JPH0638584B2 - Equalization circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] In order to equalize the transmission line characteristic distortion occurring in the carrier frequency band in a communication line based on the FM modulation method or the FSK modulation method, the present application provides a modulation signal at the transmission side or a reception side. , A signal modulated using a cleaner demodulated signal is created, and the same distortion amount as the distortion amount of the transmission line characteristic is given to this signal to mix it with the modulated carrier wave that is distorted in the transmission line. A compensation equalizing circuit is disclosed.

[Industrial application field]

The present invention relates to an equalizer circuit, and more particularly to an equalizer circuit that compensates for transmission path characteristic distortion of a modulated carrier wave.

A communication line using the FM modulation method, the FSK modulation method, or the like requires high quality transmission characteristics. Therefore, an equalization circuit that keeps the quality of the communication line good is required.

[Conventional technology]

Such a conventional equalizing circuit is shown in FIG. 26. The carrier wave modulated by the modulating circuit 100 causes distortion in the transmission characteristic circuit 101 composed of a filter or the like. Compensation (equalization). In this case, the equalizer circuit 102 includes a group delay equalizer circuit and an amplitude equalizer circuit.

[Problems to be solved by the invention]

In such a conventional equalization circuit 102, for example, amplitude distortion, group delay distortion, etc., which occur in the filter of the transmission characteristic circuit 101, etc., include high-order components, so that a filter, etc. that generates distortion as the number of equalization stages increases. There is a problem that distortion equalization cannot be satisfactorily performed in the sense that it is also very difficult to obtain the inverse characteristic of the nonlinear circuit.

Therefore, an object of the present invention is to realize an equalization circuit capable of sufficiently compensating for distortion caused by transmission line characteristics with a simple structure.

[Means for solving problems]

FIG. 1 is a diagram schematically showing an equalizing circuit according to the first invention of the present application for solving the above-mentioned problems, and 1 is a modulator for performing modulation by a modulation signal on the transmission side or a demodulation signal on the reception side. Two
Is a distortion generation circuit for giving the output signal of the modulator 1 only the same distortion amount as the distortion amount received by the modulated carrier wave which is the original signal by the characteristic circuit of the transmission line to the output of the modulator 3, and 3 is the modulated carrier wave. A mixer that mixes the output signal of the distortion generating circuit 2 to obtain the difference.

FIG. 2 is a diagram schematically showing an equalizing circuit according to the second invention of the present application for solving the above problems.
In addition to the above invention, a frequency stabilizing circuit 4 is provided for making the oscillation frequency of the modulator 1 follow the center frequency of the modulated carrier which is the original signal distorted by the characteristic circuit of the transmission line.

[Work]

In FIG. 1 showing the first invention, a modulated signal from a modulator 1 modulated by a modulation signal on the transmitting side or a demodulation signal on the receiving side has its modulated wave component removed in a distortion generating circuit 2 and an original signal. The same amount of distortion as that of the modulated carrier received by the characteristic circuit of the transmission line is added, and by mixing the output of the distortion generating circuit 2 and the modulated carrier with the mixer 3, only distortion is canceled out. Get undistorted output.

In FIG. 2 showing the second invention, when the distortion is removed from the modulated carrier as in the first invention of FIG. 1, in the second invention, the oscillation of the modulator 1 in the frequency stabilizing circuit 4 is performed. The frequency is made to follow the frequency of the modulated carrier.

〔Example〕

 Examples of the present invention will be described below.

FIG. 3 shows an embodiment of the equalizing circuit of the first invention conceptually shown in FIG. 1, and this equalizing circuit is modulated by a modulation signal on the transmitting side or a demodulation signal on the receiving side. Modulator 1 and the modulated wave component output from the modulator 1, and only the same distortion amount as the distortion amount received by the modulated carrier wave which is the original signal by the characteristic circuit of the transmission line is output to the modulator 1. The distortion generating circuit 1 for giving and the mixer 3 connected to the transmission characteristic circuit 101 for transmitting the modulated carrier wave output signal of the modulation circuit 100 for inputting the modulation signal and modulating the carrier wave with the predetermined transmission characteristic The modulated carrier wave that has been distorted and the output signal of the distortion generating circuit 2 are mixed to obtain the difference.

The distortion generation circuit 2 includes a frequency conversion circuit 7 that converts the output frequency of the modulator 1, and a pseudo transmission circuit 8 that applies the same distortion amount as the distortion amount received by the modulated carrier to the output of the modulator 1.
The frequency conversion circuit 7 and the pseudo transmission circuit 8 are mixed together to cancel the modulated wave component output from the modulator 1 and leave only the distortion amount. It is composed of a local oscillator 71 and a mixer 72.

The local oscillation source of the modulator 1 is, for example, a voltage controlled oscillator (V
CO), and the input signal may be either a modulated signal on the transmitting side or a demodulated signal on the receiving side. That is,
Since the transmission characteristic circuit 101 is not the transmission line itself, the equalization circuit of the present invention may be used as a pre-equalization system in which distortion is generated by previously installing it on the transmission side, or a demodulated signal obtained on the reception side. Therefore, it may be installed on the receiving side. In this case, since the demodulated signal is used as a feedback signal, it is a cleaner signal with less distortion than the modulated carrier signal that has been distorted, and the present invention focuses on this and tries to remove distortion.

Next, regarding the operation of the embodiment of FIG. 3, the transmission characteristic circuit 1
How to equalize the distortion generated in 01 will be described using mathematical expressions.

First, for example, the FM modulated signal A _m sin ω _m t and the modulated carrier wave are
When inω ₀ t, the modulated carrier output from the modulation circuit _{100, = sin (ω 0 t +} A m sinω m t) , and the modulated carrier wave received distorted by the transmission characteristic circuit 101, = sin (omega ₀ t + A _m sin ω _m t + g (t)). However, g (t) represents the amount of distortion received, and this can be determined in advance by knowing the characteristics of the filter used in the transmission characteristic circuit.

On the other hand, the modulated or demodulated signal that has passed through the modulator 1 having its own oscillation frequency sinω ₁ t has the following waveform.

= Sin (ω ₁ t + A _m sin ω _m t) This waveform is divided into two parts, one of which has the following waveform in the frequency conversion circuit 7.

_{= Sin (ω 1 t-ω} 2 t + A m sinω m t) However, the local oscillator 7 is intended to generate a sin .omega ₂ t becomes signal.

The other has a waveform in the pseudo transmission circuit 8.

_{= Sin (ω 1 t + A} m sinω m t + g '(t)) However, g' (t) represents the amount of strain to be generated in a pseudo-transmission circuit 8. The waveform is further in the mixer 9, and becomes: = cos (ω ₂ t + g '(t)).

When these waveforms and are mixed by mixer 3,
Since it is ×, it follows that = sin (ω ₀ t−ω ₂ t + A _m sin ω _mt + g (t) −g ′ (t)).

Therefore, the pseudo transmission circuit 8 having the relationship of g (t) = g '(t) should be used. At this time, the output of the mixer 3 is: sin (ω ₀ t−ω ₂ t + A _m sin ω _m t) In this case, ω ₂ is 0, and frequency shift is not performed unless the frequency conversion circuit 7 is used.

As is clear from the above, the modulated signal is obtained with the waveform, only the amount of distortion is added to the waveform, and the modulated wave component is removed from the waveform, so the mixer output has the form in which only the distortion of the modulated carrier is removed. .

An example of such a pseudo transmission circuit 8 is shown in FIG. 4, in which 21 is an attenuator, 22 is a delay circuit, 23 is a limiter, and 24 is a delay circuit.

In the attenuator 21, the amplitude of the modulated carrier is attenuated, the delay circuit 22 generates the AM component of the modulated carrier, the limiter 23 performs AM-PM conversion, and the AM component generated in the delay circuit 22 is phased. A flattening circuit that converts the signal into rotation to equalize the amplitude distortion component of the characteristic circuit of the transmission line, and the delay circuit 24 compensates the delay characteristic generated in the delay circuit 22 to equalize the group delay distortion of the characteristic circuit of the transmission line. It gives good delay characteristics.

This pseudo transmission circuit is a compensation system that is particularly effective when the modulated carrier wave is distorted by an RF band amplifier or the like.

As the delay circuits 22 and 24, a circuit example shown in FIG. 6 can be given as a circuit having delay characteristics I and II as shown in FIG. Therefore, the delay characteristics shown in FIG. 7 are obtained by both the delay circuits 22 and 24.

As the limiter, a well-known voltage type one as shown in FIG. 8 and a well-known current type one as shown in FIG. 9 may be used. In the figure, Tr1 and Tr2 are transistors, R1 to R6 are resistors, and D1 and D2 are diodes.

Further, the circuit shown in FIG. 10 can be used as the AM-PM conversion circuit. This is buffers B1 and B
2 is connected by a resistor R, and the input signal of the buffer B2 is phase-rotated by the bias signal via the varactor diode C and the input signal of the buffer B2. The transfer function H (j
ω) = 1 / (1 + jωCR), and the capacitance of the varactor diode C changes as the voltage V changes, and θ = tan ⁻¹
The phase is rotated by ωCR.

As the pseudo transmission circuit 8, the circuit shown in FIG. 11 can also be used. This distortion generating circuit 2 treats a higher-order distorted wave signal generated in the transmission line 101 as a fundamental wave signal when nonlinear amplifiers are connected in multiple stages in the transmission line 101 through which the modulated carrier passes. , A circuit TC for generating the transmission distortion characteristic of the first-order harmonic component as shown in the figure in order to compensate for the generation of the distortion amount of the fundamental wave.
Circuit TC for generating transmission distortion characteristics of first and second harmonic components
Circuit TC for generating transmission distortion characteristics of second and third harmonic components
3, ... Circuit TC for generating transmission distortion characteristics of nth harmonic component
n, the frequency is multiplied by each of the multipliers ML2 to MLn, the corresponding distortion is given by each of the transmission distortion characteristic circuits TC1 to TCn, and mixed by the mixers MIX2 to MIXn with the harmonic component of the first order. After the difference is obtained and converted into a fundamental wave component, a well-known selective synthesizing circuit SYN including an attenuator, an amplifier and the like generates a synthesized signal to perform distortion equalization of the fundamental wave signal due to higher order distortion.

In addition, as the pseudo transmission circuit 8, a Chebyshev-type bandpass filter shown in FIG. 12, a circuit combining an amplitude equalizer and a delay equalizer shown in FIG.
A delay / amplitude characteristic may be equalized by using a transversal filter type circuit as shown in the figure.

A circuit shown in FIG. 15 can be cited as a pseudo transmission circuit 8 that generates equalizing distortion only by delay distortion of the characteristic circuit 101 of the transmission line. In the figure, 31 is a buffer amplifier, 32 is a mixer, 33 is a delay circuit, 34 is a mixer, and 35 is a voltage controlled oscillator (VCO). These one set constitutes a one-stage delay circuit, which is provided in N stages in series. To be

Each delay circuit has a frequency (f1 ... f) as shown in FIG.
It has a delay characteristic against frequency oscillating in n), and the delay characteristic is variable in N stages in series.

Further, in order to equalize only the amplitude distortion, as shown in FIG. 17, the amplitude equalizing circuit 36 is used instead of the delay circuit 33 of FIG. 15 to make the amplitude characteristic variable. The amplitude-versus-frequency characteristic of each amplitude distortion circuit in this case is as shown in FIG.

In the embodiment of the first invention described above, if the oscillation frequency (center frequency) of the voltage controlled oscillator (VCO) as the modulator 1 is made the same as the oscillation frequency of the modulation circuit 100, the modulation circuit 100 and the modulator 1 Can use the same circuit configuration,
Similarity is maintained regarding the occurrence of distortion, and the completeness of distortion equalization can be expected.

Further, as shown in FIG. 19 in addition to the embodiment shown in FIG. 3, a frequency conversion circuit 40 (mixer 40a and local oscillator 40b) is provided between the characteristic circuit 101 of the transmission line and the mixer 3.
And a bandpass filter 41 may be provided.

The frequency conversion circuit 40 frequency-converts the modulated carrier output of the characteristic circuit 101 so that the center frequency of the modulated carrier output from the mixer 3 via a bandpass filter (not shown) can be easily selected. The band pass filter 41 extracts the high frequency band.

Further, as shown in FIG. 20, in addition to the voltage controlled oscillator as the modulator 1, an attenuator 43 is provided in front of the modulator 1 to adjust the input level of the voltage controlled oscillator to shift the output signal frequency. May be controlled. In this case, the amount of amplitude distortion can be finely adjusted by adjusting the attenuator 43.

Next, an embodiment of the second invention will be described with reference to FIG.

Also in the second invention, like the embodiment of the first invention shown in FIG. 3, this equalization circuit inputs the modulation signal in the modulation circuit 100 to modulate the carrier wave, and the transmission characteristic circuit 101.
Then, the modulated carrier output signal is transmitted with a predetermined transmission characteristic. On the other hand, the carrier wave of the modulator 1 is modulated by the modulation signal on the transmission side or the demodulation signal on the reception side, and the oscillation frequency of the modulator 1 is made to follow the center frequency of the modulated carrier wave by the frequency stabilizing circuit 4. In the output from the modulator 1, the modulated wave component is canceled in the distortion generation circuit 2, and the same distortion amount as that received by the modulated carrier wave is added. Then, the modulated carrier wave and the output signal of the distortion generating circuit 2 are mixed by the mixer 3 to obtain the difference, whereby the modulated carrier wave from which the distortion is removed is obtained.

In this embodiment, the frequency stabilizing circuit 4 includes a mixer 41 that takes a difference frequency between the modulated carrier wave and the output of the modulator 1,
It comprises a mixer 43 for taking an error frequency between the difference frequency signal and the reference signal of the reference frequency signal source 42, and a filter 44 for taking out a low frequency component of the error frequency. Further, the distortion generating circuit 2 has the same frequency conversion circuit 7 for converting the output frequency of the modulator 1 as the first invention shown in FIG. To the output of the modulator 1, and a mixer 9 that mixes the outputs of the frequency conversion circuit 7 and the pseudo transmission circuit 8 to cancel the modulated wave component output from the modulator 1 and leave only the distortion amount. It consists of and.

Therefore, in the second invention, the operation of generating distortion, removing the modulated wave component, and canceling the distortion of the modulated carrier wave due to the generated distortion are the same as in the case of the first invention described above.

That is, the second invention is characterized in that the frequency stabilizing circuit 4 is provided. In the embodiment of FIG. 21, the mixer 41 is
The frequency difference between the modulated carrier wave from the characteristic circuit 101 of the transmission line and the output signal from the voltage controlled oscillator as the local oscillation source of the modulator 1 is calculated, and this frequency difference is kept constant, that is, , So that the output of the modulator 1 follows the modulated carrier wave, the reference frequency signal from the reference oscillator 42 and the frequency difference signal thereof are compared by the mixer 43, the difference is taken, and the difference is passed through the low pass filter 44. Is detected to control the voltage controlled oscillator.

As a result, equalization can be performed corresponding to the change in distortion due to the frequency drift of the input modulated carrier wave.

FIG. 22 is a diagram showing another embodiment of the frequency stabilizing circuit 4 in the second invention. In this embodiment, the reference oscillator 4 is used.
A voltage controlled oscillator (VCO) is used as 2, a control signal is generated by the voltage controlled oscillator (VCO), and a bias circuit 45 is provided.

In this embodiment, by adjusting the bias circuit 45, the distortion can be set to "0" while observing the signal obtained by demodulating the output of the bandpass filter (not shown) after the mixer 3. . This is effective in that when there is a difference between the frequency of the modulated carrier and the frequency of the modulator 1, a constant frequency difference is provided between the two, and control is performed so as to correspond to the case where there is no distortion. Target.

FIG. 23 shows still another embodiment of the second invention.
Here, in order to stabilize the frequency, AFC (automatic frequency control) is applied between the input and output of the voltage controlled oscillator as the modulator 1.
A circuit 50 is provided.

It is needless to say that the embodiment described in FIGS. 4 to 18 and FIGS. 19 and 20 for the first invention can be used in the same manner in the second invention.

〔The invention's effect〕

As described above, according to the equalization circuit of the present application, in the first invention, the modulated wave component is generated by using the modulated signal on the transmitting side or the cleaner demodulated signal fed back on the receiving side when the modulated carrier wave is generated. Only the same amount of distortion that the modulated carrier wave receives in the characteristic circuit of the transmission line is removed, and the distortion of the modulated carrier wave itself is canceled by this generated distortion amount, so the complicated reverse characteristic of the transmission line is Sufficient equalization can be performed by obtaining a known distortion amount of the transmission line regardless of the equalizer circuit.

Further, in the second invention, since the circuit for stabilizing the frequency is provided in addition to the first invention, in addition to the above-mentioned effects, it is possible to easily cope with the fluctuation of the frequency.

[Brief description of drawings]

1 is a block diagram showing the principle of an equalizing circuit according to the first invention of the present application, FIG. 2 is a block diagram showing the principle of an equalizing circuit according to the second invention of the present application, and FIG. 1 is a block diagram showing an embodiment of an equalizing circuit of the invention of FIG. 1, FIG. 4 is a block diagram showing an embodiment of a distortion generating circuit used in the present invention, and FIG. 5 is a delay of a delay circuit shown in FIG. FIG. 6 is a graph showing the characteristics, FIG. 6 is a circuit diagram showing an embodiment of the delay circuit shown in FIG. 4, FIG. 7 is a graph showing the combined delay characteristics of the two delay circuits shown in FIG. 4, and FIG. Is a diagram showing the voltage type circuit of the limiter shown in FIG. 4, FIG. 9 is a diagram showing the current type circuit of the limiter shown in FIG. 4, and FIG. 10 is the same AM-PM conversion as the limiter shown in FIG. FIG. 11 is a block diagram showing another embodiment of the distortion generating circuit used in the present invention. FIG. 12 is a block diagram showing still another embodiment of the distortion generating circuit used in the present invention, FIG. 13 is a block diagram showing still another embodiment of the distortion generating circuit used in the present invention, and FIG. FIG. 15 is a block diagram showing still another embodiment of the distortion generating circuit used in the present invention, FIG. 15 is a block diagram showing still another embodiment of the distortion generating circuit used in the present invention, and FIG. FIG. 17 is a graph showing the delay characteristics of the delay circuit shown in the figure, FIG. 17 is a block diagram showing another embodiment of the distortion generating circuit used in the present invention, and FIG. 18 is the amplitude shown in FIG. FIG. 19 is a block diagram showing an amplitude characteristic of the distortion circuit, FIG. 19 is a block diagram showing an embodiment common to the present invention, FIG. 20 is a block diagram showing another embodiment common to the present invention, and FIG. One implementation of the equalizing circuit of the second invention shown in FIG. FIG. 22 is a block diagram showing an example, FIG. 22 is a block diagram showing another embodiment of the equalizing circuit of the second invention, and FIG. 23 is a block diagram showing yet another embodiment of the equalizing circuit of the second invention. FIG. 24 is a block diagram showing a conventional equalizing circuit system. In FIGS. 1 to 4 and FIGS. 20 to 22, 1 is a modulator, 2 is a distortion generating circuit, 3, 9, 12, 41 and 43 are mixers, 4 is a frequency stabilizing circuit, and 7 and 11 are frequencies. A conversion circuit, 8 is a pseudo transmission circuit, 21 and 43 are attenuators, 22 and 24 are delay circuits, 23 is a limiter, 42 is a reference frequency signal source, 44 is a low-pass filter, and 45 is a bias circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (15)

[Claims] 1. A modulator (1) for performing modulation by a modulation signal on a transmission side or a demodulation signal on a reception side, and an output signal from the modulator (1) are input, and are converted into an original signal by a characteristic circuit of a transmission line. A distortion generating circuit (2) for adding only the same distortion amount as that received by a certain modulated carrier to the output signal of the modulator (1) and outputting the modulated carrier and the distortion generating circuit (2). An equalization circuit comprising: a mixer (3) that mixes the output signal of the above and takes a difference. 2. The equalization circuit according to claim 1, wherein the output signal of the modulator (1) and the center frequency of the modulated carrier are the same. 3. The equalization circuit according to claim 1, wherein the modulator (1) is a voltage controlled oscillator for performing frequency modulation. 4. The attenuator (43) and a voltage controlled oscillator (44) connected thereto, wherein the modulator (1) performs frequency modulation.
The equalization circuit according to claim 1, wherein the equalization circuit comprises: 5. A frequency conversion circuit (7) for converting the output frequency of the modulator (1) by the distortion generation circuit (1).
A pseudo transmission circuit (8) for giving the same amount of distortion as that received by the modulated carrier wave to the output of the modulator (1), and the frequency conversion circuit (7) and the pseudo transmission circuit (8). The equalization circuit according to claim 1, further comprising: a mixer (9) that mixes the outputs of the above and cancels the modulated wave component output from the modulator (1) to leave only the distortion amount. . 6. The attenuator (21) in the pseudo transmission circuit (8).
And a first delay circuit (22) for generating an AM component, and
A limiter (23) for performing PM conversion to equalize the amplitude distortion component of the transmission line, and a flat for compensating the delay characteristic generated in the first delay circuit (22) to equalize the group delay distortion of the transmission line. An equalization circuit according to claim 5, comprising a second delay circuit (24) for providing a high delay characteristic. 7. A pseudo transmission circuit (8) for equalizing distortion due to an N-th order harmonic component.
The equalization circuit described in the item. 8. A modulator (1) for performing modulation by a modulation signal on the transmission side or a demodulation signal on the reception side, and an original signal in which an oscillation frequency of the modulator (1) is distorted by a characteristic circuit of a transmission line. A frequency stabilizing circuit (4) that follows the center frequency of the modulated carrier wave and an output signal from the modulator (1) are input, and the same distortion amount as the received distortion amount is applied to the modulator (1). ) In addition to the output signal of (1), and a mixer (3) for mixing the modulated carrier wave and the output signal of the distortion generating circuit (2) to obtain the difference. Equalization circuit characterized by. 9. A mixer (41) for determining the difference frequency between the center frequency of the modulated carrier wave and the center frequency of the output of the modulator (1) by the frequency stabilizing circuit (4), and the difference frequency signal. The mixer (43) for taking an error frequency between the reference frequency signal source (42) and the reference frequency signal source (42), and a filter (44) for taking out a low frequency component of the error frequency. Circuit. 10. A mixer (41) for taking the difference frequency between the center frequency of the modulated carrier wave and the center frequency of the output of the modulator (1) by the frequency stabilizing circuit (4), and the difference frequency signal. A mixer (43) for taking an error frequency with the reference signal from the reference frequency signal source (42), a filter (44) for taking out a low frequency component of the error frequency, and a control signal for the reference frequency signal source (42). 9. The equalizing circuit according to claim 8, comprising an adjusting bias circuit (45) for generating and eliminating the output distortion of the modulated carrier wave. 11. A frequency conversion circuit (7) for converting the output frequency of the modulator (1) by the distortion generation circuit (1).
A pseudo transmission circuit (8) for giving the same amount of distortion as that received by the modulated carrier wave to the output of the modulator (1), and the frequency conversion circuit (7) and the pseudo transmission circuit (8). 9. The equalization circuit according to claim 8, further comprising a mixer (9) for mixing the outputs of the above and canceling the modulated wave component output from the modulator (1) and leaving only the distortion amount. . 12. The pseudo transmission circuit (8) comprises an attenuator (2
1) and a first delay circuit (22) for generating an AM component,
A limiter (23) for performing AM-PM conversion to equalize the amplitude distortion component of the transmission line and a delay characteristic generated in the first delay circuit (22) are compensated to equalize the group delay distortion of the transmission line. The equalization circuit according to claim 11, comprising a second delay circuit (24) which gives a flat delay characteristic. 13. The pseudo transmission circuit (8) equalizes distortion due to an N-th harmonic component.
Equalization circuit described in item 11. 14. The equalization circuit according to claim 8, wherein the modulator (1) is a voltage controlled oscillator. 15. The modulator (1) comprises an attenuator (43),
The equalization circuit according to claim 8, comprising a voltage controlled oscillator (44) connected thereto.