JPH06112986A - Orthogonal amplitude modulator - Google Patents

Abstract

PURPOSE:To enhance the degree of circuit integration of a circuit by adding phase addition data by an accumulator, converting phase data into amplitude data by a ROM and using a multiplexer so as to select and modulate the amplitude/phase to be outputted. CONSTITUTION:The modulator is provided with an accumulator 1 adding phase increase data, a read only memory(ROM) 2 storing a sinusoidal waveform table to convert the phase of the output into an amplitude, a D/A converter 4 converting phase/amplitude data into an analog amplitude, and a multiplexer 3 selecting input data with a different phase/amplitude to the D/A converter 4. Then phase data being phase adding data are added to the accumulator 1 synchronously with the clock CK of a prescribed period. The phase output is converted into sinusoidal wave amplitude data by the ROM 2. Then data having amplitude/phase to be outputted in the amplitude data converted by the ROM 2 are selected by the multiplexer 3 and the selected data are converted into an analog level by the D/A converter 4 and the result is outputted as an output modulation wave.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quadrature amplitude modulator,
In particular, it relates to a direct modulation quadrature amplitude modulator.

[0002]

2. Description of the Related Art An example of a conventional quadrature amplitude modulator will be described with reference to FIG. In the conventional quadrature amplitude modulator, as shown in FIG. 3, a code converter 11 that receives signal data as an input and divides the input signal into two quadrature components, and this code converter 11
From I to Q data as input, and D / A converters 12a and 12 for converting respective signal components into amplitude values
b and multipliers 13a and 13b for modulating a sine wave orthogonal to each other with the amplitude signals from the D / A converters 12a and 12b.
And an adder 14 for synthesizing the outputs of the multipliers 13a and 13b. Reference numeral 15 is a 1/4 wavelength delay line. The I data indicates in-phase data, and the Q data indicates quadrature phase data. Then, k represents a k-bit bus, and m represents an m-bit bus.

[0003]

In this conventional quadrature amplitude modulator, an analog circuit is frequently used, and there is a problem that it is difficult to integrate the circuit. Further, when a plurality of synchronized modulation signals are required, there is a problem that it is necessary to configure the same circuit as the number of signals.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a quadrature amplitude modulator which increases the degree of integration of the circuit by replacing the analog circuit in the quadrature amplitude modulator with a digital circuit. And

[0005]

A quadrature amplitude modulator of the present invention is a read-only recording of an accumulator for adding phase increase data and a sine wave waveform table for converting the phase of the output of this accumulator into an amplitude value. Memory and
A D / A converter for converting the phase / amplitude data into an analog amplitude and a multiplexer for switching the input data of the D / A converter having different phases / amplitudes are provided.

[0006]

In the present invention, the phase addition data is added by the accumulator, the output phase data is converted into amplitude data by the read-only memory, and the amplitude / phase to be output is selected and modulated by the multiplexer.

[0007]

1 is a block diagram showing an embodiment of a quadrature amplitude modulator according to the present invention. In FIG. 1, reference numeral 1 is an accumulator for inputting phase addition data via a k-bit bus and adding phase increase data 2 ₁ , 2 ₂ ... 2
_n is a read-only memory (ROM) 4a, 4b in which phase data is input from the accumulator 1 via an l-bit bus and a sine wave waveform table for converting the phase of the output of the accumulator 1 into an amplitude value is recorded. Is a D / A converter that converts phase / amplitude data into analog amplitude,
3a and 3b are D / A converters 4a and 4 having different phases and amplitudes.
It is a multiplexer for switching the input data of b.

Here, the ROMs 2 ₁ , 2 ₂ ... 2 _n are connected to the multiplexers 3a and 3b via an m-bit bus, and these multiplexers 3a and 3b are D / A via an n-bit bus. The D / A converters 4a and 4b are respectively connected to the D / A converters 4a and 4b so that output modulated waves A and B can be obtained. C
K is a clock, and this clock CK is accumulator 1
And D / A converters 4a and 4b, respectively.
The external phase / amplitude selection signal is supplied to the multiplexers 3a and 3b via the s-bit bus.

Next, the operation of the embodiment shown in FIG. 1 will be described. First, the phase data, which is the phase addition data, is added to the accumulator 1 in synchronization with the clock CK having a constant cycle. The phase output which is the phase data of the accumulator 1 is converted into sine wave amplitude data by the read only memory (ROM) 2. Next, each amplitude data converted by the ROM 2 is selected by the multiplexer 3 as the amplitude and phase to be output, and then converted into an analog amplitude by the D / A converter 4 and output as an output modulated wave. To be done.

FIG. 2 is an explanatory diagram showing a constellation example (16QAM) of a quadrature amplitude modulation wave generated by the present invention. In FIG. 2, I indicates in-phase and Q indicates quadrature. The waveform data in the read-only memory corresponds to each black dot that represents 4-bit data.

[0011]

As described above, according to the present invention, the phase addition data is added by the accumulator, the output phase data is converted into the amplitude data by the read-only memory, and the amplitude / phase to be output by the multiplexer. Since the analog circuit does not exist up to the final stage D / A converter because it is selected and modulated, there is an effect that the circuit can be easily integrated, and a plurality of tuned modulation signals are required. In this case, there is an effect that it is sufficient to connect a plurality of multiplexers and D / A converters.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a quadrature amplitude modulator according to the present invention.

FIG. 2 is an explanatory diagram showing an example of a constellation of a quadrature amplitude modulation wave generated by the present invention.

FIG. 3 is a block diagram showing an example of a conventional quadrature amplitude modulator.

[Explanation of symbols]

1 phase accumulator 2 ₁ to 2 _n read-only memory 3a, 3b multiplexer 4a, 4b D / A converter

Claims (1)

[Claims] 1. An accumulator for adding phase increase data, a read-only memory recording a sine wave waveform table for converting a phase of an output of the accumulator into an amplitude value, and phase / amplitude data into an analog amplitude. A quadrature amplitude modulator comprising a D / A converter and a multiplexer for switching input data of the D / A converter having different phases and amplitudes.