JP2004215169A - Quadrature modulation circuit and transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a quadrature modulation circuit and a transmitter capable of canceling spurious components with a quadrature modulator by adding a simple circuit to the input side and in which increase of signal sources, increase of the number of components and increase of circuit scale are suppressed as much as possible. <P>SOLUTION: The quadrature modulation circuit is provided with each high-pass type active filer for extracting only noise components from base band signals I, Q, respectively and for amplifying them to be doubled, each synthesizer for compositing the each noise component and differential base band signals I', Q' and for outputting synthetic differential base band signals I'<SB>1</SB>, Q'<SB>1</SB>, respectively and the quadrature modulator for canceling the noise components included in each channel from the respectively corresponding base band signals I, Q and synthetic base band signals I'<SB>1</SB>, Q'<SB>1</SB>and for outputting a modulation signal by local oscillation waves. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a quadrature modulation circuit and a transmitter for obtaining a modulated signal by reducing spurious generated due to a noise component of a baseband signal in a wireless communication system or the like.
[0002]
[Prior art]
There are various schemes for modulating a carrier signal in a wireless communication system or the like. In a wideband-code division multiple access (W-CDMA) system that has recently become widespread, a QPSK (Quadrature Phase Shift Keying) scheme is used. The base station includes a quadrature modulation circuit. FIG. 6 is a block diagram showing a configuration of a conventional quadrature modulation circuit. In the figure, an I-channel baseband signal and an I-channel differential baseband signal are output from a D / A converter 1a. The D / A converter 1b outputs a Q channel baseband signal and a Q channel differential baseband signal. Each baseband signal output from the D / A converters 1a and 1b is input to the quadrature modulator 3, where it is quadrature-modulated by a local oscillation wave input from the local oscillator 2, and output as a radio frequency modulation signal. You.
[0003]
In such a quadrature modulation circuit, the modulation signal output from the quadrature modulator 3 contains sampling noise and the like generated when digital-to-analog conversion is performed by the D / A converters 1a and 1b. This noise component appears as spurious at the frequency near the modulation signal. Spurious signals generated in the vicinity degrade radio performance defined by adjacent channel leakage power and the like. Therefore, the modulation signal output from the orthogonal modulator 3 is passed through the band-pass filter 4 to remove spurious components included in frequencies near the modulation signal. Therefore, it is necessary for the band-pass filter 4 to have a steep attenuation characteristic that allows only the modulation signal to pass therethrough and removes nearby spurious components.
[0004]
As a conventional technique, FIG. 7 shows a configuration of a quadrature modulation circuit used in a wireless system or the like. In the figure, I- and Q-channel baseband signals output from D / A converters 1a and 1b and their respective differential baseband signals are sent to quadrature modulator 3 via low-pass filters 5a, 5b, 5c and 5d. I try to enter it. In this case, spurious components such as sampling noise generated in the baseband signal of each channel are removed by the low-pass filters 5a, 5b, 5c and 5d, respectively. The quadrature modulator 3 performs quadrature modulation by inputting a baseband signal of each channel from which spurious components have been removed and a local oscillation wave output from the local oscillator 2, and outputs a radio frequency modulation signal from the quadrature modulator 3. Is output.
[0005]
Further, as a circuit arrangement of a conventional technique similar to the quadrature modulation circuit of the present invention, a quadrature modulator having a differential input terminal is used, a low-pass filter is provided on the input side, and a DC component is extracted from a baseband signal. There is a quadrature modulation circuit for inputting to a differential input terminal (for example, see Patent Document 1). This is because if a baseband signal contains a DC component, a carrier is output even when there is no modulated signal, a so-called carrier leak, which occupies the frequency and interferes with other communication or wastes. This is to prevent the power consumption from becoming too high.
[0006]
[Patent Document 1]
JP-A-2002-223258 (FIG. 1)
[0007]
[Problems to be solved by the invention]
Since the conventional quadrature modulation circuit is configured as described above, there are the following problems. As shown in FIG. 6, a quadrature modulation circuit including a band-pass filter that allows a specific frequency to pass through the output terminal of the quadrature modulator cannot change the frequency of the modulation signal output from the quadrature modulator. As a result, a heterodyne transmitter will be configured in an actual wireless transmitter, and it will be necessary to add a mixer and a local oscillator for up-converting the modulated signal, increasing the number of signal sources and the number of components. However, there is a problem that the circuit scale is increased.
[0008]
Also, as shown in FIG. 7, in the case of a quadrature modulation circuit that provides a low-pass filter on the input side of the quadrature modulator and removes the noise of the baseband signal that causes spurious in advance, the modulation signal output In order to satisfy wireless characteristics defined by adjacent channel leakage power and the like, it is necessary to sufficiently remove noise components existing in the baseband signal. Therefore, a high-order low-pass filter having a good frequency characteristic is required. However, an increase in the number of components and an increase in the circuit scale have been problems.
[0009]
Further, the circuit described in Patent Document 1 is effective in reducing carrier leak since only the I and Q signals and the extracted DC components are input to the quadrature modulator. I can't do that.
[0010]
The present invention has been made in order to solve the above-described problems, and a simple circuit can be added to the input side to cancel out spurious components with a quadrature modulator.Moreover, the number of signal sources, the number of parts, and the like are increased. An object of the present invention is to obtain a quadrature modulation circuit and a transmitter in which an increase in circuit scale is suppressed as much as possible.
[0011]
[Means for Solving the Problems]
The quadrature modulation circuit according to the present invention includes a D / A converter that outputs an I-channel baseband signal I and its differential baseband signal I ′, a Q-channel baseband signal Q and its differential baseband signal Q ′. , A high-pass type active filter that extracts only noise components from the baseband signals I and Q of each channel and amplifies the noise component by a factor of two, and the respective high-pass type active filters A combiner that combines the noise components output from the filter into the differential baseband signals I ′ and Q ′ of the corresponding channel and outputs the composite differential baseband signals I ′ ₁ and Q ′ ₁ , respectively; corresponding baseband signals I, cancels a noise component contained in Q and synthetic differential baseband signals I _'1, Q' each channel from _1, is input The parts oscillation wave is obtained a quadrature modulator for outputting a modulated signal.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a quadrature modulation circuit according to Embodiment 1 of the present invention. In the figure, a D / A converter 1a outputs an I-channel baseband signal I and its differential baseband signal I ', and the other D / A converter 1b outputs a Q-channel baseband signal Q and its differential signal. The baseband signal Q ′ is output. The baseband signal I output from the D / A converter 1a is branched into two, one of which is input to a high-pass active filter 6a for extracting a noise component. In the baseband signal I input to the high-pass active filter 6a, a fundamental component required for modulation is removed, and a noise component is amplified to a signal level doubled. Noise component of the baseband signal I output from the high-pass active filter 6a is synthesizer 7a 'it is combined with the synthetic differential baseband signals I' differential baseband signal I which is in inverted relationship with _one output I do. The same applies to the Q channel component, and outputs a synthesized differential baseband signal Q _'1 with high-pass active filter 6b, the synthesizer 7b.
[0013]
And the baseband signal I of the I-channel, synthesizer 7a outputted from the combining differential baseband signals I _'1, in the fundamental wave component holds the relationship with inverted level. As for the noise component, the noise component of the differential baseband signal I ′ is doubled with the noise component of the differential baseband signal I ′ which is twice the noise component of the baseband signal I. Will exist. The same applies to the baseband signal Q of the Q channel and the combined differential baseband signal Q ′ _{1. The} fundamental wave component has a relationship of the inverted level, and the noise component has the relationship of the non-inverted level.
[0014]
The I / Q channel baseband signals I and Q and the combined differential baseband signals I ′ ₁ and Q ′ ₁ output from the combiners 7 a and 7 b are combined with the I / Q input and the differential input of the quadrature modulator 3. Input to each terminal. The quadrature modulator 3 performs quadrature modulation by inputting the local oscillation wave output from the local oscillator 2, the baseband signals I and Q of each channel, and the respective combined differential baseband signals I ′ ₁ and Q ′ _1. , Generate a modulated signal. In this case, the fundamental wave component of the baseband signal I Synthesis differential baseband signals I _'1 of I channel from the fact that keeping the inversion level is modulated as it is the modulated signal. Since the noise component is input at the non-inverting level, it is canceled inside the quadrature modulator 3. The same applies to the signal of the Q channel, and the noise component is canceled inside the quadrature modulator 3. As a result, the signal output from the quadrature modulator 3 can reduce spurious noise caused by the noise component of the baseband signal.
[0015]
As described above, according to the first embodiment, the high-pass active filters 6a and 6b respectively extract only the noise components from the baseband signals I and Q of each channel, amplify them by a factor of two, and combine them. The noise components output from the respective high-pass active filters 6a and 6b are combined into differential baseband signals I 'and Q' of the corresponding channels by the filters 7a and 7b, respectively, and the combined differential baseband signal I _'1, Q' ₁ were respectively output by the quadrature modulator 3, corresponding baseband signals I, canceling a noise component contained in Q and synthetic differential baseband signals I _'1, Q' each channel from ₁ As a result, the effect of reducing the noise component can be obtained so that the spurious component does not appear in the modulated signal. Further, the high-pass type active filters 6a and 6b and the combiners 7a and 7b used for that purpose can have a very simple circuit configuration.
[0016]
Embodiment 2 FIG.
FIG. 2 is a block diagram showing a configuration of a quadrature modulation circuit according to Embodiment 2 of the present invention. In the figure, the part different from FIG. 1 is inserted so that the high-pass type active filters 6a and 6b extract the noise components of the I-channel and Q-channel differential baseband signals and amplify them twice, and combiner 7a , 7b combine the baseband signals I, Q corresponding to the noise components of the differential baseband signals I ', Q' of the I channel and the Q channel.
[0017]
In the configuration shown in FIG. 2, noise components of the I-channel and Q-channel differential baseband signals I ′ and Q ′ are respectively extracted and amplified, and then combined with the corresponding baseband signals I and Q as inverted signals. , And the combined baseband signals I ₁ and Q ₁ whose spurious components are non-inverted. By inputting the differential baseband signals I ′ and Q ′ corresponding to the combined baseband signals I ₁ and Q ₁ to the quadrature modulator 3, noise components are canceled inside the quadrature modulator 3. Thereby, generation of spurious can be reduced.
[0018]
As described above, according to the second embodiment of the present invention, only the noise components are extracted from the differential baseband signals I ′ and Q ′ of each channel by the high-pass active filters 6a and 6b, respectively. The noise components output from the high-pass active filters 6a and 6b are combined with the baseband signals I and Q of the corresponding channels by the combiners 7a and 7b, respectively. _1, Q ₁ and outputs respectively, the quadrature modulator 3, respectively corresponding composite baseband signal I _1, Q ₁ and differential baseband signals I ', Q' to cancel the noise components included in each channel from Therefore, the effect of reducing the noise component can be obtained so that the spurious component does not appear in the modulation signal. Further, the high-pass type active filters 6a and 6b and the combiners 7a and 7b used for that purpose can have a very simple circuit configuration.
[0019]
Embodiment 3 FIG.
FIG. 3 is a block diagram showing a configuration of a quadrature modulation circuit according to Embodiment 3 of the present invention. In the figure, the difference from FIG. 1 is that the high-pass active filter 6b is inserted so as to extract the noise component of the Q-channel differential baseband signal Q ′ and amplify it twice, and the combiner 7b The point is that the noise component of the dynamic baseband signal Q and the Q channel baseband signal are combined.
[0020]
In the configuration shown in FIG. 3, the noise components of the I-channel baseband signal I and the Q-channel differential baseband signal Q are respectively extracted and amplified by a factor of two, and then the corresponding differential baseband signal, which is an inverted signal, 'by synthesizing the noise components and the baseband signal Q, spurious component synthetic differential baseband signal I becomes a relationship of non-inverted' signal I to generate a ₁ and synthetic baseband signal Q _1. Therefore, between the baseband signal I of each channel input to the quadrature modulator 3 and the combined differential baseband signal I ′ ₁ , and between the combined baseband signal Q ₁ and the differential baseband signal Q ′, Since the relationship of the fundamental wave component is at the inverted level and the noise component is at the non-inverted level, the noise component is canceled inside the quadrature modulator 3. Thereby, generation of spurious can be reduced.
[0021]
As described above, according to the third embodiment, high-pass active filters 6a and 6b extract only noise components from I-channel baseband signal I and Q-channel differential baseband signal Q ', respectively. The noise components output from the respective high-pass type active filters 6a and 6b are amplified by the combiners 7a and 7b by two times. And outputs a combined differential baseband signal I ′ ₁ and a combined baseband signal Q ₁ , respectively. The quadrature modulator 3 outputs the baseband signal I of the corresponding channel and the combined differential baseband signal I ′ _1. and synthetic base from band signals Q _1, a differential baseband signal Q 'to that as to cancel the noise component contained in each channel , The effect of spurious components to reduce noise components to not appear in the modulated signal is obtained. Further, the high-pass type active filters 6a and 6b and the combiners 7a and 7b used for that purpose can have a very simple circuit configuration.
[0022]
Embodiment 4 FIG.
FIG. 4 is a block diagram showing a configuration of a quadrature modulation circuit according to Embodiment 4 of the present invention. In the figure, the difference from FIG. 1 is that the high-pass type active filter 6a is inserted so as to extract only the noise component of the I-channel differential baseband signal I ′ and amplify the noise component twice, and the combiner 7a The point is that the noise component and the I-channel baseband signal I are combined. The configuration of the fourth embodiment is symmetric with the configuration of the third embodiment.
[0023]
In the configuration shown in FIG. 4, after extracting and amplifying noise components of the I-channel differential baseband signal I ′ and the Q-channel baseband signal Q, respectively, the I-channel baseband signals I and 'by combining the spurious component synthetic baseband signals I ₁ to a relation of the non-inverting synthetic differential baseband signal Q' differential baseband signal Q of the Q-channel to generate _one. Synthesis baseband signals I ₁ and the differential baseband signals I of each channel that is input to the quadrature modulator 3 'between, also a baseband signal Q Synthesis differential baseband signal Q' between the _1, the fundamental The components have an inverted level and the noise components have a non-inverted level, so that the noise components are canceled inside the quadrature modulator 3. Thereby, generation of spurious can be reduced.
[0024]
As described above, according to the fourth embodiment, high-pass active filters 6a and 6b extract only noise components from differential baseband signal I 'of I channel and baseband signal Q of Q channel, respectively. Then, the noise components output from the respective high-pass active filters 6a and 6b are amplified by the combiners 7a and 7b to the baseband signal I and the differential baseband signal Q 'of the corresponding channel. synthesized and synthesized baseband signals I ₁ and synthetic differential baseband signal Q _'1 were respectively output by the quadrature modulator 3, synthesized baseband signal I ₁ and the differential baseband signal I of the corresponding channel' and from the baseband signal Q and the differential baseband signal Q _'1 since so as to cancel the noise components included in each channel, Effect of spurious components to reduce noise components to not appear in the modulated signal is obtained. Further, the high-pass type active filters 6a and 6b and the combiners 7a and 7b used for that purpose can have a very simple circuit configuration.
[0025]
Embodiment 5 FIG.
FIG. 5 is a block diagram showing a configuration of a transmitter according to the fifth embodiment of the present invention, and shows an example of a transmitter to which the quadrature modulation circuit shown in the first embodiment is applied. Detailed description of the quadrature modulation circuit is omitted.
The modulated signal output from the quadrature modulator 3 is filtered by a band-pass filter 8 to remove harmonic components of a local oscillation wave, and is input to a high-frequency amplifier 9. The high-frequency amplifier 9 amplifies the modulated signal to a desired signal level and outputs the signal to the low-pass filter 10. The low-pass filter 10 removes a harmonic component generated when the signal is amplified by the high-frequency amplifier 9, feeds the output modulation signal to the antenna 11, and outputs the signal as a radio wave.
[0026]
As described above, according to the fifth embodiment, by employing the configuration using the quadrature modulation circuit of the first embodiment, it is possible to transmit a modulated signal from which spurious components have been sufficiently removed, and to remove spurious components. The effect of realizing a small transmitter with a reduced number of parts in the configuration of the means is obtained. It should be noted that a similar effect can be obtained in a transmitter to which the quadrature modulation circuit according to the second to fourth embodiments is applied.
[0027]
【The invention's effect】
As described above, according to the present invention, for the I-channel and the Q-channel input to the quadrature modulator with differential input terminals, the fundamental wave component and the baseband signal whose noise components are in a non-inverting level relationship. By generating and inputting differential baseband signals, noise components are canceled out in the quadrature modulator to obtain a modulated signal.Therefore, there is an effect of reducing spurious generated in the modulated signal. The components to be added are only a small high-pass type active filter and a combiner, and have an effect of realizing a quadrature modulation circuit capable of effectively removing spurious signals with a small number of components.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a quadrature modulation circuit according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a quadrature modulation circuit according to a second embodiment of the present invention.
FIG. 3 is a block diagram showing a configuration of a quadrature modulation circuit according to a third embodiment of the present invention.
FIG. 4 is a block diagram showing a configuration of a quadrature modulation circuit according to a fourth embodiment of the present invention.
FIG. 5 is a block diagram showing a configuration of a transmitter according to Embodiment 5 of the present invention.
FIG. 6 is a block diagram showing a configuration of a conventional quadrature modulation circuit.
FIG. 7 is a block diagram showing another configuration of a conventional quadrature modulation circuit.
[Explanation of symbols]
1a, 1b D / A converter, 2 local oscillator, 3 quadrature modulator, 6a, 6b high-pass active filter, 7a, 7b combiner, 8 band-pass filter, 9 high-frequency amplifier, 10 low-pass filter, 11 antenna .

Claims (5)

A D / A converter that outputs an I-channel baseband signal I and a differential baseband signal I ′;
A D / A converter that outputs a Q-channel baseband signal Q and a differential baseband signal Q ′;
A respective high-pass type active filter for extracting only noise components from the baseband signals I and Q of each channel and amplifying the noise components twice,
The noise components output from the respective high-pass type active filters are combined with the differential baseband signals I ′ and Q ′ of the corresponding channel to generate the combined differential baseband signals I ′ ₁ and Q ′ ₁ , respectively. Each synthesizer to output,
A quadrature modulator that cancels noise components included in each channel from the corresponding baseband signals I and Q and the combined differential baseband signals I ′ ₁ and Q ′ ₁ and outputs a modulation signal by an input local oscillation wave. And a quadrature modulation circuit comprising: A D / A converter that outputs an I-channel baseband signal I and a differential baseband signal I ′;
A D / A converter that outputs a Q-channel baseband signal Q and a differential baseband signal Q ′;
A high-pass type active filter for extracting only noise components from the differential baseband signals I ′ and Q ′ of each channel and amplifying the noise components twice,
A combiner for combining each noise component output from each of the high-pass type active filters with baseband signals I and Q of a corresponding channel to output synthesized baseband signals I ₁ and Q ₁ , respectively;
A quadrature modulator that cancels noise components included in each channel from the corresponding combined baseband signals I ₁ and Q ₁ and the differential baseband signals I ′ and Q ′ and outputs a modulation signal by an input local oscillation wave. And a quadrature modulation circuit comprising: A high-pass active filter for extracting noise components of the I-channel baseband signal and the Q-channel differential baseband signal and amplifying the noise component twice;
A quadrature modulation circuit comprising a combiner for combining a noise component output from the high-pass active filter into an I-channel differential baseband signal and a Q-channel baseband signal. A high-pass active filter for extracting noise components of the I-channel differential baseband signal and the Q-channel baseband signal and amplifying the noise component twice;
A quadrature modulation circuit comprising a combiner for combining a noise component output from the high-pass active filter into an I-channel baseband signal and a Q-channel differential baseband signal. A first high-pass active filter that extracts only a noise component from one of a baseband signal I output from an I-channel D / A converter and a differential baseband signal I ′ and amplifies the noise component twice When,
A second high-pass active filter that extracts only a noise component from one of a baseband signal Q output from a Q-channel D / A converter and a differential baseband signal Q ′ and amplifies the noise component twice. When,
A combiner that combines the noise component output from the first high-pass type active filter with the corresponding differential baseband signal I ′ or baseband signal I and outputs a composite signal I ′ ₁ or I ₁ ;
A combiner that combines the noise component output from the second high-pass type active filter with a corresponding differential baseband signal Q ′ or baseband signal Q and outputs a combined signal Q ′ ₁ or Q ₁ ;
From the respectively corresponding baseband signal I or differential baseband signal I ′ and the combined signal I ′ ₁ or I _1, and simultaneously with the baseband signal Q or differential baseband signal Q ′ and the combined signal Q ′ ₁ or Q ₁ A quadrature modulator that cancels noise components included in each channel from and outputs a modulation signal by an input local oscillation wave;
A high-frequency amplifier that amplifies the output modulated signal,
A transmitter provided with an antenna to which the amplified modulated signal is fed and transmitted as a radio wave.

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