JPS6041332A - Equalizing circuit of transmission line - Google Patents

Abstract

PURPOSE:To equalize a transmission line with respect to f<1/2>AGC characteristic and flat AGC characteristic by providing an equalizing amplifier with a flat AGC circuit and an f<1/2>AGC circuit and controlling respective AGC circuits with outputs of independent signal generating circuits. CONSTITUTION:An equalizing amplifier 1 is provided between a transmission line signal input terminal 11 and an equivalent output terminal 12 of a transmission line equalizing circuit, and this amplifier 1 is constituted of a flat AGC circuit 4 and an f<1/2>AGC circuit 5. The gain of the AGC circuit 4 is controlled by a peak-to-peak value detecting and control signal generating circuit 2 which detects the peak-to-peak value of the equalization output. The gain of the AGC circuit 5 is controlled by the output of an inter symbol interference detecting and control signal generating circuit 3 which detects an inter symbol interference of the equalization output. The AGC circuit 5 is constituted of an active filter where a capacitor C1 and a diode D1 are connected in parallel. The diode D1 is subjected to impedance control by the output of the circuit 3 to equalize the transmission line with respect to f<1/2> characteristic and flat characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission line equalization circuit when a two-wire cable such as a local cable is used as a transmission line in a PCM baseband transmission system.

In general, in the PCM baseband transmission system, the transmission path loss is β
In order to compensate for the characteristic (Jf is frequency), the peak value of the equalizing amplifier output is detected in the equalizing amplifier system, and this is used as a control signal to automatically control the β characteristic (hereinafter referred to as Jf A G C
) has been applied.

Bipolar codes are normally used as transmission path codes. Here, the frequency characteristics of city cables etc. are 200~
Since the loss characteristic of Jt is exhibited in the region of 300 kHz or higher, L
As mentioned above, it was sufficient to apply only /7 AGC to equalize the transmission path, but in recent years, the number of hundreds of kb/s has increased.
When a relatively low-speed transmission system is implemented, the equalization band of the transmission line is approximately 1z-several hundred kHz. Now, since the above-mentioned city cable exhibits a flat loss characteristic different from the -It characteristic in the frequency range of 200 to 300 kHz or less, in the case of a low-speed transmission method like this example, the conventional JfAGC Because the low frequency part is not equalized by just
There is a problem that appears as large code amount interference in the equalized waveform.

SUMMARY OF THE INVENTION An object of the present invention is to provide a transmission line equalization circuit that solves the above-mentioned problems by means that are extremely easy to design in terms of equalization design.

The transmission line equalization circuit of the present invention has a first gain control circuit which is feedback-connected from the equalized output via the peak value detection control signal generation circuit, and generates a code amount interference detection control signal from the equalized output. a second gain control circuit connected in feedback through the circuit;
The second gain control circuit is composed of an active filter inputted by a parallel connection of a capacitor and a diode, and the diode is configured to perform impedance control in the code amount interference detection control signal generation circuit. shall be.

FIG. 1 shows a block diagram of a conventional transmission line equalization circuit. 1 is an equalizing amplifier, and 2 is a peak value detection/control signal generation circuit that detects peak values and generates an AGC control signal.

11 is an input terminal for a transmission line signal, 12 is an equalization output terminal, 1
3 is an AGC control signal input terminal of the equalizing amplifier. As mentioned above, the equalizing amplifier performs the Jf AC operation based on the AGC control signal from the input terminal 13, but it also performs flat gain control (hereinafter referred to as Fran AGC) in the low frequency range. Therefore, code amount interference due to equalization deviation in the low frequency range appears in the equalized output.

Next, a block diagram of the basic configuration of a transmission line equalization circuit according to the present invention is shown in FIG. 3 is a code amount interference detection/control signal generation circuit that detects code amount interference in each time slot and creates AGC control circuit, 4 is a Takumi AGC circuit, 5 is a flat AGC circuit, and 14 is a flat AGC control signal input terminal. It is.

An embodiment of the present invention will be explained in detail with reference to FIG.

In the case of bipolar code transmission of several hundred kb/s, the transmission rate is f. It is a well-known fact that most of the spectrum of the 1-equalized waveform spectrum is distributed near f/2. Therefore, in the peak value detection control signal generation section of circuit 2, the f . It can be seen that the area near /2 is detected. Also, as mentioned above, the local cable is 200 to 300
kl (Since it exhibits 77 characteristics above z, the AGC control circuit 2
Then, the AGC circuit 4 performs /fAG'C control to detect the peak value in the region of *fo/♀ or more. On the other hand, f
The control area of AGO control in the range of 0/2 or less does not overlap with the 1%/7 A a c area, which not only improves control characteristic design and analysis, but also ensures stable operation without complicated feedback loops. This is the optimal design to obtain the following. The flat AGC circuit 5 is designed as follows. FIG. 4 shows the frequency characteristics of the AGC circuit 5. That is, the AGC circuit 5 (Fran) exhibits a flat gain change due to the control signal 11 below [f/2; 72 or higher also includes roll-off equalization, which is well known as transmission path equalization.

This operation can be realized by changing the current flowing through the diode D1 in FIG. 3 to control its impedance. Note that the circuit in which the diode p1 is replaced with a resistor is a well-known active filter.

In this way, by controlling the impedance of the diode D1 of the AGC circuit 5 in the code amount interference detection control signal generation circuit 3, AGC operation in the low frequency range is realized, and the peak value detection control signal generation circuit 2 By controlling the JfAGC circuit 4 conventionally used in the! 1l
AGC operating area and JfAGC are realized in the frequency range above fo/2.
This is achieved without overlapping operating areas.

According to the present invention, it is possible to realize a transmission line equalization circuit having both the J'j AGC characteristic and the Furan) AGC characteristic in the low frequency range with a circuit configuration that is extremely easy to design.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional example, Fig. 2 is a block diagram showing the basic configuration of the present invention, Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4 is a block diagram showing the 7 circuits in Fig. 3. ) is a characteristic diagram showing the frequency characteristics of the AGC circuit. 1... Equalization amplifier, '2... Peak value detection control signal generation circuit, 3... Intersymbol interference detection/control signal generation circuit, 4...・・・J'j A a
c circuit, death...furan) AGC circuit, 11...
...Transmission line signal input terminal, 12...--Equalization output terminal, 13...--JTAGC control signal input terminal,
14...Franc) AGC control signal input terminal. Keetan Kaya Z7

Claims (1)

[Scope of Claims] A first gain control circuit is connected in feedback from the equalized output via the peak value detection control signal generation circuit, and the feedback is connected from the equalization output via the code amount interference detection control signal generation circuit. and a second gain control circuit connected thereto. The second gain control circuit is composed of an active filter inputted by a parallel connection of a capacitor and a diode, and the impedance control of the diode is performed by the code amount interference detection control signal generation circuit. transmission line equalization circuit.