JPH0752856B2 - Demodulator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a demodulator with a transversal equalizer used in a digital carrier wave transmission system.

[Prior Art] FIG. 3 shows the configuration of a demodulator with a transversal equalizer using a conventional reset circuit.

In the figure, reference numerals 1 and 2 denote multipliers for multiplying the input modulated wave a and the reproduced carrier waves b and c having a 90 ° phase difference from each other. 3 is a 90 ° phaser. Multiplier 1,
Two columns of multilevel baseband signals d1 and e1 demodulated by 2
Is an eye pattern that is band-limited, but is generally an eye pattern in which the convergence point is expanded because it is subject to various waveform distortions in the transmission path and the like. Since the waveform distortion component of the multi-valued baseband signal subjected to the waveform distortion is equalized by the transversal equalizer 4, the outputs d2 and e2 of the transversal equalizer 4 have an eye pattern with good convergence,
The analog-digital converters (hereinafter referred to as A / D converters) 19, 20 are identified and converted into digital signals.

However, when the waveform distortion of the multi-valued baseband signals d1 and e1 is significant, the transversal equalizer 4 cannot equalize and d2, e2
Eye pattern becomes divergent. In such a case, if the normal transversal equalizer 4 is reset and the automatic equalization operation is stopped, the restoration in the case where the distortion is reduced is performed quickly.

Conventionally, in order to reset the transversal equalizer 4,
As shown in FIG. 3, a reset circuit 21 has been used which detects a state where the carrier synchronization circuit has lost synchronization and resets the transversal equalizer 4.

That is, in FIG. 3, the control signal generating circuit 7 is
The digital signal Dp1, Dp5, Dq1, Dq5 output from the D converter is input, and the control signal f for controlling the voltage controlled oscillator 8 oscillating at the carrier frequency is output. In such a synchronous circuit, the impedance at the point A in FIG. 3 is low when the carrier waves are synchronous and high when the carrier waves are asynchronous.

Therefore, the reset circuit 21 detects the carrier wave synchronization / asynchronization by detecting the impedance at the point A,
The reset signal was sent to the transversal equalizer 4.

However, when the reset circuit 21 of FIG. 3 is used, the pull-in characteristic of the carrier synchronization circuit is sufficiently strong against distortion, and d2 or
When one of the e2 baseband signals has a good convergence, the reset may be released.

Now, with the transversal equalizer 4 being reset, the side that equalizes the baseband signal d1 (hereinafter referred to as Pch) has sufficient equalization capability, but the baseband signal e1
Distortion is on the side of equalizing the baseband signal e1 (hereinafter, Qc
(It is called h).

In such a case, since the pull-in characteristic of the carrier synchronization circuit is sufficiently strong, carrier synchronization can be established by the Pch-side digital signal. Once the carrier synchronization is established, the impedance at the point A is lowered and the reset of the transversal equalizer 4 is released. For this reason, the equalizer on the Qch side, which is slightly inferior in equalization ability, is also reset at the same time, and the transversal equalizer 4 is in a divergent state. Therefore, the baseband signal of e2 does not converge until the distortion component of e1 almost disappears.

[Problems to be solved] As described above, in the conventional reset circuit that detects synchronization / asynchronization of carrier waves and resets the transversal equalizer, the equalizers on the Pch side and the Qch side are independently reset. Therefore, there is a problem that the equalization operation is not pulled in until the distortion is almost completely eliminated.

The present invention has been made in view of the above problems.
It is an object of the present invention to provide a demodulator capable of independently resetting and releasing reset of a transversal equalizer for a baseband signal of a column.

[Means for Solving Problems] In order to achieve the above object, the demodulation device of the present invention converts a demodulated multilevel baseband signal into a digital signal.
From the output of the A / D converter, the convergence state of the multi-valued baseband signal is detected by two detection circuits, and based on the detection results, two reset circuits independently for each of the two columns of baseband signals. , The Pch-side and Qch-side equalizers of the transversal equalizer are reset.

[Embodiment] Next, a demodulator according to the present invention will be described with reference to the drawings.

FIG. 1 shows a transversal equalizer 25 according to the present invention.
It is a block diagram of a 6QAM demodulator.

In the figure, the waveform distortion included in the multi-valued baseband signals d1 and e1 demodulated by the multipliers 1 and 2 as demodulators in the same manner as the conventional one is the Pch side and the Qch in the transversal equalizer 4. Since it is equalized by the equalizer on the side, the multivalued baseband signals d2 and e2 form an eye pattern with good convergence, and A
Digital signals are generated by the / D converters 5 and 6. At this time, when observing the outputs of the 5th bit and the 6th bit of the outputs of the A / D converters 5 and 6, the convergence state of the multilevel baseband signals d2 and e2 is independent of d2 and e2. I understand.

Therefore, by observing the digital signals of the 5th bit and the 6th bit, the convergence state of the multilevel baseband signal is detected,
It is possible to reset the transversal equalizer 4.

This principle will be described with reference to FIG.

In Fig. 4, the first bit output D1 of the A / D converters 5 and 6 is "1".
The relationship between the outputs (D2 to D6) of the second bit to the sixth bit and the convergence point of the multilevel baseband signal is as shown in FIG. The 6-bit coincides with the voltage that simultaneously transits from "0" to "1".

If the multivalued baseband signals d2 and e2 have good convergence, the fifth
When a bit signal and a 6th bit digital signal are subjected to exclusive OR operation (EX-OR) operation, they become "0" at all the convergence points as shown in FIG.

On the other hand, when the outputs d2 and e2 of the transversal equalizer 4 are not converged, the EX-OR output (D5 + D6) of D5 and D6 is "0".
And "1" appear with equal probability. Therefore, by observing D5 + D6, the converged states of d2 and e2 can be detected independently of d2 and e2, so use this to reset the equalizers on the Pch side and Qch side of the transversal equalizer 4. You can

In the above description, the case where the first bit output D1 of the A / D converters 5 and 6 is "1" has been described, but the same operation is performed when D1 is "0". It is effective for points.

Next, a specific embodiment of the detection circuit described above will be described with reference to FIG.

FIG. 2 is a circuit diagram of the detection circuits 9 and 10 of FIG. In the figure, 13 is an EX-OR gate, 14 to 16 are resistors, 17 is a capacitor, and 18 is an OR gate.

The inputs D5 and D6 of the EX-OR gate 13 of FIG. 2 are connected to the A / D of FIG.
The fifth bit and the sixth bit of converters 5 and 6 are input. That is, since Dp5 and Dp6 are input to the detection circuit 10 on the Pch side, it means that the logical operation of the output Dp5 + Dp6 of the EX-OR gate 13 has been received, and "0" or "1" is output depending on the convergence state of d2. To do. The output of the EX-OR gate 13 is integrated by an integrating circuit composed of the resistor 14 and the capacitor 17, and converted into a direct current.

Therefore, the higher the probability that "1" appears in the output of the EX-OR gate 13, the higher the voltage at the point B. That is, the voltage at point B changes depending on the convergence state of d2. In FIG. 2, resistors 15 and 16 are for adjusting the voltage at the point B to near the threshold level of the OR gate 18.
By changing the voltage division ratio of 5,16, the activation of reset,
You can change the release timing. OR gate 18
This is for converting the voltage change at the point B into a logical "0" or "1" to facilitate driving of the reset signal generating circuits 11 and 12.

As described above, when the circuit of FIG. 2 is used, the output of the OR gate 18 changes to “0” and “1” depending on the convergence state of d2 and e2. Therefore, the circuit of FIG. As detection circuits 9 and 10, Pch,
If they are provided on the Qch side, respectively, the convergence states of the baseband signals d2 and e2 can be detected independently.

Therefore, as shown in FIG. 1, if the outputs of the detection circuits 9 and 10 are given to the reset signal generation circuits 11 and 12, independent reset signals on the Pch and Qch sides can be sent to the transversal equalizer 4. Pch for the transversal equalizer 4
The reset can be activated and released independently on the Qch side.

The present invention is not limited to the above embodiment,
Various modifications are included within the scope of the gist. Although the present invention is applied to the demodulator of 256QAM in the above embodiment, it is needless to say that it can be applied to a transversal equalizer for equalizing distortion of all other multilevel baseband signals. That is, in the case of a binary baseband signal, the A / D converter output of the second bit and the third bit is used, and in the case of a 4-valued and 8-valued signal, the 3rd, 4th bit and
The 4th and 5th bits may be used as the input to the EX-OR gate 13 in FIG. 2, and the reset signal can be sent out by detecting the converged state like 256QAM, that is, a 16-valued baseband signal.

[Effects of the Invention] As described above, according to the present invention, a transversal equalizer for removing waveform distortion of multi-valued baseband signals in two columns is provided with a transversal equalizer according to the degree of convergence of baseband signals in two columns. Invoking reset independently for two columns of baseband signals,
It can be released.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment in which the demodulation device of the present invention is applied to a 256QAM system, FIG. 2 is a circuit diagram showing an example of the detection circuit of FIG. 1, and FIG. 3 uses a conventional reset circuit. FIG. 4 is a block diagram of the demodulator, and FIG. 4 is an operation explanatory diagram of the detection circuit. 1, 2; Demodulator 4; Transversal equalizer 5, 6; Analog-digital converter 9, 10; Detection circuit 11, 12; Reset signal generation circuit

Claims (1)

[Claims] 1. A demodulator used in a digital carrier transmission system, wherein an input modulated wave is demodulated by mutually orthogonal carrier waves.
A demodulator, a transversal equalizer having two equalizers for respectively removing distortion components of two columns of multilevel baseband signals which are outputs of the two demodulators, and the transversal equalizer Two analog-to-digital converters for converting two columns of baseband signals from which distortion components have been removed by two equalizers into digital signals, and two columns of basebands from the outputs of the two analog-to-digital converters 2 to detect the convergence of each signal
One detection circuit and a reset signal that receives the outputs of the two detection circuits as inputs and resets the two equalizers of the transversal equalizer to the multi-valued baseband signals of the two columns independently of each other And a reset signal generating circuit for resetting the signal.