose frequency is lower than the high frequency 58.75 MH2 signal. Mixed. Examples of this low frequency noise include image interference signals between upper and lower adjacent channels with respect to the video carrier being received, bead signals between the audio carrier and the video carrier, bead signals between the color subcarrier, and the like.

That is, the video intermediate frequency amplification circuit has a signal having a lower frequency of 4.5 in addition to the high frequency signal that is the video intermediate frequency signal.
There are MH2 bead interference signals, 920KH2 bead signal components, etc. When a video frequency amplification circuit is integrated, these low frequency noises are transmitted to the next stage via the substrate capacitance of the integrated transistor, causing a problem in which the image quality of the reproduced screen is degraded. Also, if you insert a filter between both circuits without directly connecting them, you will need to provide two pins, one for the video intermediate frequency amplification circuit output and one for the detection input.
- This invention was made in view of the above circumstances, and provides a television receiver that can sufficiently remove low frequency noise at a frequency lower than the video intermediate frequency even with an integrated circuit, and significantly improves the S/N ratio after detection. The purpose of the present invention is to provide a noise removal device.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

First, a block diagram is shown in Fig. 1. On the output side of a video intermediate frequency amplification circuit 1 in a television receiver, a video detection circuit 2 and a circuit 4 equivalent to this circuit in terms of low frequency are connected in parallel. The outputs of the circuits 2 and 4 are respectively applied to the differential amplifier 5. In this differential amplifier 5, low frequency noise represented by a mixed bead component between channels is canceled out and only the signal is supplied to the video amplification circuit 6. Further, a comparison and loop bias circuit 7 is connected between the output side of each of the circuits 2 and 4 and the input side of the video intermediate frequency amplification circuit 1. 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 L1 and the capacitor C6 in series, and is also connected to the base of the transistor Q1. The collector of this transistor Q1 is a resistor R
1 to the +V DC power supply, and the emitter is connected to the resistor R.
It is grounded via Q2 and connected to the base of transistor Q2. The emitter of this transistor Q2 is grounded via a resistor R4, and the collector is connected to the +DC power supply via a resistor R3.
Connected to each base of Q3.

The collector of transistor Q3 is connected to the +V DC power supply, and the emitter is grounded through resistor R5 and capacitor C1 in parallel, and is connected to transistor Q through resistor R6.
Connected to the base of 4. The base of this transistor Q4 is grounded via C2, the collector is grounded, and the emitter is connected to the +V DC power supply via a resistor R7 and to the base of the transistor Q5 via a resistor R8. The collector of this transistor Q5 is connected to the +V
It is connected to a DC power supply, and its emitter is grounded via a resistor R9 and connected to the base of a transistor Q6.
The collector of this transistor Q6 is connected to the +V DC power supply, and the emitter is connected to the emitter of a transistor Q7 via resistors RlO and Rll in series. Resistance Rl
The connection point of O and Rll is connected to each collector of transistors Q8 and Q9, and the emitter of transistor Q9 is connected to a resistor R.
It is grounded via I2, and its base is connected to the emitter of the transistor Q8. The base of this transistor Q8 is connected to the +V DC power supply via a resistor Rl4, and is also connected to the collector and base of a transistor Ql7 via a resistor Rl5. The emitter of transistor Ql7 is connected to the collector and base of transistor Ql8, and the emitter of transistor Ql8 is grounded.
On the other hand, the collector of the transistor Ql7 is connected to the resistor Rl4.
, Rl5 to the +V DC power supply. The emitter of transistor QlO is connected to resistor Rl6 and capacitor C.
5 in parallel to the +V DC power supply and to the collector of the transistor Qll. Furthermore, a variable resistor R32 is connected in parallel to the resistor Rl6. The collector of transistor QlO is connected to the base of transistor Qll, and this base is connected to the emitter via resistor R33. This emitter is grounded via a resistor Ql7 and connected to the base of a transistor Ql2, the collector of this transistor Ql2 is connected to the +V DC power supply via a resistor Rl8, and the emitter is connected to a resistor Rl.
It is grounded via 9 and connected to output terminal 9. The collector of the transistor Q2 is connected to the base of the transistor Qf, the collector of this transistor Q3' is connected to the +DC power supply, and the emitter is connected to the resistor R.
1 to ground through the transistor Q!1 and through the resistor R6' to the transistor Q! connected to the base of

The collector of this transistor Q4' is grounded, the emitter is connected to the +DC power supply through a resistor R7', is also grounded through a capacitor C3, and is connected to the base of a transistor Q5'' through a resistor R1. Its base is grounded via a capacitor C4, its collector is connected to the +V DC power supply, its emitter is grounded via a resistor R9' and connected to the base of the transistor Q7, and the resistor R2l and capacitor C8 are connected in series. The connection point between this resistor R2l and the capacitor C8 is connected to the emitter of the transistor Q5 and the base of the transistor Ql3 through the resistor R2O.The collector of this transistor Ql3 is connected to the resistor R25. The emitter is connected to the emitter of the transistor Ql4 via the resistors R22 and R23 in series.The connection point of the resistors R22 and R23 is connected to the transistor Ql9. , Q2O, the emitter of this transistor Ql is grounded via a resistor R24, and the base is connected to the emitter of the transistor Q2O.The base of this transistor Q2O is connected to the connection point of the resistors Rl4 and Rl5. The collector of the transistor Ql4 is connected to the +V to the DC power supply, and the base is connected to the +V through the resistor R27.
It is connected to a DC power source and grounded via a resistor R28. Furthermore, the emitter of transistor Ql5 is connected to resistor R.
3O to the +V DC power supply and to the collector of the transistor Ql6, and the emitter of the transistor Ql6 is connected to the base and the collector of the transistor Ql5 through the resistor R2, and through the resistor R3l. It is grounded and connected to the connection point between the coil L1 and the capacitor C6. Further, this connection point is grounded via a capacitor C7. Now, during operation, a signal is applied from the input terminal 8 to the base of the transistor Q1, and is amplified by the transistors Ql and Q2. Then, the amplified signal is transferred to the transistor Q3 and the resistor R5.
, detected by capacitor C1. Furthermore, the IF signal component is removed by a high-cut filter consisting of a resistor R6 and a capacitor C2, and the emitter follower transistors Q4 and Q5
is supplied to the base of transistor Q6 of the differential amplifier. On the other hand, as mentioned above, a part of the signal amplified by the transistors Ql and Q2 is sent to the base of the transistor Q3'', and the transistors Q3'' and Q4'' and the resistor R
In terms of low frequencies, the circuit 4 consisting of transistors Q3, Q4, resistors R5 to R9, etc. is equivalent to the video detection circuit 2 consisting of transistors Q3, Q4, resistors R5 to R9, etc. In this case, in the video detection circuit 2, the transistor Q3, the resistor R5, and the capacitor C1 perform detection as described above, but in the equivalent circuit 4, the transistor Q! , resistance R,! Since the detection is performed by the capacitor C3, the detected output waveform has opposite polarity in both circuits. Now, the low frequency noise such as the mixed bead component generated in the video intermediate frequency amplification circuit 1 is transmitted to the video detection circuit 2 and the circuit 4 which is equivalent in low frequency to this circuit 2 through the stray capacitance caused by the substrate etc. pass. Therefore, the same output appears at each emitter of transistors Q5 and Q5'. That is, an output having a waveform as shown in FIG. 3a is obtained at the emitter of the transistor Q5, which is the sum of the detection output and low frequency noise. Also, the emitter of transistor Q5'' has a third
An output with a waveform as shown in FIG. b is obtained, which is the sum of the detection output of the opposite polarity and the low frequency noise of the same polarity. Of course, when there is no signal, the emitters of transistors Q, , Q5'' are at the same potential because they are symmetrical circuits.Now, the output of the emitter of transistor Q5 and the output of the emitter of transistor Q5' are transistors forming a differential amplifier. When entering the bases of Q6 and Q7, low frequency noise does not appear on the output side, that is, the collector of transistor Q7, because the input is in common mode.In addition, leakage of high frequency signals is also canceled out because they have the same polarity.On the other hand, the detection output is a differential signal. added as input and transistor Q as output
7 collector (see Figure 3c). This output is amplified by transistors QlO and Qll, and taken out from output terminal 9 via emitter follower transistor Ql2. Note that the variable resistor R32 is a variable resistor for adjusting the no-signal level. Furthermore, if the resistance value is selected appropriately, no detection output appears at the base of the transistor Ql3, but only low frequency noise appears (see FIG. 3d).

Therefore, the base of transistor Ql3 is always at the no-signal level (
Since it is an equivalent circuit in terms of direct current, the no-signal level of each emitter is equal). Also, transistors Ql3, Ql4
A comparator circuit amplifies the difference voltage between the bias voltage at the connection point of resistors R27 and R28 and the base voltage of transistor Ql3, further amplifies and level shifts in transistors Ql5 and Ql6, and applies negative feedback to the base of transistor Q1. ing. That is, a loop bias is applied so that the bias voltage at the connection point and the base voltage are equal. Since the noise removal device of the present invention is configured as described above and shown in the drawings, low frequency noise is removed, and as a result, the S
The N ratio is significantly improved. Another advantage is that a stable loop bias can be applied by the comparison and loop bias circuit 7. As a result, the DC level applied from the input terminal 8 to the video intermediate frequency amplification circuit 1 can be clamped to a constant level, and the AGC effect on high frequency components is also improved. The low frequency noise cancellation circuit itself is a detection circuit, and the input of the loop bias circuit is also connected to the emitter follower transistor Q5, so the collector output of transistor Q2 is wasted in the loop bias circuit and low frequency noise cancellation circuit. I have nothing to give. Therefore, detection efficiency is improved. Furthermore, as shown in FIG. 4, if a filter consisting of a resistor Ral and a capacitor Ca is connected between the collector of the transistor Q2 and the base of the transistor Q3', the loss will be large unless Ra is set to a high resistance (several kΩ). However, when Ra becomes high in resistance, noise generated by resistor Ra and transistor Q3' increases, and this noise appears in the detection output. However, in the noise removal device of this invention, the base of transistor Q3 and the transistor Q
Since the base of 3' is directly connected, noise generation is also reduced. 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 drawings]

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 diagram showing a specific circuit, and FIG. 3 shows signals of various parts in the device of the present invention. FIG. FIG. 4 is a circuit configuration diagram showing a circuit used to explain the effects of this invention. 1... Video intermediate frequency amplification circuit, 2... Video detection circuit, 4...
Circuit equivalent to a video detection circuit, 5... Differential amplifier, 6... Video amplification circuit, 7... Comparison and loop bias circuit.

Claims (1)

[Claims] 1 Amplify the video intermediate frequency signal applied to the input terminal,
A video intermediate frequency amplification circuit that outputs the amplified video intermediate frequency signal to an output terminal; an input terminal is connected to the output terminal of the video intermediate frequency amplification circuit; and the video intermediate frequency signal is detected by one polarity of a positive video carrier wave. a first video detection circuit that outputs a video detection signal to an output terminal; and a video detection signal obtained by detecting a signal on the input terminal side of the first video detection circuit with the other polarity of the video carrier wave. a second video detection circuit equipped with an output terminal, and an output terminal side of the first video detection circuit is connected to the base of the transistor,
The output terminal side of the second video detection circuit is connected to the base of the other transistor, and the video detection output is inputted differentially with opposite polarity, and includes at least a differential amplifier for amplifying the same, and the first By making the stray capacitance characteristics between the respective input and output terminals of the second video detection circuit equivalent, the noise signal is removed by the operational amplification operation of the differential amplifier, and the video detection signal is A noise removal device for a television receiver, which is characterized by amplifying the noise.