JPH0637837A - Multilevel quadrature amplitude modulator - Google Patents

Abstract

PURPOSE:To provide a multilevel quadrature amplitude modulator of high quality by compensating surely the fluctuation of the output level which is caused by the temperature change of a D/A converter. CONSTITUTION:The D/A converters 1 and 2 receive the digital signals D11, D12, D21 and D22 and convert them into the base band signals B1 and B2 having the quadruple amplitude. The differential amplifiers 3 and 4 receive the signals B1 and B2 and transmits them as the smoothed base band signals B1p and B1n of positive phases and the signals B2p and B2n of the negative phases respectively. Meanwhile, the output levels are controlled in response to the control voltage Vc1 and Vc2. A multiplier 5 receives the signals B1p-B2n and produces a multilevel quadrature amplitude modulated signal Sm. The average calculating parts 61 and 71 of the control voltage generating circuits 6 and 7 calculate the average levels of the signals B1p-B2n respectively. Then, the voltage generating parts 62 and 72 generates the voltage Vc1 and Vc2 so as to set the difference of the average levels at zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-valued quadrature amplitude modulation device, and more particularly to a multi-valued quadrature amplitude modulation device for generating a multi-valued quadrature amplitude modulation signal from positive-phase and anti-phase multi-valued 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 apparatus, and shows a case where a 16-level quadrature amplitude modulation signal is generated.

Here, the D-A converters 1 and 2 are each 2
Column digital signals D11, D12 and D21, D2
It receives 2 and converts it into baseband signals B1 and B2 each having a 4-valued amplitude. Differential amplifiers 3 and 4
Receives baseband signals B1 and B2, and the balanced baseband signals B1p and B1 of positive phase and negative phase, respectively.
1n and B2p and B2n are transmitted. Multiplier 5
Are balanced baseband signals B1p, B1n and B2
p, B2n are received and multiplied, and the multilevel quadrature amplitude modulation signal Sm is received.
To generate. After that, although not shown, the carrier is modulated by the multi-level quadrature amplitude modulation signal Sm.

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

In order to compensate the output level fluctuation due to the temperature change of the DA converter, the control voltage generating circuit 8 is used.
Is provided to generate the control voltage Vc and supply it to the differential amplifiers 3 and 4, and the baseband signals B1p, B1n, B2p and B2
The level of n is controlled so as not to change. The control voltage generation circuit 8 generates the control voltage Vc by utilizing the temperature characteristics of a diode or a transistor, for example.

[0006]

In the above-mentioned conventional multi-valued quadrature amplitude modulation device, in order to compensate the output level fluctuation due to the temperature change of the DA converter, control is performed by utilizing the temperature characteristic of the diode or the transistor. A voltage is generated and this control voltage is supplied to the differential amplifier to control the output level. However, since the temperature characteristics of the D-A converters are different from each other, it is difficult to surely compensate, the modulation quality is deteriorated, and the control voltage adapted to the temperature characteristics of each D-A converter is not only reduced. There is a problem that it takes a long time to adjust.

An object of the present invention is to provide DAs having different temperature characteristics.
An object of the present invention is to provide a multi-level quadrature amplitude modulation device that can reliably and easily compensate for level fluctuations of a D-A converter even if a converter is used and realize high-quality modulation.

[0008]

A multilevel quadrature amplitude modulation apparatus according to the present invention includes a plurality of DA converters for receiving digital signals and converting the signals into multilevel amplitude baseband signals, and the plurality of DA converters. A plurality of differential amplifiers that are provided corresponding to the A converters to generate balanced baseband signals of positive phase and negative phase from the baseband signal and to control and output the output levels according to the respective control voltages; A means for receiving multi-valued quadrature amplitude modulation by receiving the balanced baseband signals transmitted by the plurality of differential amplifiers, and a control voltage provided from the balanced baseband signals provided corresponding to the plurality of differential amplifiers. And a plurality of control voltage generating means for generating each. The plurality of DA converters may each have a terminal capable of controlling an output level according to an applied voltage, and the terminals may receive the control voltage. Further, the plurality of control voltage generating means, an average calculation unit for calculating the average level value by detecting the maximum level value and the minimum level value of each of the positive and negative phase signals of the balanced baseband signal, A voltage generator that calculates the difference between the average level values of the positive-phase and negative-phase signals calculated by the average calculator and generates the control voltage so that the difference becomes zero may be configured. Good.

[0009]

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. The same parts as those of the conventional multilevel quadrature amplitude modulator shown in FIG. 4 are designated by the same reference numerals. Here, what is different from the conventional example is that the control voltage generating circuits 6 and 7 are provided.

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

Further, the control voltage generation circuits 6 and 7 generate control voltages Vc1 and Vc2 for compensating the output level fluctuation of the DA converter due to the temperature change and supply them 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 fluctuation of the DA converter.

By the way, the control voltage generating circuits 6 and 7
Are balanced baseband signals B1p, B1n and B2
It has average calculating sections 61 and 71 for calculating respective average level values of p and B2n, and voltage generating sections 62 and 72 for generating control voltages Vc1 and Vc2 based on the difference between the calculated average level values. There is.

Now, as shown in FIG. 3, for example, the levels of the positive-phase baseband signal B1p are set to p1, p2, p3.
p4 and the level of the anti-phase baseband signal B1n is n
1, n2, n3, n4, the control voltage generating circuit 6
The average calculation unit 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 are calculated. The voltage generator 62 calculates the difference ΔV between the average level values Vp and Vn, generates the control voltage Vc1 that makes ΔV zero, and sends it 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, the output level fluctuations of the DA converters 1 and 2 due to temperature changes can be compensated for.

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

The same parts as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals. Here, what is different from the first embodiment is that the D- having a terminal capable of setting an output level.
That is, the A converters 9 and 10 are provided and the control voltages Vc1 and Vc2 are supplied to control the output level.

In this case, the D-A converters 9 and 10 are each 2
Column digital signals D11, D12 and D21, D2
Control voltage Vc1, Vc2 applied to each of the two
Baseband signals B1 and B2 having output levels according to
Converted to and output.

Even with this structure, D
It is obvious that the output level fluctuations of the −A converters 1 and 2 can be compensated.

[0020]

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

[Brief description of 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 for explaining the operation of the control voltage generating circuit shown in FIGS.

FIG. 4 is a block diagram showing an example of a conventional multilevel quadrature amplitude modulator.

[Explanation of symbols]

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

Claims (3)

[Claims] 1. A plurality of DA converters for receiving digital signals respectively and converting them into multi-valued amplitude baseband signals, and a plurality of DA converters provided corresponding to the plurality of DA converters. A plurality of differential amplifiers that generate positive-phase and negative-phase balanced baseband signals and control and output the output levels according to each control voltage, and a balanced baseband signal sent by the plurality of differential amplifiers. And a plurality of control voltage generating means that are provided corresponding to the plurality of differential amplifiers and that respectively generate the control voltage from the balanced baseband signal. And a multilevel quadrature amplitude modulator. 2. The plurality of DA converters each have a terminal capable of controlling an output level according to an applied voltage, and each of the terminals receives the control voltage. A multilevel quadrature amplitude modulator as described. 3. An average calculation in which the plurality of control voltage generation means detect the maximum level value and the minimum level value of each of the positive-phase and negative-phase signals of the balanced baseband signal, and calculate the average level value. And a voltage generator that calculates the difference between the average level values of the positive-phase and negative-phase signals calculated by the average calculator, and generates the control voltage so that the difference becomes zero. Claim 1 or 2
A multilevel quadrature amplitude modulator as described.