JPH051655B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise removal device for a receiver. The receiver noise removal device of the present invention is used, for example, to remove or reduce noise such as sudden multipath noise and ignition noise superimposed on a demodulated signal in an FM radio receiver.

[Conventional technology]

Conventionally, as a method for removing sudden noise superimposed on a demodulated signal in, for example, an FM receiver, the section where the noise occurs in the demodulated signal is blanked to 0 volts using a gate circuit, etc., and the section where the noise occurs is blanked. Methods have been devised to linearly interpolate waveforms.

[Problem that the invention seeks to solve]

In the above method, the waveform is interpolated linearly, so it is only effective against relatively short-term noise, the connection points of the waveform are distorted, and the previous and subsequent signal information is not reflected in the interpolated part. There are other problems.

[Means for solving problems]

FIG. 1 shows a receiver noise removal device according to the present invention for solving the above-mentioned problems.

In FIG. 1, 1 is a noise detection circuit that detects noise superimposed on a demodulated signal; 2 is a gate circuit that prevents passage of the demodulated signal during a period when noise is detected by the noise detection circuit; 3 is a resonant circuit through which the demodulated signal after passing through the gate circuit is passed; 4 is a frequency detection circuit that detects the main signal frequency of the demodulated signal; and 5 is a period during which noise is not detected by the noise detection circuit. The resonant frequency of the resonant circuit is set to be sufficiently higher than the signal frequency of the demodulated signal, and during the period when noise is detected, the resonant frequency of the resonant circuit is set to the signal frequency detected by the frequency detection circuit. controlling the resonance signal to
While extracting the main frequency signal of the demodulated signal,
This is a control circuit that removes unnecessary frequency components that are superimposed on the frequency of the demodulated signal by being cut off by the gate circuit.

The resonant circuit 3 can be composed of a variable resistor R, an inductor L, and a capacitor C, as conceptually shown in FIG. 2, for example. As shown in FIG. 3, this resonant circuit 3 is a low-pass filter with frequency characteristics having a resonant peak at the resonant frequency f(r), and the resonant frequency f(u) and resonance sharpness Q are respectively f Determined by (r)=1/2π√・Q=R/2π・f(r)・L.

Further, the frequency detection circuit 4 can be constructed by, for example, an F-V (frequency-voltage) converter as shown in FIG. This F-V converter is composed of a limiter 41, a differentiation circuit 42, a detection circuit 43, and an integration circuit 44.

[Effect]

The operation of the apparatus of FIG. 1 will be described below with reference to FIGS. 5-11.

FIG. 5 is a signal waveform diagram of each part of the device shown in FIG. 1,
In the figure, (a) is the received wave S with superimposed noise before demodulation.
(1), (b) are detection signals S(2), (c) from noise detection circuit 1
is the demodulated signal S(3) with superimposed noise obtained by detecting and demodulating the received wave, (d) is the output signal S(4) from the gate circuit 2,
(e) shows each signal waveform of the output signal S(5) from the resonant circuit 3.

When noise is superimposed on the received wave, the signal strength changes and the high frequency component increases. Therefore, the noise detection circuit 1 detects the noise by extracting the high frequency component of the signal level fluctuation and converts it into a detected signal. S
Output (2). The gate circuit 2 is turned on and off by this detection signal S(2), and the noise generation section of the demodulated signal S(3) on which noise is superimposed is removed to obtain the gate output signal S(4). This output signal S(4) is then input to the resonant circuit 3. The demodulated signal that has passed through the resonant circuit 3 is input to the frequency detection circuit 4. The frequency detection circuit 4 is, for example, an F-V converter, in which case its detection output is as shown in FIG.
A detection signal whose voltage level increases in direct proportion to the component frequency of the demodulated signal is output.

When no noise is generated, the resonant circuit 3 has its resonant frequency f(r) set sufficiently higher than the component frequency f(s) of the demodulated signal, as shown in FIG. The constants R, L, and C are controlled by the control circuit 5 so that the sharpness Q of is in the receiving state.

On the other hand, when noise generation is detected by the noise detection circuit 1, the frequency characteristics of the resonance circuit 3 in the noise generation section are as shown in FIG.
(r) matches the component frequency f(s) of the demodulated signal detected by the frequency detection circuit 4, and the frequency Each constant of the resonant circuit 3 is controlled by the control circuit 5 based on the detection output of the detection circuit 4. In FIG. 9, both f(r) and Q with respect to the detection signal voltage level from the frequency detection circuit 4 have a characteristic that increases in direct proportion to the detection signal voltage level, so that the resonant frequency f(r ) and the component frequency f(s) of the demodulated signal always match.

In this way, the resonant frequency f(r) and the resonance sharpness Q
When the demodulated signal S(4) of the waveform from which the noise generation section has been removed passes through the resonant circuit 3 where A demodulated signal S(5) from which the components have been removed is obtained. In addition, the resonant frequency f(r) is changed so that the resonance sharpness Q is also increased at the same time, which makes it possible to sufficiently interpolate the noise generation section of the waveform even when the section becomes long. . In other words, the waveform of the demodulated signal of the resonant circuit 3, which maintains the demodulated signal level before noise detection due to the gate circuit 2 being shut off when noise is detected, instantly becomes zero when noise is detected, as shown in FIG. 5d. , the zero level is maintained for a short period of time, and returns to a constant level from the zero level after a further short period of time. Examining the frequency distribution of the signal passing through the resonant circuit 3 in this case, this frequency distribution shows that harmonic components due to stepwise waveform changes are superimposed on the demodulated signal in FIG. 5d with respect to the frequency of the demodulated signal. Contains. Therefore, in the resonant circuit 3 of the present application, the resonant frequency of the resonant circuit is set by the frequency detection circuit, the harmonic components superimposed on the demodulated wave signal are removed, and only the demodulated wave signal is extracted, thereby obtaining a signal close to the original waveform. It turns out. Detection circuit S(2) from noise detection circuit 1
When the frequency characteristic disappears, the frequency characteristic returns to the original state shown in FIG.

FIG. 10 shows how the resonant frequency f(r) and the sharpness of resonance Q change when after-sound is generated and when no noise is generated. In this case, the resonance frequency f(r) is 5 kHz when noise occurs and 1 kHz when there is no noise, and the resonance sharpness Q is set to about 350 when noise occurs and about 0.6 when there is no noise. In order to remove the harmonic components mentioned above, as shown in this figure, the sharpness Q of the resonance frequency detected when noise occurs is applied to the resonance circuit 3.
is set, and the harmonic components contained in the demodulated wave formed by the gate circuit 2 are removed, as shown in FIG. 5d.

F- as a frequency detection circuit shown in FIG.
The operation of the V converter will also be explained. 11th
The figure is a signal waveform diagram of each part of the device shown in FIG. The differential signal S(42) of the differentiating circuit 42, (d) is the detection signal S(43) of the detection circuit 43, and (d) is the integral signal S of the integrating circuit 44.
This is the signal waveform of (44).

The demodulated signal S(5) inputted from the resonant circuit 3 is limited by the limiter 41 and a pulse-shaped limit output signal S(41) is output. A dead zone is provided so that (41) is not output. The output signal S (41) is then differentiated by the differentiating circuit 42,
A pulse-like differential signal S (42) is output near the zero crossing point of the output signal S (41). By detecting and rectifying this in the detection circuit 43, a detection signal S(43) having the same polarity is obtained, which is integrated in the integrating circuit 44. Therefore, in the end, the integrating circuit S(44) outputs a voltage level proportional to the density of zero crossings, that is, the frequency, of the input demodulated signal S(5).

〔Example〕

A receiver noise removal device as an embodiment of the present invention is shown in FIG. This embodiment of the device is an example in which the present invention is implemented using a digital circuit.

In FIG. 12, a demodulated signal from a receiver is first inputted to an AD converter 10 via a gate circuit, converted into a digital signal, and then sent to a resonant circuit 11.
guided by. The resonant circuit 11 includes multipliers C0 to C4, 1
It is configured to include sample delay devices D1 to D4 and adders A1 to A3. Here, the coefficients of the multipliers C0 to C4 are _C0 to _C4 . Further, the 1-sample delay device is composed of a shift register. This resonant circuit 11
^{Let f} ( _r ) be _the resonant _{frequency at} ² /T ² +2βT C ₂ = (T ² - 2βT) / (T ² + 2βT) C ₃ = (8α - 2T ² ) / (T ² + 2βT + 4α) C ₄ = (2βT - T ^{2 -} 4α) / (T ² +2βT+4α) (However, here, α=1/4π ²・f(r) ² , β=
It can be expressed as 1/2π・f(r)・Q, where T is the sampling period.

The output signal of the resonant circuit 11 is guided to a DA converter 12 and an F-V converter 13. F-V converter 1
3 is composed of a limiter 131, a differentiation circuit 132, a detection circuit 133, and an integration circuit 134. The differentiation circuit 132 includes a delay device D5, a multiplier K-1 with a coefficient of -1,
It is included in adder A4. The integrator 134 includes multipliers K1 to K3, delay devices D1 and D2, and adder A.
5, A6. The respective coefficients of multipliers K1 to K3 are _K1 to _K3 . When the integration time constant in the F-V converter 13 is 1.6 ms, the multiplier K
The coefficients _K1 to K3 of K1 to _K3 are _K1≈7.8 × ^10-3 _K2 =1 _K3 =9.8× ^10-1 .

The output signal of the F-V converter 13 is guided to a control circuit 14. A noise detection signal is introduced to the control circuit 14 from a noise detection circuit (not shown). The control circuit 14 may include a microcomputer or may consist of a complete logic circuit.

The operation of the apparatus of the embodiment shown in FIG. 12 will be explained. This is basically the same as the apparatus shown in FIG. In the device of this embodiment, the resonant frequency f(r) and resonance sharpness Q of the resonant circuit 11 are changed by changing the coefficients _C0 to C4 of the multipliers C0 to _C4 under control from the control circuit 14. It is possible to do so. Therefore, in order to change f(r) and Q with the characteristics shown in FIG. 10 between when noise occurs and when there is no noise, each coefficient C ₀ to C ₄ should be changed according to the above formula. Bye.

〔Effect of the invention〕

According to the present invention, even when interpolating by blanking the noise generation section of the demodulated signal, the effect of the resonant circuit makes the waveform connection of the interpolated part smooth, and the signal information before and after it is reflected in the interpolated part. Therefore, the distortion of interpolation in the blank portion can be significantly reduced compared to the conventional method.

Furthermore, by increasing the resonance sharpness Q when noise occurs, sufficient interpolation is possible due to the characteristics of the resonant circuit even if the blank time becomes long. Further F
By setting a large integration time constant of the -V converter, it is possible to detect the average frequency of the demodulated signal over a long period of time, and therefore to perform better rounding.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a receiver noise canceling device according to the present invention, FIG. 2 is a diagram conceptually representing the resonance circuit in FIG. 1, and FIG. 3 is a frequency characteristic diagram of the circuit in FIG. Figure 4 is a block diagram showing an example of the configuration of the frequency detection circuit in Figure 1, and Figure 5 is a block diagram of the frequency detection circuit in Figure 1.
Figure 6 is the input/output characteristic diagram of the circuit shown in Figure 4. Figure 7 and Figure 8 are frequency characteristics diagrams of the resonant circuit with and without noise. Figure 4 shows the change characteristics of f(r) and Q with respect to the circuit output. Figure 10 shows the changes in f(r) and Q with and without noise. Figure 11 shows each part of Figure 4. Signal waveform diagram,
FIG. 12 is a block diagram of a receiver noise removal device as an embodiment of the present invention. 1...Noise detection circuit, 2...Gate circuit, 3...
... Resonance circuit, 4 ... Frequency detection circuit, 5 ... Control circuit, 10 ... AD converter, 11 ... Resonance circuit,
12...DA converter, 13...F-V converter, 1
4...Control circuit.

Claims (1)

[Claims] 1. A noise detection circuit that detects noise superimposed on a demodulated signal; a gate circuit that prevents passage of the demodulated signal during a period during which noise is detected by the noise detection circuit; and the gate. A resonant circuit through which the demodulated signal passes after passing through the circuit, a frequency detection circuit that detects the main signal frequency of the demodulated signal, and a frequency detection circuit that detects the main signal frequency of the demodulated signal; The resonant frequency is set to be sufficiently higher than the signal frequency of the demodulated signal, and the resonant signal is set so that the resonant frequency of the resonant circuit is set to the signal frequency detected by the frequency detection circuit during a period in which noise is detected. A noise removal device for a receiver, comprising: a control circuit that controls and extracts a main frequency signal of a demodulated signal, and removes unnecessary frequency components that are superimposed on the frequency of the demodulated signal by being cut off by a gate circuit.