JPS6316931B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic equalizer in data transmission, and more particularly to the use of an automatic equalizer for a transmission line with large distortion.

In an automatic equalizer, the result of signal discrimination using the equalized output is usually used to find the discrimination error with the equalized output, and the variable gain is adjusted accordingly. When such a method is used, if there is large distortion in the transmission path, an error will occur in signal identification in the initial state of the variable gain, and the incorrect signal identification will be used to adjust the incorrect variable gain automatically and stably. There is a drawback that the equalizer may not be able to converge.

An object of the present invention is to provide an automatic equalizer that can obtain stable convergence by providing a variable gain adjustment method that does not use signal discrimination.

As an example of a transmission line with large distortion, as shown in FIG. 1, a signal is delayed, a certain gain is added, and the signal is added to the original signal. For example, this may be the case when a cable transmission path includes a bridged tap that branches off in the middle. In such a case, the unit pulse response becomes a response with two peaks as shown in the waveform diagram in Figure 2. When equalizing this with a transversal type variable equalizer, the unit pulse response becomes a response with two peaks as shown in the waveform diagram in Figure 2. Significant equalization can be achieved by inverting the sign of the sample value at a point delayed by each tap interval and applying it to a tap delayed by that amount. Similarly, the decision feedback type variable equalizer is equalized by applying a sample value to the corresponding position of the feedback tap.
This sample value detection means is obtained by the value of the autocorrelation at the relevant delay time. That is, in the case of having the unit pulse response shown in FIG. 2, the received waveform Yn becomes Yn= _o+N 〓 ⁱ⁼ⁿ a _i X _oi . However, a _i is the transmission data, X _oi is the unit pulse response, and X ₀ =1. Also, N is the number of time slots affected by the unit pulse response. Therefore, assuming that data a _j is uncorrelated, the autocorrelation function Z _j becomes Z _j = _o・_o+j = | _j ² | (X _-j +X _-j +X _-j+1 +...) . If X _−j (j≠0) is small compared to X _O , the above equation can be approximately expressed as | _j ² |X _−j . | _j ² | is the average power of the transmitted data and is a known value, so this operation
This means that we have obtained X _-j . Therefore, by setting -X _-j to the tap in question, for example -X _-1 , a better equalization state than the initial state can be obtained by setting -X -j to a tap with a delay separated by one time slot from the center.

The present invention is based on the above principle, in which the first equalization means using a correlator roughly controls the variable gain of the variable equalizer in advance, and then the second equalization means uses a discrimination signal from a threshold circuit. It is characterized by more precise control using the second equalization means.

Embodiments of the present invention will be described below using the drawings.

FIG. 3 is a block diagram showing the entire embodiment of the present invention. In the figure, a received signal input from terminal 1 is branched into two, one is input to threshold circuit 3 via accumulator 2, is discriminated by threshold circuit 3, and outputs an identification signal to terminal 4. The identification signal outputted to the terminal 4 is simultaneously inputted to two delay elements 5 and 6 connected in series with a delay of one signal interval.
The outputs of delay elements 5 and 6 are added to accumulator 2 via variable gains 7 and 8, respectively. Delay elements 5 and 6, variable gains 7 and 8, and accumulator 2 constitute a decision feedback type variable equalizer. The other signal branched from the received signal is transmitted through two delay elements 2 connected in series.
The outputs of each of the delay elements are multiplied by multipliers 9 and 10, and the outputs are input to integrators 11 and 12, respectively, to obtain the autocorrelation value at the output. The outputs of integrators 11 and 12 are input to switching circuits 13 and 14. The input to the other of switching circuits 13 and 14 is provided by the output of the circuit described below. The identification signal outputted to the terminal 4 is simultaneously subtracted from the output signal of the accumulator 2 by a subtracter 15 to generate an error signal. The error signal is multiplied by the output signal of each delay circuit in multipliers 16 and 17, respectively, and added to the outputs of variable gain holding circuits 22 and 23 via fixed gains 18 and 19 in adders 20 and 21, and then added to the outputs of variable gain holding circuits 22 and 23, and then added to the outputs of variable gain holding circuits 22 and 23 through fixed gains 18 and 19. 14. The switching circuits 13 and 14 are in an initial state, that is, when the received signal arrives, the outputs of the integrators 11 and 12 are selected, and then after a preset time or by determining the state of the equalizer output and changing the equalization state. adders 20 and 2 after it is determined to be good.
1 is selected. The outputs of the switching circuits 13 and 14 are connected to the tap gain holding circuit 2.
2 and 23 to supply the adjusted tap gain to the variable equalizer. Here, subtractor 15, multipliers 16 and 17, fixed gains 18 and 19,
Adders 20 and 21 constitute a second adjusting means, and delay elements 24, 25, multipliers 9, 10, and integrators 11, 12 constitute a first adjusting means, which is a correlator. In this embodiment, a decision feedback type variable equalizer consisting of two feedback taps is constructed, but a transversal type variable equalizer can also be used with a similar configuration. In either case, it is possible to have a larger number of taps. Furthermore, although mean square type correction is used as the first adjustment means here, it is also possible to use zero focusing type correction or hybrid type correction.

As described above, the present invention enables high-precision equalization with a wide pull-in range by combining the first adjustment means using a received signal and the second adjustment means using an identification signal. shall be. In particular, a wide pull-in range can be obtained for transmission paths where signals with different delays coexist, such as the characteristics of cables with bridged taps.

[Brief explanation of the drawing]

FIG. 1 is a model of a transmission line, FIG. 2 is a waveform diagram showing a unit pulse response, and FIG. 3 is a block diagram showing an embodiment of the present invention. In the figure, 2 is an accumulator, 3 is an identification circuit, 5,
6, 24, 25 are delay elements, 7, 8 are variable gains, 9, 10, 16, 17 are multipliers, 11, 12
1 is an integrator, 13 and 14 are switching circuits, 15 is a subtracter, 18 and 19 are fixed gain circuits, 20 and 21 are adders, and 22 and 23 are tap gain holding circuits.

Claims (1)

[Claims] 1. In a data transmission receiver, a decision feedback variable equalizer that compensates for distortion occurring in a transmission path to which a received signal is applied; a threshold circuit that is connected to the output of the variable equalizer and identifies a received signal; first adjusting means for obtaining an adjusted signal using one or more correlators to which the received signal is applied and for obtaining an autocorrelation of the received signal;
a second adjustment means for obtaining an adjustment signal for automatically adjusting the variable gain of the variable equalizer using the input and output of the threshold circuit; and a second adjustment means for obtaining an adjustment signal for automatically adjusting the variable gain of the variable equalizer; a switching circuit that uses the variable equalizer to set the variable gain of the variable equalizer, and then switches to a second adjustment output signal to obtain the adjustment signal of the variable gain of the variable equalizer, and eliminates distortion generated in the transmission line. Automatic equalizer to compensate.