JPS59200533A - Adaptive decision feedback type automatic equalizer - Google Patents

Abstract

PURPOSE:To prevent a feedback loop from oscillating even when the amount of interference between codes increases by releasing the feedback loop which includes a backward equalizer for a specific period when the tap gain of a forward equalizer decreases below a specific value. CONSTITUTION:When the amount of intercode interference of an adaptive decision feedback type automatic equalizer increases, all tap gains of a transversal filter constituting the forward equalizer 1 are suppressed, so the values are smaller than the specific value and a comparator 11 generates a ''1''-level signal, which is supplied to a switch circuit 10 through a delay circuit 12. The circuits 10 opens terminals 10a and 10b to release the feedback circuit including the backward equalizer 2, preventing the oscillation. When the equalizer recovers to the normal state, the tap gains of the equalizer 1 exceed the specific value and the comparator 11 outputs ''0'', but the circuit 12 outputs the ''1''-level signal for a specific time. Consequently, the circuit 10 is closed a specific time after the equalizer recovers to the normal state, thus attaining recovery to the normal state without causing malfunction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adaptive decision feedback automatic equalizer used in high-speed data transmission lines.

Conventionally, an adaptive decision feedback automatic equalizer has been used to equalize code amount interference when transmitting high-speed data in the voice band over a wired transmission path, but in recent years this equal volume has been used over a wireless transmission path. It has also come to be used.

FIG. 1 shows an example of an adaptive decision feedback automatic equalizer used in the wireless communication field when the input signal is a passband, a forward isovolume coverspunt, and a hackword isovolume is baseband. This automatic geometric volume is a forward equalizer 1 for equalizing the code amount interference due to the leading component of the impulse response of the line, a backward equalizer 1 for equalizing the code amount interference due to the delayed component of the line impulse response, etc. demodulator 3 that converts the passband signal to baseband, data detection and error signal generator 4, timing generator 5, modulator T1 adder 8 that converts the baseband error signal to passband. It consists of Further, the forward equalizer 1 and the bankword isotropic volume 2 are usually configured as a transversal filter, and the data detection and error signal generator 4 is configured as a signal processing circuit.

This adaptive decision feedback automatic equalizer belongs to nonlinear automatic equalizers, and because it can eliminate distortion without amplifying noise compared to linear automatic equalizers, it is often used where code amount interference cancellation is required. There is.

However, in such a conventional equalizer, when the amount of code amount interference due to delayed echoes, that is, delayed components of the impulse response becomes large and exceeds its equalization capability, this becomes a trigger for backward equalizer 2. It has the disadvantage of causing oscillation.

Therefore, an object of the present invention is to provide an adaptive decision feedback automatic equalizer that does not cause oscillation of the backward equalizer even when the amount of code amount interference becomes large.

In order to achieve such an object, the present invention opens a feedback loop including a backward equalizer for a predetermined period when all tap gains of the forward equalizer become less than a predetermined value. .

Before a detailed explanation of this invention, the principle will first be explained. When the amount of code amount interference increases, the tap gain of the backward equalizer reaches its maximum, and the transversal that makes up the forward equalizer cannot receive the signal from the forward equalizer. All tap gains of the filter exhibit a phenomenon of being suppressed very small. This is the value (eye pattern) of the error signal before judgment of the received data.
This is because the error signal is created from the difference between the determined data and the determined data (output data), and the error signal will be 0 if the eye pattern before the determination is normal, regardless of whether the determined data is the correct transmission data or not. This is because it has properties.

Therefore, it is possible to escape from this state by detecting suppression of the tap gain in the forward equalizer and opening the feedback loop including the backward equalizer. Hereinafter, the present invention will be described in detail using drawings showing embodiments.

FIG. 2 is a block diagram showing an embodiment of the present invention.
The same symbols are used for the same parts as in FIG.

Reference numeral 10 denotes a switch circuit inserted in the feedback path including the bank word equalizer 2, and the terminals 10a and 3-10b are normally connected, and the terminal 10c is supplied with a [1-level signal]. The structure is such that when this happens, the terminals 10a and 10bO are disconnected. 11 is a comparator, all the taps of the transversal filter used in the forward equalizer 1 are connected to terminals 11+ to 11n, and the tap gains of all the taps are supplied from the reference voltage generator 13. An output signal of level 11 is sent out when the value is below a predetermined value. Reference numeral 12 denotes a delay circuit, which immediately outputs an input signal when it is supplied with the input signal, and continues to output the output signal for a predetermined time even if the input signal is no longer present.

The operation of the equalizer configured as described above is as follows.

When the amount of code amount interference increases, all the tap gains of the transversal filter constituting the forward equalizer 1 are suppressed, so if this value is not below a predetermined value, the comparator 11 Generate a signal. As a result,
Since the output signal from the comparator 11 is supplied to the switch circuit 10 via the delay circuit 12, the switch circuit 10 has terminals 4-10a and 10b open, and includes the backward equalizer 2 and the feedback circuit. It will be released.

In wireless communication, delayed echoes due to multipath do not always have strong energy, and there are always cases in which the demodulated eye pattern becomes almost normal within a short time even without a backward equalizer. . Therefore, in such a state, the adaptive decision feedback automatic equalizer converges and restores to the normal state even without the bankword equalizer 2, so for a short time, the feedback including the backward equalizer 2 The loop can be left open.

Once the normal state is restored, the tap gain of the transversal filter constituting the forward equalizer 1 exceeds a predetermined value, so the output signal of the comparator 11 changes from the "1" level to the "10" level.

However, since this signal is supplied to the switch circuit 10 via the delay circuit 12, the delay circuit 12 is connected to the comparator 11.
Even if the output signal reaches the "0" level, it continues to send out the "1" level output signal for a predetermined period of time. As a result, the switch circuit 12 is connected to the terminals 10a-10 after a predetermined period of time after the adaptive decision feedback automatic equalizer is restored to the normal state.
b is closed, a feedback loop including the backward equalizer 2 is formed. By setting this delay time to an appropriate value, it is possible to restore the normal state in the event of a malfunction.

As explained above, the adaptive decision feedback automatic equalizer according to the present invention opens the backward equalizer when a change in the tap gain of the transversal filter constituting the forward equalizer is detected. This has the effect that even if the amount of interference becomes large, oscillation of the feedback loop including the backward equalizer does not occur.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional equalizer, and FIG. 2 is a block diagram showing an embodiment of the equalizer of the present invention. 1...forward equalizer, 2...e backward equalizer, 10...switch circuit, 11...comparator, 12...delay circuit. 11

Claims (1)

[Claims] A forward isovolume composed of a transversal filter having a plurality of taps, and a backward isoproportion that forms a feedback loop between the input and output terminals of a signal processing circuit that processes the signal from the forward equalizer. The adaptive decision feedback automatic equalizer includes a switch circuit inserted in the feedback loop, and a comparator that supplies a control signal to the switch circuit when the tap gains at all taps of the transversal filter become below a predetermined value. , and a delay circuit that continues to generate a control signal for a predetermined period even after the signal from the comparator is no longer generated.