JPH0129324B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to Which the Invention Pertains] The present invention relates to a reset device that improves the pull-in characteristic of an automatic equalizer configured with a transversal type filter.

[Description of prior art]

Conventional methods for resetting automatic equalizers include using the output of an asynchronous state detection circuit provided in the carrier synchronization circuit of the demodulator placed before or after the automatic equalizer, and A method is known in which the code error rate is monitored using later identified and reproduced data, and a determination is made when the code error rate exceeds a certain amount. However, with these methods, once the control loop becomes asynchronous and enters the reset request state, the equalizer function stops, so it is not always possible to start pulling until the distortion in the transmission path becomes sufficiently small. Unable to do so, line usage rate (time rate)
There was a problem above.

For example, in a transversal equalizer, when the distortion in the transmission path becomes large and exceeds the equalization capability, the control loop of the equalizer becomes asynchronous. In this state, distortion will occur inside the equalizer, and even if the distortion in the transmission path becomes small, it will not be able to return to the synchronized state by itself. To cope with this, when the control loop becomes out of synchronization, a so-called reset operation is required to set and maintain the variable weighting circuit of the transversal type filter section at a cut-off value.

This reset operation means, for example, setting the weighting of the main tap and multiple other taps of the transversal filter section to ``1'' and ``0'', respectively, and temporarily stops the equalization function. means. Therefore, in the normal reset method,
At reset, the equalizer is not used at all, and unless the distortion is reduced to within the pull-in range of devices other than the equalizer (for example, the carrier synchronization circuit in the demodulator), the control loop will be in synchronization. I couldn't reach it. However, if the reset is not performed, distortion will occur inside the equalizer, as described above, and it will not be possible to return to the synchronized state.

To explain this using a specific example, Figure 1 shows:
This shows an example of a conventional reset method. In this configuration, an equalizer 1 is placed before a demodulator 2, and the demodulator 2 normally performs identification reproduction using the equalized signal. A carrier synchronization circuit 3 supplies a carrier wave for demodulation to the demodulator 2. When the distortion in the transmission line becomes large and exceeds the equalization ability of equalizer 1,
Carrier wave regeneration in the carrier wave synchronization circuit 3 becomes impossible, and the carrier wave synchronization circuit 3 generates a carrier wave synchronization loss signal. This signal is used as a reset signal for the equalizer 1.
is sent to stop the equalization function. When the transmission distortion becomes small and the synchronization of the carrier synchronization circuit 3 is established,
The reset is released and normal equalization operation resumes.

Figure 2 shows another example of the conventional reset method, and differs from Figure 1 in that the equalizer 1' consists of a baseband band and is placed after the demodulator 2'. . The function as an equalizer system is the same. Note that in the examples shown in Figures 1 and 2, a reset signal is generated from a carrier synchronization circuit as an asynchronous state detection circuit, but a completely similar signal is used to monitor the bit error rate, and when it reaches a certain value. It is also possible to adopt a method of determining that it is in an asynchronous state when the number exceeds the limit.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a reset device for an automatic equalizer that has excellent pull-in characteristics and can improve line utilization by adding a simple circuit to a conventional reset circuit. .

[Key points of the invention]

The present invention provides an automatic equalizer configured using a transversal filter, which includes a circuit for detecting an asynchronous state of an equalizer control loop and a reset control signal generator, and the output of the detection circuit is connected to the The output of the generator is a temporally intermittent signal,
The present invention is characterized in that the initial value of the variable weighting circuit of the transversal type filter section is set by this signal.

[Explanation based on examples]

FIG. 3 is a block diagram of the apparatus according to the first embodiment of the present invention.

In FIG. 3, a signal from a transmission line is input to an equalizer 11 via an input terminal 10. This equalizer 11 is an automatic equalizer composed of a transversal type filter, and the variable weighting circuit of this transversal type filter section is set to the initial value while a reset signal is input to the reset terminal 11a. Settings are retained.

The output of the equalizer 11 is led to a demodulator 12, and the output of this demodulator 12 is further led to an output terminal 13. A carrier recovery circuit 14 is connected to the demodulator 12 . The carrier wave regeneration circuit 14 is a circuit that supplies a carrier wave for demodulation to the demodulator 12,
When carrier wave regeneration becomes impossible due to increased distortion in the transmission path, a carrier wave synchronization loss signal is generated and sent from the terminal 14a as a reset signal.

A terminal 14a of the carrier regeneration circuit 14 is connected to a reset terminal 11a of the equalizer 11 via a switch 15. The switch 15 is controlled to open and close at regular intervals by a reset control signal generator 16. As the reset control signal generator 16, a synchronization signal oscillator that generates a synchronization signal, a pseudorandom signal (PN signal) generator, a noise generator, or the like is used.

Next, the operation of this device will be explained.

When the distortion of the transmission path becomes large and exceeds the equalization ability of the equalizer 1, the carrier wave recovery circuit 14 becomes unable to recover the carrier wave and generates a carrier wave out-of-synchronization signal.
This carrier synchronization signal is sent as a reset signal to the reset terminal 1 of the equalizer 11 via the switch 15.
1a, and sets the variable weighting circuit of this equalizer 11 to an initial value. At this time, since the switch 15 is intermittently opened and closed by the reset control signal generator 16, the equalizer 11 alternately repeats the reset state and its release state. This makes it possible to improve the equalizer's ability to equalize distortion even during the pull-in operation, while expanding the pull-in range of the equalizer against distortion in the transmission path.

FIG. 4 is a block diagram of an apparatus according to a second embodiment of the present invention. This device differs from the device of the first embodiment in that a two-position switch 17 is used instead of the switch 15, and the reset terminal 11a of the equalizer 11 is alternately connected to the carrier regeneration circuit 14 and the fixed bias generator 18. It is becoming more and more connected to

According to this device, when the switch 17 is periodically opened and closed and the equalizer 11 repeats the reset state and its release state, a fixed bias is applied to the reset terminal 11a in the release state. . This embodiment is used when it is better to supply different voltages to the reset terminal 11a of the equalizer 11 during equalization and reset.

That is, depending on the state of the transmission path, this equalizer resets the reset terminal 11a of the equalizer 11 in the released state.
This is an automatic equalizer that applies a specific fixed bias to the For example, if the length of the transmission path differs from the standard value, the equalization conditions will differ accordingly, so equalization control is performed by applying a specific fixed bias to the equalizer 11 under steady use in response to this condition. This is an equalizer. The device of the second embodiment is used to reset an automatic equalizer to which a constant fixed bias is applied under such normal equalization operating conditions.

[Explanation of effects]

As described above, by using the present invention, by simply adding a simple circuit to a conventional device, the pull-in range against distortion in the transmission line can be widened, and the utilization rate of the line to which an equalizer is applied can be greatly improved. can do. Moreover, it can be applied without depending on the asynchronous state detection method or the equalizer configuration, and can be applied, for example, to resetting an equalizer that is given a fixed bias in the equalization operation state depending on the transmission path state. Therefore, it is highly versatile.

[Brief explanation of drawings]

1 and 2 are block configuration diagrams of a conventional device.
FIG. 3 is a block diagram of a device according to a first embodiment of the present invention. FIG. 4 is a block diagram of an apparatus according to a second embodiment of the present invention. 11...Equalizer, 12...Demodulator, 14...Carrier regeneration circuit, 15, 17...Switch, 16...
. . . Reset control signal generator, 18 . . . Fixed bias generator.

Claims (1)

[Claims] 1. A circuit that detects an asynchronous state of the equalizer control loop and sends out a reset signal, and is set and held at the initial value while the reset signal sent from this circuit is input. A transversal filter automatic equalizer having a variable weighting circuit, comprising intermittent means for performing intermittent control so that the reset signal supplied from the sending circuit to the variable weighting circuit becomes a temporally intermittent signal. An automatic equalizer reset device characterized by: 2. A reset device for an automatic equalizer, characterized in that the disconnection means is configured to supply a constant bias voltage to the variable weighting circuit while the reset signal is disconnected.