JPH01205631A - Demodulator - Google Patents

Abstract

PURPOSE:To attain an analog signal input by a conventional level diagram by providing an IF transversal equalizer to the 1st stage of a demodulator using a conventional digital transversal equalizer, etc. CONSTITUTION:An IF transversal equalizer 1 is provided to the 1st stage of a demodulator using a conventional digital transversal equalizer. As a result, an input signal to A/D converters 10, 11 is a signal without waveform distortion due to fading, it is not required to compress the analog input signal and the analog signal by a conventional level diagram is inputted. Since the waveform distortion is eliminated from the input signal of the A/D converters 10, 11, a control signal of a carrier recovery circuit is generated from the output signal of the A/D converters 10, 11. Thus, a loop band taking the bit delay into account is not required but a loop band with a required-and-sufficient band is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a demodulator in a digital carrier transmission system, and in particular! A demodulation device includes an F-type transversal equalizer and a digital transversal equalizer.

[Prior Art] In conventional demodulators, in order to overcome multipath fading in the transmission path in digital carrier wave transmission systems,
An IF type transversal equalizer was used.

FIG. 2 is a block diagram of a conventional demodulator using an IF type transversal equalizer.

In the figure, l is an IF type analog transversal filter, 2 is a control signal generation circuit, 3 and 4 are multipliers, 5 is a π/2 phase shifter, 6 and 7 are low-pass filters, 8, 9 is an amplifier,
10.11 is an A/D converter, 15 is a carrier control signal generation circuit, 16 is a voltage controlled oscillator, and 17.18 is a control signal generation circuit that serves as an automatic gain control circuit and an automatic drift control circuit.

In the demodulation device having the above configuration, the modulation which has undergone waveform distortion due to multipath fading etc. is performed using human power, and the output is obtained from the A/D converters 10 and 11.

At this time, the output signal rl+r2 of the A/D converter 10.11
controls the control signal generation circuit 2, and controls the transversal filter 1 in a negative feedback manner using its output signal r3. After obtaining the modulated wave m from which waveform distortion has been removed, carrier waves (carriers) T4. T5 and the modulated wave m are synchronously detected by multipliers 3 and 4 to obtain a baseband signal nl+n2.

This baseband signal nl+n2 is passed through low-pass filters 6 and 7.
After the waveform is shaped by the amplifier 8.9, the signal is input to the amplifier 8.9. The amplifiers 8 and 9 have their gains and DC drifts automatically controlled by control signals 85 to s8 generated by control signal generation circuits 17 and 18 that also serve as automatic gain control circuits and automatic drift control circuits, and furthermore, this control signal generation circuit 17.1
8 is controlled by output signals 81 to S4 of A/D converter 10.11. As a result, the A/D converter 10.
11, the baseband signal g++g2 is such that a correct judgment is always made.

On the other hand, the output signal Tl+T2 of the A/D converter 10.11 is inputted to the carrier wave control signal generation circuit (CARR) 15 and becomes the carrier phase control signal T3. This control signal T3 is manually inputted to the voltage controlled oscillator (VCO) 16 to control the carrier oscillation yiR shoulder wave number, and the reproduced carrier is synchronized with the manually input signal during normal operation.

Incidentally, in recent years, in order to increase frequency utilization efficiency and enable highly efficient information transmission, multi-level quadrature amplitude modulation methods such as 256 QAM methods have been attempted. Therefore, in order to realize such a system, it is more important than ever to improve the accuracy of the technology for overcoming multipath fading that occurs in the transmission path.

However, since the IF-type transversal equalizer in the demodulator described above was configured with an analog circuit, there were problems such as the frequency characteristics of the delay line, distortion caused by the analog multiplier, and noise addition, and there were also many adjustment points. There were ten locations, making it difficult to achieve high precision.

Therefore, full digitization has recently been proposed as a means of increasing precision (1986 IEICE Communications Division National Conference 419 ``Configuration and Characteristics of Digitized Transversal Equalizer'').

FIG. 3 is a block diagram of a demodulator using such a digital transversal equalizer.

In the figure, 12 and 14 are digital transversal equalizers, and 13 is a control signal generation circuit.

In the demodulator having the above configuration, first, a carrier wave (carrier) d2+di having a phase difference of π/2 and a modulated wave input μ which has undergone waveform distortion are synchronously detected by multipliers 3 and 4 to generate a baseband signal nl+n2. obtain. This baseband signal n1pn2 is waveform-shaped by low-pass filters 6 and 7 and then input to amplifiers 8 and 9 manually. Here, the gain and DC drift in the amplifiers 8 and 9 are controlled by a control signal generation circuit 13 that functions as a carrier wave control signal generation circuit, an automatic gain control circuit, and an automatic drift control circuit.

~b4 is automatically controlled. Further, this control signal generation circuit 13 is controlled by the output signal al+82 of the digital transversal equalizer 12.14.
．． 14 equalizes waveform distortion by performing a logical operation on the signal y++y2 identified by the A/D converter 10.11.

By passing through such a loop, the A/D converter 10.1
An input of 1 results in a baseband signal X15X2 that always makes a correct determination. Further, the control signal d is input to the voltage controlled oscillator (VCO) 1G to control the carrier oscillation frequency, and the reproduced carrier is synchronized with the human input signal during normal operation.

However, a demodulator using such a digital transversal equalizer also has the following two drawbacks.

First, the carrier recovery circuit generates a control signal from the output of the digital transversal equalizer, resulting in a delay of several tens of bits in the circuit.

Second, since A/D conversion is performed using a signal before waveform distortion is equalized as an input signal, if a normal level diagram is used, the large amplitude part of the signal will likely be interfered with and go out of range. This has the disadvantage of causing nonlinear distortion.

For this reason, in order to compensate for these drawbacks, conventional techniques have been to address the first drawback by narrowing the loop band of the carrier wave regeneration circuit, and to address the second drawback, by narrowing the loop band of the A/D converter. The solution has been to compress the signal, expand the discrimination S range isometrically, and provide a post-processing circuit in the final stage to obtain the original signal from the output signal of the digital transversal equalizer.

[Problems to be Solved] The above-described conventional demodulator has the problem that a sufficient loop band of the carrier wave regeneration circuit cannot be obtained, and that the S/N ratio is deteriorated by compressing the analog human input signal.

The present invention has been made in view of the above-mentioned problems, and it is possible to obtain a sufficient loop band in a carrier wave regeneration circuit, and to demodulate the A/D converter, which can be identified by a normal level diagram. The purpose is to provide equipment.

[Means for Solving Problems] In order to achieve the above object, the demodulator of the present invention includes an IF type transversal equalization means, a carrier wave regeneration means for regenerating a carrier wave, and an output of the IF type transversal equalization means. a multiplication means for obtaining a baseband signal by synchronous detection with the carrier wave regenerated by the carrier wave regeneration means; an amplification means for amplifying the baseband signal which is the output of the multiplication means after waveform shaping; and an output of the amplification means. A/
A/D conversion identification means that performs D conversion and identification, and this A/D conversion identification means.
The configuration includes digital transversal equalization means for equalizing the output signal of the conversion identification means, and automatic gain drift control means for controlling the gain and drift of the amplification means, and the automatic gain drift control means for controlling the gain and drift of the amplification means. The means is controlled by the output signal of the digital transversal equalization means, and the carrier regeneration means is controlled by the digital transversal equalization means output signal.
It is controlled by the output signal of the A/D conversion identification means.

[Example] Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 is a block diagram of a demodulator according to an embodiment of the present invention. Note that parts common to or corresponding to those of the conventional example are denoted by the same reference numerals.

In the demodulator having the configuration shown in the figure, a manually modulated signal a that has undergone waveform distortion due to multipath fading in the transmission path passes through a transversal filter l to become a modulated wave from which the waveform distortion has been removed. Here, the transversal filter l is controlled by the output control signal 3 of the control signal generation circuit 2;
is controlled by the output signal kl+2 of the A/D converter 10.11.

Next, carrier waves (carriers) j with a phase difference of π/2
4+js and the modulated wave are synchronously detected by multipliers 3 and 4 to obtain a baseband signal CI+C2, and then this baseband signal CI+C2 is waveform-shaped by low-pass filters 6 and 7 and then sent to amplifiers 8 and 9. to use human power. The gain and DC drift in the amplifiers 8 and 9 are automatically controlled by control signals 11 to 14 generated by a control signal generation circuit 13. The control signal generation circuit 13 also includes a digital transversal equalizer 1 that equalizes waveform distortion by performing logical operations on the signals f, , f2 identified by the A/D converters 10 and 11.
The output signal of 2.14 is controlled by 2.

As a result, the input to the A/D converter 10.11 is a baseband signal el+82 at a normal level such that a correct determination is always made.

On the other hand, the carrier regeneration circuit is different from a conventional demodulation device using a digital transversal equalizer. That is, first, the output signal 11 of the A/D converter 10°11
+12 to carrier control signal generation circuit (CARR)
15 to obtain a carrier phase control signal j3, and the control signal j3 controls the voltage controlled oscillator (VCO) 1B.
is controlled to reproduce a carrier wave synchronized with the input signal.

As described above, in this embodiment, an IF type transversal equalizer is placed at the first stage of a demodulation device using a conventional digital type transversal equalizer.

As a result, the input signal of the A/D converter becomes a signal from which waveform distortion due to fading etc. has been removed, eliminating the need to compress the analog human signal, which is the second problem mentioned above, and eliminating the need to compress the analog human input signal, which is the second problem mentioned above. Signals can be generated manually.

Furthermore, since waveform distortion has been removed from the human input signal of the A/D converter, the control signal for the carrier regeneration circuit can be generated from the output signal of the A/D converter. Therefore, it is not necessary to create a loop band that takes into account the bit delay, which is the first problem mentioned above, and it is possible to create a loop band that is as wide as necessary.

Note that the equalization ability of the IF type transversal equalizer placed at the first stage may be such that the input of the A/D converter does not fall outside the identification range and cause nonlinear distortion. Therefore, this IF type transversal equalizer may be small-scale. For this reason, digital transversal equalizers no longer need to take bit delay into consideration.
The number of taps can be increased to increase equalization capability.

[Effects of the Invention] As explained above, the present invention has the following features by placing an IF type transversal equalizer at the first stage of a demodulation device using a conventional digital type transversal equalizer. This has the advantage that it is possible to provide a demodulator with a high level of accuracy.

(2) The human input signal of the A/D converter used as a discriminator becomes a signal from which waveform distortion due to fading etc. has been removed, and it is possible to manually input an analog signal based on a normal level diagram.

■The output signal of the A/D converter is also a signal with some waveform distortion removed, so that output signal can be used in the carrier wave regeneration circuit, and there is no need to create a loop band that takes bit delay into consideration. You can get a loop band as wide as you need.

Furthermore, since the present invention does not require consideration of bit delay, the number of taps of the digital transversal equalizer can be increased in order to increase the equalization capability of the digital transversal equalizer. It's also effective.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a demodulator according to an embodiment of the present invention, Fig. 2 is a block diagram of a conventional demodulator using an IF type transversal equalizer, and Fig. 3 is a block diagram of a conventional demodulator using an IF type transversal equalizer. 1 is a block diagram of a conventional demodulator using a demodulator. 1: IF type analog transversal filter 2: Control signal generation circuit 3.4: Multiplier 5: π/2 phase shifter 6.7: Low-pass filter 8.9: Amplifier 10, 11: A/D conversion Device 12.14: Digital transversal equalizer 13
: Control signal generation circuit 15 : Carrier control signal generation circuit 16 : Voltage controlled oscillator

Claims (1)

[Claims] IF-type transversal equalization means, carrier-wave regeneration means for regenerating a carrier wave, and multiplication means for obtaining a baseband signal by synchronously detecting the output of the IF-type transversal equalization means with the carrier wave regenerated by the carrier-wave regeneration means. , an amplifying means for shaping and amplifying the baseband signal which is the output of the multiplication means, an A/D conversion identifying means for A/D converting and identifying the output of the amplifying means, and an A/D conversion identifying means for performing A/D conversion on the output of the amplifying means. In a demodulation device comprising digital transversal equalization means for equalizing the output signal of the conversion identification means, and automatic gain drift control means for controlling the gain and drift of the amplification means, the automatic gain drift control means comprises: A demodulation device characterized in that the demodulation device is controlled by the output signal of the digital transversal equalization device, and the carrier wave regeneration device is controlled by the output signal of the A/D conversion identification device.