JP2005252931A - Orthogonal modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an orthogonal modulator capable of easily attenuating transmission spurious caused by signals of two input frequencies existent in a mixer output or of frequencies of its sum and its difference inside the orthogonal modulator or by using a filter that is inserted after outputting. <P>SOLUTION: The orthogonal modulator comprises a phase shifter 5 for generating two signals having a phase difference of 90° from an output of a first local oscillator 1; an orthogonal modulating circuit 6 for obtaining a modulated wave signal by integrating and adding a baseband I signal and a baseband Q signal, respectively; a mixer 9 for performing frequency conversion up to a carrier frequency by integrating the modulated wave signal output by the modulating circuit 6 and an oscillation signal of a second local oscillator 3; and an amplifier 10 for amplifying and outputting an output signal of the mixer. An fIF signal output by the mixer is attenuated by a trap circuit 12 which attenuates the neighborhood of frequencies of the signals generated by the phase shifter, thereby reducing spurious in a transmission output caused by non-linearity of an amplifier on a post-stage or the like. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a quadrature modulator used in a transmission unit of a mobile terminal, and is particularly configured so that a spurious component is not included in a modulated wave signal.

  In recent years, quadrature modulators that constitute a modulation unit that performs multilevel digital modulation such as quadrature phase shift keying (QPSK) have become common in mobile communications.

  FIG. 2 is a block diagram showing a configuration of a conventional general quadrature modulator. In FIG. 2, 1 is a first local oscillator (hereinafter referred to as VCO1), 2 is an input terminal of VCO1, 3 is a second local oscillator (hereinafter referred to as VCO2), and 4 is an input terminal of VCO2. Reference numeral 5 denotes a phase shifter that generates a carrier wave having a phase difference of 90 degrees with higher accuracy than the local oscillation signal generated by the VCO1. In order to generate an intermediate carrier wave having a phase difference of 90 degrees in this way, for example, a method of dividing by four is known, and the frequency of the first local oscillator 1 is previously oscillated at a frequency four times that of the intermediate carrier wave. It is necessary to keep it. Reference numeral 6 denotes a quadrature modulation circuit that modulates the intermediate carrier wave generated by the phase shifter and having a phase difference of 90 degrees with a baseband signal, and includes a multiplier 6a and 6b and an adder 6c. . Reference numeral 7 is an input terminal for a baseband I signal, and 8 is an input terminal for a baseband Q signal. Reference numeral 9 denotes a mixer that obtains a desired transmission carrier frequency by mixing the modulated wave signal output from the quadrature modulator 6 and the oscillation signal generated by the second local oscillator 3, and 10 is an amplifier that amplifies the transmission carrier. , 11 are transmission carrier output terminals.

  Next, the operation will be described. The local oscillator 1 generates a first local oscillation signal having a frequency four times that of the carrier wave. This first local oscillation signal is input to the phase shifter 5 from the input terminal 2 of the VCO 1 and is divided by 4 by the phase shifter to become an intermediate carrier having a phase difference of 90 degrees. After a modulated wave signal is obtained by integrating and adding the baseband I signal and the baseband Q signal input from the terminals 7 and 8 respectively, the second local part input from the modulated wave signal and the input terminal 4 The second oscillation signal of the oscillator 3 is integrated by a mixer 9 to obtain a modulated wave signal frequency-converted to a carrier frequency, amplified by an amplifier 10 and output from an output terminal 11.

The frequency fIF * 4 of the first local oscillator 1 and the frequency fLo of the second local oscillator 3 are set so as to be, for example, fc = fLo + fIF with respect to the carrier frequency fc. Here, the frequency of the difference (fLo-fIF) (hereinafter referred to as an image component) is a signal generated in the calculation, and it is necessary to insert and remove a filter in the subsequent stage. Further, the frequencies of fIF and fLo are generally set to satisfy the relationship of fIF << fLo in order to ensure the modulation accuracy of the modulator. Patent Document 1 discloses such a modulator.
JP-A-7-226890

  However, in addition to the sum frequency of the desired transmission carrier wave, the frequency of the difference (fIF-fLo), fIF, fLo and their respective harmonic signals are present at the output of the mixer 9. This is because the mixer circuit generally uses a double balance type circuit in order to reduce the output other than the desired output, and the signals of fIF and fLo frequencies cancel each other out by 180 degrees in phase and are ideal. However, the phase difference of 180 degrees is shifted due to the influence of DC offset of the differential circuit and parasitic resistance and parasitic capacitance between the wiring of the preceding stage and the fIF and fLo signals. Spurious is caused by passing through a non-linear circuit in the amplifier in the mixer or in the subsequent stage.

  Here, considering the occurrence of spurious when the fIF and fLo signals are output, fLo + 2 is generated by the combination of fLo + fIF, fLo-fIF and fIF generated at the mixer output. Similarly, * fIF, fLo, fLo-2 * fIF generates spurious of 2 * fLo + fIF, fIF, 2 * fLo-fIF by a combination of fLo + fIF, fLo-fIF and fLo. Here, looking at the above spurious frequency, it is separated by + fIF, -fIF (= fLo), -2 * fIF, fLo, -fIF (= fLo), -fIF compared to the desired transmission carrier fLo + fIF. It becomes frequency. That is, a spurious signal is generated at a position away from the desired transmission carrier fLo + fIF by ± fIF, and the −fIF signal has the same frequency as the fLo signal (hereinafter, the fLo spurious signal is referred to as a local leak). Considering that fIF << fLo, a signal of ± fLo of a desired transmission carrier has a frequency farther than that of ± IF, and can be sufficiently attenuated by a filter inserted in order to reduce image components. .

  However, the local leak and the spurious of the desired transmission carrier + fIF are closer to the transmission carrier than the image components, and thus cannot be sufficiently attenuated. As a result, local leaks remain in the transmission output, causing the modulation accuracy to deteriorate, or causing local leaks to VCO2 to deteriorate the characteristics. In order to prevent this, it is necessary to take measures such as narrowing the subsequent filter.

  In view of the above, an object of the present invention is to reduce the spurious, particularly local leak.

  To achieve the above object, the quadrature modulator according to the present invention integrates and adds a phase shifter that generates two orthogonal signals from the output of the first local oscillator, a baseband I signal, and a baseband Q signal, respectively. And a quadrature modulator that obtains a modulated wave signal, and a trap that attenuates only the fIF signal to the same output as the mixer that converts the frequency to the carrier frequency by integrating the modulated wave signal and the oscillation signal of the second local oscillator. A circuit and an amplifier that amplifies and outputs the modulated wave signal are provided.

  The quadrature modulator according to the present invention can reduce the fIF signal of the mixer output, and can reduce the spurious due to the combination with the fIF generated by the non-linearity of the subsequent amplifier or the like.

(First embodiment)
Hereinafter, a quadrature modulator according to a first embodiment of the present invention will be described with reference to the drawings.

  First, as shown in FIG. 1, 1 is a first local oscillator (hereinafter referred to as VCO1), 2 is an input terminal of VCO1, 3 is a second local oscillator (hereinafter referred to as VCO2), and 4 is an input terminal of VCO2. It is. Reference numeral 5 denotes a phase shifter that generates a carrier wave having a phase difference of 90 degrees with higher accuracy than the local oscillation signal generated by the VCO1. In order to generate an intermediate carrier wave having a phase difference of 90 degrees in this way, for example, a method of dividing by four is known, and the frequency of the first local oscillator 1 is previously oscillated at a frequency four times that of the intermediate carrier wave. It is necessary to keep it. Reference numeral 6 denotes a quadrature modulation circuit that modulates the intermediate carrier wave generated by the phase shifter and having a phase difference of 90 degrees with a baseband signal, and includes a multiplier 6a and 6b and an adder 6c. . Reference numeral 7 is an input terminal for a baseband I signal, and 8 is an input terminal for a baseband Q signal. Reference numeral 9 denotes a mixer that obtains a desired transmission carrier frequency by mixing the modulated wave signal output from the quadrature modulator 6 and the oscillation signal generated by the second local oscillator 3, and 12 denotes an fIF signal output from the mixer. The trap circuits 13 and 14 are mixer output terminals. Reference numeral 10 denotes an amplifier for amplifying a transmission carrier wave, and 11 denotes a transmission carrier output terminal.

  With the above configuration, the fIF signal is attenuated by the trap circuit 12 at the output of the mixer 9, and spurious due to the combination of the fIF generated by the non-linearity of the subsequent amplifier and the desired transmission carrier or image component can be reduced. Similarly, spurious due to a combination of fIF harmonics, carrier wave signals, image components, and the like can be reduced.

  The quadrature modulator according to the present invention can reduce spurious such as local leak and is useful for configuring a transmitter with little deterioration in modulation accuracy.

The block diagram which shows the structure of the quadrature modulator in the 1st Embodiment of this invention Block diagram showing the configuration of a conventional quadrature modulator

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st local oscillator 2 VCO1 input terminal 3 2nd local oscillator 4 VCO2 input terminal 5 Phase shifter 6 Quadrature modulation circuit 6a Multiplier 6b Multiplier 6c Adder 7 Baseband I signal input terminal 8 Baseband Q signal input terminal 9 Mixer 10 Amplifier 11 Transmission carrier output terminal 12 fIF trap circuit 13 Mixer output terminal 14 Mixer output terminal

Claims (1)

A phase shifter that generates two orthogonal signals from the output of the first local oscillator, an orthogonal modulator that obtains a modulated wave signal by integrating and adding the baseband I signal and the baseband Q signal, and the orthogonal A mixer that integrates the modulated wave signal output from the modulator and the oscillation signal of the second local oscillator to integrate the frequency to the carrier frequency, and a trap that attenuates the vicinity of the oscillation frequency of the first local oscillator to the output of the mixer An orthogonal modulator comprising a circuit and an amplifier that amplifies and outputs an output signal of the mixer.

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