JPH0644188Y2 - Radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a circuit for removing noise of an in-vehicle radio receiver, and more particularly to an ignition noise canceller device for suppressing noise caused by an ignition device of a vehicle.

[Prior Art] A receiver installed in a vehicle is usually provided with a noise canceller circuit for removing ignition noise.

Ignition noise is generally pulsating noise, and when it is superimposed on a voice signal, it is very uncomfortable to hear.

FIG. 4 is a block diagram showing a conventional example of an ignition noise canceller circuit installed in a receiver, which circuit is provided in an audio signal circuit of a radio receiver.

In the figure, 1 is an input terminal to which an audio signal is supplied, 2 is a buffer circuit that matches the impedance of the signal, 3 is a low-pass filter that passes signals below the audio band, and 4 is spike-like noise that is superimposed on the audio signal. It is a high-pass filter that passes only the component. Reference numeral 5 is a low-pass amplifier that amplifies the output signal of the low-pass filter 3, and 6 is a high-pass amplifier that amplifies the output signal of the high-pass filter 4.

Reference numeral 7 denotes a noise detector, which receives a constant detection condition from the outside and outputs a noise detection signal according to the result. The conditions given to the detector 7 are a bypass input terminal 8 for bypassing the signal of the detector 7, an adjustment input terminal 9 for appropriately adjusting the noise detection sensitivity from the outside, and a noise
It consists of an input terminal 10 for adjusting the time constant of AGC. Note that the noise detection sensitivity cannot be set too high so as to prevent malfunction due to random noise when the antenna is weakly input.

Next, 11 is a monostable multi-circuit, which has an input terminal 12 for setting the output pulse width corresponding to the pulse width of noise, and the output pulse width can be appropriately adjusted by an external operation. There is.

Reference numeral 13 is a gate circuit, which has a gate time constant adjustment input terminal 17 for adjusting the gate cutoff time, and is provided with a time constant for removing distortion of the pilot signal. Reference numeral 14 is a gate circuit which receives a monostable multi-circuit output pulse and cancels noise superimposed on the audio signal. Also,
15 is a subtraction circuit.

Now, the receiver is operating, and ignition noise is mixed into the receiver as the engine of the vehicle rotates. As a result, in the output signal of the buffer circuit 2, spike noise is superimposed on the sinusoidal audio signal as shown in FIG. 5 (A). Further, as the engine speed increases and the ignition noise increases, the noise superimposed on the audio signal increases as shown in FIG. 5 (B).

The high-pass filter 4 passes only this noise component, and the low-pass filter 3 passes only the audio signal. The noise component amplified by the high-frequency amplifier 6 is input to the noise detector 7 and given constant detection conditions, and a noise signal that triggers the monostable multi-circuit 11 at the next stage is detected. The monostable multi-circuit 11 outputs a pulse signal with a predetermined width based on this noise signal.

On the other hand, in the audio signal amplified by the low-frequency amplifier 5, the noise component superimposed on the audio signal is canceled in the gate circuit 14 by the monostable multi-output pulse having the same width as the noise, and further, in the subtraction circuit 15, distortion is generated. Etc. are canceled, the signal at the output terminal 16 is shown in FIG.
As shown in (B), ignition noise in a certain range is suppressed.

[Problems to be Solved by the Invention] The noise canceller circuit shown in FIG. 4 gives a certain condition to the noise detector 7, and the time constant of the circuit is always fixed. For this reason, as shown in FIG. 6, the operating range of this circuit covers the shaded area in the figure where the noise amount increases in proportion to the engine speed, but at the point B beyond the range, the suppression effect is obtained. There was an inconvenience that there were few.

The present invention was made in view of the above points, and it is possible to provide a radio receiver provided with a noise canceller circuit that can obtain a noise suppression effect in all ranges by making the time constant of the circuit variable. To aim.

[Means for Solving the Problems] In order to achieve the above object, the radio receiver of the present invention is
A high-pass filter for passing a high-frequency component of an audio signal, a noise detector that detects noise from the high-frequency component from the high-pass filter, and a predetermined pulse according to the noise detected by the noise detector Noise including a pulse generation circuit that generates a signal and sets and outputs the pulse width of the pulse signal, and a gate circuit that blocks noise superimposed on the audio signal according to the pulse width from the pulse generation circuit In a radio receiver including a canceller unit, a rotation speed detection unit that detects the engine rotation speed of a vehicle and outputs a detection signal, and the noise detection sensitivity and the noise detection sensitivity of the noise detector according to the detection signal from the rotation detection unit. And a control unit for controlling the pulse width of the pulse generation unit to increase the noise detection sensitivity when the engine speed of the vehicle is high. Widening the Rutotomoni the pulse width, when the engine speed is low in the vehicle is achieved by that so as to narrow the pulse width with decreasing the noise detection sensitivity.

[Operation] Ignition noise superimposed on the audio signal of the receiver increases in proportion to the engine speed. That is, the absolute amount of noise increases as the engine speed increases. Then, the noise level becomes high and the pulse width also increases.

Therefore, in the present invention, the engine speed is detected,
The obtained signal is generated by the frequency-voltage conversion circuit into a DC voltage proportional to the engine speed, and thereby the noise detection sensitivity of the noise canceller circuit and the pulse width of noise are controlled.

[Embodiment] Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a noise canceller circuit installed in the radio receiver of the present invention. The first
In the figure, the same components as those of the conventional example of FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, 20 is a rotation speed detector for detecting the rotation speed of the engine, 21 is an amplifier for amplifying the detected signal, and 22 is a frequency-voltage conversion circuit for converting the output signal of the amplifier 21 into a DC voltage. The rotation detector 20 can be configured, for example, by extracting a rotation pulse from the negative side of the ignition coil of the vehicle and shaping the waveform. Frequency-voltage conversion circuit
22 is for obtaining a voltage proportional to the engine speed, and is configured so that a low voltage level is obtained when the engine speed is low, and a high voltage level is obtained when the engine speed is high.

Next, the operation of the present invention will be described.

The rotation speed detector 20 detects a signal having a period proportional to the engine rotation speed, and this signal is amplified by the amplifier 21. Further, the frequency-voltage conversion circuit 22 converts the voltage into a DC voltage proportional to the engine speed. Then, this DC voltage is applied to the noise detection sensitivity adjustment terminal 9 of the noise detector 7 and the input terminal 12 of the monostable multi-circuit 11 to control the noise detector 7 and the monostable multi-circuit 11.

The detector 7 automatically adjusts the detection sensitivity according to the amount of the noise signal input from the high frequency amplifier 6 by this control signal. That is, when the engine speed is low and the noise amount is small, the detection sensitivity is lowered, and when the noise amount increases in accordance with the engine speed, the detection sensitivity is raised to detect all noise.

The signal detected by the detector 7 operates as a trigger signal for the monostable multi-circuit 11, and the output pulse of the monostable multi-circuit 11 is controlled by the DC voltage applied to the input terminal 12. That is, when the DC level is low, the output pulse of the monostable multi-circuit 11 is narrow, and when the DC level is high, a wider pulse width is output. The gate circuit 14 is a monostable multi-circuit 11
The output pulse of cancels the noise component of the input audio signal, and obtains the audio signal with the ignition noise removed at its output terminal 16.

FIG. 2 shows the relationship between the engine speed and the noise amount that increases in proportion to the engine speed. The noise amount (A) when the engine speed is low and the noise amount (B) when the engine speed is high are They are represented by (A) and (B) in FIG. 3, respectively.

Further, the waveforms of (A) and (B) at the output point of the buffer circuit 2 are waveforms obtained by removing the ignition noise at the output terminal 16 as shown in FIG. 3 (C) due to the effect of the circuit.

[Effects of the Invention] As described above, according to the radio receiver of the present invention,
A high-pass filter for passing a high-frequency component of an audio signal, a noise detector that detects noise from the high-frequency component from the high-pass filter, and a predetermined pulse according to the noise detected by the noise detector Noise including a pulse generation circuit that generates a signal and sets and outputs the pulse width of the pulse signal, and a gate circuit that blocks noise superimposed on the audio signal according to the pulse width from the pulse generation circuit In a radio receiver including a canceller unit, a rotation speed detection unit that detects the engine rotation speed of a vehicle and outputs a detection signal, and the noise detection sensitivity and the noise detection sensitivity of the noise detector according to the detection signal from the rotation detection unit. And a control unit for controlling the pulse width of the pulse generation unit to increase the noise detection sensitivity when the engine speed of the vehicle is high. Along with increasing the pulse width, when the engine speed of the vehicle is low, the noise detection sensitivity is lowered and the pulse width is narrowed, so that it corresponds to the noise amount that changes in proportion to the engine speed. It is possible to expect an excellent effect that the noise detection sensitivity can always be set to high sensitivity and that no malfunction occurs with respect to noise other than the ignition noise when the incoming radio wave is weakly input.

Also, because the output pulse width of the monostable multi-circuit is changed in proportion to the engine speed, there is no waste in the operation of canceling the ignition noise superimposed on the audio signal, and as a result, the audio signal with less distortion Can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of a noise canceller circuit installed in a radio receiver of the present invention, FIG. 2 is a diagram showing the relationship between engine speed and the amount of noise generated, and FIG. 3 is a diagram superimposed on an audio signal. It is a waveform diagram of ignition noise. FIGS. 4 to 7 are diagrams for explaining the prior art. FIG. 4 is a block diagram of a noise canceller circuit, FIGS. 5 and 7 are audio signal waveform diagrams in which noise is superimposed, and FIG. It is a figure which shows the relationship between engine speed and the noise amount. 3 ... Low-pass filter, 4 ... High-pass filter, 7
...... Noise detector, 11 …… Monostable multi-circuit, 14 …… Gate circuit, 20 …… Rotation speed detector, 22 …… Frequency-voltage conversion circuit.

Claims (1)

[Scope of utility model registration request] 1. A high-pass filter for passing high-frequency components of an audio signal, and a noise detector for detecting noise from high-frequency components from the high-pass filter,
A pulse generation circuit that generates a predetermined pulse signal according to the noise detected by the noise detector and sets and outputs the pulse width of the pulse signal, and an audio signal according to the pulse width from the pulse generation circuit. In a radio receiver provided with a noise canceller section composed of a gate circuit for blocking superimposed noise, a rotation speed detection section for detecting an engine rotation speed of a vehicle and outputting a detection signal, and a rotation speed detection section from the rotation detection section. A noise detection sensitivity of the noise detector and a control unit for controlling the pulse width of the pulse generation unit according to a detection signal are provided, and when the engine speed of the vehicle is high, the noise detection sensitivity is increased and the pulse width is widened. However, when the engine speed of the vehicle is low, the noise detection sensitivity is lowered and the pulse width is narrowed. Radio receiver to be.