JP3230787B2 - Digitized quadrature phase modulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is applied to a digital radio communication system. In particular, it relates to a digitized quadrature phase modulation circuit for modulating a digital signal. The present invention is particularly suitable for use in a transmission circuit using an image suppression type frequency converter.

[0002]

2. Description of the Related Art In a digital radio communication system, a quadrature phase modulation circuit is widely used as a modulation circuit for a digital signal. In addition, digitalization of the circuit of the modulation section has been promoted in view of downsizing, low power consumption, and no adjustment of the device. As a technique for performing quadrature phase modulation in a digital circuit, the one shown in Sakata et al., “Digitized π / 4 Shift QPSK Modulator”, 1993 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers, lecture number B-303 is known. I have. FIG. 2 shows the circuit configuration.

This circuit includes a waveform shaping circuit 201, a selecting circuit 202, a D / A converter 203, and a low-pass filter 204. The waveform shaping circuit 201 receives the in-phase component data 251 and the quadrature component data 252 as input, performs waveform shaping and sign inversion on each of them, and performs in-phase component baseband signal 253 and quadrature component baseband signal 25.
4 is output. The selection circuit 202 alternately selects the in-phase component baseband signal 253 and the quadrature component baseband signal 254 to obtain a quadrature phase modulation signal 255. The D / A converter 203 converts the quadrature-phase modulated signal 255 into an analog signal, and the low-pass filter 204 removes its harmonics and outputs a modulated intermediate frequency signal 256.

Assuming that the waveform-shaped in-phase component baseband signal (the signal before sign inversion) is I (n) and the waveform-shaped quadrature component baseband signal (same as above) is Q (n).
(0), Q (1), -I (2), -Q (3), ..., I (t), Q (t
+1), −I (t + 2), −Q (t + 3),..., By sequentially performing sign inversion and selection, a quadrature phase modulation signal can be obtained. Here, the period in which the minus sign is given is constant, and only the even number is used for the in-phase component side and only the odd number is used for the quadrature component side for the modulation operation. The data is output with a minus sign in advance. The calculation is omitted for data in the order not used for the modulation calculation.

The modulated intermediate frequency signal 25 obtained by this circuit
6 to obtain a radio frequency signal or a higher-frequency modulated intermediate frequency signal, frequency conversion is performed using the mixer 205 and the oscillator 210, and unnecessary frequencies are removed by the bandpass filter 209 for image suppression, or the low-frequency Phase shifter 208, image suppression type frequency converter 20
9. Frequency conversion is performed using the oscillator 210 and the phase shifter 211, and unnecessary frequencies are removed by the image suppression band-pass filter 212. The image suppression type frequency converter 209 is a frequency converter capable of suppressing one side band. Specifically, the image suppression type frequency converter 209 includes two quadrature phase modulation signals whose phases are different from each other by 90 ° and a carrier wave whose phases are different from each other by 90 °. By mixing and adding or subtracting, only one side band can be obtained.

[0006]

However, in this conventional example, when the mixer 205 and the oscillator 206 attempt to obtain a radio frequency signal or a higher frequency modulation intermediate frequency signal, the frequency of the modulation intermediate frequency signal 258 is compared. Bandpass filter 2 for image suppression
07 requires a stopband in the vicinity of the passband, which causes a problem that the difficulty of designing the bandpass filter 207 increases.

On the other hand, a low frequency phase shifter 208, an image suppressing type frequency converter 209, an oscillator 210 and a phase shifter 21
When an attempt is made to obtain a radio frequency signal or a higher-frequency modulated intermediate frequency signal by using 1, the conditions for the image suppression band-pass filter 212 are relaxed, but it is difficult to realize the low-frequency phase shifter 208. There are issues.

An object of the present invention is to solve these problems and to provide a digitized quadrature phase shift modulation circuit capable of shifting the phase of a quadrature phase modulated signal by a digital circuit and outputting the shifted signal.

[0009]

A digitized quadrature phase modulation circuit according to the present invention performs a waveform shaping operation of a baseband waveform of input data and a periodic sign inversion to convert two baseband signals whose phases are orthogonal to each other. Waveform shaping means for outputting, selecting means for selecting the two baseband signals corresponding to their phases to output a quadrature phase modulation signal, and digital / analog conversion for converting the quadrature phase modulation signal into an analog signal Means for selecting the two baseband signals alternately so that the phases of the carrier waves are mutually different.
In this configuration, two quadrature phase modulation signals different by 0 ° are output, and the digital / analog conversion means includes two conversion means for respectively converting the two quadrature phase modulation signals into analog signals. It is preferable to further include two low-pass filters for removing harmonic components of the analog signals output from the two conversion units. The outputs of the two low-pass filters are two quadrature-phase modulated signals whose phases are different from each other by 90 °.
It may be connected to an image-suppressed frequency converter that generates a frequency-converted output in which one sideband is suppressed by performing frequency conversion with a carrier different by 0 ° and performing addition or subtraction.

[0010]

The low frequency phase shifter becomes unnecessary by directly supplying the modulated signal shifted by the digital circuit to the image suppression type frequency converter. Since the image suppression type frequency converter is used, the requirement for the image suppression band-pass filter is reduced.

That is, in the same manner as in the prior art, a first modulated signal subjected to quadrature phase modulation is obtained by alternately selecting waveform shaping outputs for in-phase component data and quadrature component data. On the other hand, by alternating the waveform shaping output for the in-phase component data and the quadrature modulation component data in a different order from the case of the first modulation signal, the phase-shifted second modulation signal for the image suppression type frequency converter Get.

The baseband signals after waveform shaping of the in-phase component data and the quadrature component data are I (n) and Q (n), respectively.
Then, the first modulation signal M1 (n) is given by M1 (n) = I (n) × cos (nπ / 2) + Q (n) × sin (nπ / 2). Since this signal becomes 0 when one of the cosine signal and the sine signal of the orthogonal carrier indicates 1 or −1, the baseband signals are I (0), Q (1), and −.
I (2), -Q (3), ..., I (t), Q (t + 1), -I (t +
2), -Q (t + 3),... Also, the second modulation signal M obtained by shifting the phase of M1 (n) by π / 2.
For 2 (n), M2 (n) = I (n) × cos (nπ / 2 + π / 2) + Q (n) × sin (nπ /
2 + π / 2). The modulated signal M2 (n) is obtained by converting the baseband signal into -Q (0), I (1), Q (2), -I (3), ..., -Q
(t), I (t + 1), Q (t + 2), −I (t + 3),...

The operation of the negative sign is realized by inverting the sign at the time of the waveform shaping operation.

[0014]

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

FIG. 1 is a block diagram showing a digitized quadrature phase modulation circuit according to an embodiment of the present invention. This digitized quadrature phase modulation circuit performs two waveform shaping operations and periodic sign inversion of the baseband waveforms of the in-phase component input data 151 and the quadrature component input data 152 and two baseband signals whose phases are orthogonal to each other, that is, the in-phase component. A waveform shaping circuit 101 that outputs a signal 153 and a quadrature component signal 154; a selection circuit 102 that outputs a quadrature phase modulation signal by selecting the in-phase component signal 153 and the quadrature component signal 154 according to their phases; Digital / analog converting means for converting the modulated signal into an analog signal. Here, a feature of the present embodiment is that the selection circuit 102 alternately selects the in-phase component signal 153 and the quadrature component signal 154 so that the phases of the carrier waves are 90
And outputs two different quadrature phase modulated signals, that is, a first modulated signal 155 and a second modulated signal 156, and converts the two modulated signals 155 and 156 into analog signals as digital / analog converting means. That is, two D / A converters 103 and 104 are provided. Also, two low-pass filters 105 and 106 are provided for removing harmonic components of analog signals output from the D / A converters 103 and 104, respectively.

The waveform shaping circuit 101 outputs the in-phase component data 1
51 and the orthogonal component data 152 are input, and each waveform shaping operation and sign inversion are performed. Waveform shaping circuit 1
01 is set to M (M is 4
If the digital filter sampling timing is 1 to M, the waveform shaping circuit 101 calculates the sign of the waveform shaping operation result for the in-phase component data under the condition given by mod4 (M) = 0 or 3. Is output. For orthogonal component data, an orthogonal component signal 154 is output in which the sign of the waveform shaping operation result is inverted under the condition given by mod4 (M) = 0 or 1. Where mod
4 represents the remainder when dividing by 4.

Here, the in-phase component signal 153 output from the waveform shaping circuit 101 is Xi (n), and the quadrature component signal 154 is Xq (n).
(n), the selection circuit 102 converts each signal into Xi (0), Xq
(1), Xi (2), Xq (3), ..., Xi (M), Xq (M + 1), Xi (M +
2), Xq (M + 3),...
Output as Xq (0), Xi (1), Xq (2), Xi
(3), ..., Xq (M), Xi (M + 1), Xq (M + 2), Xi (M + 3), ...
, And outputs the selected signal as the second modulated signal 156.

The D / A converters 103 and 104 are respectively
The first modulation signal 155 and the second modulation signal 156 are converted into analog signals, and the low-pass filters 105 and 106 are converted.
Output the first and second modulated intermediate frequency signals 157 and 158 by removing the respective harmonics.

The first and second modulated intermediate frequency signals 157 and 158 obtained in this manner are phase-shifted by 90 ° by a digital circuit, and thus have a highly accurate phase relationship. The first and second modulated intermediate frequency signals 15
7 and 158 are inputted to an image suppression type frequency converter constituted by an image suppression type frequency converter 107, an oscillator 108 and a phase shifter 109, and an unnecessary wave is removed from an output thereof by an image suppression band pass filter 110. To obtain a radio frequency signal or a higher frequency modulated intermediate frequency signal.

[0020]

As described above, the digitized quadrature phase modulation circuit of the present invention directly supplies the second modulation signal, which has been phase-shifted by the digital circuit, to the image suppression type frequency converter, The phase shifter can be eliminated. Also, since an image suppression type frequency converter is used,
The requirement for the image suppression bandpass filter is relaxed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a digitized quadrature phase modulation circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

[Explanation of symbols]

101, 201 Waveform shaping circuit 102, 202 Selection circuit 103, 104, 203 D / A converter 105, 106, 204 Low-pass filter 107, 209 Image suppression type frequency converter 108, 206, 210 Oscillator 109, 211 Phase shift Devices 110, 207, 212 Bandpass filters for image suppression 205 Mixers 208 Low frequency phase shifters

Continuation of front page (56) References JP-A-5-244207 (JP, A) JP-A-61-205021 (JP, A) JP-A-63-260247 (JP, A) "High-speed frequency switching π / 4 shift" QPSK modulator ", Kazuhiko Seki, et al., Proceedings of the IEICE 1993 B-311, 1993 (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 27/00-27/38

Claims (3)

(57) [Claims] 1. A waveform shaping means for performing a waveform shaping operation and a periodic sign inversion of a baseband waveform of input data to output two baseband signals whose phases are orthogonal to each other; A digitizing quadrature phase modulation circuit comprising: selecting means for outputting a quadrature phase modulation signal by selecting corresponding to the phase; and digital / analog converting means for converting the quadrature phase modulation signal into an analog signal. The means is configured to alternately select the two baseband signals and output two quadrature-phase modulated signals whose carrier phases are different from each other by 90 °, and the digital-to-analog converting means converts the two quadrature-phase modulated signals. A digitized quadrature phase modulation circuit comprising two conversion means for respectively converting analog signals. 2. The digitized quadrature phase modulation circuit according to claim 1, further comprising two low-pass filters for removing harmonic components of the analog signals output from said two conversion means. 3. The output of the two low-pass filters is:
An image suppression type frequency that generates a frequency conversion output in which one sideband is suppressed by frequency-converting and adding or subtracting two quadrature phase modulation signals having phases different from each other by 90 ° with carrier waves having phases different from each other by 90 °. 3. A circuit according to claim 2, wherein the circuit is connected to a converter.