JPH026459B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise removal circuit for in-vehicle radios, wireless devices, etc., and particularly to a circuit for removing impulsive noise such as ignition noise of automobiles.

Conventionally, this is the first impulsive noise removal circuit of this type.
I got what is shown in the figure. In the figure, 1 is a preamplifier circuit, 2 is a delay amplifier circuit, 3 is a gate circuit inserted in the signal path, 4 is an output circuit, and 5 is a noise
Noise detection circuit, including AGC (automatic gain control) circuit,
6 is a trigger circuit that shuts off the gate circuit based on the detection output of the noise detection circuit 5; 7 is a capacitor 9;
and a resistor 11, and 8 is a gate cutoff time setting circuit composed of a capacitor 10 and a resistor 12. In addition, 1~
These days, most of the parts of 6 are integrated circuits, and their operations are well known, so a detailed explanation of their operations will be omitted.

However, although such an impulsive noise removal circuit can effectively remove impulsive noise such as ignition noise, it cannot remove continuous noise such as horn noise or wiper noise. This is because the noise detection circuit 5 is operated by the white noise of the receiver, and in order to prevent negative effects such as distorting the desired signal and lowering the S/N, noise detection circuit 5 is used for continuous noise. So-called noise that reduces the detection sensitivity of circuit 5
This is because the AGC function is added. this is,
This is a necessary function to prevent impulsive noise removal circuits from performing a so-called squelch-like operation in which continuous noise completely removes the audio output, and most normal noise removal circuits have this function. It is something.

However, although this noise AGC function is effective against receiver white noise, it also works against highly disturbing continuous noise such as horn noise and wiper noise, so it is difficult to effectively eliminate these noises. Therefore, it was not possible to fully perform the function as a noise removal circuit.

The present invention provides an impulsive noise removal circuit that eliminates the above-mentioned drawbacks, and an embodiment of the present invention will be described below with reference to FIG. 2.

In Figure 2, 1 to 8 and 9 to 12 are the first
It is similar to that shown in the figure, and 13 to 15 are resistances,
16 is a transistor, and 17 is a capacitor.

Next, the operation will be explained. Note that the operations of each circuit No. 1 to No. 6 are the same as those of the conventional circuit, so the explanation thereof will be omitted.

Now, it is assumed that the capacitor 10 and resistor 12 set the cutoff time of the gate circuit 3, and the capacitor 9 and resistor 11 set the noise AGC integration circuit 7 optimally so as not to detect the white noise of the receiver.

By the way, when the level of white noise in the receiver is high, the noise detection circuit 5 detects the white noise, drives the trigger circuit 6, and attempts to turn on and off the gate circuit 3. But the noise AGC
As described above, the function lowers the sensitivity of the noise detection circuit 5 according to the detection frequency.

The noise AGC integration circuit 7 determines how often the noise AGC function is activated.

Trigger circuit 6 and gate cutoff time setting circuit 8
A charge/discharge voltage corresponding to the noise detected by the noise detection circuit 5 is obtained on the line connecting the two. The capacitor 17 is for DC cut, and the resistors 14 and 1
5 is transistor 1 for receiver white noise
The resistance value is set so that 6 is not conductive.

Now, when the noise detection circuit 5 detects continuous noise such as horn noise or wiper noise, the noise AGC function is activated and the sensitivity of the noise detection circuit 5 tends to decrease. However, since the charging/discharging voltage is introduced to the capacitor 17, the resistors 14 and 1
Even if the voltage is divided by 5, the transistor 16 becomes conductive when a voltage sufficient to make the transistor 16 conductive is supplied to ground. As a result, the resistor 13 is grounded, and the time constant of the noise AGC integration circuit 7 becomes small, as determined by the parallel resistance value of the capacitor 9, resistor 11, and resistor 13.
The AGC function will no longer be able to reduce the sensitivity of the noise detection circuit 5 unless it detects continuous noise greater than what has just been detected. In other words, this impulsive noise removal circuit can effectively remove continuous noise such as horn noise and wiper noise without leaking the noise into the audio signal using the noise AGC function. Can be done.

As described above, according to the present invention, the noise AGC function works effectively against white noise, etc., and relaxes the noise AGC function against continuous noise such as horn noise and wiper noise. Therefore, since these noises can be removed, it is possible to provide an impulsive noise removal circuit that can effectively remove a wide range of noises other than impulsive noise.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional impulsive noise removing circuit, and FIG. 2 is a block diagram showing an embodiment of the impulsive noise removing circuit of the present invention. 3...gate circuit, 5...noise detection circuit, 7...
...Integrator circuit for noise AGC, 16...transistor. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Impulsive noise comprising a noise detection circuit, a gate circuit inserted into a signal path and cut off based on the detection output of the noise detection circuit, and an integrating circuit for automatic noise gain control attached to the noise detection circuit. In the removal circuit, a switching element is provided which becomes conductive or non-conductive depending on a voltage corresponding to the noise detected by the noise detection circuit, and the time constant of the integrating circuit is changed by the conduction or non-conduction of this switching element. An impulsive noise removal circuit characterized in that it is configured to