JPS6331963B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a receiver noise removal method for removing sudden noises such as multipath and ignition noise.

BACKGROUND TECHNOLOGY During reception of conventional frequency modulation broadcasting, etc., noise suppression is performed not only when sudden noise occurs, but also when constant persistent noise occurs in the weak electric field of the broadcast frequency signal. It will be done. Therefore, the frequency characteristics and distortion rate when receiving a weak electric field broadcast frequency signal are deteriorated,
As a result, the quality of broadcasting deteriorated.

Purpose The purpose of the present invention is to provide a receiver noise removal method that eliminates only sudden noise without suppressing and eliminating noise when steady noise occurs in a weak electric field. The goal is to provide the following.

Configuration of the Invention The present invention includes a high-pass filter into which a received acoustic signal is input and which filters noise contained in the acoustic signal, a detection circuit which makes the output from the high-pass filter unipolar, a first time constant circuit that receives the output from the detection circuit and derives a detection signal corresponding to the sudden noise and the steady noise that persists longer than the sudden noise; a second time constant circuit that derives a detection signal corresponding only to the first time constant circuit; a logic circuit that derives a discrimination signal when there is no detection signal;
This is a noise removal method for a receiver characterized in that it includes a circuit that cuts off an acoustic signal in response to a discrimination signal from a logic circuit.

Embodiment FIG. 1 is an electrical circuit diagram of an embodiment of the present invention. The frequency modulated broadcasting is tuned by a tuning circuit 1, and given to a mixing circuit 2, where it is mixed together with a signal from a local oscillation circuit 3, and the output from the mixing circuit 2 is given to an intermediate frequency amplification circuit 4, where it is amplified.
It is demodulated by a demodulation circuit 5 and an acoustic signal is derived from a line 6. This acoustic signal 6 is applied from a delay circuit 7 to a separation circuit 9 via a noise suppression circuit 8. The separation circuit 9 separates the acoustic signal into a left channel and a right channel, and supplies the signal to amplifier circuits 10 and 11, where each channel is converted into sound by speakers 12 and 13.

The acoustic signal from line 6 is also applied to high pass filter 14. This high pass filter 1
4 includes transistors 15, 16, etc., and outputs the noise of, for example, 100 kHz or more contained in the acoustic signal to a line 17. The signal from line 17 is rendered unipolar by detection circuit 18 . This detection circuit 18 includes a capacitor 19, a transistor 20 that receives the output from the capacitor 19, and a variable resistor 21 that adjusts the base voltage of the transistor 20. The output from the detection circuit 18 is given to a first time constant circuit 23 and a second time constant circuit 24 from a line 22, respectively.

The first time constant circuit 23 includes a transistor 31 and
It includes a resistor 32 and a capacitor 33. Capacitor 33 is charged via resistor 32 when transistor 31 is turned off. When transistor 31 is conducting, capacitor 33 is rapidly discharged.

The second time constant circuit 24 includes a transistor 25;
It includes resistors 26 and 27, a diode 28, and a capacitor 29. A diode 28 is connected to the resistor 27.
are connected in parallel. Capacitor 29 can be rapidly charged via resistor 26 and diode 28 when transistor 25 is cut off. When transistor 25 is conductive, a discharge current flows through capacitor 29 via resistor 27 and transistor 25.

The outputs from the first and second time constant circuits 23 and 24 are shaped and inverted by waveform shaping circuits 34 and 35, and the outputs are sent to the line 3.
6 and 37, respectively.

Outputs from lines 36 and 37 are provided by logic circuit 38
given to. Logic circuit 38 includes an AND gate 39 receiving the detection signal from line 37 on one input and inverting the detection signal from line 36.
and an inverting circuit 40 that is applied to the other input of AND gate 39. AND gate 39 to line 41
The discrimination signal derived from the above is applied to the transistor 42 included in the noise suppression circuit 8.

In the noise suppression circuit 8, the output from the delay circuit 7 is applied to the aforementioned separation circuit 9 via resistors 43 and 44. Connection point 45 of resistors 43 and 44
A series circuit of a transistor 42 and a capacitor 46 is connected to.

FIG. 21 shows the acoustic signal derived from the demodulation circuit 5 on line 6. This acoustic signal includes sudden noises p1, p2, p3 such as multipath and ignition noise, and their sudden noises p.
A stationary noise p4 that lasts for a longer time than 1, p2, and p3 is included. The stationary noise p4 occurs, for example, when the received broadcast frequency signal has a weak electric field. The acoustic signal having the waveform shown in FIG.
4, thereby causing the line 17 to receive sudden noises p1, p2, p2, as shown in FIG.
A signal containing only p3 and stationary noise p4 is derived. This signal is applied from the capacitor 19 of the detection circuit 18 to the base of the transistor 20. The base-emitter voltage of this transistor 20 is indicated by line l1 in FIG. The base voltage of this transistor 20 can be adjusted by a variable resistor 21, and therefore the discrimination level l2 can be changed.
On line 22, a signal having an amplitude ΔV3 less than the discrimination level l2 of FIG. 2 is inverted and derived as shown in FIG. 2. The collector signal of the transistor 25 of the second time constant circuit 24 is
This is shown in FIG. This transistor 25 is
The base-emitter voltage is set to the discrimination level l3 shown in FIG. 2, and the signal on line 22 is level-discriminated and waveform-shaped. line 22
When the voltage of the signal exceeds the base-emitter voltage of transistor 25, transistor 25 becomes conductive, thereby causing its collector to go low. Due to the conduction of this transistor 25, the capacitor 29 is connected to the resistor 27 and the transistor 25.
It discharges after passing through. When transistor 25 is cut off, capacitor 29 is rapidly charged via resistor 26 and diode 28. Thus, the voltage on the output line 49 of the second time constant circuit 24 changes as shown in FIG. 5. resistance 2
6 and the time constant defined by capacitor 29 is large. Therefore, the voltage on the line 49 does not fall below the discrimination level l4, which is the base-emitter voltage of the transistor 50 included in the waveform shaping circuit 35, when the sudden noises p1, p2, p3 occur. When stationary noise p4 occurs, the voltage on line 49 reaches discrimination level l4.
This causes transistor 50 to conduct, the following transistor 51 to conduct, and line 37 to go low as shown in FIG.

Even if the steady noise p4 is interrupted and continues, the resistance 27
By choosing large time constants for capacitor 29 and capacitor 29, line 49 can be kept at a high level. In summary, due to the functions of the second time constant circuit 23 and the waveform shaping circuit 35, the line 37 is at a high level when sudden noises p1, p2, and p3 occur, and when there is no noise in normal conditions, and is at a steady level. When the noise p4 occurs, it becomes low level.

Transistor 31 in first time constant circuit 23
The collector signal of is shown in FIG. line 22 applied to the base of transistor 31
When the signal exceeds the discrimination level, which is the base-emitter voltage of the transistor 31, the transistor 31 becomes conductive, and this discrimination level is as shown in FIG.
This is similar to the value shown at reference numeral 13 in .
Due to the conduction of the transistor 31, the capacitor 33
is rapidly discharged and capacitor 33 is charged via resistor 32 when transistor 31 is cut off. The time constant determined by the resistor 32 and the capacitor 33 is relatively small, so the collector voltage of the transistor 31 is at the discrimination level l5, which is the base-emitter voltage of the transistor 52 of the subsequent waveform shaping circuit 35. be discriminated against. When the collector voltage of transistor 31 is below discrimination level l5, transistor 52 conducts, which causes subsequent transistor 53 to conduct, so that line 36 goes low as shown in FIG. . When the collector voltage of the transistor 31 is above the discrimination level l5, the transistors 52 and 53 are cut off and the line 3
6 is a high level. To summarize, due to the functions of the first time constant circuit 24 and the waveform shaping circuit 35, the line 37 is at a high level during normal operation, and when sudden noises p1, p2, p3 occur and when stationary noise p4 occurs. A signal that becomes a low level is derived.

In the logic circuit 38, a high level signal is derived on the line 41 only when the line 37 is at a high level and the line 36 is at a low level, that is, only when sudden noises p1, p2, and p3 occur. be done. As a result, the transistor 42 included in the noise suppression circuit 8 becomes conductive, and the acoustic signal derived via the delay circuit 7 is cut off.
The line 41 is at a low level when the stationary noise p4 occurs and when there is no noise, the transistor 42 is cut off, and no noise suppression is performed. Since the output impedance of the delay circuit 7 is low, the resistor 43 functions to make the impedance on the input side (left side in FIG. 1) higher than the connection point 45 so that the acoustic signal can be reliably blocked. .

When the transistor 42 in the noise suppression circuit 8 becomes conductive, the acoustic signal at the connection point 45 is interrupted as shown in FIG. 31. The capacitor 55 holds the value 56 just before the acoustic signal is interrupted for a period W during which the acoustic signal is interrupted due to the conduction of the transistor 42, and the value 56 is maintained as shown in FIG.
A signal indicated by is given to the separation circuit 9. In this way, it is possible to prevent the quality of the audio signal from deteriorating as much as possible due to noise suppression.

The delay circuit 7 delays the acoustic signal on the line 6 by the delay time due to the circuit configuration from the high-pass filter 14 responding to the acoustic signal on the line 6 to the logic circuit 38 and the operation of the transistor 42.
It functions to provide a signal to the noise suppression circuit 8. This ensures the removal of sudden noises p1, p2, and p3.

The present invention is not only implemented in connection with a receiver that receives frequency modulated signals, but can also be widely implemented in connection with receivers of other modulation schemes.

Effects As described above, according to the present invention, only sudden noises such as multipath and ignition noise are removed, and when steady noise occurs in a weak electric field, the noise is not suppressed and removed. Therefore, the quality of the received acoustic signal is prevented from deteriorating.

[Brief explanation of the drawing]

Fig. 1 is an electrical circuit diagram of an embodiment of the present invention;
3 and 3 are waveform diagrams for explaining the operation. 5... Demodulation circuit, 7... Delay circuit, 8... Noise suppression circuit, 9... Separation circuit, 14... High pass filter, 18... Detection circuit, 23... First time constant circuit, 24... 2 time constant circuit, 34, 35...
Waveform shaping circuit, 38...logic circuit.

Claims (1)

[Scope of Claims] 1. A high-pass filter to which a received acoustic signal is input and which removes noise contained in the acoustic signal; and a detection circuit which makes the output from the high-pass filter unipolar; a first time constant circuit that receives the output from the detection circuit and derives a detection signal corresponding to sudden noise and steady noise that persists beyond that; a second time constant circuit for deriving a corresponding detection signal; and a second time constant circuit responsive to the outputs from the first and second time constant circuits, in which the detection signal from the first time constant circuit is present and the detection signal from the second time constant circuit is present. A noise removal method for a receiver, comprising a logic circuit that derives a discrimination signal when there is no detection signal, and a circuit that blocks an acoustic signal in response to the discrimination signal from the logic circuit.