JPS5814631A - Noise eliminating device for car radio signal receiver - Google Patents

Abstract

PURPOSE:To prevent the distortion of waveform which is easily caused in an audio signal and to reduce the deterioration of sound quality, by discontinuing a noise eliminating operation when the level of a received signal exceeds a prescribed value. CONSTITUTION:A switch 16 is opened by the detecting output of ignition noises obtained through a noise detecting circuit 7 when an AGC controlling voltage Ea is lower than a prescribed level, i.e., the received input level is small. Then the level of the wave detecting signal of a wave detecting circuit 4 which is so far charged by a capacitor 10 is held and delivered, and the output of the wave detecting signal is cut off to eliminate ignition noises. When the received input level increases and the voltage Ea exceeds the prescribed level, a switch 18 is closed with the switch 16 by-passed. As a result, the wave detecting signal is delivered to a voice amplifying circuit 5 via the switch 18 althrough the switch 16 is opened by the output of a noise detecting circuit 7. Thus the noise eliminating operation is discontinued.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise removal device for a vehicle radio receiver, which removes pulse noise such as ignition noise.

Conventionally, as a vehicle receiver equipped with this type of noise removal circuit, there is one shown in FIG. 1, for example.

In FIG. 1, 1 is a receiving antenna, 2 is a front end having a high frequency amplifier and a tuning circuit, 3 is an intermediate frequency amplification circuit, 4 is a detection circuit, 5 is an audio amplification circuit, and 13 is a speaker, which is a general radio. It has the same circuit configuration as the receiver. As a noise removal device in such a radio receiver, an antenna 6 for noise detection is installed in the engine room 6'.
A noise detection circuit 7 detects ignition noise using the voltage induced in the antenna 6, and a noise removal circuit 8 provided at the output stage of the detection circuit 4 is activated based on the detection signal of the noise detection circuit 7. I try to do that.

This noise removal circuit 8 is composed of a gate switch 9 that is opened while the noise detection circuit 7 is producing a noise detection output, and a holding capacitor 10, and as shown in the time chart of FIG. When detected, the gate switch 9 is opened to cut off the detection signal from the detection circuit 4, hold and output the detection signal just before the noise that is charged in the capacitor 10, and when the noise is no longer detected, the gate switch 9 is opened. 9) to remove pulse noise contained in the detected signal.

In the conventional example shown in FIG. 1, the antenna 6 installed in the engine room detects and removes ignition noise, but pulse noise can be caused by various electrical components, in addition to ignition noise. For example, surge noise generated during the operation of air conditioners, power windows, etc. is common.Such surge noise should also be input from the battery power line to the noise detection circuit 7 via a DC cut capacitor. Surge noise can be removed. In addition, in the noise removal circuit 8 shown in FIG. 1, the gate switch 9 is opened and closed to block the passage of chivalrous noise and hold the detected signal. Connect resistor 11 in parallel with
A method is also used in which a p-pass filter is formed by opening the gate switch 9 when noise is detected, and pulse noise is reduced by cutting off the high frequency range of the detected signal.

By the way, in general, the relationship between the audio output from the speaker and the magnitude of the sound field force with respect to the magnitude of the reception input level of a radio receiver with an AGC function is as shown in Fig. 43. As the reception signal level increases, the AGC increases. Working audio output (
Curve 8) The ratio of background noise (curve N) to K decreases to 8
/N ratio is good], noise is not noticeable.

The noise suppression effect by this AGC function is the same for pulse noise, and the pulse noise input Np1 (peak level) decreases as the Fi reception input level increases, so it is close to the broadcasting antenna. When the vehicle is running in a medium or strong electric field region, pulse noise such as ignition noise does not bother the ears even without special noise removal.

However, in the conventional radio receiver shown in Fig. 1, even when the reception input level is strong and the noise level is sufficiently suppressed and the 8/N ratio is good, the detection signal is not output when pulse noise is detected. Since noise removal is performed by temporarily blocking and holding the noise, the signal waveform of the audio signal becomes distorted due to this noise removal. 41. In the case of an AM receiver, since the frequency bandwidth of the audio signal is narrow, the time width in which pulsed noise is mixed is long, and while the noise is occurring, the output of the audio signal is blocked and maintained. If noise removal is performed, waveform distortion due to this noise removal tends to become large, and there is a problem that the received broadcast becomes difficult to hear due to the waveform distortion.

The stupid invention was made in view of the above, and when ffK detects pulse noise included in the received signal, it cuts off the output of the audio signal while the noise is being detected, and instead outputs a signal!
! In a noise removal device that outputs a signal maintained at the audio signal level immediately before the signal is cut off.

When the 87N ratio improves due to an increase in the received signal level, K also performs the above noise removal to suppress the deterioration in sound quality.
K is such that the #i sound is not removed when the average amplitude value of the received signal exceeds a predetermined value.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 4 is a book diagram showing one embodiment of the present invention.

First, to explain the configuration, 12 is a radio receiver, receiving antenna 11 front end 2° intermediate frequency amplification circuit 3
, a detection circuit 4, an audio amplification circuit 5, and a speaker 13.

On the other hand, the noise removal device includes a noise detection antenna 6 provided in the engine room 6', a noise detection circuit 7 that detects and outputs ignition noise from the voltage induced in the antenna 6, and a noise detection circuit 7. The noise detection circuit 14 performs noise removal based on the detection output of the noise detection circuit 14.

In addition, in the radio receiver 12, an AGC control voltage E corresponding to the level of the received signal from the detection circuit 4 is outputted to the intermediate frequency amplifier circuit 3 and the high frequency amplifier (not shown) of the front end 2. The AGC control voltage E,' is also given to the noise removal circuit 14 as a signal for determining the received signal level at which noise removal is to be stopped.

The noise removal circuit 14 includes a two-circuit gate switch 16.1.
8 are connected in parallel, and a capacitor 10 is connected to the output of the gate switch ≠ 16゜18.
6 is open while the noise detection circuit 7 is producing a detection output, and the gate switch 18 is open when the voltage controlled by A G C1114 is below a certain value, and is operated to close when it exceeds a certain value. .

Next, the effect will be explained.

FIG. 5 shows the characteristics of the speaker output with respect to the reception input level in the embodiment of FIG.
i is the input level of pulsed noise, curve NpFi is the pulsed noise level by the conventional noise removal device, and curve Npo is
The pulse noise level according to the embodiment of FIG. 4 is expressed by curve A.
GC represents human GC control voltage E8.

In FIG. 5, - lines S and N indicate rms values, and curves Npi, Np, and Npod peak values.

Here, the operating point of the gate switch 180 in the noise removal circuit 14 of FIG. 4 is such that the pulse noise input Npi is lower than the pulse noise level Np due to opening and closing of the gate switch 160 in the characteristic graph of FIG. , the AGC control voltage Eao when the reception input level is Eo is set as the operating point.

That is, when the AGC control voltage Ea is below the set value Eao, the gate switch 18 is opened and the set value gao
, the gate switch 18 is closed.

Next, the operation will be explained.

First, when the AGC control voltage F2+a is less than or equal to the set value Eao, that is, when the reception input level is small.

Due to the detection output of ignition noise by the noise detection circuit 7, the gate switch 16 of the noise removal 1 or 14 is opened while the noise detection output is generated, and the gate switch 16 is closed.
The level of the detection signal of the detection circuit 4 that was charging the capacitor 10 when the capacitor 10 was opened is held and output, and while the ignition noise is generated, the output of the detection signal is cut off to remove the ignition noise. .

Next, if the reception input level increases and the AGC control voltage Ha becomes one level higher than the set value Eao, the gate switch 18
closes and bypasses the gate switch 16. Therefore, even if the gate switch 16 is opened by the output of the noise detection circuit 7, the detected signal is output to the audio amplification circuit 5 via the gate switch 18, and the noise removal operation is stopped.

In this case, as is clear from the characteristic graph in Figure 5, the peak noise level Np is sufficiently suppressed with respect to the audio output S, so even if noise removal is stopped, the pulse noise will hardly disappear. On the contrary, stopping noise removal prevents waveform distortion from occurring in the audio signal, and improves the sound quality.

In the above embodiment, the noise removal is stopped by closing the gate switch 18 so that the differential voltage Ba is applied to the AGC III control voltage Ba. This may be done by detecting the level.

Also, regarding the noise removal method in which a resistor is connected in parallel with the gate switch 16 and a girth-pass filter is formed when the gate switch 16 is opened, the gate switch 18 is closed as in the embodiment shown in FIG. In some cases, a bypass circuit may be formed to prevent the high-frequency cut filter operation by the low-pass filter.

As explained above, according to the present invention, when pulse noise is detected, the output of the audio signal is cut off while the noise is being detected, and the signal level at the time of noise detection is maintained. When the signal level of the received broadcast signal exceeds a predetermined value, the device that removes noise stops the above-mentioned noise removal operation. When the noise removal operation is sufficiently performed, waveform distortion occurring in the audio signal is reliably prevented, and the deterioration in sound quality due to noise removal can be suppressed.

[Brief explanation of drawings]

Figure 1 is a schematic block diagram showing a conventional example, and Figure 2 is a block diagram of a conventional example.
1114 is a signal waveform diagram showing the operation of noise removal in the conventional example; FIG. 3 is a graph diagram showing the relationship between the speaker output and the receiving input of a conventional radio receiver; FIG. Ryo 1 road block diagram, tJS5 diagram is 4th
It is a graph showing the relationship between the speaker output direction and the AGC control voltage with respect to the reception input in the illustrated embodiment. 1...Receiving antenna 2...Front end 3
...Intermediate frequency amplification circuit 4...Detection circuit 5...Audio amplification circuit 13...Speaker 6...Antenna (for noise detection) e, l...Engine room 7...
Noise detection circuit 8,14・-Noise removal circuit 9.16
．． 18...Gate switch 1o...Conf y
-9-11...Resistance 12...Radio receiver section

Claims (1)

[Claims] When pulse noise included in the received signal is detected, the output of the audio signal is cut off while the noise is being detected, and the K! ! A noise canceling device that outputs a signal held at the audio signal level immediately before the audio signal is cut off includes a detection means for detecting and outputting an average amplitude value of a received signal, and a noise reduction device that outputs a signal maintained at the audio signal level immediately before the signal is cut off. 1. A noise removal device for a vehicle radio receiver, comprising: 1 stop command means for instructing the stop of the noise removal operation when the noise removal operation is stopped.