JPH02116227A - Transmission distortion removing circuit - Google Patents

Abstract

PURPOSE:To receive a modulating signal without any distortion by generating a removing signal equivalent to an interruption wave from a received modulating signal and cancelling the interrupting wave, in a base band signal step after the FM of a receiver is detected. CONSTITUTION:The title circuit provides a means to subtract the higher harmonic of a second band component, a higher harmonic obtained by forming a cross modulation wave signal and the cross modulation wave signal from a first band component signal taken out from a band filter based on the output signal of the filter of the band filter and the low area filter. At this time, an output A of an adder circuit 117 is a secondary higher harmonic cancelling signal and respective outputs of multiplying circuits 129 and 131 are the tertiary interruption wave cancelling signals. Consequently, the output A of the adder circuit 117 becomes the approximately same waveform as the interruption wave included in a signal B obtained by delaying a signal (b) only by the delaying quantity of low area filters 108 and 123 by a delaying circuit 132. Namely, a signal A is an interruption wave cancelling signal included in the signal B, and by subjecting the signal A from the signal (b) by an adder circuit 118, the multiple data signal attenuated by the interruption wave can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] When an FM modulated wave has distortion in the amplitude/phase frequency characteristics of a transmission path, that is, a transmitter, broadcaster, repeater, or receiver, or when a reflection It relates to a transmission distortion removal circuit that removes (at the receiver) linear distortion interference waves that occur when passing through a transmission line with waves, a radio wave transmission line with multipath, etc.
F of stereo broadcast receivers, TV audio receivers, FM multiplex data broadcast receivers, TV multiplex facsimile receivers, etc.
It is applied to wired and wireless receivers that do not use M modulation.

The present invention also relates to a circuit for removing (in a receiver) nonlinear distortion caused by a nonlinear system of a transmission path in in-shell signal transmission.

[Summary of the invention]

The present invention is directed to a baseband signal stage after FM detection in a receiver, in order to reduce interference waves due to linear distortion, which occurs when an FM modulated wave passes through a transmission line with distortion in amplitude/phase frequency characteristics, for example. , a distortion removal signal corresponding to the interference wave is created from the received modulation signal, and by canceling out the interference wave, the modulation signal can be received without distortion. It also makes it possible to reduce nonlinear distortion in general signal transmission.

[Conventional technology]

The technology for removing interference caused by distortion in the transmission path of FM modulated waves (signals) at the intermediate frequency stage of the receiver is in the research stage and has not yet been perfected.

Inventive ideas for removing distortion in the baseband signal stage after FM demodulation are disclosed in Japanese Patent Application No. 329869/1986 and Japanese Patent Application No. 62-329869.
There is No. 329870, which relates to FM multiplex data broadcasting, and the center frequency of the multiplex data signal is 76 Hz, and the modulation method is limited to the QPSK modulation method. In addition, Japanese Patent Application No. 150055/1999 does not limit the multiplex data signal modulation method and its center frequency, or is limited to the removal of second harmonic interference of a suppressed carrier amplitude modulated difference signal in the case of FM broadcasting. It was a great invention.

[Problem to be solved by the invention]

The FM multiplex data broadcasting receiver according to the invention proposed in Japanese Patent Application No. 62-329869 is limited to the removal of disturbances related to the second harmonic of the stereo difference signal generated by distortion in the transmission path, especially multipath, and is further This method could not be applied to the cross-modulation components resulting from the following combination.

Furthermore, it could not be applied to interference removal for facsimile signals multiplexed with television audio signals of different stereo modulation methods.

SUMMARY OF THE INVENTION An object of the present invention is to provide a transmission distortion removal circuit that eliminates the above-mentioned drawbacks, and is capable of eliminating distortion regardless of the coupling order of harmonics or cross-modulation, or regardless of the format of the modulation signal. The present invention provides a transmission distortion removal circuit that can eliminate interference using the same principle and circuit configuration regardless of the band in which it falls, and can be applied to a wide range of linear distortions of FM modulated waves.

[Means to solve the problem]

The present invention provides a bandpass filter for extracting a first band component from a transmission signal having a first band component and a second band component having a lower frequency than the first band component; a low-pass filter that extracts the harmonics and cross-modulation wave signals of the second band component based on the output signals of the two filters; and means for subtracting the wave signal from the first band component signal extracted from the band pass filter.

Further, the present invention provides, in the FM detection output stage of the FM modulation wave receiver, for each harmonic or cross modulation order of the interference wave due to linear distortion to be removed, the first order power corresponding to the established number of the modulation wave is A circuit that generates a signal, that is, a square circuit,
A cube circuit or the like, or a circuit that generates a third-order signal using a square circuit and a multiplication circuit, and a Hilbert transform circuit or a differentiation or integration circuit that generates a second signal that has a Hilbert transform relationship with the first signal. and the third signal, which is the time average of the multiplication of the first signal and the human signal in the band involved in interference removal.
a circuit that generates a signal, a circuit that generates a fourth signal that is the time average of the multiplication of several human input signals and a second signal, and a circuit that generates a fourth signal that is the time average of the square of the first signal or the second signal. a fifth
a circuit that generates a signal, a circuit that divides the third signal by a fifth signal to generate a sixth signal, and a circuit that divides the fourth signal by the fifth signal to generate a seventh signal. circuit and the first
A circuit that multiplies the signal and the sixth signal to generate the eighth signal, a circuit that multiplies the second signal and the seventh signal to generate the ninth signal, and a circuit that generates the eighth signal by multiplying the second signal and the seventh signal. A transmission distortion removal circuit configured to subtract the signal and the ninth signal to remove interference waves of already coupled orders, and added to each harmonic or cross modulation order for which interference wave removal is required. and further by the above configuration, or by the configuration excluding the system related to the second signal from the above configuration, - harmonics generated due to non-linear distortion of the transmission path in a receiver for in-shell signal transmission;
Includes a transmission distortion removal circuit that removes cross-modulation wave distortion.

[Function] According to the above configuration, the interference wave in the transmission signal is canceled out by the distortion removal signal corresponding to the interference wave, and the transmission distortion can be removed.

〔Example〕

The present invention will be described in detail below with reference to the drawings.

The principle of removing linearly distorted interference waves caused by distortion in the transmission path of FM modulated waves according to the present invention will be explained using an example of application to FM multiplex data broadcasting.

In FM multiplex data broadcasting, distortion in the transmission path due to multipath of broadcast waves is a particular problem, and reception of the multiplex data signal becomes difficult due to harmonics and cross-modulation waves of the stereo signal or falling into the band of the multiplex data signal. In some cases, it is necessary to remove these interference waves. The same thing happens with TV multiplex facsimile broadcasts.

FIG. 3 shows the baseband spectrum of a modulated wave of FM multiplex data broadcasting, and shows how harmonics and cross-modulation waves are generated when this FM broadcast wave is received through a transmission path with distortion due to multipath interference.

201 is a stereo pilot signal, 202 is a stereo sum signal, 203 is a stereo difference channel signal, and 204 is an example of multiplexed data No. 13.

205 to 210 are harmonics or cross modulation waves of the stereo signal, OK l (z and pyrower 1 - signal frequency 19
Frequency that is an integer multiple of kllz, that is, 19.38, 57
71i This is an interference wave that falls around 95KHz and interferes with signal reception.

In such a case, in the FM detection stage of the receiver, 2
Signals 01 to 204 and interference waves 205 to 210 are output simultaneously. Therefore, when demodulating a stereo signal, the interference waves 205 to 207 appear as distortion, and when demodulating the data signal 204, the interference waves 209 mainly have no adverse effect.

The principle of interference removal will be explained below using an example in which the interference waves of 209 are removed with respect to the multiplexed data signal of 204.

Let S (t) be the sum of the transmitted stereo signal, that is, the pilot signal, sum signal, and difference channel signal, and let D (t) be the multiplexed data signal.

When S (shi) is squared, if the harmonic that falls in the 76-11z band is 12ft), then 12 (t) = U (t) cos4wpt
(Wp is the angular frequency of the pilot signal).

If +2(t) is Hilheld transformed and 02(t) is obtained, then 02(t) = 11(t) sin4wpt.

If the cross-modulation between the sum signal, the difference channel signal, and the pilot signal that falls into the 76 Hz band when S (t) is raised to the third power is h(t), then +3(t) = V(t) cos4w,, It can be shown as t.

+3 If the Hilbert transform of (t) is Q3(t), then (h(t) = V(t) sin4wpt).

According to the transmission theory of FM modulation, the linear distortion caused by distortion in the transmission path falls in the 76111 band in the above case.
As the second and third harmonics and cross-modulation waves, α12ft) + βq2(t) + δr3ft) + γ01
(t). This approximation holds true when the fractional band of the diaphragm signal band is relatively small.

Let the received 76 llz band signal be n(t), then
n (t) Cape D(t) + α12(t) 1βq2ft)
+δ13(t)+γQ3(t)+... The first term is the multiplex data signal, the second term is the multiplex data signal, and the second term is the multiplex data signal. The third term is 2
The next harmonic interference wave, 3rd. The fourth term is a third-order cross-modulation interference wave.

R(t) further includes harmonics of the fourth or higher order and intermodulation interference waves, but these levels are relatively small;
The principle for removing these interferences is the same as that for removing secondary and tertiary interference waves, so the explanation will be omitted here.

12 (t) , Q2 shown in the formula of R(1) above
(t), +3 (t).

Since a3(tl can be created from the received sB), each of these coefficients α, β, γ, and δ need only be found in order to remove the interference waves included in R(t).

The values of each of these coefficients are 12 (t) , Q2 (t)
, 13 (t)Q3(tl There is a small correlation between them, and there is a certain time interval T between them and the data signal.
It can be found by taking the correlation, taking advantage of the fact that the correlation converges to zero.

Regarding α, (1/T)S:”R(t)12(t)dt (1/
T) a5:”I:(t)dt(+/T) S t”B(
t) dt (1/T) Stt”■: (t) d
t, and the average value when the received signal R(t) is multiplied by 12ft) and integrated over an appropriate period T is expressed as r:(t
) by the average value integrated over the period of T, we get
The expected value of α is found.

Similarly, for β, γ, and δ, (1/T) S H''!; (t) dt (1/T) S
:”R(t) 13 (t)dt(1/T) S ′
Each expected value is found as t''B(t)dt.

Using the obtained α, β, γ, and δ, αh(t) + βq2(t) + δl3(t) + γQ3(t
) and subtracting it from R(t), the interference included in n(t) is reduced and the multiplexed data signal D(0 is extracted).

Next, an example of a circuit configuration for realizing the present invention will be explained with reference to FIG. 1, using an example when applied to FM multiplex data broadcasting.

The input signal a of the circuit is an FM detection output signal of an FM tuner, and the output signal C is an FM multiplex data signal with reduced interference waves.

First, 101- as a system for reducing secondary harmonic interference.
116 will be explained.

Signal a is 5(t)+D(t)+a 12(t)+β0*
(1)+δL+(t)”γQ3 (t) +W (t)
s (g is the stereo signal, D (t) is the multiplexed data signal, αl2(t) ÷ βq2(t) is 761HI
Second harmonic interference falling in the z band, δr3(t)+y
q3ft) indicates third-order cross-modulation falling in the 76 kHz band, and W (t) indicates interference waves falling in bands other than the 1-1z band at 76.

101 is a 76 Hz bandpass filter that passes the multiplex data signal and the interference wave falling in the 76 KIIz band. A delay circuit 102 delays the signal by the same delay time as that of the low-pass filter 103.

The signal S which is the output of the delay circuit 102 is the above-mentioned n (t
), and R(t) = o (t) + α12(t)
+βq2(t)+δl3(t)+γQ3(t).

103 is a 53 KHz low-pass filter that passes stereo signals and blocks multiplex data signals, and its output g is a stereo signal. 112 is a square circuit that converts the human signal g into 2
By multiplying, a square wave of the stereo signal S (t) is created, and by passing this output signal through the Hz band filter 76 of 113, the band filter 11
3, I2(t) is obtained as the output signal l.

02(1) can be created by Hilbert transforming 12(t), but since the fractional band of the bandpass filter 113 is small, a differentiating circuit or an integrating circuit may be used instead of the Hilbert transform circuit. Here, a 115 differentiating circuit is used, and q2(t) is obtained as its output j.

104 is a multiplication circuit that multiplies the signal, i.e., n(t), and the signal i, i.e., 12(t), and passes the output signal C through the low-pass filter of 105, so that the output d becomes (1 /T)αSdo"■', (t) Obtain dt.

109 is a multiplication circuit that multiplies the signal b1, that is, R(t), and the signal j, that is, q2(t), and passes the output signal e through a low-pass filter 110, so that the output f is (1/T) βS: “Q: (t) Obtain dt.

107 is a square circuit that converts the signal i, that is, 12(t) into 2
This output k is passed through 108 low-pass filters, and the sono output x ni(1/r)s:”rH(t+dt
get. Instead of No. 13 i, signal J, that is, Q2 (1
) may be done manually. It is 12ft) and 02(t
) has the same power.

+06 is a division circuit which divides the signal d to obtain the value of α as its output m. Similarly, III is a division circuit, and by dividing the signal f by the signal division, the value of β is obtained as the output n.

li4 is a multiplication circuit that receives signal i, i.e. 12(1:)
is multiplied by the signal m, that is, the value of α, and the output is 0 to obtain αh(t). A multiplication circuit 116 multiplies the signal j, that is, Q2(t), by the signal n, that is, the value of β, and obtains β02(1) as the output p.

117 is an adder circuit whose output A has α12 (t)
+βq2(t). These are second harmonic cancellation signals.

Next, in the systems 119 to 131 for reducing third-order cross-modulation wave interference, 127 is different from the second-order system, and the rest has the same configuration and function as the second-order system. 127 is a multiplication circuit. ,
The signal g is multiplied by the signal 11, and as a result, a signal of 5(t) to the third power is generated as q. +28 is 76H
If z bandpass filter, its output signal r is +3(
t). 130 is a Hilheld transform circuit, or a differentiating circuit or an integrating circuit replacing this, and its output S is q3
[).

119 and 124 are multiplication circuits that multiply n (t) and h (t) and R (t) and Q3 (L), respectively, and their outputs are passed through low-pass filters 120 and 125. , obtain the respective outputs t and u. t is (1/T)δS;
"B (t) dt is (1/T) γS" QH (t) dt
It is. 122 is a square circuit, which receives the signal r, that is, 13f
t) to the power of 2 and passing it through a low-pass filter of 123, the signal V is (1/T) S t”rH(t
) Obtain dt.

121.12 [i is a division circuit that divides the signal t and the signal U by the signal V, and outputs the value of δ as W to each output,
Obtain the value of γ as X.

129 and 131 are multiplication circuits that respectively multiply the signal r and the signal W, and the signal S and the signal X, and obtain δI3 (t) as y and γQ3 (t) as Z at each output.

These are third-order interference wave canceling signals.

Therefore, the output A of the 117 adder circuits is αl2(t)+
βq2(t)+6+a(tl+γa3(t).A is the signal 1) by the delay circuit 132 to 108,12
Signal B obtained by delaying the delay amount of the low-pass filter in step 3
The waveform is almost the same as that of the interference wave included in . That is, signal A is a canceling signal for the interference wave contained in signal B,
By subtracting the signal A from the signal in the 118 adder circuit,
The output signal C is a multiplexed data signal D with the interference waves attenuated.
(t) can be obtained.

In addition, in FIG. 1, the second and third harmonics are shown.

This shows a configuration that removes intermodulation interference waves, but in order to remove even higher order intermodulation interference waves, one for each order is required.
It is okay to add the circuit configurations from 04 to 116, however,
The circuit corresponding to 112 is a circuit that squares the signal g in the fourth order, and a circuit that multiplies the square output of the signal g and the signal g in the fifth order.

The invention can also be applied to the RDS system used in Europe, which multiplexes data signals into the 57 old 1Z band of FM stereo broadcasting. 57 old 1z 1
．． : From the multiplexed data signal, the interference wave in the 57 Kllz band shown at 208 (FIG. 3) can be removed by the configuration shown in FIG. 1. However, in this case, 101,1
The passband of each IF band filter of 13,128 is 57K.
Let it be of a bandwidth of 4 K II z centered at II z.

When the present invention is applied to a system in which the multiplex data signal has a center frequency of 85.5 Kllz and interference waves are removed from the multiplex data signal, this can be similarly achieved by the circuit configuration shown in FIG. However, in this case, the pass band of each band filter of 101113.128 is set to pass both the 85.5 old)2 multiplex data signal band and the 76 old 1z band interference wave band.

The present invention can also be applied to the case of removing interference waves from facsimile signals transmitted in television multiplex facsimile broadcasting. In this case, the modulation method for audio multiplexing is the FM-FM modulation method, and although it is different from the M-FM modulation method for the suppressed carrier wave used in FM broadcasting, the circuit configuration of the tree invention can be applied. However, in this case, the pass band of each band filter of 101.113.128 is assumed to pass the band of the multiplexed facsimile signal and the band of the interference wave to be removed.

The present invention can also be applied to the case of removing linear distortion interference that falls around a stereo pilot signal and around a sum channel signal or a difference channel signal in stereo broadcasting and television audio reception. In this case as well, it is assumed that the bandpass filter passes those signal bands.

The present invention can also be applied to the case where nonlinear distortion occurring in a transmission path with nonlinear distortion in general signal transmission is removed in a receiver. In this case, the configuration shown in FIG. 1 may be applied as is. However, in principle, nonlinear distortion does not generate a component corresponding to the already explained Hilbert transform, so this system can be omitted.

That is, 109, 110, 111, 115, 1 in Figure 1
11i, 124, 125°126.13Q, 131 are unnecessary. FIG. 2 shows an example of such a circuit configuration.

Distortion generated in the transmission path of FM modulated waves has been thought to be extremely difficult to remove, but the present invention eliminates distortion in a relatively simple manner at the Goesband signal stage after FM demodulation. This is the first time that it has been possible to remove Of course, the original method is to correct transmission distortion at the intermediate frequency stage, and it is desirable that this research progresses further. However, the present invention has made it possible to remove distortion effectively for the time being from a practical standpoint.

Regarding FM multiplex data broadcasting, the characteristics can be improved even in the 76 and 117 bands, which have hitherto been subject to large multipath interference. A similar effect can be obtained for RDS in the 57Kllz band.

Regardless of the coupling order of harmonic interference, including secondary, tertiary, and harmonic interference, it is now possible to eliminate interference using the same principle and the same circuit configuration.

Furthermore, the response speed of the interference removal according to the present invention is determined by the integration time of the integrating circuit, that is, the cutoff frequency of the low-pass filter, but if this is about +00 Hz, it will respond sufficiently to fading in mobile reception. It may also be applicable to

The circuit configuration of the tree invention can be constructed from either analog circuits or digital circuits, and by integrating each circuit, it is possible to create a small and low-level practical circuit.

The invention is effective not only in multiplex broadcasting, but also in stereo broadcasting, television audio broadcasting, and other general FM modulated wave linear distortion removal for band portions where the fractional band is relatively small. With some configurations of the present invention, it is also possible to eliminate nonlinear distortion that occurs in general signal transmission.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to reliably remove transmission distortion with respect to an extremely wide variety of transmission signals.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a circuit for eliminating linear distortion in FM modulated waves according to the present invention, FIG. 2 is a diagram showing an example of a circuit for eliminating non-linear distortion in general signal transmission according to the present invention, FIG. 3 is a diagram illustrating the baseband spectrum of FM multiplex data broadcasting and the spectrum of linearly distorted interference waves generated in the transmission path of the same signal. 101.113.128... bandpass filter, 102.
132...Delay circuit, 103.105, 108, 110, 120, 123.1
25...Low pass filter, 104.109,114,1
16.119, 121, 124, 127.129.13
1...Multiplication circuit, 106.111,121,126...Division circuit, 10
7.112,122...square circuit, 115.130.
... Differential circuit.

Claims (1)

[Claims] 1) A bandpass filter that extracts a first band component from a transmission signal having a first band component and a second band component having a lower frequency than the first band component, and the transmission signal a low-pass filter for extracting a second band component from the filter; a signal forming means for forming harmonic and cross-modulation wave signals of the second band component based on the output signals of the two filters; and the signal forming means 1. A transmission distortion removal circuit comprising means for subtracting the harmonic and cross-modulation wave signals obtained by the above from the first band component signal taken out from the band filter.