JPS5920290B2 - Interference distortion amount indicating device in an interference distortion removal device generated in a demodulated signal due to interference between FM wave signals - Google Patents

Description

[Detailed Description of the Invention] When another FM wave signal interferes with the FM wave signal that should originally be demodulated, the FM wave signal is demodulated by an FM demodulator. Interference distortion occurs in the FM demodulated signal.

Interference distortion that occurs in the FM demodulated signal due to such interference between FM wave signals occurs when the received radio wave at the FM broadcast receiver is a composite wave of multiple FM signal waves that have passed through many propagation paths (multipaths). , or when reflection occurs due to impedance mismatch between the cable and input/output equipment in cable transmission of FM wave signals, or when recording signals in various recording media are in the form of FM signals. If crosstalk occurs between adjacent channels during high-density recording, it will cause problems in many cases, including interference between the main information signal and tracking signal on a grooveless disc. This will be explained below using the case of so-called multipath interference in an FM broadcast receiver as an example.

In other words, in addition to the direct waves of FM broadcast waves, indirect waves such as reflected waves and diffracted waves may also be input to the FM receiver, and therefore, the FM demodulated signal contains a combination of direct waves and indirect waves. Interference distortion occurs due to interference, and the occurrence of interference distortion in the FM demodulated signal (multipath interference) described above has become a serious problem in recent years as urbanization progresses and the number of high-rise buildings increases significantly. It has come to be taken up as a And conventionally,
A commonly used measure to eliminate or reduce multipath interference in FM broadcast waves is to use a receiving antenna with sharp directivity to prevent the FM radio waves from being received. Only the direct wave of F
However, as mentioned above, with the recent increase in the number of high-rise buildings, it depends on the directional characteristics of the receiving antenna used to send only direct waves to the FM receiver. This makes it extremely difficult to get input into the receiver. Therefore, in recent years, attempts have been made to eliminate or reduce multipath interference using electric circuits, and the applicant company has also been trying to eliminate or reduce FM interference such as multipath interference.
Many proposals have been made regarding methods (removal devices) for removing interference distortion caused in demodulated signals due to interference between wave signals.

First, the principle of construction of the interference distortion removing device in the previously proposed method described above will be explained with reference to FIG. 1 of the accompanying drawings.

That is, FIG. 1 is a diagram for explaining the concept of multipath interference, and in this FIG. 1, At is a transmitting antenna, B is a reflecting object, Ar is a receiving antenna,
The FM broadcast waves reaching the receiving antenna Ar are direct wave CDs.
(t) and the reflected wave CR(t) (where A
= 1, ωcτ = θ) In the above equation (3),
En(t) is a term indicating the amplitude fluctuation caused in the composite FM wave signal C'(t) due to interference between the direct wave CJt) and the reflected wave CR(t), These are terms that indicate phase fluctuations, and these are the FM wave signal Clt between the direct wave and the reflected wave (or the target wave and the interference wave);
The carrier frequency of the M broadcast wave is ωc, the modulation signal is f(t), the delay time due to the path difference between the direct wave CD(t) and the reflected wave CR(,) is τ, and the direct wave CD(t) and the reflected wave are wave CR(t)
If the relationship is CD(t)>CR(t),
The above-mentioned direct wave CD(t), reflected wave CR(t), composite wave FM wave signal C'(t), etc. are each expressed in the following (1).
~ (3) It is shown by formula.

Letting the interference ratio of k be K, the following (4) and (5) are obtained, respectively.
It is shown as follows. When the FM wave signal C(t) shown by the above equation (3) is demodulated by the FM demodulator, the FM wave signal C(t) shown by the above equation (6) becomes the FM wave signal C(t) shown by the above equation (6). A demodulated signal EO(t) is generated, but this (c) 6)
As is clear from the equation (3), the FM wave signal C'(t
) using an FM demodulator, the demodulated signal EO obtained by demodulating the
(t) includes a signal component other than the originally required demodulated signal ν(t), that is, an interference distortion component Dls(t).

Under the condition that the interference ratio K is smaller than 1, the above equation (6) becomes the following (6a') IX::. It is shown as follows. (Interference distortion component DiS(t
) is expressed by the following equation (7). The interference distortion as shown in equation (7) above, which occurs in the demodulated signal due to interference between FM wave signals, is determined by the modulation degree of the modulation signal f(t), F
The time τ caused by the path difference between the direct wave CD(t) and the reflected wave CR(t) of the M-wave signal, the direct wave CD(t) and the reflected wave CR
The nature of the distortion, especially the frequency of the distortion, changes depending on the difference in signal level between the demodulated signal and the The existence of interference distortion that occurs in
Interference distortion that occurs in a demodulated signal due to interference between wave signals is, for example, when receiving television radio waves, images of direct waves and reflected waves simply appear as multiple images on the receiving screen, resulting in deterioration of image quality. The type of reception disturbance that causes this is completely different.

In other words, since the video signals in the direct waves and reflected waves of television radio waves are amplitude modulated waves, the reconstructed image of the direct waves and reflected waves appears on the receiving screen due to the time difference between the direct waves and the reflected waves. They appear independently at positions separated by a distance corresponding to t) as in equation (3) (1)
The signal content changes to something completely different from the direct wave shown by equation (2) or the reflected wave shown by equation (2).

Figure 2 shows the relationship between the distortion rate of interference distortion caused in the demodulated signal due to interference between FM wave signals and the frequency of the modulated signal, when the interference ratio K is 10 dB, the direct wave CD(t) and the reflected wave CR. (t
) The time difference τ is 10μS1 The frequency deviation △f is ±75K
This chart shows an example of the case of Hz (monaural signal), and as is clear from FIG. 2, the distortion rate of interference distortion increases as the harmonic frequency becomes higher.

Figure 3 shows a case where the frequency of the modulated signal is 3Gz1, the frequency polarization is ±75 imaginary, the interference ratio K is 10dB1, and the time difference between the direct wave CO(t) and the reflected wave CR(t) is 10μS (one half of the stereo signal). An example of a frequency spectrum due to interference distortion components appearing in a frequency band of 3 KHz to 45 pulses in a channel (only those exceeding the noise level in FIG. 3 are shown).

Note that the noise level in FIG. 3 indicates the noise level that the receiver itself has.

), and it can be seen from FIG. 3 that the interference distortion components tend to appear concentrated in the high frequency range of 10 KHz or higher. As mentioned above, the interference distortion that occurs in the demodulated signal due to interference between FM wave signals gives the listener an extremely unpleasant audible sensation, so eliminating and reducing interference distortion is an important aspect of FM broadcasting. Since it is extremely useful in high-fidelity reception and reproduction and in many other fields of application of FM signal waves, various proposals regarding interference distortion removal have been made in recent years.

The applicant company also uses the demodulated signal E obtained from the FM demodulator.
As an interference distortion removal method or interference distortion removal device that obtains a distortion-free demodulated signal f'(t) from O(t), (
6) Demodulated signal E shown by formula. We have completed a number of interference distortion removal methods (devices) based on the construction principle of subtracting the interference distortion component Dls(t) shown by equation (7) from (t). , patent application 1972-7
No. 0254, Japanese Patent Application No. 70255, Japanese Patent Application No. 1982-
Jmo V556, patent application 1986, JMo V557, patent application 1983
-60470. FIG. 4 is a block diagram of an example of an interference distortion removing device disclosed in Japanese Patent Application No. 53-60470, and FIG. 5 shows the structure of the interference distortion removing device shown in FIG. This is a block diagram of a simplified configuration for sharing elements.

In FIGS. 4 and 5, DETd, DETr, DE
Tdr and the like are FM demodulators, and the subscripts D, r, and dr are added with the following meanings (
The usage of subscripts is the same for other constituent parts.)
. That is, the direct wave CD(t) and the reflected wave CR. The subscript d is given to the component parts of the interference distortion removal device used when the relationship in magnitude with (t) is CO(t)>CR(t), and CD(t) A subscript r is attached to the component of the interference distortion removal device used in the state of CR(t), and furthermore, the state of CD(t)>CR(t) and the state of CD(t)
The subscript d is attached to the component parts of the interference distortion removal device that are commonly used in both the CR(t) state and the CR(t) state, and the description of the subscript will be omitted in the following explanation. Sometimes.

DEdl and DEr in FIG. 4, DEdr in FIG. 5, etc. are the component parts having the function of producing the interference distortion component DlS(4), and the interference distortion component Dis(t) from the demodulated signal from the FM demodulator. AGC is an automatic gain control circuit, ED is an envelope detection circuit, C is a DC blocking capacitor, SC is a waveform conversion circuit, M is an analog multiplier, SUB and SU are subtracters, and DL is a delay circuit, and the interference component Dls(t) created by the operation of these components is transmitted to the subtracter S.
By subtracting it from the output signal of the FM demodulator DET at UB, an output signal from which interference distortion has been removed is obtained from the output terminal 2.

Note that 1 is a composite signal C' in which FM wave signals interfere with each other.
(t) input terminal, SAVl, SW2 in Fig. 4
S1 to S3 in FIG. 5 are changeover switches, and each movable contact V of these changeover switches is connected to two fixed contacts D.
, r.

The operation of removing interference distortion in the interference distortion removing device shown in FIG. The removal operation is also exactly the same as that of the interference distortion removal device shown in FIG. 4).

Now, when using such an interference distortion elimination device, it is necessary to adjust the delay time of the delay circuit provided in the interference distortion elimination device according to the time difference τ between the direct wave and the reflected wave. However, if you judge whether the delay time of the delay circuit is being adjusted properly by listening to the reproduced sound, it is necessary to use an interference distortion removal device so that the interference distortion is minimized. It is very difficult to adjust.

This is because even if interference distortion exists in the reproduced sound, it may be difficult to distinguish it by ear.Therefore, if you want truly high-fidelity reproduction, you must use some kind of measurement method. However, in this case, if the equipment used as the measuring means is expensive, the problem is that it cannot be applied to consumer equipment that requires low cost. The present invention provides two methods for obtaining an interference distortion component signal based on a signal at an input section and a signal at an output section of an interference distortion removal device.
means for obtaining two original signals, means for individually rectifying the two original signals to obtain two rectified signals, and means for subtracting one of the two rectified signals from the other to obtain an interference distortion component; Provided is an interference distortion amount indicating device in an interference distortion removal device comprising means for supplying the interference distortion component to a meter via an integrating time constant circuit, a meter sensitivity switching circuit, a DC amplifier, etc. The degree of removal of interference distortion can be read by the deflection of the meter pointer, and the amount of interference distortion can be minimized to make it easier to listen to good reproduced sound. The specific contents of the invention will be explained in detail with reference to the accompanying drawings. 6th
FIG. 6 is a block diagram of one embodiment of the interference distortion amount indicating device in the interference distortion removal device that occurs in the demodulated signal due to interference between FM wave signals of the present invention.
In the figure, 1 is an input terminal, 2 is an output terminal, DETdr is an FM demodulator, and DEdr is the main part of the interference distortion removal device.

As an example, the main body DEdr of the interference distortion removing device shown in FIG. 6 has the same configuration as the interference distortion removing device shown in FIG.
Of course, any other configuration may be used in practice.

Now, in Fig. 6, the FM wave signal c'(t) in which the FM wave signals input to the input terminal 1 are interfering with each other is the FM demodulator DETdr and the main body DEd of the interference distortion removal device.
When added to the automatic gain control circuit AGCdr in be done.

Main body DEdr (main body D
Edr), when each switch S1 to S3 is switched to the state shown in the figure, that is, when each movable contact V is switched to the fixed contact d side, the direct wave is stronger than the indirect wave. This is a case where interference distortion is removed in response to a state where the signal level is high.Contrary to the above, interference distortion is removed in response to a state where the indirect wave has a higher signal level than the direct wave. When the removal is to be performed, each changeover switch S, ~ in the main body DEdr
Each movable contact V of S3 is switched to the fixed contact r side.

Setting states of the changeover switches S, ~S3 as shown in Fig. 6,
That is, in a state where each movable contact V of each changeover switch S1 to S3 is switched to the fixed contact d side, the demodulated signal EO(t) from the FM demodulator DETdr is transmitted between the fixed contact d and the movable contact of changeover switch S1. V and subtractor S through
It is added to UBdr as its minuend signal and is also supplied to the bandpass filter BPF.

The subtraction signal for the subtracter SUBdr in the main body DEdr described above is the distortion canceling signal -Dis(t), and if the delay time in the delay circuit DLd is appropriate, the subtracter SUBdr outputs a distortion-free signal to the output terminal 2. The output signal f
'(t) is output, and an undistorted output signal f'(t) is also supplied to the bandpass filter BPF2.

In addition, each changeover switch S, ~S in the main body DEdr
In a state where each movable contact V of No. 3 is switched to the fixed contact r side, the demodulated signal E from the FM demodulator DETdr
O(t) is added to the subtracter SUBd via the delay circuit DLrl.
r as its minuend signal, and is also supplied to the bandpass filter BPF. The subtracter SUBdr uses the distortion canceling signal - given from the analog multiplier Mdr from the minuend signal given from the delay circuit DLrI described above.
By subtracting Dis(4), delay circuits DLrl and DLr2
If the delay time in is appropriate, the subtracter SUBdr
An undistorted output signal ν(t-2τ) is output from the output terminal 2 to the bandpass filter BPF2. The details of the interference distortion removal principle and removal operation in the main body DEdr of the interference distortion removal device mentioned above are described in detail in the specification of Japanese Patent Application No. 53-60470, so please refer to it.

Now, the interference distortion removal effect by the interference distortion removal device is the delay circuit DLdl or delay circuit D in the main body DEdr.
It is best when the delay time τ set by Lrl and DLr2 is equal to the time difference τ between the direct wave and the indirect wave, and the larger the difference between the above values, the smaller the interference distortion removal effect becomes. When removing interference distortion using a distortion removing device, the delay circuit DLdl or the delay circuits DLrl, DLr2 in the main body DEdr of the interference distortion removing device
The delay circuit DLdl or the delay circuits DLrl, D
The delay time in Lr2 is adjusted and set.

Therefore, the delay circuit DLdl in the main body DEdr
Alternatively, as the delay times of the delay circuits DLrl and DLr2 are adjusted, the amount of interference distortion in the output signal sent from the output section of the interference distortion removal device to the output terminal 2 will increase or decrease; FM demodulator DE for main body DEdr
The amount of interference distortion contained in the demodulated signal EO given from Tdr is determined by the delay circuit DL in the main body DEdr.
d. Or, since there is no change even if the delay time of the delay circuits DLrl and DLr2 is variably adjusted, the main body DEdr
Delay circuit DLdl or delay circuit DLrl,D in
The amount of interference distortion in the output signal sent from the output section of the interference distortion canceling device to the output terminal 2, which changes by variable adjustment of the delay time of Lr2, is determined by the amount of interference distortion in the output signal sent from the output section of the interference distortion canceling device to the output terminal 2. This can be determined by comparing the signal with

In the embodiment shown in FIG. 6, the signal at the input section of the interference distortion removing device is applied to the bandpass filter BPF from the input terminal side of the minuend signal in the subtractor SUBdr of the main body DEdr, and the interference distortion The signal from the output section of the removal device is applied to the bandpass filter BPF2 from the output terminal side of the subtracter SUBdr of the main body section DEdr.

As the above-mentioned bandpass filters BPF, , BPE2, those having the same bandpass characteristics are used.

Although it is possible to implement the present invention without using the above-mentioned bandpass filters BPF, , BPF2,
As is clear from the figure, the interference distortion component exhibits a distribution pattern in which it is concentrated in a frequency band of 10K1Iz or higher, so for example, if the passband is 10KH to 50KH,
z1 or 10? ~25Z1 or 25K1Iz~
Bandpass filter BPE, , BPF2 such that 50 KIz
The use of the circuit has the advantage that, for example, the configuration of an arithmetic circuit in a subsequent circuit can be simplified.
The signal extracted by the above bandpass filter BPF is rectified by the rectifier circuit RCTl and then sent to the arithmetic circuit 0C.
Also, the signal extracted by the bandpass filter BPF2 is passed through a rectifier circuit R having the same configuration as the rectifier circuit RCTl.
After being rectified by CT2, it is given to the arithmetic circuit 0C, but in the illustrated example, in the arithmetic circuit 0C, the output signal from the rectifier circuit RCTl is subtracted from the output signal from the rectifier circuit RCT2, and the output signal from the arithmetic circuit 0C is The signal is given to an integral time constant circuit 1CT.

The output signal from the integral time constant circuit CT is given to the DC amplifier DCA via the meter sensitivity switching circuit MSC, where it is amplified as required and then supplied to the meter MT〇3
is a bias voltage supply terminal, VR is a variable resistor, and the variable resistor VR is used to set the pointer of the meter MT to the maximum scale position (the right end position of the scale) when the input signal to the DC amplifier DCA is zero. It is used to adjust the bias voltage so that the

In the interference distortion amount indicating device shown in FIG. Since the obtained rectified signal is subtracted, the output signal of the arithmetic circuit 0C becomes a signal that increases in the negative direction as the interference distortion removal function of the interference distortion removal device is sufficiently performed. By the way, the original signals of the two rectified signals given as the two input signals through the arithmetic circuit 0C described above are obtained based on the demodulated signal from the FM demodulator DETdr, and the interference signal of the present invention is Strain indicating devices use special measurement signals (e.g.
Since it is used to instruct the amount of interference distortion using a signal based on a normal program (e.g., audio signal, music signal) without using a specific single frequency signal, it requires an arithmetic circuit. The output signal from 0C is such that the meter pointer swings to both positive and negative sides, so if the integral time constant in the integral time constant circuit TC is the same regardless of the positive or negative polarity of the input signal, is the delay circuit DLdl or DLrl in the main body DEdr,
Since it may be difficult to clearly perceive the deflection of the pointer of the meter MT due to changes in the amount of interference distortion due to variable adjustment of DLr2, in the case of the configuration example shown in Figure 6, an integral time constant circuit is used. 1TC, when the input signal to it changes from positive to negative direction, it shows a small time constant, and conversely, when the input signal changes from negative to positive direction, it shows a large time constant. It is desirable to use something configured to indicate a constant.

In addition, the meter sensitivity switching circuit MSC is configured using, for example, a multi-contact switching switch and a resistor network, and this is because the demodulated signal from the FM demodulator DETdr originally contains only a small interference distortion component. Even in such cases,
This is provided so that the state where the amount of interference distortion in the output signal is minimum can be easily determined by the deflection of the pointer of the meter MT.By switching and using this meter sensitivity switching circuit MSC, the main body Delay circuit D in section DEdr
By variable adjustment of the delay time of Ldl or the delay circuits DLrl and DLr2, it is possible to easily know the state of the minimum amount of interference distortion in the output signal.

FIGS. 7(a) to 7(c) illustrate and explain how the extent of interference distortion removal by the interference distortion removal device can be determined by the deflection of the pointer of the meter MT. In Fig. 7(a), the pointer of the meter MT is set to swing to the maximum scale position by adjusting the variable resistor VR (7) with no signal being input to the DC amplifier DCA. Figure 7 (
b) The figure shows the state of the pointer deflection when both the input section signal and the output signal from the output section of the interference distortion removal device contain large interference distortion components (the meter sensitivity switching circuit MSC has a low meter sensitivity). or if the signal at the input section of the interference distortion canceller contains only a small amount of interference distortion component, the interference distortion canceler removes the interference distortion component from the output signal. The state of the pointer deflection when it is made sufficiently small (meter sensitivity switching circuit MS
Fig. 7(c) shows a case where a large interference distortion component is included in the signal at the input section of the interference distortion removal device. The state of the pointer deflection when the interference distortion component in the output signal is sufficiently reduced by the interference distortion removal device (the meter sensitivity switching circuit MSC is set to the lower meter sensitivity) or, even when the amount of interference distortion components in the output signal is sufficiently reduced by the interference distortion remover, the deflection of the pointer of the meter MT will be as shown in FIG. 7(b). In such a situation, the meter sensitivity switching circuit MSC is switched to the one with higher meter sensitivity, and the amount of interference distortion components in the output signal is sufficiently reduced by the interference distortion removal device. This diagram illustrates and explains the state of the pointer's deflection. When the same amount of interference distortion components are included in both the input section signal and the output section signal of the interference distortion removal device, the pointer of the meter MT is at the maximum graduation position of the scale of the meter MT, so it is actually The size of the gap between the position where the pointer of the meter MT swings and the maximum scale position of the scale of the meter MT represents the amount of reduction in interference distortion in the output signal due to the operation of the interference distortion removal device. The size of the gap between the position of the pointer of the meter MT and the maximum scale position of the scale of the meter MT when the amount of interference distortion in the output signal is minimized by the interference distortion removal device is , can be considered to represent the amount of interference distortion contained in the input signal to the interference distortion removal device.

In the explanation so far, the pointer of the meter MT is set in advance at the maximum graduation position of the scale of the meter MT,
We have described a case in which the deflection of the pointer becomes smaller as the interference distortion removal effect of the interference distortion removal device becomes larger, but the pointer deflection becomes smaller as the interference distortion removal effect of the interference distortion removal device becomes larger. In this case, the signal from the input section of the interference distortion removal device is applied to the bandpass filter BPF2, and the signal from the output section is applied to the bandpass filter BPF2. At the same time, the variable resistor VR is adjusted so that the deflection of the pointer of the meter MT in the absence of an input signal to the DC amplifier DCA becomes the minimum scale position (left end position of the scale) of the meter MT scale.

As is clear from the above explanation, in the interference distortion amount indicating device of the present invention, the interference distortion removal state in the interference distortion removal device can be immediately known from the pointer of the meter MT. Main body part DEdr while watching the shake
By changing the delay time of the delay circuit DLdl or DLr, DLr2, the interference distortion removal device can be quickly adjusted so that the amount of interference distortion contained in the output signal is minimized. In addition, the above-mentioned adjustment of the interference distortion canceling device can be performed without using a special measurement signal, by using a normal program signal (e.g., audio signal, music signal), and by using a special measuring device. In addition, the total amount of interference distortion in the demodulated signal can be approximately determined from the deflection of the meter pointer. By adjusting the delay time of the delay circuit in the main body of the interference distortion removal device while checking the amount of interference distortion by the deflection of the pointer of the meter MT using the device, the amount of interference distortion in the output signal can be minimized. High-fidelity reproduction signals can be easily obtained.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the causes of multipath interference, Figures 2 and 3 are diagrams for explaining the nature of interference distortion, and Figures 4 and 5 are for previously proposed interference. FIG. 6 is a block diagram of an example of a device for indicating the amount of interference distortion in the interference distortion eliminating device of the present invention;
FIGS. 7(a) to 7(e) are diagrams for explaining how the amount of interference distortion is indicated by the deflection of the meter pointer. 1...Input terminal, 2...Output terminal, D
ETd, DETr, DETdr...FM demodulator, SUBd, SUB, r, SUBdr, SUr, SUd
, SUdr...subtractor, AGCd, AGCr,
AGCdr・・・Brain gain control circuit, EDd, ED
r, EDdr... Envelope detection circuit, Cd
, Cr, Cdr...DC blocking capacitor, SC
d, SCr, SCdr... Waveform conversion circuit, Md
, Mr, Mdr...analog multiplier, DLd,
DLrl, DLr2... Delay circuit, SWl, S
W2, Sl~S3......Selector switch, DEd,
DEr, DEdr...Main part of interference distortion removal device, BPF,,BPF2...Band filter, RCT
l..., RCT2... Rectifier circuit, 0C...
... Arithmetic circuit, ICT... Integral time constant circuit, MSC
...Meter sensitivity switching circuit, DCA...
DC amplifier, MT...meter, VR...variable resistor.

Claims (1)

[Claims] 1. Signals at the input section and output section of an interference distortion removal device that is provided after the FM demodulator and is capable of removing interference distortion that occurs in the demodulated signal due to interference between FM wave signals. means for obtaining two original signals for obtaining interference distortion components based on the signals; means for individually rectifying the two original signals to obtain two rectified signals; Interference between FM wave signals consisting of means for subtracting one from the other to obtain an interference distortion component, and means for supplying the interference distortion component to the meter via an integration time constant circuit, a meter sensitivity switching circuit, a DC amplifier, etc. A device for indicating an amount of interference distortion in a device for removing interference distortion caused in a demodulated signal by