JPS61193543A - Multi-value orthogonal amplitude modulation circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution by constituting the titled circuit of a control circuit for phase modulator, a binary-multivalue converting circuit, an oscillator, an amplitude modulator, and a phase modulator arranged at the pre-stage or the post-stage of the amplitude modulator and applied further with phase modulation by the output of the control circuit for phase modulator. CONSTITUTION:The control circuit for phase modulator, e.g., an EPS control circuit 8 discriminates at which position a binary 4-series digital signal fed to a terminal IN is controlled among 12 phase states. Further, the binary - multi-value converting circuit 10 discriminates to which amplitude state the 2nd path input signal corresponds among three amplitude states. On the other hand, after an output of an oscillator 12 generating a microwave is converted into an amplitude modulation signal by an output from the binary-ternary converting circuit 10 by an amplitude modulator 11 comprising, e.g., a pin diode, the result is fed to the phase modulator, e.g., an EPS 9. Since a control signal from the EPS control circuit 8 is fed to the EPS 9, the amplitude modulation signal is subjected to phase shift further and a 16-value QAM modulation signal with high accuracy is sent from a terminal OUT. Since the signal is modulated directly, the circuit constitution is simplified.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multi-value quadrature amplitude modulation circuit (hereinafter abbreviated as multi-value QAM modulation circuit) used in a multi-value quadrature amplitude modulation radio device.
This is related to the improvement of.

In recent years, from the perspective of effective frequency utilization, a multi-value quadrature amplitude modulation signal (hereinafter abbreviated as multi-value QAM modulation signal), for example, a 16-value QAM modulation signal, is sometimes used, but this modulation signal is transmitted by two ring modulators. It is obtained by combining the obtained orthogonal amplitude modulated signals.

However, when such a ring modulator generates a multi-level 0 static modulation signal such as a 64-value QAM modulation signal or a 256-value QAM modulation signal, signal points due to phase and amplitude errors generated in this modulator The ratio of the deviation from the normal position to the interval between signal points becomes large.

Therefore, there is a need for a multilevel QAM modulation circuit that can place signal points at more accurate positions.

[Conventional technology]

FIG. 6 shows a block diagram of a conventional example of a 16-value QAM modulation circuit, and FIG. 7 shows a signal point arrangement diagram of a 16-value QAM modulation signal.

Therefore, the operation shown in FIG. 6 will be explained with reference to FIG. 7.

In FIG. 6, four series of binary digital signals applied to terminal IN are converted into two series of four-level signals by binary-to-four-level conversion circuits 1 and 2, and then amplitude modulated using a ring modulator. Add to vessels 3 and 4. On the other hand, the output of the oscillator 6 with an oscillation frequency of about 100 MHz is converted into an orthogonal carrier wave by the 90-degree hybrid circuit 5, and then sent to the amplitude modulator 3.
4 (X-axis and y-axis portions in Figure 7), this amplitude modulated signal is in-phase synthesized in the hybrid circuit 7, and a 16QAM modulated signal with 16 signal points is generated as shown in Figure 7. Sent from terminal OUT.

[Problem that the invention seeks to solve]

Here, the normal position of the signal point of the amplitude modulated signal obtained by the amplitude modulator is the point marked X on the X and y axes in FIG. Because of the distortion, for example, the point marked by X comes to the point marked by Δ. For this reason, the spacing between signal points may become narrow.

However, the signal points of the 16-level QAM modulated signal obtained by synthesizing these shifts also have worse accuracy at the shifted position than at the correct position. Therefore, when such signal points are received, the error rate may deteriorate.

Also, since the operating frequency of the ring modulator is approximately 100MHz, after generating a multilevel 0^i modulation signal in the intermediate frequency band,
must be converted to a specified transmission frequency. Therefore, a frequency conversion circuit using a local oscillator, mixer, etc. is required, making the circuit configuration complicated.

That is, since a multi-value QAM modulation circuit using a ring modulator cannot correct positional deviations of signal points, it is difficult to generate a highly accurate multi-value QAM modulation signal, and the circuit configuration becomes complicated. There is a point.

[Means for solving problems]

The above problem is solved by a phase modulator control circuit and a binary-to-multilevel conversion circuit that extract the phase information and amplitude information that the signal point of the multilevel AM modulation signal corresponding to the input digital signal should have, and the carrier wave. an amplitude modulator that amplitude-modulates the output of the oscillator with the output of the binary-to-multi-value conversion circuit; This problem is solved by the multi-level QAM modulation circuit of the present invention, which is composed of a phase modulator that performs phase modulation.

[Effect]

The present invention is based on the state of the input digital signal and the multilevel QA.
Since the relationship between the positions of the signal points of the M modulation signal and the relationship between the amplitude and phase state of each signal point are known in advance, the amplitude and phase state of the corresponding signal point are determined from the input digital signal, and the amplitude and phase are calculated. The carrier wave is modulated by an amplitude modulator and a phase modulator to obtain a multilevel QAM modulated signal.

In other words, since amplitude modulation and phase modulation are performed separately on the carrier wave, for example, if you know in advance the phase error caused by the amplitude modulator and the amplitude error caused by the phase modulator, you can take this into account and calculate the normal amplitude. Since it is possible to apply amplitude and phase modulation so that the state of You can get it.

In addition, these modulators have been developed that operate on microwaves, so if you use them, you can directly modulate with microwaves, so you can replace the conventional local oscillator,
Since a circuit such as a mixer is not required, the circuit configuration is simplified.

That is, a highly accurate multilevel QAM modulation signal can be generated with a simple circuit configuration.

〔Example〕

The contents of the present invention will be explained in detail below with reference to illustrated embodiments.

Note that the same reference numerals indicate the same objects throughout the figures.

FIG. 2 shows a signal point constellation diagram of an example of a 16-level AM modulated signal.

In the figure, there are 16 signal point positions of the 16-value QAM modulated signal, 4 in each quadrant, but the relationship between these positions and the input binary 4-series digital signal is as follows. I can do things.

That is, of the input binary four-series digital signals, for example, a quadrant with a signal point is specified using the first and second series digital signals (referred to as the first path input signal), and the third and fourth series The position of the signal point within the quadrant specified by the digital signal (referred to as the second pass input signal) is specified.

Therefore, in order to know where the input digital signal is in the 120 phase states indicated by the dotted line in FIG. 2, the signals of the first and second paths are required. However, although there are three amplitude states as shown by the arrows in FIG. 2, it is determined by the position of the signal point regardless of the quadrant, so only the second path signal is sufficient.

FIG. 1 shows a block diagram of an embodiment in which the present invention is applied to a 16-value QAM modulation circuit.

In the figure, a control circuit for a phase modulator, such as an infinite phase shifter (
(hereinafter abbreviated as EPS) usage system? ! 1 circuit 8 determines which position among 12 phase states the digital signal of four binary values applied via the terminal IN should be controlled to. Also, 2
A value-to-multivalue conversion circuit, for example, a binary-to-ternary conversion circuit 10 is a second
It is determined which of the three amplitude states the input signal of the path is in.

On the other hand, the output of an oscillator 12 that generates microwaves, for example, is converted into an amplitude modulation signal by an output from a binary-to-ternary conversion circuit 10 by an amplitude modulator 11 configured with a bin diode, and then a phase modulator. For example, it is added to EPS9.

Since a control signal from the EPS %lJ control circuit 8 is applied here, a phase shift is given to the amplitude modulation signal and a highly accurate 16-value ΩAM modulation signal is sent from the terminal 011T.

If the modulator has an amplitude error or a phase error, if the output of the 2-3 conversion circuit 10 or the EPS control circuit 8 is controlled in consideration of the amplitude error or phase error, a highly accurate 16-value QAM modulated signal can be obtained.

FIG. 3 shows a block diagram of the UPS control circuit.

In the figure, the read-only memories 13 and 14 store the EPS control amount for adjusting the phase of the carrier wave to the phase state of the signal point corresponding to the state of the binary 4-series digital signal. Reads the control amount corresponding to the input digital signal, converts it to an analog amount, and converts it to an EP
In addition to S (not shown), a predetermined phase shift is applied to the amplitude modulation modulation signal.

FIG. 4 shows a block diagram of the binary-to-ternary conversion circuit, and FIG. 5 shows an operating state diagram.

The amplitude of each signal point is (0,1
), the point (1,0) is approximately 2.2, and the point (0,0) is approximately 3, so voltages of this ratio are obtained from S 3 and S 4.

Note that, for example, ■ in FIG. 5 indicates the operating state of ■ in FIG. 4. Therefore, the operation shown in FIG. 4 will be explained with reference to FIG.

In FIG. 4, when the second path signals S3 and S4 are, for example, 0.0, they are inverted to 1,1 by inverters 17 and 18, and are passed through an OR circuit 19 and an exclusive OR circuit 20 to level converters 21 and 22. l and O are added to.

Therefore, after this level is converted, 3V is output from the differential amplifier 23.

That is, signal S3. When S4 is 0.0, the forward current of the pin diode forming the amplitude modulator is increased to minimize loss. s3. When s and i are 1.0 or 0°1, the forward current is reduced and the loss is increased to output 2.2V, and when s and i are 1.1, the loss is maximized and IV is output, resulting in three values. performs amplitude modulation.

Further, a read-only memory and a digital-to-analog converter may be used as the binary-to-multivalue conversion circuit, as in the EPS control circuit shown in FIG.

In the above explanation, the multi-level modulation signal is arranged in a lattice pattern, but it is also possible to deal with a case where the signal points are arranged in a honeycomb arrangement other than the lattice arrangement.

〔Effect of the invention〕

As explained in detail above, the signal points can be arranged with high precision not only in a lattice arrangement but also in other arrangements, and the circuit configuration is simple because direct modulation can be performed. You can get the effect of .

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
Value QAM signal point constellation diagram, Figure 3 is a block diagram of the Eps control circuit, Figure 4 is a binary -
A block diagram of the three-value conversion circuit, FIG. 5 shows the operating state diagram of FIG. 4, FIG. 6 shows a block diagram of a conventional example, and FIG. 7 shows a signal point arrangement diagram. In the figure, 8 is an EPS control circuit, and 9 is an EPS. 10 is a binary-to-ternary conversion circuit, 11 is an amplitude modulator, and 12 is an oscillator. $ 1 day z (a potato, 3 mouths and a half 4 days rod, 5''' solid time)

Claims (1)

[Claims] A phase modulator control circuit and a binary-to-multi-value conversion circuit for extracting phase information and amplitude information that a signal point of a multi-value orthogonal amplitude modulation signal corresponding to an input digital signal should have; an oscillator that generates a carrier wave; An amplitude modulator that amplitude-modulates the output of an oscillator using the output of the binary-to-multi-value conversion circuit; and a phase modulator that is arranged before or after the amplitude modulator and further modulates the phase with the output of the phase modulator control circuit. A multilevel quadrature amplitude modulation circuit comprising: