JP3074920B2 - Transmission signal transceiver and transmission / reception equalization circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission signal transceiver for transmitting information, and more particularly to a transmission signal transceiver characterized by a control method of a transmission signal correction function for correcting a signal attenuation of a transmission medium. The present invention relates to a PCM signal transmission / reception equalization circuit for transmitting a 4-wire metallic cable, and more particularly to an equalization circuit for performing transmission / reception waveform equalization using only one side of the cable.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 13, a transmission signal transceiver of this type has a transmission equalizing amplifier 6 for correcting the attenuation characteristics of a cable 2 (hereinafter referred to as a line) on both sides.
1A and 61B are provided outside the transmission signal transceivers 60A and 60B based on correction amount information that is previously known according to the line length or correction amount information input from a result of observing a transmission waveform at a certain point on the line. Was more controlled. Also,
A conventional waveform equalizing circuit is installed between the receiving sides of the opposing transmitting and receiving circuits, or is installed between the transmitting sides. When installed on the transmitting side, the frequency characteristics of the cable loss that affect the signal waveform at the opposing receiving circuit are often unknown, so the person in charge of construction and maintenance will estimate the cable loss and manually The transmission equalization circuit was set by the operation. In addition, regardless of whether the cable is installed on the transmission side or the reception side, the cable is installed at both ends of the cable.

[0003]

In this conventional transmission signal transmitter / receiver, in addition to the problem that the line length must be known in advance, it is necessary to input and correct the correction amount information every time the line length is changed. There was a problem.
On the other hand, in the other conventional technology, a signal waveform can be observed in the middle of the line, for example, a problem that a terminal board must be provided, and each time the line length is changed, the correction amount information is slightly reduced while observing the signal waveform on the line. There was a problem that it had to be changed and set.

Further, the conventional transmission equalization circuit has a disadvantage that a manual operation is required.

When one of the transmission / reception circuits is installed in a station facility or the like and cannot be touched by a general user, and the other transmission / reception circuit is at hand, the user is required to further extend the transmission distance. Sometimes there was a problem that the user alone could not do anything.

[0006]

According to the present invention, there is provided a transmission signal transceiver for transmitting and receiving information between a plurality of points via a transmission medium having an attenuation characteristic with respect to a transmission signal amplitude. A configuration comprising: an attenuation determining unit that estimates an amount of attenuation of the transmission medium from a received signal; and a transmission signal correction unit that multiplies an original signal waveform by an inverse characteristic of an attenuation characteristic of the transmission medium based on the amount of attenuation. And

According to a second aspect of the present invention, in a waveform equalization circuit connected to each of a transmission line and a reception line of a four-wire communication line, a first band-pass filter for passing a reception signal through a signal band component is provided. , The control signal level increases, the loss frequency characteristic of the line having less loss passes through the first pseudo line whose gain frequency characteristic including the first band pass filter is simulated, and the first amplifier in order. Then, the transmission signal is sequentially transmitted to the attenuator, the second bandpass filter having the same configuration as the first bandpass filter, the second pseudo line having the same configuration as the first pseudo line, and the second amplifier. A peak detection circuit for charging the low-pass filter when the peak of the output of the first amplifier exceeds a fixed threshold, and preventing discharge of the low-pass filter when the peak does not exceed the fixed threshold; It is configured to apply a force as the control signal of the first and second pseudo line.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram of a four-wire digital transmission signal transceiver according to one embodiment of the present invention. A receiving transformer 10 for receiving a transmission signal of a transmitting and receiving device through a pair of paired lines 20;
Attenuation determination unit 12 for estimating the amount of signal attenuation, reception equalization amplification unit 13 for correcting the reception signal from reception transformer 10 based on the determination amount information 17, and the reception-equalized output signal An identification unit 14 for identifying at retiming and outputting a reception logic signal 18;
7, a transmission equalizing amplifier 15 for correcting the signal attenuation of the other pair line 21 on the transmission side, and a transmission transformer for transmitting the transmission signal to the receiving side of the opposing transceiver via the line 21. 11.

FIG. 2 is a connection diagram showing an example of use of the digital transmission signal transceiver shown in FIG. 1. The digital transmission signal transceiver 1 shown in FIG. 1 having a function of correcting the attenuation of a transmission signal,
The conventional digital transmission signal transceiver 3 which does not have the function of correcting the attenuation of the transmission / reception signal has one transmission / reception.
They are connected by a cable 2 including a pair of transmission lines. As will be described later, by simply providing the digital transmission signal transceiver of the present invention on only one side, the signal attenuation characteristics are automatically corrected on the transmission line, and accurate transmission over a long distance can be performed.

Prior to explaining the operation of FIG.
A pattern of signal attenuation of a signal passing through a line connecting two transceivers will be described. FIG. 3 is a representative example showing the relationship between the signal frequency of a paired line and the signal attenuation per unit line length, and it is known that most lines have substantially the same characteristics. From FIG. 3, it can be seen that the signal attenuation increases as the signal frequency increases, and that the signal attenuates even at a lower frequency.

Now, the transmission logic signal 19 in FIG.
As shown in (a), it is assumed that they are 1, _0, 1... And their period T (transmission signal center frequency f ₀ = １ ／ T) is 5 μm.
s, if the transmission signal amplitude is a 100% rectangular wave of 1 v, f
_{Since 0} = 100 kHz and a frequency component higher than that, little by little, it is assumed that the transmission equalizer / amplifier 15 of FIG. 1 transmits a rectangular wave as shown in FIG. Then, at the opposing receiving end, a signal having a very small amplitude (0.5 mmφ in the example of FIG. 3) distorted as shown in FIG. 3A due to the signal attenuation characteristic of the line 21 as described in FIG.
If the pair wire is used, it will be attenuated by about 9 dB per 1 km of line length) and it will not be possible to receive accurately. Here, if if-equalization amplification unit 15 knew the signal attenuation amount of advance line 21, transmission equalization amplification unit 15 as shown in FIG. 4 (b) rather than 1v rectangular wave, the f ₀ A transmission signal waveform that is a voltage amplified by the amount of attenuation (in the example of FIG. 4B, the line length is 1 km and corrected to about 3 V), and further amplifies the high-frequency component (this is generally called high-frequency emphasis). Is output, and even if the signal is attenuated by the line 21, the signal at the receiving end that is opposed to the signal can be identified sufficiently accurately.

The signal attenuation is estimated by utilizing that the line 21 is housed in the same cable as the line 20.
This can be performed based on the determination amount information 17 of the attenuation amount determination unit 12 in FIG. By the way, by detecting the peak amplitude voltage of the received signal, the attenuation amount judging unit 12 can almost judge that it is the signal attenuation amount at f _0. Therefore, the ratio between the amplitude voltage 1v transmitted by the opposite side and the received peak voltage is calculated. By outputting it as the determination amount information 17, the transmission equalization amplification unit 15
From the characteristics shown in FIG. 3, it can be seen how much the corrected waveform should be generated for the rectangular wave.

Next, an example of the configuration of the transmission equalization amplification unit 15 will be described with reference to a functional block diagram of FIG. 5. An AND gate 44 that takes an AND condition between the 4-bit determination amount information 17 and the transmission logic signal 19 is provided. Each time the lower 4 bits of the initial load data are fixed to "0" and the upper 4 bits of the initial load data are connected to the output of the AND gate 44 and each transmission logic signal is transmitted (each transmission cycle, that is, in FIG. (In the example, every 5 μs)
A ROM address generating unit 40, which is set by an initial value load signal and includes a counter 43 which counts up by a 16-times clock of 1/16 of the transmission cycle, and transmits the 8-bit data with its output as an address. 256 words × 8 bits waveform R containing data for equalization
It comprises an OM 41 and a D / A converter 42 for converting the 8-bit output into an analog transmission waveform.

The operation of the transmission equalization amplification section will be briefly described. This transmission equalization amplification section uses a 16-times speed clock as shown in FIG.
(B) The transmission signal of the transmission equalization amplification unit is divided into 16 within the period T, the transmission amplitude at each point is converted into 8-bit data, and the output information stored in 16 words of the waveform ROM 41 is read out. By generating 16 consecutive waveform ROM addresses, a transmission waveform corresponding to the transmission logic signal “1” and according to the determination information amount 17 can be output from the waveform ROM 41 through the D / A converter 42.

Next, an embodiment of the transmission / reception equalization circuit of the present invention will be described. FIG. 6 is a block diagram of a transmission / reception equalization circuit according to one embodiment of the present invention. A reception signal input from a reception line (not shown) via the reception input terminals RI1 and RI2 is subjected to balanced-unbalance conversion by the reception transformer T1, and then input to the filter FIL1. The filter FIL1 is a BPF (bandpass filter) for removing high-frequency noise and crosstalk. This filter output is input to the automatic pseudo line ALBO1. The amount of attenuation of this circuit and the zero-point frequency are interlocked, change according to the control signal, and move in a lower direction as the cable loss increases.

Since the output of the automatic pseudo line ALBO1 is very small, the voltage is amplified by the amplifier AMP1 and the reception output terminal RO
1, RO2. This output signal is input to a receiver main body (not shown). The output of the amplifier AMP1 is simultaneously input to the peak detection circuit PDET, and the fixed threshold value and the peak value are compared. A signal of a constant level is applied to the low-pass filter L only during the period when the peak value exceeds the fixed threshold
Input to PF.

The filter LPF extracts and holds a DC component from the input signal, and stores the two automatic pseudo lines ALBO1, ALBO.
BO2 is commonly supplied. The received signal passes through the automatic pseudo line controlled in this way, and the high-frequency components lost are emphasized, and the received signal has a waveform free of intersymbol interference.

On the other hand, the transmission signal is input to the attenuator ATT, and is attenuated by a certain amount.
Input to L2. Attenuator ATT is the transmission input terminal T
It is used because the output signal level of a transmitter (not shown) connected to I1 and TI2 is generally too high for the dynamic range of the automatic artificial line ALBO2.

The two filters FIL1 and FIL2 have the same circuit, and have two automatic pseudo lines ALBO1 and ALBO1.
LBO2 is the same circuit. The transmission-side amplifier AMP2 amplifies the transmission signal whose high frequency band is emphasized, and transmits the transmission signal to a transmission line (not shown) via the transmission transformer T2 for unbalanced-balanced conversion from the transmission output terminals TO1 and TO2. I do.

Next, FIG. 7 shows a block diagram of the entire system including the opposing transmission / reception circuit and cable. Opposite transmitter TRS
AMI code (Alternate) of the PCM signal transmitted from
MarkInversion) transmits the receiving line LINE1 and
And after reception equalization, the signal is input to the receiver REC1. Similarly, the transmitting side equalizes the AMI code output from the transmitter TRS1 by the transmission circuit (TEQL) shown in FIG.
2 and transmitted to the opposing receiver REC0.
Here, the transmission line and the reception line are names based on the transmission / reception equalization circuit of the present invention.

The principle of waveform equalization will be described with reference to FIG. The Fourier transform of the transmission signal of the transmitter TRS0 is X
(Ω), and the transfer function of the transmission line LINE1 is H ₁
(Ω), the winding ratio of the receiving transformer T ₁ is 1, the filter FI
The transfer function of L1 is F ₁ (ω), and the automatic pseudo line ALBO1
Is the transfer function of A ₁ (ω) and the amplification degree of the amplifier 1 is G ₁ , the Fourier transform Y of the output signal of the receiving circuit RQL
(Ω) is

(Equation 1) Becomes Near the center of the signal band

(Equation 2) The transfer function on the left side is designed so that

In the high frequency range, the equation (2) generally does not hold due to the cutoff characteristic of the filter FIL1, but this is not a problem since it is necessary that no intersymbol interference occurs in the signal after reception equalization. In the received output signal obtained by inversely Fourier-transforming Y (ω) in the expression (1), the intersymbol interference is sufficiently removed.

On the other hand, regarding the transmission circuit, the transmitter TRS1
X ′ (ω), the attenuation of the attenuator ATT is L, the transfer function of the filter FIL2 is F ₂ (ω), and the transfer function of the automatic pseudo line ALBO2 is A.
₁ (ω), the amplification factor of the amplifier AMP2 is G ₂ , the winding ratio of the transmission transformer T2 is 1, and the transfer function of the transmission line LINE2 is H ₂ (ω). The transformation Y '(ω) is

(Equation 3) Becomes Here, H ₁ (ω) = H from the identity of the transmitting system and the receiving system.
₂ (ω), F ₁ (ω) = F ₂ (ω), A ₁ (ω) = A ₂ (ω). Equation (3) uses equation (1).

(Equation 4) Becomes Here, since the transmission signal pulse waveforms of the two transmitters TRS0 and TRS1 are generally the same, the Fourier transform is also equal, and X ′ (ω) = X (ω). Furthermore,

(Equation 5) Equation (4) gives

(Equation 6) Becomes As described above, since the intersymbol interference has been removed from the output signal of the receiving circuit REQL, the intersymbol interference has also been removed from the input signal of the opposing receiver REC0 from Equation (6). That is, the transmission equalization is automatically performed.

FIG. 8 is a circuit diagram showing one embodiment of the present invention. The filters FIL1 and FIL2 constitute a second-order BPF, and the Laplace transform F (s) is obtained from the inverse circuit condition of each element.

(Equation 7) Becomes Here, ω ₀ , Q, and a are constants determined from circuit constants.

The Laplace transform A (s) of the automatic pseudo lines ALBO1 and ALBO2 has one low-pass pole and one mid-zero.

(Equation 8) Becomes Here, K ₁ , K ₂ , a ′, and b are constants. In the same figure, a capacitor C _DC is for DC cut, and a diode D1 (D2) and an NPN transistor Q1 (Q2)
Between the emitter and the base constitutes a parallel resistance to the signal in an AC manner. The value of the combined equivalent resistance is determined by the value of the DC current flowing from the positive power supply V _CC to the ground through the NPN transistor Q1 (Q2) and the diode D1 (D2). The larger the current value, the smaller the resistance value. NPN
The bases of the transistors Q1 and Q2 are AC grounded by a capacitor C, and the signal is supplied to a diode D1 (D2) and N
The PN transistor Q1 (Q2) branches and passes.

The output voltage of the amplifier AMP1 is the high potential threshold V
_P and two comparators CM having a low potential threshold V _N
P1 and CMP2 compare with each threshold value. The PN connected to the positive power supply V _CC only during the period exceeding any threshold
The P-transistor Q0 is turned on, and charges the low-pass filter LPF including the resistor R and the capacitor C. This is the output voltage V _C of the filter LPF appears DC component, even when 0 is input to the received signal, and holds the value.

[0027] The cable loss is large lower output signal level of the amplifier AMP1, the threshold V _P, narrows the time width exceeding V _N, the charging current becomes less for a result low-pass filter LPF, the filter LPF output voltage V _C also decreases. Therefore, the DC bias voltage applied to the series circuit of the NPN transistor Q1 (Q2) and the diode D1 (D2) decreases, and the current flowing through the series circuit decreases. As a result, the diode D1 (D2) and the NPN transistor Q1
The parallel equivalent AC resistance of (Q2) increases. Then, the attenuation of the automatic pseudo lines ALBO1 and ALBO2 decreases, and at the same time, the zero point moves to a low frequency. As a result, the high frequency emphasis on the received signal is enhanced, and the automatic pseudo lines ALBO1 and ALB
O2 output level is increased, the output level of the amplifier AMP1 is increased, the threshold value V _P, the time width of over V _N becomes wider. That is, negative feedback is applied. Finally output level threshold V _P of the amplifier AMP1, stabilized where a level slightly exceeding V _N. At this time, circuit constants are set based on the equations (2) and (5) so that the frequency characteristics of the automatic pseudo lines ALBO1 and ALBO2 match the cable loss. In this state, as described above, the frequency characteristic is also set optimally on the transmitting side.

Note that, based on the output impedance of the filters FIL1 and FIL2, the automatic pseudo lines ALBO1 and ALB
The input impedance of O2 is set high so as not to affect each other.

Next, the state of equalization will be described with reference to the frequency characteristic diagram of FIG. FIG. 9A shows a bandpass filter FI.
It is a gain characteristic of L1 and FIL2. As is clear from the equation (7), the attenuation is flat at a frequency lower than f _a = a / 2π, and has a peak at f ₀ = ω ₀ / 2π. f ₀
Is generally chosen to pass most of the signal spectrum.

FIG. 9B shows an automatic pseudo line ALBO1, A
Graph 1 shows the gain characteristic of LBO2, and graph 1 shows the case where the cable loss is large, and graph s shows the case where the cable loss is small. From the equation (8), by setting the circuit constants to be a'a, the receiving circuit REQL and the transmitting circuit TEQ are set.
The gain of L as a whole is as shown in FIG. In other words, the zero point moves to a lower frequency as the cable loss increases (f
_l ), the gain also increases (L _l ). This is expressed by equation (8)
Is smaller. The fact that b becomes smaller is due to the negative feedback effect described above. (8) Zero point frequency b / 2 and attenuation (b−K ₂ ) of automatic pseudo line ALBO1 represented by equation (8)
Relationship / K ₁ is the straight line shown in FIG. 10.

Next, a description will be given with reference to the timing chart of FIG. The five graphs on the left side of FIG. 11 show the case where the cable loss is small, and the five graphs on the right side show the case where the cable loss is large. The larger the cable loss, the lower the input level to the filter FIL1 and the lower the output level of the amplifier AMP1. Therefore, the threshold value V _P, the time width of over V _N is narrow, resulting switching PNP time transistor Q0 is conducting is shortened charging current to the low-pass filter LPF is decreased, the output voltage of the filter LPF V _C is low. Therefore, as described above, the attenuation of the automatic pseudo line ALBO1 is stabilized at the reduced value (L ₁ ). Next, the operation of the transmission circuit TEQL will be described with reference to the timing chart of FIG. Attenuator ATT
The frequency characteristic of the signal attenuated by is emphasized in the high frequency range (see FIG. 1).
2 (b)), the high frequency band is attenuated in the opposite receiver REC0 after transmitting the cable, and appears as a waveform without intersymbol interference (FIG. 12 (c)).

[0032]

As described above, according to the transmission signal transceiver of the present invention, the signal attenuation of the line is determined from the received signal by utilizing the fact that the lines on the transmission side and the reception side are generally the same cable. However, there is an effect that the transmission signal can be automatically corrected without receiving any control from the outside. Therefore, there is no need for a person to prepare line length data, observe the transmission signal waveform in the middle of the cable, or to redo these every time the line length is changed. However, since each line has the same tendency with respect to frequency, there is an effect that the transmission correction function can be used without changing the transmission correction function for various lines. In addition, although the operation in the case where the transmitter / receiver without the correction function is provided on one side has been described, it is clear that the effect is the same even when the transmitter / receiver of the present invention is provided on both sides. Since the amount is corrected, there is an effect that transmission can be performed over a long distance.

According to the transmission / reception equalization circuit of the present invention, the control signal corresponding to the cable loss generated from the reception circuit is commonly used for the transmission circuit. It is only necessary to install this circuit on the side, and there is an effect that it is not necessary to manually adjust the transmission equalization circuit.

[Brief description of the drawings]

FIG. 1 is a functional block configuration diagram of a transmission signal transceiver according to an embodiment of the present invention.

FIG. 2 is a connection diagram showing a usage example of the present invention.

FIG. 3 is a characteristic diagram showing an example of a frequency characteristic of a signal attenuation amount of a line.

FIG. 4 is a signal waveform diagram showing waveforms at various points in FIG. 1;

FIG. 5 is a functional block diagram of a transmission equalization amplifier shown in FIG. 1;

FIG. 6 is a block diagram of one embodiment of the present invention.

FIG. 7 is a block diagram of the entire system including the opposition.

FIG. 8 is a circuit diagram of one embodiment of the present invention.

FIG. 9 is a frequency characteristic diagram of the receiving circuit shown in FIG. 3;

FIG. 10 is a characteristic diagram of the automatic pseudo line shown in FIG.

FIG. 11 is a timing chart of the receiving circuit shown in FIG. 3;

FIG. 12 is a timing chart of the transmission circuit shown in FIG. 8;

FIG. 13 is a functional block diagram of a conventional transmission signal transceiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Receiving transformer 11 Transmitting transformer 12 Attenuation determination part 13 Reception equalization amplification part 14 Identification part 15 Transmission equalization amplification part 20, 21 Line 40 ROM address generation part 41 Waveform ROM 42 D / A converter 43 Counter 44 AND gate T1 Reception Transformer T2 Transmission transformer AMP1, AMP2 Amplifier FIL1, FIL2 Band-pass filter ALBO1, ALBO2 Automatic pseudo line PDET Peak detection circuit LPF Low-pass filter ATT Attenuator TRS0, TRS1 Transmitter REC0, REC1 Receiver REQL Reception equalization circuit TEQL Transmission equalization circuit

Continuation of front page (56) References JP-A-52-6011 (JP, A) JP-A-3-13130 (JP, A) JP-A-58-17712 (JP, A) JP-A-3-136416 (JP) JP-A-2-305033 (JP, A) JP-A-58-88991 (JP, A) JP-A-62-107532 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H04B 1/76-3/44 H04B 3/50-3/60 H04B 7/005-7/015

Claims (1)

(57) [Claims] 1. A waveform equalization circuit connected to each of a transmission line and a reception line of a four-wire communication line, wherein the waveform equalization circuit performs increase / decrease correction according to a control signal level which is connected to the reception line and separately receives a reception signal. A first pseudo line for outputting, and a second pseudo line connected to a transmission line and having the same gain characteristics as the first pseudo line for correcting increase and decrease according to the control signal level for separately inputting a transmission signal and outputting the signal. A simulated line; and a control signal having a level that increases and decreases in accordance with a time length in which the corrected received signal output from the first simulated line is input and the signal level of the corrected received signal exceeds a predetermined threshold. And a peak detection circuit that outputs a signal to each of the first pseudo line and the second pseudo line. Amended rate A transmission / reception equalization circuit having characteristics of decreasing the gain, increasing the correction gain when the control signal level decreases, and controlling the frequency region to be amplified by increasing or decreasing the correction gain.