JPS5946453B2 - noise canceler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise canceling device for a device that receives amplitude modulated (hereinafter abbreviated as AM) signals, such as a television receiver, and particularly relates to a noise canceling device for a device that receives an amplitude modulated (AM) signal, such as a television receiver. It is an object of the present invention to provide a novel configuration of a circuit arrangement for eliminating unstable or erroneous operation of a receiver.

The noise dealt with here is RF (radio frequency) noise mixed into the input stage of the receiver, that is, the signal input terminal of the high frequency amplification stage, and is usually caused by pulses generated by hair dryers, car ignition systems, etc. It is a sexual thing. The receiver generally has a frequency conversion stage including the above-mentioned high frequency amplification stage and local oscillation circuit, and an intermediate frequency amplification and detection circuit, and the high frequency and intermediate frequency amplification circuits are controlled by an AGC (automatic gain control) circuit. It is well known that the invention is designed to be controlled. Traditionally, the most serious problem among receiver failures caused by RF impulse noise is noise-induced A.
It was a malfunction of the GC circuit.

In particular, in the AGC method that keeps the peak level of the received signal constant (peak value type), the AG
Due to the operation of C, the output signal level of the detection circuit is significantly reduced. It is well known that such a phenomenon causes an abnormality in the operation of a synchronization signal separation circuit arranged to synchronize a scanning circuit with an input signal in a television receiver. Furthermore, among the noise contained in the output signal of the detection circuit, noise in the image information in particular causes a change in the DC component of the reproduced image, and this phenomenon occurs in devices that do not reproduce the DC component, such as black-and-white television receivers. The impact is extremely large. For the reasons described above, a circuit device is usually provided to eliminate noise contained in the output signal of the detection circuit. FIG. 1 shows an example of a conventional device of this type. For convenience of explanation, the following explanation will be made using a video detection circuit of a television receiver. In the noise canceling device shown in Fig. 1, the detection circuit 1
White noise detection circuit 2, white noise detection circuit 3 and black noise detection circuit 3 are installed on the output side of
are arranged independently, indicating that the output of these circuits and the input signal are subjected to subtraction processing.

If the detection circuit 1 is configured to obtain a known envelope response, noise in the white direction that exceeds the zero carrier level will not occur at the output end in principle; The shown white noise detection circuit and its subtraction processing circuit are not required in practice. On the other hand, in the detection circuit 1 as shown in FIG. L. In the case of using a synchronous detection method in which a synchronous carrier wave component is regenerated and utilized using a predetermined filter such as L or a crystal oscillator, this circuit operates as a phase detection circuit of the same phase axis, so white noise} and Both the black noise detection circuits 2 and 3 and a subtraction processing circuit using them are required. In the case of a noise canceling device having the configuration shown in Fig. 1 above, the noise canceling signal generated on the synchronizing signal side of the output signal of the detection circuit, that is, on the negative modulation receiver, is black. It has a distinct structural feature of using the output of the noise detection circuit 3. However, detection and noise cancellation of black noise in forming a negative feedback loop such as an AGC circuit is accompanied by various limitations and associated drawbacks.

First of all, since the AGC circuit is constructed by direct current coupling in all stages, the mode of the AGC loop completely changes from negative feedback to positive feedback at the moment when noise cancellation is performed. On the other hand, there are amplitude separation type and frequency separation type for detecting black noise, and the amplitude separation type is usually used because of its accurate detection. In this case, the amplitude separation type noise detection circuit requires DC coupling with the detection circuit, so if a sudden increase in the received signal level occurs, the AGC circuit cannot respond instantly, so the increased output signal of the detection circuit Then the operation begins. In other words, even though the signal increases, the input signal level to the AGC circuit is reduced by the noise canceling device, so the AGC circuit operates to further increase the output signal level of the detection circuit, resulting in so-called AGC lockout. A phenomenon will occur. Therefore, conventional receivers require a new circuit to prevent this lockout phenomenon, and receivers equipped with this have the drawback of deteriorating noise cancellation characteristics. The second drawback based on the response of the AGC circuit is that a margin must be given to the detection level so that the black noise detection circuit does not malfunction due to the synchronization signal, especially for the flutter phenomenon caused by passing airplanes. This value is usually relatively large because it is necessary to consider the time of occurrence, and as a result, the residual component of the noise after cancellation is large and the cancellation effect is low. What has been described above is mainly related to the inherent performance of the noise canceling device, but it also has various disadvantages in practical use, such as the need for two systems of noise detection circuits. In the noise canceling device according to the present invention, only a white-direction noise detection circuit placed on the output side of the detection circuit is required to detect noise, and the output of this detection circuit has a waveform such as a predetermined delay circuit or filter circuit. Subtraction for noise cancellation, via shaping circuit
Alternatively, it has a configuration in which it is supplied to an addition processing circuit.

It will be explained in detail below with reference to the drawings that all white noise and black noise contained in the output signal of the detection circuit are detected by the present invention and canceled by appropriately processed white noise. . FIG. 2 is a process diagram showing one embodiment of the present invention.

A noise detection circuit 4, which is DC-coupled to the output terminal of the detection circuit 1 and detects white noise in a direction exceeding the zero carrier level, includes a level comparator and at least a filter for obtaining a substantially envelope response of the output of the level comparator. It is composed of a signal processing circuit having a wave function or a delay function. For example, when this signal processing circuit is configured with a normal RC filter or an integrated circuit, it is possible to actively utilize the accumulation effect caused by the saturation operation of transistors, the signal delay effect of lateral PNP transistors, etc. alone or in combination. This can be achieved by using it for example. The white noise detected and appropriately processed by the noise detection circuit 4 has a difference in the time domain not only with respect to the white noise contained in the output signal of the detection circuit 1 but also with respect to the envelope response of the black noise. The widths may be approximately equal. It will become clearer if we assume that the noise detection circuit outputs only the noise envelope response. This is RF
This is due to the fact that the pulse noise has no regularity in terms of amplitude and phase information, and its frequency components are included within the frequency band of the receiving channel. Similarly, it is converted into an intermediate frequency band. Similarly, since the signal is subjected to frequency conversion again in the synchronous detection circuit 1, the envelope waveforms of the RF signal and the noise at the output end of the detection circuit match, and only the frequencies differ. Therefore, the relatively wide noise that causes interference to ordinary receivers has hundreds to thousands of different frequency components!
As described above, the present invention has a clear structural feature in which the black noise is canceled by using the approximate envelope response of the noise in the white direction. . It has been shown that by performing subtraction processing between the white noise detected in this way and the output of the detection circuit 1, white noise is eliminated, while by performing addition processing, black noise is eliminated. However, these may be selected as necessary. The advantages obtained by eliminating black noise in the detection output signal supplied to the AGC circuit using the above configuration are extremely large. That is, the noise detection circuit 4 arranged according to the present invention detects any signal component of the output of the detection circuit 1,
For example, the AGC circuit is significantly different from conventional devices in that it does not respond at all to synchronization information, image information, etc., and as a result, the AGC circuit can always detect the peak level only for synchronization signals. This means that even if a sudden increase in the received signal level occurs, the noise detection circuit 4 remains in a stopped state, so that the AGC circuit lockout phenomenon described in the conventional example of FIG. 1 does not occur. be. Although Fig. 2 shows a configuration in which the signal supplied to the AGC circuit is noise-canceled, the addition process can be performed at least in the preceding stage of the AGC smoothing circuit, and its position and configuration can be arbitrarily selected in various ways. V). Needless to say, this is within the scope of the present invention, as long as the AGC circuit is configured to detect black noise in the incoming input signal and thereby prevent it from operating in a direction that reduces the gain of the intermediate frequency amplifier, etc. It is within. As mentioned above, even if the amplitude of the detected output signal increases or decreases due to the flutter characteristics of the AGC circuit, the operation of the noise detection circuit 4 is not affected in any way. Therefore, since the margin necessary for setting the detection level of the noise detection circuit 4 according to the present invention is extremely small, the noise cancellation effect can be greatly improved.

Although the above description relates to a receiver for negative modulation, it will be described below that the present invention can also be applied to a receiver for positive modulation. Since the peak value level of the detection output signal of the positive modulation receiver is not constant and changes depending on the station information, it is not appropriate to apply the peak value AGC as described for the negative modulation receiver. Instead, average value type AGC is usually used. Since the average value ice AGC operates to keep the average DC level of the detection output signal constant, the average brightness level AP in the image information
It is known that L causes the amplitude of the detected output signal to change approximately twice as much. In such a positive modulation receiver, especially when the detection circuit uses a known envelope detection method, the amplitude separation type cannot be applied to noise detection.

On the other hand, the peak level of noise on the synchronization signal side of the input signal of the synchronization signal separation circuit, which is one element for synchronizing the scanning circuit and the input signal, that is, the output signal of the detection circuit, is the same as that of the synchronization signal and the zero carrier wave level. Since the difference in DC level between them is usually small, detection of such noise is very difficult considering the margin required for detecting the noise. From the above, it is clear that in a positive modulation receiver, any noise in the white and black directions cannot be properly processed by the amplitude separation type noise detection circuit. On the other hand, when the detection circuit is configured by synchronous detection, the noise on the synchronous signal side increases significantly compared to the case of envelope detection, so this noise can be detected with an amplitude separation type configuration. , resulting in black noise in the detected output signal,
In other words, noise on the synchronization signal side can be eliminated.

However, as is clear from the above, in a positive modulation receiver, noise in the white direction still remains, which causes the following drawbacks. For example, the effect on the scanning circuit is that the remaining white noise causes a change in the average DC level of the signal to the synchronization signal separation circuit, and since the input of this circuit is usually AC coupled, the output signal contains not only the synchronization signal but also the synchronization signal. There is a possibility that part of the image information may be mixed in. In addition, white noise causes various other drawbacks, such as significantly deteriorating the quality of reproduced images. When the present invention is applied to a positive modulation receiver, there is no need to change the configuration described for the negative modulation receiver, and only the functions of the circuits arranged according to the present invention are different.

In this case, the noise detection circuit 4 shown in FIG. 2 operates not as a white noise detection circuit but as a black noise detection circuit. Also AGC
It is practically possible to remove the addition processing circuit (subtraction processing circuit in this case) arranged for the signal to the circuit for noise cancellation if the AGC circuit is of the average-average type. Therefore, the advantage obtained by applying the present invention to a positive modulation receiver is mainly due to the elimination of white squares and black noise in the detected output signal. First, since the influence on the scanning circuit, that is, the average DC level of the signal to the synchronization signal separation circuit, does not change due to noise, it is possible to prevent image information from being mixed into the synchronization signal of the separated output.

In addition, in conventional devices, relatively wide pseudo synchronization signals may be generated due to noise, but in this embodiment, these widths can be made extremely narrow, thereby improving the synchronization stability of the scanning circuit. Significantly improved. On the other hand, the quality of the reproduced image is significantly improved, especially by eliminating white noise in the luminance information. This has an extremely negative impact in practice, as in conventional receivers, if white noise that is higher than white occurs, it not only significantly increases the noise contrast, but also causes the generation of grid current in the cathode ray tube. In the present invention, it is reduced to a predetermined level, ie, eliminated. Black noise in the signal used as luminance information can also be reduced to a predetermined level, but the subtraction processing circuit for noise cancellation is shared with the cancellation level necessary for separating the synchronization information mentioned above. Alternatively, it should be selected as appropriate whether to arrange it as an independent unit. Next, another embodiment of the noise canceling device of the present invention will be described. FIG. 3 shows a configuration in which a clip circuit 5 is arranged on the output side of a noise detection circuit 4 (here detecting white noise), and this is controlled by a smoothing circuit 6. The clipping circuit 5 clips at a predetermined level the residual component of white noise generated by the necessary margin when detecting white noise, but this clipping operation is limited to only when noise is detected by the noise detection circuit 4. By doing so, the practical advantages as described below can be obtained. Figure 3 shows the circuit arrangement for white noise cancellation in a receiver for negative modulation, but it is possible to replace the subtraction processing circuit and the clipping circuit, and furthermore, in a receiver for positive modulation, these circuits can be replaced. The operation as a black noise canceling circuit is the same as that described using FIG. 2.

FIG. 4 shows an example of a specific configuration suitable for carrying out the present invention. The differential level comparator consisting of transistors Ql and Q2 is a white noise detector, and the pulse width extension PN indicated by 4''
The noise detection circuit 4 shown in FIG. 2 is configured together with a waveform shaping stage consisting of a P transistor Q3 and a buffer transistor for output Q4. The output of this circuit is resistor Rl, R2
, R3 are arranged to generate three different levels of white noise. One of them is sent to a subtraction processing circuit 7 for black noise cancellation for the detection output signal, which is made up of transistors Q5 and Q6, and the other is sent to a processing circuit r for the AGC circuit, which is made up of transistors Q7 and Q8. Supplied. Another signal processing circuit for white noise cancellation, namely the first transistor consisting of transistors Q, , Q, and O.
Both the switch circuit and the second switch circuit consisting of transistors Qll and QlO are driven by noise from the emitter of transistor Q4, and this configuration allows the output level of the noise detection circuit to change even when the transistors in the switch circuit are saturated. Care has been taken to ensure that this does not occur. The first switch circuit instantaneously responds to the output of the noise detection circuit 4 and adjusts the noise level of the output of the transistor QlO to the resistors R4 and R5.
It has a function of fixing the voltage to a desired level determined by the saturation voltage of the transistor Q and the saturation voltage of the transistor Q. In addition, the transistor Qll of the second switch circuit is supplied with the output of the noise detection circuit 4 via the resistor R and the capacitor C that constitute the smoothing circuit 6, so it is always in a conductive state during the period when white-direction noise is occurring. All noise exceeding the level determined by resistors R4, R5, R7 and the saturation voltage of transistor Ql is clipped by cutting off transistor QlO. The white noise cancellation and clip levels provided by the first and second switch circuits are typically set to be different. This problem is based solely on reducing the contrast of the noise by setting the instantaneous level of the detection output signal, which is fixed in the white noise cancellation operation, within the amplitude range of the luminance information. is the fourth
This does not mean that the configuration is limited to the specific configuration shown in the figure. That is, the other end of the resistor R7 connected to the transistor Qll constituting the second switch circuit can also be connected to the emitter terminal of the transistor Qll.
The clipping operation by the second switch circuit arranged according to the invention is essentially different in its operation from the known method using a Zener diode or a base-emitter blocking action of a transistor. Among the known methods, the former has the disadvantage that its clip level is constant and therefore does not follow changes in the power supply voltage of this type of circuit, while the latter has the disadvantage that it does not track changes in the power supply voltage of this type of circuit due to the reduction in bias current. It has the drawback that distortion occurs in areas with high brightness levels regardless of the presence or absence of noise. According to the present invention, the clip level follows the power supply voltage, and has the advantage that no distortion occurs when normal noise does not occur, and the clip circuit operates only when noise occurs. Therefore, there is no limitation to the specific configuration of the second switch circuit. In addition to the various performance advantages discussed above, the present invention is a novel noise canceling device that is well suited for implementation in integrated circuits. In particular, there is no need for a lockout prevention circuit for the AGC circuit, and the noise detection circuit required to eliminate all white noise and black noise is only necessary for negative modulation receivers to detect white noise; In terms of the receiver, it is also a great practical advantage that the circuit can be simplified, such as by only needing to detect black noise.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a conventional example of a noise canceling device;
3 is a block diagram showing one embodiment of the noise canceling device of the present invention, FIG. 3 is a block diagram showing another embodiment of the present invention, and FIG.
The figure is a circuit configuration diagram showing an example of the specific circuit. 4... Noise detection circuit, 5... Clip circuit, 6... Smoothing circuit.

Claims (1)

[Scope of Claims] 1. A synchronous detection means whose input signals are an amplitude-modulated signal and an output signal of a carrier wave generation means for reproducing the carrier wave component of the signal using a predetermined filter means; It is DC coupled to the output end of the means and the amplitude is in the positive direction (
a noise detection means for detecting noise increasing in the direction exceeding the zero carrier level), and the output of the noise detection means is used as a noise cancellation signal for at least negative noise in the output of the synchronous detection means. A noise canceling device characterized by being used as a noise canceling device. 2. The noise canceling device according to claim 1, wherein the output of the noise detecting means is used as a noise canceling signal for the AGC circuit. 3. The noise canceling device according to claim 2, wherein the AGC circuit uses a peak value type AGC method. 4. The noise canceling device according to claim 1, wherein the carrier wave generation means includes at least one of a phase-locked loop and a filter using a crystal resonator. 5. Claim 1, wherein the carrier wave generating means includes an oscillator for generating a carrier wave component of an intermediate frequency signal.
Noise canceling device as described in section. 6. A patent claim in which the noise detection means comprises a noise detection circuit for detecting noise exceeding a predetermined DC level, and a noise processing circuit for changing the waveform or phase of the noise pulse output from the noise detection circuit. The noise canceling device according to item 1. 7 The noise processing circuit is a lateral P formed of an integrated circuit.
7. The noise canceling device according to claim 6, which is a circuit that changes the phase of a noise pulse using a signal delay effect of an NP transistor.