JPH06105866B2 - Automatic equalizer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic equalizer using a transversal filter type automatic equalizer circuit, and more particularly to improvement of the pull-in characteristic of the automatic equalizer.

(Prior Art) In digital wireless transmission systems, line quality deterioration occurs due to waveform distortion due to multipath fading that occurs in the propagation path. This is due to the use of an automatic equalizer that uses a transversal filter type automatic equalizer circuit. It is known to be improved by applying.

This kind of automatic equalizer is applied in the IF band or the base band. FIG. 2 shows a configuration example of an automatic equalizer that equalizes transmission line distortion in the IF band. This automatic equalizer comprises a transversal filter type automatic equalizer circuit 1 and a demodulator 2
Basically, a carrier wave regenerator 3, an oscillator 4, a carrier wave asynchronous detector 20, a periodic signal generator 24, and a reset signal generator 5 are provided. FIG. 3 shows the overall configuration including the demodulator 2, the carrier regenerator 3, and the oscillator 4, and FIG.
The figure shows the configuration of the reset signal generator 5.

The IF band input signal 6 is input to the automatic equalization circuit 1, and the IF band signal 7 in which distortion is equalized therein is demodulated by the demodulator 2 into a base band signal. The demodulation process in 2 is performed by transmitting and receiving the control signal 8 for carrier wave reproduction to the carrier wave regenerator 3 and the reproduced carrier wave 9 from the carrier wave regenerator 3.

FIG. 3 shows a 16-value quadrature amplitude modulation system. In FIG. 3, the IF band signal 7 is a hybrid of the demodulator 2.
Multiplier 26 for quadrature detection after halving at 25
Each is supplied to 27. The reproduced carrier wave 9 supplied from the voltage controlled oscillator (VCO) 28 of the carrier wave regenerator 3 is divided into two, one of which is directly applied to the multiplier 26 and the other of which is a 90 ° phase shifter 29.
And is supplied to the multiplier 27.

The detected signals pass through the low-pass filters 30 and 31, respectively, and then are supplied to the identifiers 32 and 33 for identifying the signals. The output signals 39 and 40 of the P-channel side discriminator 32 represent the first bit (quadrant) signal and the second bit signal, respectively.
Similarly, 41 and 42 are the first signals obtained by the Q-channel side discriminator 33.
The bit signal and the second bit signal are shown.

Reference numeral 43 indicates an error signal (E _P ) obtained by the P-channel side discriminator 32, and 44 indicates an error signal (E _Q ) obtained by the Q-channel side discriminator 33.

The multiplier 34 multiplies the P-channel side first bit signal 39 and the Q-channel side error signal (E _Q ) 44, and the multiplier 35 calculates the P-channel side error signal (E _P ) 43 and the Q-channel side error signal (E _P ). 1
The control signal 8 for controlling the reproduced carrier wave is obtained by taking the product of the bit signal 41 and subtracting the outputs of the multipliers 34 and 35 by the subtractor 36.

The control signal 8 is amplified by the DC amplifier 37 of the carrier regenerator 3 and input to the integrator 38.

The output of the integrator 38 is supplied to the control voltage oscillator (VCO) 28 as a control voltage, and the VCO 28 generates the regenerated carrier wave 9.

The oscillator 4 is connected between the output of the DC amplifier 37 and the input of the integrator 38. This oscillator 4 does not oscillate because the output impedance of the DC amplifier 37 is low when carrier synchronization is established, but when carrier synchronization is lost, the output impedance of the DC amplifier 37 becomes high because the compression degree of the carrier synchronization control loop is lost. Start operation.

The output signal (frequency signal) 10 of the oscillator 4 is superimposed on the input of the integrator 38, and the VCO 28 is modulated. As a result, the frequency range for carrier synchronization of the demodulator 2 is expanded.

Next, in FIG. 2, when the distortion of the transmission line increases and exceeds the equalization limit of the automatic equalization circuit 1, the carrier synchronization is lost and the oscillator 4 starts oscillating operation.
The output signal (frequency signal) 21 is detected by the carrier asynchronous detector 20. The oscillation frequency of the oscillator 4 is generally several tens to several tens.
It is about 0 Hz, and the detection time constant of the carrier asynchronous detector 20 is a sufficiently large value with respect to the frequency.

The detection signal 22 of the carrier wave asynchronous detector 20 takes "1" level when the oscillator 4 oscillates, that is, when carrier wave is asynchronous, and outputs "0" level when oscillation is stopped, that is, carrier wave is synchronized.
The detection signal 22 is input to the periodic signal generator 24. The periodic signal generator 24 outputs the periodic signal 11 when the detection signal 22 is at level "1".
And the periodic signal 11 is not generated when the level is “0”. The periodic signal 11 is composed of a pulse signal or the like that repeats at a substantially constant period, and is input to the reset signal generator 5.

The reset signal generator 5 is for setting each tap coefficient of the automatic equalization circuit 1 to an initial value in a carrier asynchronous state, and is composed of, for example, a switch 45 and an initial value setter 46 as shown in FIG. To be done.

In the switch 45, the control terminal a is switched and connected to one of the switch terminals b and c in response to the input of the periodic signal 11.

The tap coefficient control signal from the automatic equalization circuit 1 is applied to the switching terminal b.
47 is input, the initial value is input to the switching terminal c from the initial value setter 46, and the tap control signal 12 is output to the automatic equalization circuit 1 from the control terminal a. For example, the periodic signal 11
Is low level, the control terminal a is connected to the switching terminal c and the initial value is given to the automatic equalization circuit 1 as the tap control signal 12.
When the periodic signal 11 is at a high level, the control terminal a is connected to the switching terminal b so that the tap coefficient control signal 47, that is, the original control signal is given to the automatic equalization circuit 1 as the tap control signal 12.

That is, in this kind of automatic equalizer, when the distortion of the propagation path becomes large and exceeds the equalization limit value of the transversal filter type automatic equalization circuit 1, the carrier synchronization of the demodulator 2 is lost and The control loop of the equalization circuit 1 becomes asynchronous. If this is left as it is, distortion will occur inside the automatic equalization circuit 1, and even if the distortion of the transmission path becomes small, it will not be possible to return to the synchronized state by itself. Therefore, in the asynchronous state, a reset operation is performed in which each tap coefficient of the automatic equalization circuit 1 is set to an initial value and held, but the tap coefficient is kept at the initial value until carrier synchronization of the demodulator 2 is established. Then, since the control loop is in a stopped state, the automatic equalization circuit 1 does not return to the synchronized state unless the distortion becomes sufficiently small.

In order to avoid this, the reset signal generator 5 is intermittently controlled by using the periodic signal generator 24 so that the pull-in range with respect to the distortion of the transmission line can be expanded while exhibiting the equalization function even during the pull-in operation. Is there. Therefore, in the past, a pseudo random signal generator, a noise generator, or the like may be used instead of the periodic signal generator 24.

(Problems to be Solved by the Invention) However, the frequency of the oscillator 4 that operates when the carrier wave is out of synchronization is selected as a relatively low frequency because the upper limit is restricted to facilitate establishment of carrier wave synchronization. There is.
Therefore, in the configuration of the conventional automatic equalizer described above, a long detection time is required because the output of the oscillator 4, that is, the detection time constant of the asynchronous detector 20 for detecting the carrier wave asynchronous state must be set to a large value. become.

In other words, even if the distortion of the transmission path is reduced to a value that can be pulled in by the automatic equalizer circuit 1, the reset release operation is delayed due to the long detection time of the carrier wave asynchronous detector 20. There is a problem that the pull-in operation is not performed unless the amount of distortion that the digitizing circuit has is equalizable.

The present invention has been made in view of such a problem, and an object thereof is to improve the pull-in characteristic by preventing the reset operation for the automatic equalizer circuit from interfering with the pull-in operation of the automatic equalizer circuit. An object of the present invention is to provide an automatic equalizer that can be achieved.

(Means for Solving Problems) In order to achieve the above object, the automatic equalizer of the present invention has the following configuration.

That is, the automatic equalizer of the present invention uses either a signal in the IF band or a signal in the baseband as an input signal, and a transversal filter type automatic equalizer for equalizing the transmission path distortion included in the input signal. Equalization circuit; obtains a baseband signal by demodulating the output signal of an automatic equalization circuit that takes an IF band signal as an input signal, or directly inputs an IF band signal as an input signal to the input signal A demodulator that performs demodulation processing and gives a signal in the baseband as an input signal to an automatic equalizer circuit; and a carrier wave that is received by receiving a carrier wave control signal from the demodulator or the automatic equalizer circuit A carrier regenerator that supplies it to the demodulator; an oscillator that is activated when the carrier is asynchronous to generate a predetermined frequency signal and supplies it to the carrier regenerator; and a tap coefficient of the automatic equalization circuit when the carrier is asynchronous. In order to set the initial value to the automatic equalization circuit, the output of the oscillator is used as a switching control signal, and the tap control signal from the automatic equalization circuit and the internally generated initial value are used. A reset signal generator that switches between a value signal and outputs to an automatic equalizing circuit;
It is an automatic equalizer characterized by having.

(Operation) Next, the operation of the automatic equalizer of the present invention configured as described above will be described.

When the automatic equalizer of the present invention is, for example, one that performs distortion equalization in the IF band transmission line, that is, the input signal of the automatic equalizer circuit is an IF band signal, and the input of the demodulator is automatic etc. It is assumed that the signal is in the IF band through the conversion circuit.

When the distortion of the transmission line increases and exceeds the equalization limit value of the automatic equalization circuit, the carrier synchronization of the demodulator is lost, the automatic equalization circuit goes into an asynchronous state, and the oscillator is activated. Then, the reset signal generator starts a so-called reset operation, which intermittently supplies the initial value to the automatic equalization circuit.

Then, after that, when the distortion of the transmission line becomes small and enters the range of the equalization limit value of the automatic equalization circuit and carrier synchronization is established, the oscillator stops oscillation.

Then, the reset signal generator also stops the reset operation without a time delay.

That is, in the automatic equalization circuit, when the distortion of the transmission line falls within the range of the equalization limit value, the pull-in operation can be started quickly.

As described above, according to the automatic equalizer of the present invention, the start and stop timings of the reset operation for the automatic equalizer circuit are set to be substantially the same as the start and stop timings of the oscillation operation of the oscillator. It is possible to eliminate the conventional adverse effect that hinders the pull-in operation of the automatic equalization circuit.

(Examples) Examples of the present invention will be described below with reference to the drawings. It should be noted that parts having the same names as the conventional ones are given the same reference numerals and the description thereof is omitted.

FIG. 1 shows an automatic equalizer according to an embodiment of the present invention. FIG. 1 (a) shows an IF band automatic equalizer, and FIG. 1 (b) shows a baseband automatic equalizer. Show.

1 (a) and 1 (b), the automatic equalizer according to the present invention uses an IF band signal 6 or a base band signal.
A transversal filter type automatic equalization circuit 1 for equalizing the transmission path distortion contained in the input signal, and an automatic equalization circuit for inputting an IF band signal 6 1 output demodulation processing to obtain a baseband signal, or IF band signal 13 as an input signal is directly demodulated and the baseband signal 14 as an input signal for automatic equalization A demodulator 2 that either gives to the circuit 1 receives a carrier reproduction control signal 8 or 15 from the demodulator 2 or the automatic equalization circuit 1 to reproduce the carrier and reproduce the reproduced carrier 9 to the demodulator 2. The carrier wave regenerator 3 to be supplied, the oscillator 4 which is started when the carrier wave is asynchronous and generates a predetermined frequency signal 10 and supplies it to the carrier wave regenerator 3, and each tap coefficient of the automatic equalization circuit 1 when the carrier wave is asynchronous are initialized. Set to The initial value A to supply to the automatic equalization circuit 1 to the output 11 of the oscillator 4 '
Is used as a switching control signal, and a reset signal generator 5 for switching between the tap coefficient control signal 47 from the automatic equalization circuit 1 and the initial value signal from the initial value setting device 46 and outputting to the automatic equalization circuit 1 is basically used. Prepared for.

In short, according to the present invention, in the conventional automatic equalizer as illustrated in FIG. 2, the carrier asynchronous detector 20 and the periodic signal generator 24 are omitted, and the reset signal generator 5 outputs the output 11 ′ of the oscillator 4. In response to the above, the initial value supply (reset operation) to the automatic equalization circuit 1 is intermittently performed.

In this embodiment, the oscillator 4 delivers the frequency signal 10 as an output 11 'to the reset oscillator 5.

Since the output 11 'is a sine wave signal, the reset signal transmitter 5 sets an appropriate threshold level and outputs 1'.
During the period when the signal level of 1'exceeds the threshold level, the control terminal a (see FIG. 4) and the switching terminal c are connected.

In the above configuration, when the distortion of the transmission line increases and exceeds the equalization limit value of the automatic equalization circuit 1, the carrier synchronization of the demodulator 2 is lost and the automatic equalization circuit is deviated, as described above (FIG. 3). 1 becomes an asynchronous state, and the oscillator 4 is activated. Then, the reset signal generator 5 starts to intermittently give the initial value to the automatic equalization circuit 1.

Then, after that, when the distortion of the transmission path becomes small and enters the range of the equalization limit value of the automatic equalization circuit 1, the carrier wave synchronization is established, the oscillator 4 stops the oscillation. Then, the reset signal generator 5 also stops the reset operation without a time delay.

That is, in the automatic equalization circuit 1, when the distortion of the transmission line falls within the equalization limit value, the pull-in operation can be started immediately.

In the embodiment described above, the reset signal generator 5
However, the present invention is not limited to this. For example, in the oscillator 4, the frequency signal 10 is subjected to appropriate waveform processing and different from the frequency signal 10. The output 11 'of the signal waveform may be formed, and the reset signal generator 5 may perform the intermittent reset operation depending on whether the signal level of the output 11' is the "1" level or the "0" level. The point is that the reset signal generator 5 may perform an intermittent reset operation directly depending on the oscillation operation of the oscillator 4.

Further, how often the reset signal generator 5 performs the "intermittent operation" is also an arbitrary design matter.

(Effect of the Invention) As described in detail above, according to the automatic equalizer of the present invention, the start and stop timings of the reset operation for the automatic equalizer circuit are substantially the same as the start and stop timings of the oscillation operation of the oscillator. Therefore, it is possible to eliminate the conventional adverse effect that the reset operation hinders the pull-in operation of the automatic equalization circuit.

As a result, in the automatic equalizer circuit, when the distortion of the transmission line falls within the range of the equalization limit value, the pull-in operation can be started quickly, which is an excellent effect that the pull-in range of the automatic equalizer can be improved. Is obtained.

[Brief description of drawings]

FIG. 1 shows an automatic equalizer according to an embodiment of the present invention. FIG. 1 (a) is a block diagram of the IF band automatic equalizer, and FIG. 1 (b) is a baseband automatic equalizer. Block diagram of the container
Fig. 2 is a block diagram of a conventional IF band automatic equalizer.
FIG. 4 is an overall block diagram showing the relationship between a demodulator, a carrier regenerator and an oscillator, and FIG. 4 is a block diagram showing the reset signal generator. 1 ... Automatic equalization circuit, 2 ... Demodulator, 3 ... Carrier regenerator, 4 ... Oscillator, 5 ... Reset signal generator, 20 ...
Carrier asynchronous detector, 22 ... Carrier asynchronous detection signal, 24
...... Periodic signal generator, 25 …… Hybrid, 26,27,34,3
5 …… Multiplier, 28 …… Voltage controlled oscillator (VCO), 29 …… 90
゜ Phase shifter, 30, 31 ...... Low-pass filter, 32,33 …… Identifier, 36 …… Subtractor, 37 …… DC amplifier, 38 …… Integrator,
45 …… Switching device, 46 …… Initial value setting device.

Claims (1)

[Claims] 1. A transversal filter type automatic equalization circuit for equalizing transmission line distortion contained in an input signal, which is either an IF band signal or a baseband signal, and an IF; To obtain a baseband signal by demodulating the output signal of an automatic equalization circuit that uses a band signal as an input signal, or directly demodulate the input signal using an IF band signal as an input signal A demodulator that either gives a band signal as an input signal to an automatic equalizer circuit; receives a carrier reproduction control signal from the demodulator or automatic equalizer circuit, reproduces a carrier wave, and supplies it to the demodulator A carrier regenerator for generating a predetermined frequency signal that is activated when the carrier is asynchronous and supplies it to the carrier regenerator; and sets each tap coefficient of the automatic equalization circuit to an initial value when the carrier is asynchronous. In order to supply the initial value to the automatic equalization circuit, the output of the oscillator is used as a switching control signal to switch between the tap control signal from the automatic equalization circuit and the internally generated initial value signal. And an automatic equalizer circuit for outputting a reset signal generator to the automatic equalizer circuit;