JPH0513414B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a demodulator, and particularly to a demodulator used in a quadrature amplitude modulation method or a polyphase phase modulation method.

[Conventional technology]

Quadrature amplitude modulation and polyphase modulation have recently been widely used as digital carrier transmission systems with high frequency utilization efficiency.

Two mutually orthogonal reference carrier signals are required to perform orthogonal detection and demodulation of a digital modulation signal such as a quadrature amplitude modulated wave or a multiphase phase modulated wave. Usually, one reference carrier wave signal is regenerated from an input signal by a carrier wave regeneration circuit, this reference carrier wave signal is divided into two, and one of the two is phase-shifted by a π/2 phase shifter to obtain two reference carrier wave signals.

The reference carrier signal must be maintained in a correct phase relationship with the input signal, and if this phase relationship deviates, the bit error rate characteristics will deteriorate. Various types of carrier synchronization circuits that maintain this correct phase relationship have been proposed in the past, and among them, a very simplified circuit is described in Japanese Patent Laid-Open No. 131151/1983.

A π/2 phase shifter is also composed of a combination of coils, capacitors, amplifiers, etc., and if the phase shift value deviates from 90 degrees due to changes in ambient temperature, power supply voltage, or changes in circuit constants over time, the bit error rate characteristics will deteriorate. to degrade. An automatic phase adjustment circuit that maintains this phase shift value correctly is described in Japanese Patent Application Laid-Open No. 59-80048.

The demodulator equipped with a carrier synchronization circuit and an automatic phase adjustment circuit described in the above two publications can maintain two reference carrier signals in correct phase with a very simplified circuit.

FIG. 2 is a block diagram showing an example of a conventional demodulator.

The conventional example shown in FIG. 2 demodulates the 16-value orthogonal amplitude modulated input signal IN1 to generate the main data signal D1-
1, D1-2, D2-1, and D2-2.

A reference carrier signal CA1, which is the output of a voltage controlled oscillator (hereinafter referred to as VCO) 7, is supplied to the phase detector 1. Further, a reference carrier wave signal CA2, which is a signal obtained by phase-shifting the reference carrier wave signal CA1 by 90 degrees by a variable phase shifter 10, is supplied to the phase detector 2.

Phase detectors 1 and 2 perform quadrature detection on input signal IN1 and output baseband signals S1 and S2.

3 and 4 are 3-bit A-D converters. A-
The D converters 3 and 4 convert the baseband signals S1 and S2 into 3-bit digital signals X1 to X3, respectively.
Convert to Y1 to Y3 (hereinafter, higher-order bits are represented by smaller subscript numbers). Digital signal
1, X2, Y1, Y2 are main data signals D1-1,
D1-2, D2-1, D2-2, among which the digital signals X1 and Y1 are 16 of the input signal IN1.
This is the result of determining the quadrant in which the point signal is located.
Digital signals X3 and Y3 are the results of detecting shifts in signal positions at 16 points.

Exclusive OR (hereinafter referred to as EX-OR) circuit 5
performs EX-OR operation on digital signals X3 and Y1 and outputs control signal C1. EX-OR circuit 8 performs EX-OR operation on digital signals X1 and Y3 and outputs control signal C2.

A subtracter 11 takes the difference between the control signals C1 and C2, and this difference is applied to a low frequency filter (hereinafter referred to as LPF) 6.
By inputting the reference carrier wave signal CA1 to the VCO 7 via the oscillation frequency and controlling the oscillation frequency of the VCO 7, the reference carrier wave signal CA1 is synchronized to the correct phase. The subtracter 11 is omitted and one of the control signals C1 and C2 is directly input to the LPF 6.
Carrier synchronization can be achieved simply by inputting the This carrier synchronization operation is described in the above-mentioned Japanese Patent Application Laid-Open No. 57-131151.
It is explained in detail in the publication no.

The adder 12 sums the control signals C1 and C2, inputs this sum to the variable phase shifter 10 via the LPF 9, and controls the phase shift value of the variable phase shifter 10, thereby converting the reference carrier signal CA2 to the reference carrier signal CA2. carrier signal CA
The phase shift is adjusted to be exactly orthogonal to 1. This orthogonal phase adjustment operation is described in the above-mentioned Japanese Patent Application Laid-Open No.
It is explained in detail in Publication No. 80048.

In the conventional example shown in FIG. 2, as explained above, the control signals C1 and C2 are shared by the carrier synchronization operation and the quadrature phase control operation.

[Problem that the invention seeks to solve]

As explained above, conventional demodulators share the same control signal for carrier synchronization operation and quadrature phase control operation by simply changing the algorithm, and since these operations converge while influencing each other, the convergence time is short. It has the disadvantage of being long.

SUMMARY OF THE INVENTION An object of the present invention is to provide a demodulator that solves the above drawbacks and has a short convergence time.

[Means for solving problems]

The demodulator of the present invention performs orthogonal detection of a digital modulation signal by first and second phase detectors that use first and second reference carrier signals that are orthogonal to each other, and In a demodulation device that performs multi-value identification of the output of a phase detector using first and second A-D converters, at least the signal of the digital modulation signal among the outputs of the first A-D converter. A first control signal is generated by logically manipulating an output signal that makes it possible to detect a positional deviation and an output signal that makes it possible to determine at least the quadrant of the signal position among the outputs of the second A-D converter. first logic means for outputting the first reference carrier signal; first reference carrier signal generating means for outputting the first reference carrier signal with the output frequency or output phase controlled by the first control signal; Among the outputs of the A-D converter, at least an output signal that enables quadrant determination of the signal position, and of the output of the second A-D converter, at least a shift in the signal position can be detected. a second logic means for outputting a second control signal by logically operating the output signal; and a second reference for outputting the second reference carrier signal, the output phase of which is controlled by the second control signal. and carrier wave signal generating means.

〔Example〕

The present invention will be described in detail below with reference to drawings showing embodiments.

FIG. 1 is a block diagram showing a first embodiment of a demodulator according to the present invention.

The embodiment shown in FIG.
Phase detectors 1 and 2 input IN1 and reference carrier signals CA1 and CA2 and output baseband signals S1 and S2, input baseband signals S1 and S2 and output digital signals X1 to X3 and Y1 to Y3. The A-D converters 3 and 4 are connected to the digital signal
3. EX- which inputs Y1 and outputs control signal C1
The control signal C1 is input through the OR circuit 5, the LPF 6, and the LPF 6, and the reference carrier signal CA1 is output.
VCO 7, an EX-OR circuit 8 which inputs digital signals X1 and Y3 and outputs a control signal C2,
Input LPF9 and reference carrier signal CA1 and LPF9
Input the control signal C2 via the reference carrier signal
The variable phase shifter 10 outputs CA2.

The embodiment shown in FIG. 1 removes the subtracter 11 and adder 12 from the conventional example shown in FIG.
1 and C2 are input directly to LPF6/9.

Input signal IN1 is orthogonally detected by phase detectors 1 and 2 to become baseband signals S1 and S2, and further A
-D converters 3 and 4 output digital signals X1 to X3,
The conversion into Y1 to Y3 and the EX-OR circuits 5 and 8 outputting the control signals C1 and C2 are the same as described in the description of the conventional example shown in FIG.

FIG. 3 is a diagram for explaining a 16-value orthogonal amplitude modulation signal.

In FIG. 3, the circles indicate the correct signal positions. The direction of axes S1 and S2 is the reference carrier signal
Corresponding to the phase of CA1 and CA2, the axis S of the signal position
1, the orthogonal projection onto S2 is the baseband signal S1, S
It becomes 2. FIG. 3 shows the baseband signals S1, S
2 and the data signals X1 to X3 and Y1 to Y3 are also shown.

When the phase of the reference carrier signal CA1 shifts and the signal position rotates in the direction of the arrow with respect to the axis S1 shown in FIG. 3, the control signal C1 becomes "1", and when the phase rotates in the opposite direction, the control signal C1 becomes "0". '', the direction of the phase shift of the reference carrier signal CA1 can be detected using the control signal C1. By controlling the oscillation frequency of the VCO 7 using the control signal C1, the reference carrier signal CA1 is controlled to have the correct phase.
The LPF 6 is used to suppress jitter components of the control signal CA1.

The relationship between the phase rotation of the signal position with respect to the axis S2 due to the phase shift of the reference carrier signal CA2 and the control signal CA2 is also such that the correspondence between the direction of phase rotation and "1" and "0" is opposite to that of the control signal CA1. Therefore, by suppressing the jitter component of the control signal CA2 with the LPF 9 and controlling the phase shift value of the variable phase shifter 10, the reference carrier wave signal CA2
is controlled to the correct phase. In addition, variable phase shifter 1
If the variable range of the phase shift value of 0 is too wide, the phase shift value may converge to an erroneous stable point that is an integral multiple of 90 degrees away from the predetermined 90 degrees (or 270 degrees).
For example, change the phase shift value variable range to 90 degrees ± 10 degrees (or
(270 degrees ± 10 degrees).

As explained above, the control signals C1 and C2, which are generated from different data signals, independently control the phases of the reference carrier signals CA1 and CA2, and these two phase control operations influence each other. The convergence time for these operations is short because there is no

FIG. 4 is a block diagram showing a second embodiment of the demodulator of the present invention.

The embodiment shown in FIG. 4 removes the VCO 7 and variable phase shifter 10 from the embodiment shown in FIG.
3, an endless variable phase shifter 14 which inputs the LPF6 output and the oscillator 13 output and outputs the reference carrier wave signal CA1, a limiting circuit 15 which inputs the outputs of the LPFs 6 and 9, and the oscillator 13 output and the limiting circuit 15 output. It is configured by adding an endless variable phase shifter 16 which inputs the reference carrier signal CA2 and outputs the reference carrier signal CA2.

The oscillation frequency of the oscillator 13 is set to be close to the carrier frequency of the input signal IN1. The variable phase shifter 14 is controlled by the control signal C1 via the LPF 6 to endlessly shift the phase of the output of the oscillator 13, and outputs a reference carrier signal CA1 having the correct phase. The variable phase shifter 16 is the LPF 9/limiting circuit 15
is controlled by control signal C2 through
Create CA2. The limiting circuit 15 is a reference carrier signal
This is to ensure that the phase of CA2 converges to a stable point that is 90 degrees behind (or ahead of) the phase of the reference carrier signal CA1, and does not converge to an incorrect stable point. The phase shift value of the variable phase shifter 16 is compared with the output of the variable phase shifter 14.
The output of the LPF 9 is limited to a range that is larger (or smaller) than the phase shift value of, for example, 90 degrees ±10 degrees.

Also in the embodiment shown in FIG. 4, the phases of the reference carrier signals CA1 and CA2 are independently controlled by the control signals C1 and C2.

Replace the VCO 7 in the embodiment shown in FIG. 1 with the oscillator 13 and variable phase shifter 14 in FIG.
By inputting the output of the LPF 6 to the variable phase shifter 14, the demodulator of the present invention for the 16-value orthogonal amplitude modulation system can be constructed.

FIG. 5 is a block diagram showing a third embodiment of the demodulator of the present invention.

The embodiment shown in FIG. 5 is for a 64-value orthogonal amplitude modulation system, and the A-D converters 3 and 4 of the embodiment shown in FIG. Replaced with 4-bit A-D converters 17, 18 that output ~X4, Y1 ~ Y4, input digital signals X4, Y1 to EX-OR circuit 5, and input digital signals X4, Y1 to EX-OR circuit 8. It is composed of

The input signal IN2 subjected to 64-value orthogonal amplitude modulation is orthogonally detected by the phase detectors 1 and 2 to become baseband signals S1 and S2.
are converted into digital signals X1 to X4 and Y1 to Y4. Digital signals X1-X3, Y1-Y3
are main data signals D1-1 to D1-3, D2-1 to
It is D2-3. The digital signals X1, Y1 are the results of determining the quadrant in which the 64-point signals of the input signal IN2 are located, and the digital signals
This is the result of detecting a shift in the signal position of a point.

The reference carrier signal CA1 is generated by the control signal C1 obtained by EX-ORing the digital signals X4 and Y1.
It is possible to detect the direction of the phase shift of the digital signal
1. Control signal CA2 obtained by EX-OR operation of Y4
As in the embodiment shown in FIG. 1, it is possible to detect the direction of the phase shift of the reference carrier signal CA2. Control signals CA1 and CA2 are LPF6,
9 to control the VCO 7 and variable phase shifter 10,
The phases of reference carrier signals CA1 and CA2 are controlled independently.

The demodulation device of the present invention for the 64-value orthogonal amplitude modulation method can also be obtained by replacing the A-D converters 3 and 4 of the embodiment shown in FIG. 4 with the A-D converters 17 and 18 of FIG. can be configured.

The embodiments of the present invention have been described above for use in 16-value and 64-value orthogonal amplitude modulation systems, but the present invention also applies to quadrature amplitude modulation systems with various numbers of values such as 4-value and 256-value, or for various number of values such as 8-value. The present invention can also be applied to a demodulator for a multi-phase phase modulation method. For example, if the A-D converters 3 and 4 of the embodiment shown in FIG. 3 or 4 are each replaced with a 2-bit A-D converter, it will be 4-value, and if each is replaced with a 5-bit A-D converter, A demodulator of the present invention for a 256-value orthogonal amplitude modulation method is obtained. In the case of a system such as an 8-phase phase modulation system in which the baseband signal takes multi-values that are not evenly spaced, the interval between the discrimination points is suitable for the value that the baseband signal takes, and an A-D converter that is not equally spaced is used. use

Furthermore, in all of the embodiments described above, EX-OR circuits are used as the first and second logic means, but the first and second logic means are
It is not limited to EX-OR circuits. For example, in the embodiment shown in FIG.
2, X3, Y2, Y3 and the digital signals X4, Y1 to output a first control signal for detecting the direction of the phase shift of the reference carrier signal CA1. It can also be used as the first logic means instead of the circuit 5. However, the first logic means and the second logic means must not share the same digital signal among the two digital signals that are the signals that detect the shift in signal position.

In the above explanation, it is assumed that the signal position of the input signal is correct, but the demodulation device of the present invention also takes into account deviations in orthogonality of the signal position during signal modulation on the transmitting side and orthogonal distortion occurring in the transmission path. will be compensated.

〔Effect of the invention〕

As explained in detail above, the demodulation device of the present invention is capable of converting two baseband signals obtained by orthogonal detection of a digital modulation signal to each other among a plurality of digital signals obtained by A-to-D conversion. The signals are logically manipulated to create two control signals, and these control signals independently control the phases of the two reference carrier signals, and these two phase control operations do not affect each other. This has the effect of shortening the convergence time of these control operations.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the demodulating device of the present invention, FIG. 2 is a block diagram showing an example of a conventional demodulating device, and FIG. 3 is a block diagram showing a 16-value orthogonal amplitude modulation signal. The drawings, FIGS. 4 and 5, are block diagrams showing second and third embodiments of the present invention. 1, 2... Phase detector, 3, 4... A-D converter, 5, 8... EX-OR circuit, 6, 9... LPF,
7...VCO, 10...variable phase shifter.

Claims (1)

[Claims] 1. A digital modulation signal is orthogonally detected by first and second phase detectors using mutually orthogonal first and second reference carrier signals, and the first and second reference carrier signals are orthogonally detected. In a demodulation device that performs multi-value identification of the output of a phase detector using first and second A-D converters, the signal of at least the digital modulation signal among the outputs of the first A-D converter is provided. A first control signal is generated by logically manipulating an output signal that makes it possible to detect a positional deviation and an output signal that makes it possible to determine at least the quadrant of the signal position among the outputs of the second A-D converter. first logic means for outputting the first reference carrier signal; first reference carrier signal generating means for outputting the first reference carrier signal with the output frequency or output phase controlled by the first control signal; Among the outputs of the A-D converter, at least an output signal that enables quadrant determination of the signal position, and of the output of the second A-D converter, at least a shift in the signal position can be detected. a second logic means for outputting a second control signal by logically operating the output signal; and a second reference for outputting the second reference carrier signal whose output phase is controlled by the second control signal. 1. A demodulating device comprising carrier wave signal generating means. 2. The demodulator according to claim 1, wherein the first reference carrier signal generating means is a voltage controlled oscillator whose output frequency is controlled by the first control signal. 3. The first reference carrier signal generating means includes a fixed frequency oscillator and a first variable phase shifter that shifts the phase of the output of the fixed frequency oscillator using the first control signal. A demodulator according to range 1. 4. The demodulation device according to claim 1, wherein the second reference carrier signal generating means is a second variable phase shifter that shifts the phase of the first reference carrier signal by the second control signal. . 5. The demodulation device according to claim 3, wherein the second reference carrier signal generation means is a third variable phase shifter that shifts the phase of the output of the fixed frequency oscillator according to the second control signal.