JP3161054B2 - Multi-level quadrature amplitude modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilevel quadrature amplitude modulator and, more particularly, to a multilevel quadrature amplitude modulator for generating a multilevel quadrature amplitude modulation signal from positive and negative phase multilevel amplitude baseband signals.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an example of a conventional multi-level quadrature amplitude modulation device, in which a 16-level quadrature amplitude modulation signal is generated.

Here, DA converters 1 and 2 are each composed of 2
Column digital signals D11, D12 and D21, D2
2 and converted into baseband signals B1 and B2 each having a quaternary amplitude. Differential amplifiers 3 and 4
Receives the baseband signals B1 and B2 and receives the positive-phase and negative-phase balanced baseband signals B1p and B1p, respectively.
1n and B2p, B2n. Multiplier 5
Are the balanced baseband signals B1p, B1n and B2
p and B2n are multiplied, and the multi-level quadrature amplitude modulation signal Sm
Generate Thereafter, although not shown, the carrier is modulated by the multilevel quadrature amplitude modulation signal Sm.

By the way, the balanced baseband signal B1p,
When the levels of B1n, B2p, and B2n fluctuate, the signal points arranged on the two-dimensional phase plane fluctuate, and the phase and amplitude of the signal change, thereby deteriorating the modulation quality. Generally, the output level of the DA converter is likely to fluctuate due to a temperature change.

In order to compensate for such an output level fluctuation due to a temperature change of the DA converter, a control voltage generating circuit 8 is provided.
, A control voltage Vc is generated and supplied to the differential amplifiers 3, 4, and the baseband signals B1p, B1n, B2p, B2
Control is performed so that the level of n does not change. The control voltage generation circuit 8 generates the control voltage Vc using, for example, temperature characteristics of a diode or a transistor.

[0006]

In the conventional multi-level quadrature amplitude modulation apparatus described above, in order to compensate for the output level fluctuation due to the temperature change of the DA converter, control is performed using the temperature characteristics of a diode or a transistor. A voltage is generated, and this control voltage is supplied to a differential amplifier to control an output level. However, since the temperature characteristics of the DA converters are different from each other, it is difficult to reliably compensate the temperature characteristics, and not only does the modulation quality deteriorate, but also a control voltage adapted to the temperature characteristics of each DA converter is required. There is a problem that it takes a long time to adjust.

An object of the present invention is to provide a DA having different temperature characteristics.
It is an object of the present invention to provide a multi-level quadrature amplitude modulation device that can reliably and easily compensate for the level fluctuation of a DA converter and realize high-quality modulation even when a converter is used.

[0008]

Multilevel quadrature amplitude modulation system of the present invention, in order to solve the problems] includes a plurality of D-A converter for converting the baseband signal of the multilevel amplitude receives the digital signal, respectively, this
The output level is sent respectively controlled to according to the control voltage to generate a positive phase and negative-phase balanced baseband signals by receiving the baseband signal provided corresponding to these D-A converter Multiple differential amplifiers and this
A balanced baseband signal Luo differential amplifier sends it
Is received and means for generating a multilevel quadrature amplitude modulated signal, and a plurality of control voltage generating means for generating respectively said control voltage from said balanced baseband signal provided corresponding to said plurality of differential amplifier The plurality of control voltage generators
Stages provide positive and negative phase signals of the balanced baseband signal.
Detect the maximum and minimum level values of each of the signals
To calculate the average level value of the positive phase signal and the negative phase signal
The average calculation unit, and the average calculated by the average calculation unit
The average level of the positive-phase signal and the average level of the negative-phase signal
The control voltage is generated such that the difference from the control value becomes zero.
And a voltage generator . In addition, the plurality of D
-A converter having the applied terminal which can control the output level in accordance with the voltage, respectively, it may constitute the control voltage to the terminal so that be applied respectively.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention, in which the same parts as those of the conventional multilevel quadrature amplitude modulator shown in FIG. Here, the difference from the conventional example is that control voltage generating circuits 6 and 7 are provided.

As in the prior art, the DA converters 1 and 2
Are digital signals D11, D12 and D2 of two columns each.
1 and D22, and converts them into baseband signals B1 and B2 having quaternary amplitudes, respectively. Differential amplifier 3
And 4 receive the baseband signals B1 and B2,
The positive-phase and negative-phase balanced baseband signals B1 respectively
p, B1n and B2p, B2n. Further, the output level is controlled according to the control voltages Vc1 and Vc2. The multiplier 5 outputs the balanced baseband signal B1p,
B1n and B2p and B2n are received and multiplied to generate a multilevel quadrature amplitude modulation signal Sm.

The control voltage generating circuits 6 and 7 generate control voltages Vc 1 and Vc 2 for compensating output level fluctuations of the DA converter due to temperature changes, and supply the control voltages Vc 1 and Vc 2 to the differential amplifiers 3 and 4. The differential amplifiers 3 and 4 control the output levels of the balanced baseband signals B1p, B1n and B2p, B2n according to the control voltages Vc1 and Vc2, and prevent the level change of the DA converter.

Incidentally, the control voltage generating circuits 6 and 7
Are the balanced baseband signals B1p, B1n and B2
Average calculators 61 and 71 for calculating respective average level values of p and B2n, and voltage generators 62 and 72 for generating control voltages Vc1 and Vc2 based on a difference between the calculated average level values. I have.

Now, as shown in FIG. 3, for example, the levels of the positive-phase baseband signal B1p are p1, p2, p3,
p4, and the level of the opposite-phase baseband signal B1n is n
1, n2, n3, and n4, the control voltage generation circuit 6
The average calculator 61 calculates the maximum level values p1 and n4 and the minimum level value p of the positive-phase and negative-phase baseband signals.
4, n1 is detected and the average level value Vp = (p1 + p4)
/ 2 and Vn = (n1 + n4) / 2. The voltage generator 62 calculates a difference ΔV between the average level values Vp and Vn, generates a control voltage Vc1 such that ΔV becomes zero, and sends the control voltage Vc1 to the differential amplifier 3. Similarly, the control voltage generation circuit 7 generates the control voltage Vc2 and sends it to the differential amplifier 4.

By doing so, it is possible to compensate output level fluctuations of the DA converters 1 and 2 due to temperature changes.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

The same parts as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals. Here, the difference from the first embodiment is that the D-
That is, A converters 9 and 10 are provided, and control voltages Vc1 and Vc2 are supplied to control the output level.

In this case, each of the DA converters 9 and 10 has 2
Column digital signals D11, D12 and D21, D2
2 respectively, and the applied control voltages Vc1 and Vc2
Baseband signals B1 and B2 having output levels corresponding to
And output.

Even with this configuration, D due to temperature change
It is clear that output level fluctuations of the -A converters 1 and 2 can be compensated.

[0020]

As described above, according to the present invention, the averages of the maximum level value and the minimum level value are respectively applied to the positive-phase baseband signal and the negative-phase baseband signal output from the differential amplifier. Calculate and generate a control voltage such that the difference between the average level values of the positive phase and the negative phase becomes zero,
By controlling the output level by feeding back to the differential amplifier or DA converter, even if DA converters with different temperature characteristics are used, the level fluctuation of the DA converter can be reliably and easily compensated. Therefore, high-quality multilevel quadrature amplitude modulation can be realized.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram illustrating the operation of the control voltage generation circuit shown in FIGS.

FIG. 4 is a block diagram illustrating an example of a conventional multilevel quadrature amplitude modulation device.

[Explanation of symbols]

 1,2,9,10 DA converter 3,4 Differential amplifier 5 Multiplier 6,7 Control voltage generator 61,71 Average calculator 62,72 Voltage generator D11-D22 Digital signal B1, B2 Baseband Signal B1p, B2p Positive-phase baseband signal B1n, B2n Negative-phase baseband signal Sm Multi-level quadrature amplitude modulation signal Vc1, Vc2 Control voltage Vp, Vn Average level value

Claims (2)

(57) [Claims] 1. A receiving a plurality of D-A converter for converting the baseband signal of the multilevel amplitude receives the digital signal, respectively, the baseband signal provided corresponding to these D-A converter A plurality of differential amplifiers that generate positive-phase and negative-phase balanced baseband signals and control and output output levels in accordance with respective control voltages, and receive balanced baseband signals transmitted by these differential amplifiers, respectively. Means for generating a multi-level quadrature amplitude modulation signal, and a plurality of control voltage generating means provided corresponding to the plurality of differential amplifiers and respectively generating the control voltage from the balanced baseband signal , Multiple control electronics
Pressure generating means for generating a positive phase of the balanced baseband signal;
The maximum level value and the minimum level value of each
To calculate the average level value of the positive-phase and negative-phase signals.
The average calculator to be calculated and the average calculated by the average calculator.
Of the average level value of the positive-phase signal
The control voltage is adjusted so that the difference from the average level value becomes zero.
Multilevel quadrature amplitude modulator according to claim Rukoto to have a voltage generator that generates. We claim 2 wherein said plurality of D-A converter, according to an applied voltage having a terminal which can control the output level, respectively, characterized that you respectively applied said control voltage to the terminal Item 4. The multi-level quadrature amplitude modulator according to Item 1.