JPS6318188Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a circuit for suppressing pulse noise, and particularly to a pulse noise suppression circuit suitable for integration.

Since FM receivers are susceptible to pulse noise such as ignition noise, a circuit for suppressing this pulse noise is provided between the FM detection output and the stereo demodulation circuit.

FIG. 1 is a circuit diagram showing an example of a conventionally commonly used pulse noise suppression circuit, in which an input signal IN containing pulse noise supplied from an FM detection circuit (not shown) is used for timing adjustment. It is extracted through a low-pass filter 1 and a gate 2 which is normally open. The output signal of the gate 2 is supplied to a stereo demodulation circuit (not shown) via a level hold circuit 3 that interpolates the output when the gate 2 is closed.

On the other hand, a part of the input signal IN is supplied to a high-pass filter 4 for noise detection with a cut-off frequency of about 100KHz.
Only the pulse noise included in IN is extracted. The noise extracted in this way is amplified in the noise amplifier 5 and then full-wave rectified in the rectifier circuit 6. When the rectified output exceeds a predetermined level, the mono multivibrator circuit 7 is triggered to The output closes gate 2 momentarily. Here, since the time delay of the high-pass filter 4 is compensated by the low-pass filter 1, the output signal of the mono multivibrator circuit 7 is not controlled by the gate 2 during the period when the input signal IN contains pulse noise. It will be closed. Therefore, the pulse noise is removed at the gate 2, interpolation for the period during which the gate 2 is closed is performed in the level hold circuit 3, and only the detected output signal from which the pulse noise has been removed is sent to the stereo demodulation circuit (not shown). will be supplied. Note that 8 is an automatic gain control circuit that controls the gain of the noise amplifier 5 using the output of the rectifier circuit 6, and when pulse noise increases, the gain of the noise amplifier 5 is lowered and the gain of the noise amplifier 5 is reduced. This is to prevent new noise from occurring due to frequent closing of the door.

However, in the circuit with the above configuration, it is necessary to use a high-pass filter with sharp cut-off characteristics to detect noise, but when such a high-pass filter is integrated, it requires many external components, making it difficult to integrate. In addition to being unsuitable, this method also has problems such as a time delay resulting in the need for a low-pass filter with a large delay time for time adjustment.

Therefore, an object of this invention is to provide an inexpensive pulse noise suppression circuit suitable for integration, which eliminates the need for a high-pass filter for noise detection and a low-pass filter with a large delay time for time adjustment. The pulse noise suppression circuit according to this invention will be explained in detail below with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the pulse noise suppression circuit according to this invention, and the same parts as in FIG. 1 are shown using the same symbols. In the figure, 9 is a comparator that compares the output level of the rectifier circuit 6 with a preset reference value and generates an output when the rectifier output level exceeds the reference value to trigger the mono-multivibrator circuit 7. .

In the circuit configured in this way, the difference from FIG. This is because the circuit 6 is provided with an automatic gain control circuit 8 for making its output constant.

In a circuit configured in this way, when an input signal IN containing pulse noise is supplied from an FM detection circuit (not shown), this input signal IN is full-wave rectified in the rectifier circuit 6, and the pulse noise is added to the signal. is supplied to the comparator 9. According to experiments, the pulse height value of the pulse noise that is unpleasant to the ear has a modulation depth of 100%.
(75KHz) or higher.
Therefore, the reference value of comparator 9 is set to a modulation depth of 100.
By setting the level to be a little higher than the level that corresponds to %, the output will be generated only when the level is above this level. And this comparator 9
Since the output triggers the mono-multivibrator circuit 7, the gate 2 is controlled to close for the part containing pulse noise, as in the case of FIG. 1, and the pulse noise is suppressed. . In such a configuration, since a high-pass filter and a noise amplifier are unnecessary, the number of components other than that in the case of integration is significantly reduced.

In the above embodiment, a basic type of pulse noise suppression circuit is shown, but it may be applied to a circuit to which a 19 KHz correction circuit, a pilot cancel circuit, or other auxiliary circuits are added. Also,
When applied to a detection system in which the output level of the FM detection circuit becomes low at weak input, the automatic gain control circuit can be omitted. Furthermore, regarding automatic gain control, the output level of the rectifier circuit 6 may be controlled using the output of the mono multivibrator circuit 7, or the set level of the comparator 9 may be controlled using the output of the mono multivibrator 7.

As explained above, the pulse noise suppression circuit according to this invention eliminates the need for a high pulse filter for noise detection, making it suitable for integration. This has the effect of simplifying the matching low-pass filter.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional pulse noise suppression circuit, and FIG. 2 is a circuit diagram showing an embodiment of the pulse noise suppression circuit according to this invention. 1...Low pass filter, 2...Gate, 3...
...Level hold circuit, 6... Rectifier circuit, 7...
Mono multivibrator circuit, 8... automatic gain control circuit, 9... comparator.

Claims (1)

[Scope of utility model registration request] A rectifier circuit that performs full-wave rectification of an input signal containing pulse noise, a comparator that generates an output when the output level of this rectifier circuit exceeds a level slightly higher than a predetermined level of modulation depth, and a trigger that is triggered by the output of this comparator. A mono multi-vibrator circuit is connected to the input signal, and a low-pass filter to which the input signal is input, is normally open and passes through the output of the low-pass filter, and is closed when the output of the mono multi-vibrator circuit is generated to generate pulse noise. A pulse noise suppression circuit comprising a gate that prevents an input signal included in the part from passing through, and a level hold circuit that is connected to the output side of the gate and interpolates the output when the gate is closed.