JPH051186Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a noise canceler circuit used in VTRs and the like.

[Summary of the idea]

The present invention supplies the output signal of the first high-pass filter to which the input signal is supplied to the first limiter circuit, and also transmits the limiter output signal to the first limiter circuit.
the subtracted output signal is supplied to a second high-pass filter having a cut-off frequency higher than the cut-off frequency of the first high-pass filter, and the output signal is supplied to a second limiter circuit. By subtracting the output signal of the first limiter circuit and the output signal of the second limiter circuit from the input signal, the difference between the first high-pass filter and the first limiter circuit is reduced. The present invention is designed to reduce the noise remaining in the output signal of the conventional noise canceler circuit.

[Conventional technology]

The noise canceler circuit shown in FIG. 3 is conventionally known as a noise canceler circuit used in VTRs and the like.
FIG. 4 shows output waveforms at points a to d in FIG. 3.

In Fig. 3, an input signal Si such as a reproduced video signal
is supplied to a high pass filter 1 and an adder 2 from point a. It is assumed that the input signal Si is a signal having a rectangular wave as shown in FIG. 4a. This input signal Si contains noise N. From the high-pass filter 1, an output signal with noise superimposed on a positive/negative differential waveform as shown in FIG. 4b is obtained. By limiting this output signal to a predetermined level in the limiter circuit 3, a waveform shown in FIG. 4c is obtained. Next, by subtracting this waveform from the input signal Si in the adder 2, the noise N component is canceled and the output signal shown in FIG.
S _p is obtained.

Incidentally, as a circuit for removing a carrier component from an FM demodulated signal, a technique disclosed in Japanese Patent Publication No. 1063/1983 is known.

[Problem that the invention attempts to solve]

As is clear from the waveform of the output signal S _p in FIG. 4d, noise N ₁ remains at the edge portion of the rectangular wave at time t ₁ . This residual noise _N1 is caused by the limiter circuit 3 limiting the level of the differential waveform shown in FIG. 4b as shown in FIG. 4c. That is, since the above differential waveform is subject to level restrictions together with the noise N, in the adder 2, the input signal
The noise in the portion corresponding to the portion subjected to the above-described level restriction of Si remains without being canceled.

In order to remove this residual noise, it is conceivable to increase the cutoff frequency of the high-pass filter 1, but doing so causes the disadvantage that low-frequency noise cannot be canceled sufficiently. It is also conceivable to increase the limiter level of the limiter circuit 3 to narrow the width of the portion subject to level restriction, but this would cause the problem of increased distortion of the output signal S _p .

[Means for solving problems]

In the present invention, in addition to the conventional circuit consisting of the first high-pass filter and the first limiter circuit 3, the first high-pass filter 1
a circuit 4 for subtracting the output signal of the first limiter circuit 3 from the output signal of the first limiter circuit 3; and a second circuit 4 to which the subtraction output signal is supplied and having a cut-off frequency f _C2 higher than the cut-off frequency f _C1 of the first high-pass filter. a high-pass filter 5; a second limiter circuit 6 to which the output signal of the second high-pass filter 5 is supplied;
Circuits 2 and 7 are provided for subtracting the output signal of the limiter circuit 3 and the output signal of the second limiter circuit 6.

[Effect]

As the above-mentioned subtraction output signal, only a differential waveform on which noise is superimposed is obtained, and this differential waveform is passed through a second high-pass filter with a high cutoff frequency and a second high-pass filter with a high cutoff frequency.
By communicating with the limiter circuit, a narrow limiter output signal including noise can be obtained. Therefore, by subtracting this limiter output signal and the output signal from the conventional circuit section from the input signal Si, the period t ₁ of the residual noise N ₁ can be shortened.

〔Example〕

FIG. 1 shows an embodiment of the present invention, and the same parts as in FIG. 3 are given the same reference numerals. Further, FIG. 2 shows output waveforms at points a to g in FIG. 1.

In this embodiment, an adder 4 that subtracts the output signal of the limiter circuit 3 from the output signal of the high-pass filter 1, and a high-pass filter 5 and a limiter circuit 6 to which the subtracted output signal is added are provided. The output signals of the limiter circuits 3 and 6 are added together in an adder 7, and the signal is then subtracted from the input signal Si in the adder 2. Further, the cutoff frequency f _c2 of the high pass filter 5 is selected to be higher than the cutoff frequency f _c1 of the high pass filter 1.

According to the above configuration, the waveforms at points a to c match the waveforms at points a to c in FIG. 4. Further, the waveform obtained at point d is a differential waveform in which noise is removed from the portion corresponding to the flat portion excluding the edge portion of the rectangular wave input signal Si, and noise remains in the portion corresponding to the edge portion.

By passing the waveform at point d through the high-pass filter 5, which has a cutoff frequency f _c2 higher than that of the high-pass filter 1, noise is superimposed on the differential waveform smaller than the differential waveforms b and d in the same figure, as shown in Figure 4 e. A waveform is obtained. By further passing this waveform to the limiter circuit 6, the waveform shown in the figure f is obtained. The width of the level-limited portion of this waveform is sufficiently smaller than the width of the level-limited portion in FIG. 4c, as shown.

Therefore, by subtracting the signal obtained by adding the waveform at point f and the waveform at point c in adder 7 from the input signal Si in adder 2, the output signal S _p shown in Fig. 2g is obtained. . As shown in the waveform of the signal S _p , the period t ₂ in which the residual noise N ₁ exists is sufficiently shorter than the period t ₁ in FIG. 4d. Note that during the period indicated by _t3 in FIG. 2d, some noise remains depending on the difference between the two cut-off frequencies f _c1 and f _c2 , but there is no problem in practical use.

According to the above, low-frequency noise is removed by the loop of the high-pass filter 1, limiter circuit 3, and adders 7, 2, and high-frequency noise is removed by the loop of the adder 4, high-pass filter 5, limiter circuit 6, and adders 7, 2. Since the area noise is removed, the residual noise
It is possible to obtain a noise canceller circuit in which N ₁ is reduced and noise in a wide band is removed.

[Effect of idea]

It is possible to remove noise ranging from low to high frequencies and reduce residual noise. The waveform distortion of the output signal can be minimized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an output waveform diagram at points a to g in FIG. 1, FIG. 3 is a block diagram of a conventional noise canceler circuit, and FIG. 4 is an output waveform diagram at points a to d in FIG. 3. FIG. In addition, in the symbols used in the drawings, 1, 5...
...High pass filter, 3,6...Limiter circuit,
2, 4, 7...adders.

Claims (1)

[Claims for Utility Model Registration] A first high-pass filter to which an input signal is supplied; a first limiter circuit to which an output signal of the first high-pass filter is supplied; a circuit for subtracting the output signal of the first limiter circuit; a second high-pass filter to which the subtraction output signal is supplied and having a cut-off frequency higher than the cut-off frequency of the first high-pass filter; an output signal of the second high-pass filter; A noise canceller circuit comprising: a second limiter circuit to which a signal is supplied; and a circuit for subtracting an output signal of the first limiter circuit and an output signal of the second limiter circuit from the input signal.