JPS634732B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM receiver equipped with a pulse noise canceling circuit and a circuit for controlling muting, high cut, etc.

In-vehicle FM receivers detect noise and control muting, high cut, and separation. In this case, for noise detection, a signal obtained by extracting the noise and converting it to DC is used as a control signal, so it takes time to detect the noise, making it impossible to control instantaneously generated noise. On the other hand, a method has been proposed in which the speed of noise processing is increased by using envelope detection, but this method has the problem of being sensitive to impulse-like ignition noise.

In order to solve this problem, a pulse noise canceling circuit A shown in FIG. Methods are used to control radiation. In this case, the pulse noise canceling circuit A captures the detection output using a buffer circuit 1, and supplies the output of the buffer circuit 1 to a gate circuit 3 for noise canceling via a low-pass filter 2 for delay. . On the other hand, the output of the buffer circuit 1 is supplied to a high-pass filter 4 to extract only the high-frequency noise component of the pulse noise, and the output is supplied to an automatic gain control amplifier 5. This automatic gain control amplifier 5 increases the gain when the input signal is small,
When the input signal rises above a certain level, the output is held at a constant value. In this way, when a signal indicating that noise is detected is output from the automatic gain control amplifier 5, the monostable multi-circuit 6 is activated and the gate circuit 3 is turned off. Noise is removed by blocking the delayed signal containing noise. In this case, when the gate circuit 3 is cut off, a large level change occurs and this becomes noise, so the level hold circuit 7 holds the signal immediately before the gate circuit 3 is cut off and outputs it via the output circuit 8. configured to send.

However, when trying to obtain a control signal corresponding to noise using the output of such a pulse noise canceling circuit A, the signal passes through the low-pass filter 2, so the high-frequency noise component decreases, and the high-pass filter 16 In order to detect high-frequency noise components, considerable amplification is required before the high-pass filter 16. In addition, even if the previous stage amplifies the noise component considerably, the high-pass filter 16 extracts only the noise component and completely blocks the signal component.The high-pass filter 16 must be configured to have a sharp rise characteristic due to L, C, etc. . Furthermore, the pulse noise canceling circuit A has a problem in that automatic gain control for instantaneously generated multi-noise is delayed, so that noise processing in subsequent stages is delayed accordingly.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an FM receiver having a means for simplifying the high-pass filter for detecting noise components and quickly detecting noise.

Hereinafter, the FM receiver according to the present invention will be explained in detail using the drawings.

FIG. 2 is a circuit diagram showing an embodiment of a pulse noise canceling circuit and a noise detection circuit for obtaining control signals for muting, high cut, etc. according to the present invention, and the same parts as in FIG. 1 are denoted by the same symbols. It is shown using In the figure, reference numeral 9 denotes an automatic gain control amplifier which receives the output of the high-pass filter 4 as an input, and uses its output to trigger the monostable multi-circuit 10. Reference numeral 11 denotes a gate circuit which receives the output of the high-pass filter 4 as an input, and is gate-controlled by the output of the monostable multi-circuit 10. In this case, by making the time constant of the automatic gain control amplifier 9 sufficiently shorter than the time constant of the automatic gain control amplifier 5 of the pulse noise cancel circuit A, the circuit operation is faster than that of the pulse noise cancel circuit A. This speeds up the noise detection process. In addition, this automatic gain control amplifier 9
is used only to detect noise, so there is no problem with sound quality. Therefore, this automatic gain control amplifier 9 increases its gain as much as possible. Furthermore, the gate time of the gate circuit 11 is sufficiently narrower than that of the gate circuit 3 so that ignition noise does not become dull. Next, the level hold circuit 12 functions to continue to hold the midpoint potential during the gate cutoff period in order to prevent the DC output component from greatly fluctuating when the gate circuit 11 is cut off. And this level hold circuit 1
The output signal of 2 is passed through a low-pass filter 13 that removes noise components when the gate circuit 11 is opened and closed;
is supplied to the DC conversion circuit 15 via the amplifier 14,
Here, it is converted into a DC signal and the mutating signal is converted into a DC signal.
It is supplied to control units such as high cut and separation.

In the FM receiver configured in this way, when a high-frequency noise signal such as ignition noise is output from the high-pass filter 4 of the pulse noise cancel circuit A, the pulse noise cancel circuit A performs the above-described operation. to cancel the noise contained in the output signal.

On the other hand, the automatic gain control amplifier 9 quickly processes the noise signal output from the high-pass filter 4 and supplies its output to the monostable multi-circuit 10 for triggering. The triggered monostable multi-circuit 10 sends out a narrow pulse to control the opening of the gate circuit 11, takes in the noise sent out from the high-pass filter 4, and controls the level-hold circuit 12, low-pass filter 13,
It is supplied to the DC conversion circuit 15 via the amplifier 14.
Therefore, from this DC conversion circuit 15, a control signal at a DC level corresponding to the detected noise is obtained. In the circuit configured in this way, since the high-pass filter 4 of the pulse noise canceling circuit A is used, the circuit configuration is simplified and the cost is correspondingly reduced. In addition, since the automatic gain control amplifier 9 uses a separate automatic gain control amplifier with a short time constant,
Instantly generated noise can be quickly processed.

In the above embodiment, the case where the low-pass filter 13 is used has been described, but it is not necessarily necessary if the gate circuit 11 does not generate spike noise or if it does generate spike noise, it can be ignored.

As explained above, according to the FM receiver according to the present invention, instantaneously generated noise can be quickly detected and processed, and the high-pass filter of the pulse noise canceling circuit can be used. It has various excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a pulse noise canceling circuit in a conventional FM receiver, and FIG. 2 is a circuit diagram showing an embodiment of the FM receiver according to the present invention. 1... Buffer circuit, 2, 13... Low pass filter, 3, 11... Gate circuit, 4, 16...
High-pass filter, 5, 9... Automatic gain control amplifier, 6, 10... Monostable multi-circuit, 7, 12...
...Level hold circuit, 8...Output circuit, 14...
...Amplifier, 15...DC conversion circuit, A...Pulse noise canceling circuit.

Claims (1)

[Claims] 1. An FM receiver equipped with a pulse noise canceling circuit and a circuit for controlling muting, high-cutting, and separation, an automatic gain control amplifier whose input is the output of a high-pass filter provided in the pulse noise canceling circuit;
a monostable multi-circuit triggered by the output of the automatic gain control amplifier; a gate circuit whose input is the output of the high-pass filter and controlled by the output of the monostable multi-circuit; and an output of the gate circuit. The gate circuit includes a level hold circuit that holds the DC level when the gate circuit is open, and a DC conversion circuit that converts the output of the level hold circuit to DC and sends out a control signal, and mutes the control signal from the DC conversion circuit. , a control signal for high-cut and separation control, and a time constant of the automatic gain control amplifier is set to be faster than a circuit operation of the pulse noise canceling circuit.