JPS6110327A - Pulse noise eliminating circuit - Google Patents

Abstract

PURPOSE:To eliminate noise by interrupting an input signal when the noise is detected and amplifying an output signal of a gate circuit with an amplification factor in response to the interrupting time. CONSTITUTION:A signal where noise is superimposed continuously is inputted to an input terminal 11. A level of an output signal of a detection circuit 13 goes to logical ''1'' at the noise generating timing and gate circuits 14, 20 are turned off. A voltage across a resistor R1 is fed to a differential amplifier 23 via a voltage controlled amplifier 21 whose amplification factor is controlled by an output voltage of a differential amplifier 23 and an LPF22. A voltage controlled amplifier 15 amplifies an output signal of the circuit 14 and since the duty ratio of signals (g), (f) are corresponded together, an output signal (h) of the amplifier 15 is equal to a signal on which no noise is superimposed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pulse noise removal circuit that removes pulse noise.

BACKGROUND OF THE INVENTION In audio devices such as conventional radio receivers, it is necessary to take measures against noise in order to obtain high quality reproduced sound. In particular, noise countermeasures are an important issue in in-vehicle audio installed in vehicles that have a lot of noise such as ignition noise and spark noise.

FIG. 6 is a circuit diagram showing an example of a conventional pulse noise removal circuit, in which 1 is an input terminal into which the output signal a of the demodulation circuit is input, 2 is a delay circuit for delaying and smoothing the signal a; 3 is a bypass filter, 4 is a detection circuit, 5 is a monostable multi-bi break, 6 is a gate circuit, 7 is a sample hold circuit consisting of a capacitor C and an operational amplifier OP,
8 is an output terminal. Note that the gate circuit 6 is turned off when the output signal C of the monostable multivibrator 5 is "1".

The pulse noise removal circuit shown in the figure is configured to bypass the bypass circuit (3). During this time, the gate circuit 6 is turned off and the voltage immediately before the noise held in the sample hold 7 is outputted to the output terminal 8, thereby removing the noise superimposed on the signal a. Therefore, when the signal a on which a single noise is superimposed as shown in Fig. 7(A) is applied to the input terminal 1, the output signal of the delay circuit 2 is as shown in Fig. 7(B). And the output signal C of the monostable multi-bi break 5 is
As shown in FIG. 3(C), a certain period of time T is 1° from the noise occurrence time t1.

Therefore, from time t1 to time t2, the gate circuit 6
is turned off, and the voltage held in the sample-and-hold circuit 7 is output from the output terminal 8, so that the output signal d has noise removed, as shown in FIG.

In this way, if a single noise is superimposed, the 6th
Although it is possible to remove noise using the conventional device shown in the figure, when a signal a on which noise is continuously superimposed as shown in FIG. 8(A) is applied to the input terminal 1, , noise generation timing and gate circuit 6 on,
Since the off-timing is off, there is a drawback that distortion occurs in the output signal d as shown in FIG. 8(D).

Problems to be Solved by the Invention The present invention solves the above-mentioned drawbacks, and its purpose is to ensure that pulse noise can be removed. Examples will be described in detail below.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention, in which 11 is an input terminal into which the output signal e of the demodulation circuit is input, 12 is a bypass filter, 13 is a detection circuit, ]4 is a gate circuit, and 15
16 is a voltage control amplifier, 16 is a low-pass filter, 17 is an output terminal, and 18 is a control voltage generation circuit consisting of a DC power supply 19, a gate circuit 20, a voltage control amplifier 21, a low-pass filter 22, a differential amplifier and a resistor R1. Note that the gate circuits 14 and 20 are configured so that the output signal f of the detection circuit 13 is "1".
It is in the off state for a period of time. Further, the voltage control amplifiers 15 and 21 amplify the input signal with an amplification factor corresponding to the output voltage of the differential amplifier, and have almost the same characteristics.

If, for example, the signal e shown in FIG. 2 (A>) is input to the input terminal 11 on which noise is continuously superimposed, the output signal f of the detection circuit] 3 will be affected by the noise generated as shown in FIG. 2 (B). 1" at the timing, and the gate circuit 1
4.20 is in the off state while the signal f is "1" as described above, so the output signal g of the gate circuit 14 and the voltage across the resistor R1 are as shown in FIG.
D).

Here, the voltage across the resistor R1 is controlled by the voltage control amplifier 21 whose amplification factor is controlled by the output voltage of the differential amplifier.
and is applied to one terminal of the differential amplifier 23 via the low-pass filter 22, and the differential amplifier voltage is applied to the reference voltage E applied to the child terminal from the DC power supply 19 and the voltage applied to one terminal from the low-pass filter. Therefore, even if the gate circuit 20 is turned on or off and the voltage across the resistor R1 changes, the output voltage of the low-pass filter 22 will change in the direction that matches the reference voltage E. .

That is, the differential amplifier voltage is applied to the voltage control amplifier 21 to make the output voltage of the low-pass filter 22 match the reference voltage E. In other words, the differential amplifier outputs a voltage that makes the gain Ga of the voltage control amplifier 21 as shown in the following equation (1), assuming that the duty ratio of the signal f is DuXloo (%). .

Ga = 1/ (1-Du) --- (1) On the other hand,
The output voltage g of the gate circuit 14 shown in FIG. 2(C) is applied to the low-pass filter 16 via the voltage control amplifier 15, but the voltage control amplifier 15 has almost the same characteristics as the voltage control amplifier 21 as described above. Since the input signal is amplified by the amplification factor corresponding to the output voltage of the differential amplifier 15, the output signal of the voltage control amplifier 15 is as shown in the figure (
It will be as shown in E). That is, the voltage control amplifier 15 amplifies the output signal of the gate circuit 14 with the amplification factor shown in equation (1), and the duty ratio of the signal g also corresponds 1:1 to the duty ratio of the signal f. Therefore, in terms of area (power), the output signal of the voltage control amplifier 15 is equal to a signal on which no noise is superimposed. Therefore,
The output signal of the voltage control amplifier 15 is passed through a low pass filter 1.
6, it is possible to obtain a signal i from which noise has been removed, as shown in FIG. 6(F).

Figure 3 (A) and CB) are respectively Figure 2 (A).

FIG. 4 is a diagram showing the frequency components of signals a and f shown in FIG. As described above, since the output signal of the voltage controlled amplifier 5 has less low frequency distortion due to noise than the signal e, the noise can be removed by passing it through the low pass filter 16.

FIG. 4 is a block diagram of an embodiment of the present invention;
1 is an input terminal to which the output signal j of the demodulation circuit is input; 32
One bald circuit, one wing is a bypass filter, another is a detection circuit,
A is a pulse ordering circuit, A is a gate circuit, r is an amplifier, wings are a low-pass filter, 39 is an output terminal, and R2-R4 are resistors. Note that the gate circuit n is in an off state during the output signal hA ("1") of the detection circuit 34, and the pulse generator circuit is in an off state during the output signal hA ("1") of the detection circuit 34.
is the time during which the signal k is 1'', and W is a predetermined constant).The output signal m is set to 12. In addition, the gate circuit is in an off state while the signal m is "1", and the amplifier section has an amplification factor of 1 when the gate circuit is off, and when the gate circuit is on. The amplification factor is (1+W)/W.

Therefore, if the signal j shown in FIG. 5(A) is input to the input terminal 31, the output signal of the detection circuit will be as shown in FIG. 5(B), and the output signal l of the gate circuit section will be as shown in FIG. The circuit shown in FIG. 2C is added to the amplifier section. Here, as mentioned above, the pulse ordering circuit section sets the output signal m to "1" between T and W at the falling edge of the signal.
When the gate circuit A is off, the amplification factor is 1, and when the gate circuit A is on, the amplification factor is (1+W)/ Since the output signal n is assumed to be W, the output signal n of the amplifier section is as shown in FIG. That is, the output signal n of the amplifier is equal in area (power) to a signal on which no noise is superimposed. Therefore, by passing the output signal n of the amplifier through the low-pass filter blades, it is possible to remove the noise superimposed on the signal j.

As described in detail, the present invention includes a noise detection means consisting of a bypass filter 12°, a detection circuit 13, 34, etc. for detecting noise superimposed on an input signal, and a noise detection means that detects noise by the noise detection means. a gate circuit consisting of a gate circuit 14, 32, etc., which interrupts an input signal at a certain time; and an amplification means consisting of a voltage control amplifier 15, an amplifier section, etc., which amplifies an output signal of the gate circuit with an amplification factor corresponding to the interruption time of the gate circuit. Therefore, even when continuous noise is superimposed on the signal, there is an advantage that the noise superimposed on the signal can be removed. Therefore, if it is applicable to devices placed in noisy places such as car radios,
The effect will be huge.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is an explanatory diagram of the operation of Fig. 1, and Fig. 3 (A) and (B) are signal a.
, d, FIG. 4 is a block diagram of another embodiment of the present invention, FIG. 5 is an explanatory diagram of the operation of FIG. 4, FIG. 6 is a circuit diagram of the conventional example, and FIG. FIG. 8 is an explanatory diagram of the operation of FIG. 6. 1.11.31 is an input terminal, 2 is a delay circuit, 3.12° is a bypass filter, 4.13.34 is a detection circuit, 5
is a monostable multi-bi break, 6.14.20.32゜A is a gate circuit, 7 is a sample and hold circuit, 8゜17
．． 39 is an output terminal, 15.21 is a voltage control amplifier, 16
゜Feather is a low-pass filter゜, 1B is a control voltage ordering circuit,
19 is a DC power supply, 23 is a differential amplifier, 35 is a pulse generation circuit, 37 is an amplifier, C is a capacitor, oP is an operational amplifier, and R1-R4 are resistors. Patent applicant Fujitsu Ten Ltd. Representative Patent Attorney Gobe Tamamushi (1 other person) Figure 6 Figure 4 Figure S

Claims (1)

[Claims] noise detection means for detecting noise superimposed on an input signal; a gate circuit for cutting off the input signal when noise is detected by the noise detection means; 1. A pulse noise removal circuit comprising: amplification means for amplifying the output signal of the circuit; and a low-pass filter for filtering the output signal of the amplification means.