JP2008278035A - Quadrature modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain excellent modulation precision by a quadrature modulator using even-harmonic mixers. <P>SOLUTION: A 1/4-wavelength line (ÐRF frequency) 13 as a first impedance transforming means, and a resistance 10, a 1/4-wavelength line (ÐLO frequency) 11, and a ground 12 as a second impedance transforming means are added to the quadrature modulator using the even-harmonic mixers 5 and 6. When the value of the resistance 10 is set to the same value as that of input impedance of an in-phase distributor 4, impedance matching of a front stage of the in-phase distributor 4 at an RF frequency becomes possible, and while a low-pass filter (π type) 3 is used, isolation between the two even-harmonic mixers 5 and 6 can be secured, thereby obtaining excellent modulation precision. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a quadrature modulator, and more particularly to a quadrature modulator used in a radio communication system or a radar system transmission / reception device.

  The configuration of a conventional quadrature modulator is shown in FIG. In FIG. 5, 1 is a local oscillator that generates a local oscillation wave (LO signal) (hereinafter referred to as LO), 2 is an amplifier that amplifies the LO signal output from LO1, and 3 is an LO signal that is output from amplifier 2. A low-pass filter (π type) that passes through 4 is an in-phase distributor that distributes the LO signal output from the low-pass filter (π type) 3 into two with equal phase and equal amplitude, and 5 is from the in-phase distributor 4. One of the distributed LO signals to be output and an I component (baseband signal) of an IF signal (IF: Intermediate Frequency) output from an I channel baseband signal generation unit 7 described later are mixed to generate an RF signal (RF : The first even harmonic mixer that outputs (Radio Frequency), 6 is the other distributed LO signal output from the in-phase distributor 4 and the IF signal output from the Q channel baseband signal generation unit 8 to be described later Q of A second even harmonic mixer that outputs an RF signal by mixing the signal (baseband signal), and an I channel base that outputs an I component of the baseband IF signal to the first even harmonic mixer 5 A band signal generation unit, 8 is a Q channel baseband signal generation unit that outputs the Q component of the baseband IF signal to the second even harmonic mixer 6, and 9 is an RF output by the first even harmonic mixer 5. The 90 ° synthesizer synthesizes the signal and the RF signal output from the second even harmonic mixer 6 with a phase difference of approximately 90 °. Thus, the first even harmonic mixer 5 and the second even harmonic mixer 6 are connected between the in-phase distributor 4 and the 90 ° combiner 9 so as to be in parallel with each other. The I component and the Q component are baseband signals orthogonal to each other.

  In the configuration of FIG. 5, the frequency of LO1 can be halved by using the even harmonic mixer 6 instead of the normal fundamental wave mixer. Furthermore, since the even harmonic mixer 6 can greatly suppress the occurrence of even-order distortion, in this case, the frequency component twice the LO signal, which is a problem as spurious, can be set to a very low level. As a result, the modulation accuracy can be improved.

  In order to obtain this effect to the maximum, it is important not to input the second harmonic generated by the LO 1 and the amplifier 2 to the even harmonic mixer 6. The low-pass filter (π-type) 3 in FIG. 5 plays its role (see, for example, Patent Document 1 and Patent Document 2).

JP-A-8-242261 (particularly, the [Effect] column of the summary described on page 1; claim 11 described on page 2; and paragraph [0182] on page 16) JP-A-2000-252753 (particularly, FIG. 16 described on page 14; FIG. 19 described on page 15; and FIG. 27 described on page 16)

  In general, in order to obtain good modulation accuracy in a quadrature modulator, it is important to ensure isolation between two mixers. However, in the conventional quadrature modulator described above, as shown in FIG. 6, the output impedance of the low-pass filter (π-type) 3 at the radio frequency (hereinafter referred to as RF) is almost zero, and therefore, between the two mixers. There was a problem that the isolation of this would be extremely deteriorated.

  The present invention has been made to solve such a problem, and in a quadrature modulator using an even harmonic mixer, a low-pass filter (π type) is used and between two even harmonic mixers. It is an object of the present invention to obtain a quadrature modulator capable of ensuring isolation.

  The present invention relates to a local oscillator that generates a local oscillation wave, an amplifier that amplifies a local oscillation wave signal output from the local oscillator, a low-pass filter that passes a local oscillation wave signal output from the amplifier, A first impedance transformer for transforming an output impedance at an RF frequency of the local oscillation wave signal output from the low-pass filter to substantially infinite; and a resistor connected to the first impedance transformer. The output impedance at the LO frequency of the local oscillation wave signal whose output impedance is transformed by the first impedance transformation means is made infinite, and the output impedance at the RF frequency of the local oscillation wave signal is the same value as the value of the resistor. Second impedance transformation means for transforming into the first impedance and the second impedance An in-phase distributor that distributes the local oscillation wave signal whose impedance is transformed by the transforming means into two in equal phase and equal amplitude, an I channel baseband signal generation unit that outputs an I component of the IF signal, and a Q of the IF signal A Q channel baseband signal generation unit that outputs a component, a first LO signal distributed by the in-phase distributor and an I component of an IF signal output from the I channel baseband signal generation unit, A first even harmonic mixer that outputs an RF signal, the other LO signal distributed by the in-phase distributor, and the Q component of the IF signal output from the Q channel baseband signal generator A second even harmonic mixer that outputs a second RF signal; a first RF signal that is output from the first even harmonic mixer; and a second that is output from the second even harmonic mixer. And F signal is a quadrature modulator and a 90 ° combiner for combining with a phase difference of approximately 90 °.

  The present invention relates to a local oscillator that generates a local oscillation wave, an amplifier that amplifies a local oscillation wave signal output from the local oscillator, a low-pass filter that passes a local oscillation wave signal output from the amplifier, A first impedance transformer for transforming an output impedance at an RF frequency of the local oscillation wave signal output from the low-pass filter to substantially infinite; and a resistor connected to the first impedance transformer. The output impedance at the LO frequency of the local oscillation wave signal whose output impedance is transformed by the first impedance transformation means is made infinite, and the output impedance at the RF frequency of the local oscillation wave signal is the same value as the value of the resistor. Second impedance transformation means for transforming into the first impedance and the second impedance An in-phase distributor that distributes the local oscillation wave signal whose impedance is transformed by the transforming means into two in equal phase and equal amplitude, an I channel baseband signal generation unit that outputs an I component of the IF signal, and a Q of the IF signal A Q channel baseband signal generation unit that outputs a component, a first LO signal distributed by the in-phase distributor and an I component of an IF signal output from the I channel baseband signal generation unit, A first even harmonic mixer that outputs an RF signal, the other LO signal distributed by the in-phase distributor, and the Q component of the IF signal output from the Q channel baseband signal generator A second even harmonic mixer that outputs a second RF signal; a first RF signal that is output from the first even harmonic mixer; and a second that is output from the second even harmonic mixer. Since the quadrature modulator includes a 90 ° synthesizer that synthesizes the F signal with a phase difference of approximately 90 °, a low-pass filter (π type) is provided in the quadrature modulator using an even harmonic mixer. It is possible to ensure isolation between the two even harmonic mixers while in use.

Embodiment 1 FIG.
The configuration of the quadrature modulator according to Embodiment 1 of the present invention is shown in FIG. In FIG. 1, reference numerals 1 to 9 are the same as those of the conventional quadrature modulator shown in FIG. In FIG. 1, 10 is a resistor connected to a quarter-wave line (@RF frequency) 13 described later so as to be in parallel with the in-phase distributor 4, and 11 is a quarter wavelength connected to the resistor 10. Line (@LO frequency), 12 is a ground to which a quarter-wave line (@LO frequency) 11 is connected, 13 is connected between a low-pass filter (π type) 3 and an in-phase distributor 4 / 4 wavelength line (@RF frequency). Here, the quarter wavelength line (@RF frequency) 13 constitutes a first impedance transformation means. The resistor 10 and the quarter wavelength line (@LO frequency) 11 grounded to the ground 12 constitute a second impedance transformation means.

  Next, the operation of the quadrature modulator according to the first embodiment will be described with reference to FIG. First, a local oscillator (hereinafter referred to as LO) 1 generates a local oscillation wave (LO signal). The amplifier 2 amplifies the LO signal output from the LO1. The low-pass filter 3 extracts and passes only an LO signal in a desired band set in advance from the amplified LO signal output from the amplifier 2. Next, a ¼ wavelength line (@RF frequency) 13, which is a first impedance transformation means, transforms the output impedance at the RF frequency of the LO signal that has passed through the low-pass filter 3 to infinity. Next, the output impedance of the resistor 10, the quarter wavelength line (@LO frequency) 11 and the ground 12, which are the second impedance transformation means, is transformed by the quarter wavelength line (@RF frequency) 13. The output impedance of the LO signal at the LO frequency is set to infinity, and the output impedance of the LO signal at the RF frequency is transformed to the same value as that of the resistor 10 and input to the in-phase distributor 4. The in-phase distributor 4 distributes the input LO signal into two with equal phase and equal amplitude. One distributed LO signal output from the in-phase distributor 4 is input to the first even harmonic mixer 5, and the other LO signal is input to the second even harmonic mixer 6. The first even harmonic mixer 5 mixes one distributed LO signal input from the in-phase distributor 4 with the I component of the IF signal output from the I channel baseband signal generation unit 7 to generate an RF signal. Is output. The second even harmonic mixer 6 mixes the other distributed LO signal input from the in-phase distributor 4 with the Q component of the IF signal output from the IQ channel baseband signal generator 8 to generate an RF signal. Is output. The RF signal output from the first even harmonic mixer 5 and the RF signal output from the second even harmonic mixer 6 are input to the 90 ° synthesizer 9, and the 90 ° synthesizer 9 has a position of approximately 90 °. Synthesized by phase difference.

  At the RF frequency, the output impedance of the low-pass filter (π-type) 3 is almost zero. In the present embodiment, the quarter wavelength line (@RF frequency) 13 is an impedance transformer (SHORT⇔OPEN). Therefore, the output impedance of the ¼ wavelength line (@RF frequency) 13 becomes almost infinite.

  On the other hand, the ¼ wavelength line (@LO frequency) 11 operates as an impedance transformer (SHORT⇔OPEN) at the LO frequency, and fRF≈2 × fLO at the RF frequency, so that it becomes a ½ wavelength line. Save the front and back impedance. Therefore, the impedance of the shunt circuit constituted by the resistor 10, the quarter wavelength line (@LO frequency) 11, and the ground 12 is infinite at the LO frequency and the value of the resistor 10 at the RF frequency.

  In this way, by setting the value of the resistor 10 to the same value as the input impedance of the in-phase distributor 4, impedance matching becomes possible, and isolation between the two mixers 5 and 6 can be ensured.

  As described above, in the quadrature modulator configured as described above, the resistor 10, the quarter wavelength line (@LO frequency) 11, the ground 12, and the quarter wavelength line (@RF frequency) 13 are added. As a result, impedance matching of the front stage of the in-phase distributor 4 at the RF frequency is possible, and isolation between the two mixers 5 and 6 can be ensured, and good modulation accuracy can be obtained.

Embodiment 2. FIG.
The configuration of the quadrature modulator according to Embodiment 2 of the present invention is shown in FIG. 3, 1 to 3 and 5 to 8 are the same as the conventional quadrature modulator shown in FIG. 5, and 10 to 13 are the first embodiment of the present invention shown in FIG. Since this is the same as the quadrature modulator according to FIG. In FIG. 3, 14 is a 45 ° distributor provided in place of the in-phase distributor 4 in FIG. 1, and 15 is an in-phase combiner provided in place of the 90 ° combiner 9 in FIG. is there.

  Next, the operation of the quadrature modulator according to the second embodiment will be described with reference to FIG. First, LO1 generates a local oscillation wave (LO signal). The amplifier 2 amplifies the LO signal output from the LO1. The low-pass filter 3 extracts and passes only an LO signal in a desired band set in advance from the amplified LO signal output from the amplifier 2. A quarter wavelength line (@RF frequency) 13, which is the first impedance transformation means, transforms the output impedance at the RF frequency of the LO signal that has passed through the low-pass filter 3 to infinity. Next, the output impedance of the resistor 10, the quarter wavelength line (@LO frequency) 11 and the ground 12, which are the second impedance transformation means, is transformed by the quarter wavelength line (@RF frequency) 13. The output impedance of the LO signal at the LO frequency is infinite, and the output impedance of the LO signal at the RF frequency is transformed to the same value as the value of the resistor 10 and input to the 45 ° distributor 14. The 45 ° distributor 14 distributes the input LO signal to equal amplitude with a phase difference of 45 °. One of the distributed LO signals output from the 45 ° distributor 14 is input to the first even harmonic mixer 5, and the other LO signal is input to the second even harmonic mixer 6. The first even harmonic mixer 5 mixes one of the distributed LO signals input from the 45 ° distributor 14 with the I component of the IF signal output from the I channel baseband signal generation unit 7 to generate RF. Output a signal. The second even harmonic mixer 6 mixes the other distributed LO signal input from the 45 ° distributor 14 with the Q component of the IF signal output from the IQ channel baseband signal generation unit 8 to generate RF. Output a signal. The RF signal output from the first even harmonic mixer 5 and the RF signal output from the second even harmonic mixer 6 are input to the in-phase synthesizer 15 and synthesized in phase by the in-phase synthesizer 15.

  At the RF frequency, the output impedance of the low-pass filter (π-type) 3 is almost zero. In the present embodiment, the quarter wavelength line (@RF frequency) 13 is an impedance transformer (SHORT⇔OPEN). Therefore, the output impedance of the ¼ wavelength line (@RF frequency) 13 becomes almost infinite.

  On the other hand, the ¼ wavelength line (@LO frequency) 11 operates as an impedance transformer (SHORT⇔OPEN) at the LO frequency and becomes a ½ wavelength line because fRF≈2 × fLO at the RF frequency. Save the front and back impedance. Therefore, the impedance of the shunt circuit constituted by the resistor 10, the quarter wavelength line (@LO frequency) 11, and the ground 12 is infinite at the LO frequency and the value of the resistor 10 at the RF frequency. Therefore, impedance matching can be performed by setting the value of the resistor 10 to the same value as the input impedance of the 45 ° distributor 14.

  As described above, in the quadrature modulator configured as described above, the resistor 10, the quarter wavelength line (@LO frequency) 11, the ground 12, and the quarter wavelength line (@RF frequency) 13 are added. As a result, impedance matching of the previous stage of the 45 ° distributor 14 at the RF frequency is possible, and isolation between the two mixers 5 and 6 can be ensured, and good modulation accuracy can be obtained.

It is a block diagram which shows the structure of the quadrature modulator by Embodiment 1 of this invention. It is explanatory drawing which shows the reason which can ensure the isolation between two mixers in the quadrature modulator according to the first embodiment of the present invention. It is a block diagram which shows the structure of the quadrature modulator by Embodiment 2 of this invention. It is explanatory drawing which shows the reason which can ensure the isolation between two mixers in the orthogonal modulator by Embodiment 2 of this invention. It is a block diagram which shows the structure of the conventional quadrature modulator. It is explanatory drawing which shows the reason for the isolation between two mixers degrading in the conventional quadrature modulator.

Explanation of symbols

  1 local oscillator, 2 amplifier, 3 low-pass filter (π type), 4 in-phase distributor, 5 first even harmonic mixer, 6 second even harmonic mixer, 7 I channel baseband signal generator, 8 Q channel baseband signal generator, 990 ° combiner, 10 resistor, 11 1/4 wavelength line (@LO frequency), 12 ground, 13 1/4 wavelength line (@RF frequency), 14 45 ° distributor, 15 In-phase synthesizer.

Claims (2)

A local oscillator that generates a local oscillation wave;
An amplifier for amplifying a local oscillation wave signal output from the local oscillator;
A low-pass filter that passes a local oscillation signal output from the amplifier;
First impedance transformation means for transforming an output impedance at an RF frequency of the local oscillation wave signal output from the low-pass filter to substantially infinite;
The local oscillation wave has a resistance connected to the first impedance transformation means, the output impedance at the LO frequency of the local oscillation wave signal whose output impedance is transformed by the first impedance transformation means is infinite, and the local oscillation wave Second impedance transformation means for transforming the output impedance at the RF frequency of the signal to the same value as the value of the resistor;
An in-phase distributor that distributes the local oscillation wave signal whose impedance is transformed by the first and second impedance transformation means into two with equal phase and equal amplitude;
An I channel baseband signal generation unit for outputting an I component of the IF signal;
A Q channel baseband signal generator for outputting the Q component of the IF signal;
A first even harmonic mixer that outputs a first RF signal by mixing one of the LO signals distributed by the in-phase distributor and the I component of the IF signal output from the I channel baseband signal generation unit. When,
A second even harmonic mixer that outputs the second RF signal by mixing the other LO signal distributed by the in-phase distributor and the Q component of the IF signal output from the Q channel baseband signal generator. When,
A 90 ° combiner that combines the first RF signal output from the first even harmonic mixer and the second RF signal output from the second even harmonic mixer with a phase difference of approximately 90 °; A quadrature modulator comprising: A local oscillator that generates a local oscillation wave;
An amplifier for amplifying a local oscillation wave signal output from the local oscillator;
A low-pass filter that passes a local oscillation signal output from the amplifier;
First impedance transformation means for transforming an output impedance at an RF frequency of the local oscillation wave signal output from the low-pass filter to substantially infinite;
The local oscillation wave has a resistance connected to the first impedance transformation means, the output impedance at the LO frequency of the local oscillation wave signal whose output impedance is transformed by the first impedance transformation means is infinite, and the local oscillation wave Second impedance transformation means for transforming the output impedance at the RF frequency of the signal to the same value as the value of the resistor;
An in-phase distributor that distributes a local oscillation wave signal whose impedance has been transformed by the first and second impedance transformation means into two LO signals of equal amplitude with a phase difference of 45 °;
An I channel baseband signal generation unit for outputting an I component of the IF signal;
A Q channel baseband signal generator for outputting the Q component of the IF signal;
A first even harmonic mixer that outputs a first RF signal by mixing one of the LO signals distributed by the in-phase distributor and the I component of the IF signal output from the I channel baseband signal generation unit. When,
A second even harmonic mixer that outputs the second RF signal by mixing the other LO signal distributed by the in-phase distributor and the Q component of the IF signal output from the Q channel baseband signal generator. When,
An in-phase synthesizer for synthesizing the first RF signal output from the first even harmonic mixer and the second RF signal output from the second even harmonic mixer in the same phase; A quadrature modulator.

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