JPH0526374B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a multipath distortion removal device for an FM receiver. The multipath distortion removal device for an FM receiver according to the present invention removes multipath distortion that occurs in a demodulated signal to make it easier to hear when multipath interference occurs in a wireless receiver such as an FM radio receiver. Used to make sound. [Prior Art] Multipath interference is generally caused by interference between direct radio waves and reflected waves reflected from mountains, buildings, etc. When this multipath interference occurs, multipath interference occurs in the demodulated signal of the received wave. Distortion occurs and the sound quality deteriorates. This multipath distortion contains many high-frequency components, so when multipath interference occurs, the high-frequency characteristics of the receiver's output frequency characteristics are lowered as shown in Figure 12, thereby making the multipath distortion sound less perceptible. It makes it hard to hear. In FIG. 12, the ordinate represents the output level and the abscissa represents the frequency, the solid line represents the frequency characteristic when there is no multipath interference, and the broken line represents the frequency characteristic when there is multipath interference. [Problems to be Solved by the Invention] The above-described method of lowering the high frequency characteristics at the time of multipath interference deteriorates the frequency characteristics of musical performance sounds, etc., and deteriorates the sound quality of the receiver output sound. [Means for Solving the Problems] In order to solve the above problems, the present invention includes, as one form, a high frequency reception section, a frequency conversion section, an intermediate frequency amplification section, and an FM detection section,
an FM receiving section 2 into which a received wave input from an antenna 1 is introduced and outputting a composite signal; a stereo demodulation circuit 3 which demodulates and outputs L and R channel signals from the composite signal; a multipath interference detection unit 11 that detects an increase in high-frequency components of the composite signal to detect the occurrence of multipath interference; and a signal obtained by sampling the demodulated output of the stereo demodulation circuit 3 and converting it into a digital quantity; When multipath interference is detected by the signal prediction unit 6 which performs digital signal processing and calculates and outputs the predicted value of the next output signal, and the multipath interference detection unit 11, the signal prediction unit 6 calculates and outputs the predicted value of the next output signal. Multipath distortion removal of an FM receiver equipped with multipath interference switching units 51 and 52 that perform circuit switching so that the output signal of the signal prediction unit 6 is used as a demodulated signal instead of the output signal of the stereo demodulation circuit 3. Equipment is provided. In addition, in the present invention, as other forms, a high frequency receiving section, a frequency converting section, an intermediate frequency amplifying section, and
Contains an FM detection section, receives the received wave input from antenna 1, and outputs a composite signal.
An FM receiving section 2, a stereo demodulation circuit 3 which demodulates and outputs L and R channel signals from the composite signal, which inputs the composite signal, detects the low frequency AM component of the pilot carrier of the composite signal, and performs multiplexing. A signal obtained by sampling the demodulated output of the stereo demodulation circuit 3 and converting it into a digital quantity is input to a multipath interference detection unit 11 that detects the occurrence of path interference, and processes the digital signal to obtain a predicted value of the next output signal. When multipath interference is detected by the signal prediction unit 6 that calculates and outputs it, and the multipath interference detection unit 11, the stereo demodulation circuit 3
multipath distortion of an FM receiver, characterized in that it is equipped with multipath interference switching sections 51 and 52 that perform circuit switching so that the output signal of the signal prediction section 6 is used as a demodulated signal instead of the output signal of the signal prediction section 6. A removal device is provided. Further, the signal prediction unit 6 includes a plurality of filter circuits 21 to 24 that divide the demodulated output of the stereo demodulation circuit 3 into a plurality of frequency bands, and the signal prediction unit 6 has a plurality of filter circuits 21 to 24 corresponding to each of the plurality of filter circuits 21 to 24. 25 to 28 are provided, and the multipath disturbance switching units 51 and 52 add and output the plurality of output signals 25 to 28 instead of the output signal of the stereo demodulation circuit 3 during the period when the multipath disturbance occurs. A multipath distortion removal device for an FM receiver that performs circuit switching to generate a demodulated signal is provided. [Operation] According to one embodiment of the present invention, when multipath interference occurs, the multipath interference detection unit 11 detects the occurrence of multipath interference, and the multipath interference switching circuit selects a digital signal processing circuit to detect the multipath interference. A predicted signal from the digital signal processing circuit is used as a demodulated signal. Therefore, even in the event of multipath interference, multipath distortion can be removed without degrading the high frequency characteristics of the radio receiver. According to another aspect of the present invention, when multipath interference occurs, the demodulated signal is passed through a plurality of filter circuits 21.
After being divided into multiple frequency band components in step 24, predicted values are calculated in the corresponding digital signal processing circuits, and the predicted values of each frequency band component are added and output, so that the demodulated signal contains many frequency components. Even if the waveform is complex, it is possible to obtain a predicted waveform that approximates the original waveform. [Example] As an example of one embodiment of the present invention
A multipath distortion removal device for an FM receiver is described below. FIG. 1 is a block diagram showing an embodiment in which a multipath distortion removal device for an FM receiver according to the present invention is used in an FM radio receiver. In FIG. 1, received waves input from an antenna 1 are guided to an FM receiver 2. The FM receiving section 2 includes a high frequency receiving section, a frequency converting section, an intermediate frequency amplifying section,
It is configured to include an FM detection section and the like, and a composite signal is outputted as an output signal to the stereo demodulation circuit 3 and the multipath interference detection circuit 11. The stereo demodulation circuit 3 receives L from the composite signal.
and a circuit that demodulates and outputs the R channel signal. In order to simplify the drawing, FIG. 1 shows only the case where the output signal of one channel is output. The demodulated signal of one channel from the stereo demodulation circuit 3 is guided to digital signal processing indicated by a dashed line in FIG. In the digital signal processing section, the demodulated signal is sent to an adder 7 via an analog-to-digital (AD) converter 4 and a multiplier 51.
is led to one input end of the The output of the adder 7 is guided to a digital-to-analog (DA) converter 8 and also to the other input terminal of the adder 7 via the signal prediction section 6 and the multiplier 52. The output of the DA converter 8 is led to an amplifier 9, where it is amplified and then applied to a speaker 10. The multipliers 51 and 52 each function as a switch circuit that conducts between the input and output when the multiplication coefficients Ka and Kb are "1" and disconnects when the multiplication coefficients are "0". coefficient
Ka and Kb are variably controlled by the output signal of the multipath interference detection circuit 11, and have a relationship of Kb=1-Ka. Ka=1, Kb when there is no multipath interference
= 0, and when there is multipath interference, Ka
= 0, Kb = 1. FIG. 2 shows a detailed configuration of the signal prediction unit 6. The signal prediction unit 6 includes three delay devices 601, 602, and 60 connected in series to delay the signal input from the input terminal 611 by one sample time.
3. Multipliers 53, 54, and 55 connected to each output terminal of each delay device 601, 602, and 603, and an adder 604 that adds the respective outputs of multipliers 53, 54, and 55, and sends the result to output terminal 612. Contains and consists of. This signal prediction unit 6, multiplier 52,
The circuit including adder 7 constitutes a cyclic digital filter. Various types of multipath interference detection sections 11 have been known. For example, the third
As shown in the figure, it is possible to configure the detector 112 with a high-pass filter 111 that passes a band of approximately 60 kHz or higher. This circuit focuses on the fact that high-frequency components (frequency components higher than modulation components) in a composite signal increase when multipath interference occurs, and detects the increase in high-frequency components to detect the occurrence of multipath interference. It is. In addition, FIG. 4 shows the capacitor 113 and the detector 1.
Another example of the multipath interference detection unit consisting of 14 is shown. This circuit focuses on the fact that the pilot carrier undergoes amplitude modulation at the frequency period of the L and R channel signals when multipath interference occurs, and detects the low frequency AM component (several hundred Hz to several kHz) of this pilot carrier. It is something to do. The operation of the device of this embodiment will be explained below. First, when there is no multipath distortion, no detection output is sent from the multipath interference detection section 11, and the coefficients Ka and Kb of the multipliers 51 and 52 are Ka=1 and Kb=
0, the multiplier 51 becomes conductive and the multiplier 52 becomes inactive. In this case, the stereo demodulator 3
The demodulated signal is AD-converted by the AD converter 4, then inputted to the DA converter 8 via the multiplier 51 and adder 7, where it is DA-converted again and then sent to the speaker 11 via the amplifier 9. . When multipath interference occurs, multipath distortion is superimposed on the output signal to the speaker 10.
The output signal waveform to the speaker and the multipath detection signal waveform of the multipath interference detection section 11 in this case are shown in FIG. In FIG. 5, a is the output signal waveform to the speaker that has undergone multipath distortion, the section indicated by D in the figure is the distortion generation part, and b
is the multipath detection signal waveform. As is clear from FIG. 5, when multipath interference occurs, the output waveform to the speaker is intermittently distorted. The intermittent time of this distorted portion is approximately several milliseconds. When the multipath interference detection unit 11 detects the occurrence of multipath interference, the coefficients Ka, Ka, and
Kb becomes Ka=0 and Kb=1, so that the multiplier 51 becomes inactive and the multiplier 52 becomes conductive. As a result, the output signal from the signal prediction section 6 is outputted to the speaker 10 in the multipath distortion occurring portion. The signal prediction unit 6 sequentially stores the signal sequence of the demodulated signal sampled by the AD converter 4 in delay units 601 to 603, and applies these signal values to multipliers 53 to 55.
After multiplying the coefficients K1 to K3 by the adder 60
4, the predicted value of the next signal is calculated and output. This predicted output signal is sent to the multiplier 5
2. After passing through the adder 7 and being returned to an analog signal by the DA converter 8, it is applied to the speaker 10 via the amplifier 9, and is again input to the signal prediction unit 6 to calculate the next predicted value. used. In the above-described embodiment, a second-order predictor as shown in FIG. 2 is used in the signal prediction section. The reason for this is as follows. That is, when prediction is performed by the signal prediction unit, the accuracy of prediction is improved by sampling the signal over a long period of time before and after the multipath distortion occurrence portion, storing the signal sequence, and performing prediction. However, as shown in FIG. 5, multipath distortion generally occurs intermittently one after another, so it is not appropriate to sample and store signals over a long period of time to make predictions. Therefore, it is necessary to predict the signal of the distorted part over several milliseconds from the signal sampled over a time of about one millisecond, and for this purpose, a second-order predictor as shown in Figure 2 is used. . On the other hand, when the signal prediction unit 6 is configured with a second-order predictor, if the prediction time, that is, the time length of the distortion occurrence portion is long with respect to the input signal frequency, the predicted value will deviate significantly from the actual value. This situation is shown in FIG. 6, where the solid line waveform is the actual demodulated signal waveform, and the broken line waveform is the predicted output signal waveform. As is clear from the figure, as the prediction time becomes longer, the value of the predicted output signal becomes a value that is significantly different from the original demodulated signal. Another configuration example of the signal prediction section for solving this problem is shown in FIG. In FIG. 7, three delay devices 601 to 603 are connected in series, and three multipliers 5 multiply each output of the delay devices 601 to 603 by coefficients K1, K2, and K3.
The circuit consisting of an adder 604 that adds the respective outputs of multipliers 3 to 55 and multipliers 53 to 55 is the same as that shown in FIG. The difference is that the adder 60
The output of delay device 602 is led to one input terminal of adder 605 via multiplier 58, and the output of delay device 602 is guided to the other input terminal of adder 605 via multiplier 59. The output of this adder 605 is the output terminal 6
12, it is output as a predicted output signal of the signal prediction section. On the other hand, the input terminal 611 is also connected to a peak holding circuit 61 surrounded by a dashed line in FIG. In the peak holding circuit 61, the input signal Si from the input terminal 611 is sequentially input to delay devices 607 and 608 via a multiplier 56 and an adder 606. The output of the delay device 607 is also returned to the input side of the delay device 607 via the multiplier 57 and the adder 606. The multipliers 56, 57, 58, and 59 described above have coefficients Kc, Kd, Ke, and Kf, respectively, and when the coefficients of these multipliers are set to "1", the input and output are conductive, and when the coefficient is set to "0", the multipliers are conductive. It functions as a switch circuit that is sometimes turned off. Note that the circuit in FIG. 7 further includes an input terminal 611.
A detection circuit is provided for detecting the magnitude of the input signal Si, the output signals Sq and Sr of the delay devices 607 and 608, and the prediction signal Sn output from the adder 604, and also detects the magnitude relationship between the signals Si and Sq. Comparison circuit to judge, absolute value of signal Sn and signal
Comparison circuits are provided to determine the magnitude relationship of Sr, and the coefficients of each multiplier are variably controlled according to the outputs of these comparison circuits. These circuits are omitted. Coefficients Kc, Kd, Ke, Kf are signals Si, Sq, Sn, Sr
It changes as shown in Table 1 and Table 2 below depending on the magnitude relationship of .

【table】

〔Effect of the invention〕

According to the present invention, even when multipath interference occurs, multipath distortion can be removed without deteriorating the high frequency characteristics of the FM receiver.
The quality of performance sounds such as music can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a multipath distortion removing device as an embodiment of one embodiment of the present invention, FIG. 2 is a block diagram showing details of the signal prediction section in the device of FIG. 1, and FIGS. The figures are a block diagram showing the details of the multipath interference detection section in the device shown in FIG. 1, FIG. 5 is a signal waveform diagram for explaining the operation of the device shown in FIG. 1, and FIG. 6 is a problem with the circuit shown in FIG. 2. 7 is a block diagram showing another embodiment of the signal prediction unit in the device shown in FIG. 1, and FIGS. 8 and 9 are diagrams for explaining the operation of the circuit shown in FIG. FIG. 10 is a block diagram showing a multipath distortion generator for an FM receiver as an embodiment of another embodiment of the present invention.
FIG. 1 is a diagram for explaining a signal waveform obtained by the apparatus shown in FIG. 10, and FIG. 12 is a diagram showing frequency characteristics in a conventional receiver. 4...AD converter, 51-59...multiplier, 6
...Signal prediction unit, 7,604-606...Adder, 8...DA converter, 601-603,60
7,608...Delay device.

Claims (1)

[Scope of Claims] 1. An FM receiving section 2 including a high frequency receiving section, a frequency converting section, an intermediate frequency amplifying section, and an FM detecting section, into which a received wave inputted from the antenna 1 is introduced and outputting a composite signal; a stereo demodulation circuit 3 that demodulates and outputs L and R channel signals from a composite signal; and a stereo demodulation circuit 3 that receives the composite signal;
A multipath interference detection section 11 detects an increase in high-frequency components of the composite signal to detect the occurrence of multipath interference, and a signal obtained by sampling the demodulated output of the stereo demodulation circuit 3 and converting it into a digital quantity is input. , a signal prediction unit 6 that performs digital signal processing to calculate and output a predicted value of the next output signal, and when multipath interference is detected by the multipath interference detection unit 11, during the period in which the multipath interference occurs, a multipath disturbance switching unit 5 that performs circuit switching so that the output signal of the signal prediction unit 6 is used as a demodulated signal instead of the output signal of the stereo demodulation circuit 3;
1. A multipath distortion removal device for an FM receiver, characterized by comprising: 1.52. 2. An FM receiving section 2 that includes a high frequency receiving section, a frequency converting section, an intermediate frequency amplifying section, and an FM detecting section, into which a received wave input from the antenna 1 is introduced and outputs a composite signal, and an FM receiving section 2 that outputs a composite signal from the composite signal. a stereo demodulation circuit 3 that demodulates and outputs the channel signal, and inputs the composite signal;
a multipath interference detection section 11 that detects the low frequency AM component of the pilot carrier of the composite signal to detect the occurrence of multipath interference; and a signal obtained by sampling the demodulated output of the stereo demodulation circuit 3 and converting it into a digital quantity. a signal prediction unit 6 that inputs the signal, performs digital signal processing to calculate and output a predicted value of the next output signal, and the multipath interference detection unit 11.
When multipath interference is detected by the multipath interference, the circuit is switched so that the output signal of the signal prediction unit 6 is used as the demodulated signal instead of the output signal of the stereo demodulation circuit 3 during the period of occurrence of the multipath interference. 1. A multipath distortion removal device for an FM receiver, comprising path interference switching sections 51 and 52. 3. A plurality of filter circuits 21 to 3 that divide the demodulated output of the stereo demodulation circuit 3 into a plurality of frequency bands.
24, and the signal prediction unit 6 includes a plurality of filter circuits 25 to 2 corresponding to each of the plurality of filter circuits 21 to 24.
8 is provided, the multipath disturbance switching unit 51,
52 is characterized in that, during the period when the multipath interference occurs, the circuit is switched so that the output signals of the plurality of output signals 25 to 28 are added together and the demodulated signal is used instead of the output signal of the stereo demodulation circuit 3. 2. A multipath distortion removal device for an FM receiver according to claim 1 or 2.