JP2010245962A - Modulation apparatus and modulation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modulation apparatus capable of reducing cost, while reducing circuit scale. <P>SOLUTION: A modulation apparatus includes a signal processor 11 for performing quadrature modulation on a digital signal and converting the digital signal into an I-signal and a Q-signal; a timing generator 13 for generating a first timing signal of a reference frequency; first and second D/A converters 12a, 12b each for performing analog conversion on the I signal and the Q-signal in accordance with a clock of 1/4 reference frequency; and a gate control switch 14 for polarity-inverting the I-signal and the Q-signal, in accordance with a second timing signal which is obtained by frequency-dividing the first timing signal into two, and alternately outputting the I signal and the Q-signal, in accordance with the first timing signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a modulation apparatus and a modulation method used for a radio base station or the like.

  A device that outputs a modulated signal such as a transmitter of a radio over fiber (ROF) or a transmitter of a base station that relays wireless communication between a mobile phone base station and a mobile phone terminal as a radio wave of an RF signal, First, after performing digital signal processing on the transmission signal, analog signal conversion using a D / A converter is performed to convert the signal to an RF frequency.

  This RF frequency conversion process is either an analog signal is converted to an RF frequency by an analog modulation circuit or a frequency conversion circuit, or a digital signal is operated at a high speed by a D / A converter to directly obtain an RF frequency. It is realized by. In the former case, the circuit scale is increased, and in the latter case, the device itself is expensive, and the cost burden is large in any of the methods.

  In addition, as a well-known document relevant to this application, there exist the following, for example (refer patent document 1).

JP-A-6-2444876

  The present invention has been made paying attention to the above circumstances, and an object thereof is to provide a modulation device and a modulation method capable of reducing the cost while reducing the circuit scale.

  In order to achieve the above object, an aspect of the present invention includes a signal processing unit that orthogonally modulates a digital signal to convert it into an I signal and a Q signal, a timing generator that generates a first timing signal of a reference frequency, First and second D / A converters for analog conversion of the I signal and Q signal with a clock of 1/4 of the reference frequency, and a second timing signal obtained by dividing the first timing signal by two Accordingly, there is provided a modulation apparatus comprising gate means for inverting the polarity of the I signal and the Q signal and alternately outputting the I signal and the Q signal according to the first timing signal.

  According to another aspect of the present invention, a digital signal is orthogonally modulated and converted into an I signal and a Q signal to generate a first timing signal having a reference frequency, and the I signal and the Q signal are The analog signal is converted with a clock of / 4, the I signal and the Q signal are inverted in polarity according to the second timing signal obtained by dividing the first timing signal by 2, and the I signal and the I signal according to the first timing signal A modulation method for alternately outputting Q signals is provided.

  Therefore, according to the present invention, it is possible to provide a modulation device and a modulation method capable of reducing the cost while reducing the circuit scale.

The block diagram which shows one Embodiment of the modulation apparatus which concerns on this invention. The figure which shows the waveform in the time domain of the output signal of each part in the modulation apparatus of FIG. The figure which shows the waveform in the frequency domain of the output signal of each part in the modulation apparatus of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In this embodiment, a modulation apparatus and a modulation method for directly converting a digital signal for transmission into an analog RF signal are proposed. FIG. 1 is a block diagram showing an embodiment of a modulation device according to the present invention. The modulation device includes a signal processing unit 11, a first D / A converter 12a (DAC0), a second D / A converter 12b (DAC1), a timing generation unit 13, and a gate control switch 14. . Further, an amplifier 15 and an antenna 16 are provided at the end of the modulation device, and an analog RF signal modulated by the modulation device is amplified by the amplifier 15 and then transmitted from the antenna 16.

  FIG. 2 shows the waveform in the time domain of the output signal of each part in the modulation device of FIG. The signal processing unit 11 orthogonally modulates the digital signal for transmission and converts it into an I / Q signal, and outputs the I signal to the DAC 0 and the Q signal to the DAC 1. The timing generation unit 13 generates a selection timing signal of the reference frequency Fs (500 MHz), and operates the DAC0 and DAC1 with a sampling clock (125 MHz) that is ¼ of the reference frequency Fs. Observing the I and Q signals analog-converted by DAC0 and DAC1, the waveforms in the time domain are as shown in FIG. 2 (DAC0 output, DAC1 output in FIG. 2).

  The timing generation unit 13 gives the generated selection timing signal to the gate control switch 14 (selection timing 0 in FIG. 2). The gate control switch 14 divides the selection timing signal by 2 (selection timing 1 in FIG. 2), and x1 (normal rotation) when the selection timing 1 is High with respect to the I signal output from the DAC0. When it is low, x-1 (polarity inversion) is performed (DAC0 switch in FIG. 2). Similarly, the gate control switch 14 performs x1 (normal rotation) when the selection timing 1 is High, and x-1 (polarity inversion) when the selection timing 1 is Low, with respect to the Q signal output from the DAC0. (DAC1 switch in FIG. 2). Further, the gate control switch 14 selects the DAC0 switch when the selection timing 0 is High, selects the DAC1 switch when the selection timing 0 is Low, and outputs a gate signal obtained by combining the I signal and the Q signal (see FIG. 2 middle gate output).

  FIG. 3 shows a waveform in the frequency domain of the output signal of each part in the modulation device of FIG. Thus, switching the DAC output by the selection timing signal means that the I component DAC0 is multiplied by COS (250 MHz × t), and the Q component DAC1 is multiplied by SIN (250 MHz × t) to perform IQ synthesis. In other words, the operation is the same as performing complex modulation.

  In normal interpolation, only one DAC is used. However, in this case, the band that can be reproduced is only 1/8 of the reference frequency Fs based on the principle of sampling. Further, since the power is distributed to each image generated by the interpolation, the power is reduced by the amount corresponding to the interpolation of the power value of the desired frequency. In the present embodiment, a band that is 1/4 and twice the reference frequency can be used. Also, since power is weighted on the image, it can be output with almost no deterioration.

  Therefore, according to the above embodiment, it is possible to realize a modulation device that directly converts a digital signal into an analog RF signal with a simple configuration using an inexpensive D / A converter that is relatively slow.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. For example, here, the operation has been described when the ratio of the clock to the DAC and the gate switch is 1: 4, but an integer ratio different from this may be used. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 11 ... Signal processing part, 12a ... 1st D / A converter (DAC0), 12b ... 2nd D / A converter (DAC1), 13 ... Timing generation part, 14 ... Gate control switch, 15 ... Amplifier, 16 ... antenna.

Claims (2)

A signal processing unit that orthogonally modulates a digital signal to convert it into an I signal and a Q signal;
A timing generator for generating a first timing signal of a reference frequency;
First and second D / A converters for analog conversion of the I signal and the Q signal with a clock of 1/4 of the reference frequency;
Gate means for inverting the polarity of the I signal and the Q signal according to a second timing signal obtained by dividing the first timing signal by 2, and alternately outputting the I signal and the Q signal according to the first timing signal And a modulation device. Digital signal is quadrature modulated and converted into I signal and Q signal,
Generating a first timing signal of a reference frequency;
The I signal and the Q signal are converted into analog signals with a clock of 1/4 of the reference frequency,
Inverting the polarity of the I signal and the Q signal according to the second timing signal obtained by dividing the first timing signal by 2, and alternately outputting the I signal and the Q signal according to the first timing signal. A characteristic modulation method.

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