Patent Application
20110300823
The present invention relates to an image rejection mixer and a wireless communication device such as a communication device or a radar device that uses the image rejection mixer.
As a conventional art, there is an image rejection mixer that performs distribution of a radio frequency (hereinafter, referred to as RF) signal with a 90 degrees hybrid circuit and performs in-phase distribution of a local oscillator (hereinafter, referred to as LO) power with a Wilkinson power distributor. In addition, there is a harmonic mixer for extracting intermediate frequency (hereinafter, referred to as IF) signal and RF signal components by using an antiparallel diode pair in which diodes are connected to each other at reversed polarity (see Non-Patent Document 1).
Non Patent Document 1: Masayoshi Aikawa, Takashi Ohira, Tsuneo Tokumitsu, Tetsuo Hirota, and Mashiro Muraguchi, “Monolithic microwave integrated circuit (MMIC)”, The Institute of Electronics, Information and Communication Engineers, Jan. 25, 1995 first edition, Page 118-119 and Page 120-122.
The conventional image rejection mixer is used for a main purpose of suppressing an image signal, but there is a problem that a lot of unwanted frequency components exist at the vicinity of a certain RF frequency as a desired wave in the case of a harmonic mixer.
The present invention is created in view of the above-mentioned problem, and it is an object of the present invention to provide an image rejection mixer and a communication device that may suppress unwanted frequency components of a high power output assuming a fourth-order harmonic mixer.
An image rejection mixer according to the present invention includes: first and second fourth-order harmonic mixers, each including an LO terminal, an IF terminal, and an RF terminal, and outputs, as a desired wave, an RF as a mixed wave of a fourth order component of an input LO signal frequency and a first order component of an IF, or the IF as a mixed wave of an even order component of the input LO signal frequency and a first order component of the RF; a 90-degree IF synthesis distributor which distributes and outputs an input signal at a first terminal from second and third terminals with a phase difference of 90 degrees, or synthesizes an input signal at a second terminal and an input signal at a third terminal after delaying a phase of the input signal at the second terminal by 90 degrees and outputs the synthesized signal from the first terminal; a 90-degree LO distributor which distributes and outputs an input signal at a first terminal from second and third terminals with a phase difference of 90 degrees; and a 90-degree RF synthesis distributor which distributes and outputs an input signal at a first terminal from second and third terminals with a phase difference of 90 degrees and outputs from a third terminal a signal having a phase delay of 90 degrees with respect to a phase output from the second terminal, or synthesizes an input signal at a second terminal with an input signal at a third terminal after leading a phase of the input signal at the second terminal by 90 degrees and outputs the synthesized signal from the first terminal, in which: the second terminal of the 90-degree IF synthesis distributor is connected to the IF terminal of the first fourth-order harmonic mixer; the third terminal of the 90-degree IF synthesis distributor is connected to the IF terminal of the second fourth-order harmonic mixer; the second terminal of the 90-degree LO distributor is connected to the LO terminal of the first fourth-order harmonic mixer; the third terminal of the 90-degree LO distributor is connected to the LO terminal of the second fourth-order harmonic mixer; the second terminal of the 90-degree RF synthesis distributor is connected to the RF terminal of the first fourth-order harmonic mixer; and the third terminal of the 90-degree RF synthesis distributor is connected to the RF terminal of the second fourth-order harmonic mixer.
Further, a wireless communication device according to the present invention is the image rejection mixer using the above-mentioned structure.
According to the present invention, a 90-degree LO distributor having a phase difference of 90 degrees is used instead of an LO distributor in a structure of the conventional image rejection mixer so that unwanted frequency components of a high power output may be suppressed.
In this case, the second terminal of the 90-degree IF synthesis distributor 4 is connected to an IF terminal of the first fourth-order harmonic mixer 7a, the third terminal of the 90-degree IF synthesis distributor 4 is connected to an IF terminal of the second fourth-order harmonic mixer 7b, the second terminal of the 90-degree LO distributor 5 is connected to an LO terminal of the first fourth-order harmonic mixer 7a, the third terminal of the 90-degree LO distributor 5 is connected to an LO terminal of the second fourth-order harmonic mixer 7b, the second terminal of the 90-degree RF synthesis distributor 6 is connected to an RF terminal of the first fourth-order harmonic mixer 7a, and the third terminal of the 90-degree RF synthesis distributor 6 is connected to an RF terminal of the second fourth-order harmonic mixer 7b.
Next, an operation is described. The present invention uses, similarly to the conventional example, the first and the second fourth-order harmonic mixers 7a and 7b that input the IF signal and the LO signal and extract frequency components of ±IF+4×LO by using a nonlinear element such as an antiparallel diode pair (hereinafter, referred to as APDP) in which diodes are connected antiparallel to each other so that unwanted frequency components are suppressed by this connection method.
A transmission system is exemplified for description. Note that the 90-degree IF synthesis distributor 4 operates as a 90-degree IF distributor and the 90-degree RF synthesis distributor 6 operates as a 90-degree RF synthesizer in the transmission system. A signal input from the IF input and output terminal 1 is distributed by the 90-degree IF synthesis distributor 4 with a phase difference of 90 degrees and is input to the two mixers 7a and 7b. In this case, it is supposed that a phase of the signal input to the second mixer 7b leads 90 degrees to a phase of the signal input to the first mixer 7a.
In addition, the LO signal input from the LO input terminal 2 is distributed by the 90-degree LO distributor 5 with a phase difference of 90 degrees and is input to the two mixers 7a and 7b. In this case, it is supposed that a phase of the LO signal input to the second mixer 7b is delayed by 90 degrees to a phase of the LO signal input to the first mixer 7a.
In the first mixer 7a, the input LO signal and IF signal are mixed so that a mixed wave of A times a frequency of the LO signal frequency and B times a frequency of the IF signal frequency is output. Here, each phase of the LO signal and the IF signal input to the first mixer 7a is regarded as a reference (0 degree). Then, a phase of the output signal component (A×LO+B×IF) is 0 degree.
Similarly, also in the second mixer 7b, the LO signal and the IF signal are mixed so that a mixed wave of A times a frequency of the LO signal frequency and B times a frequency of the IF signal frequency is output. A phase of the IF signal input to the second mixer 7b is +90 degrees with respect to the phase of the IF signal input to the first mixer 7a, and a phase of the LO signal is −90 degrees. Therefore, a phase of the output signal component (A×LO+B×IF) is as follows.
A×(−90)+B×90 degrees (1)
The signals output from the two mixers 7a and 7b are synthesized in the 90-degree RF synthesis distributor 6 and output from an RF terminal 3. Here, when the signal from the second mixer 7b is delayed by a phase of 90 degrees and is synthesized with the signal from the first mixer 7a, a phase φ of the synthesized signal is as follows.
When this phase φ becomes “0 degree” or “multiple of 360 degrees”, the in-phase synthesis is performed so that a maximum power may be extracted. If it is a “180 degrees+multiple of 360 degrees”, it is suppressed by the opposite phase synthesis.
(The Case of Fourth-Order Harmonic Mixer)
It is understood that the RF signal components of the desired wave have A=4, B=1, and φ=−360 degrees, and are synthesized in phase, while image frequencies have A=4, B=−1, and φ=−540 degrees, and are synthesized in opposite phase, which operates as an image rejection mixer.
Further, as an example of the harmonic components that are output at the vicinity of the desired wave, components of relatively low order and relatively high output level such as 2LO+IF (=−180 degrees), 2LO−3IF (=−540 degrees), 3LO+2IF (=−180 degrees), 3LO−2IF (=−540 degrees), 4LO+3IF (=−180 degrees), 5LO (=−540 degrees), 5LO−4IF (−900 degrees), and 6LO−3IF (=−900 degrees) are also synthesized in opposite phase and may be suppressed in theory.
In this way, the structure has an effect of suppressing in theory undesired waves generated by a combination of the LO signal frequency and the IF signal frequency to be φ=180+360N (N is an integer) illustrated in the equation (2) like 2LO+IF, 3LO+2IF, 5LO, or the like, in which image rejection function remains. The mixer uses a fourth order of the LO signal, and hence even if the LO signal has a difference of 90 degrees, a phase difference of the 4L0 signal component in the two mixers becomes 360 degrees=0 degree. As to the desired wave and the image wave, the same operation as the conventional operation may be performed, and it may be said that the structure is unique to the fourth-order harmonic mixer.
As a concrete example, a list of spurious is shown in Table 1.
It is supposed that LO signal frequency is 13 GHz, IF signal frequency is 2 GHz, LO signal order is four. The fourth-order harmonic mixer is considered to have a desired wave of 54 GHz that is an output frequency when the IF signal order is one. Components of mixed waves that exist at the vicinity of the desired wave (±10 GHz) are shown. Here, the upper limit of the order of the LO signal and the order of the IF signal is five. There are 18 frequency components including the desired wave.
As illustrated in
Specifically, in the case of
Although the case of the transmission system is described above, the case of the reception system also has the same effect.
An operation of the image rejection mixer according to Embodiment 2 is similar to that in Embodiment 1. When the 90-degree RF synthesis distributor 6 synthesizes the signals from the two mixers 7a and 7b, the phase φ of the synthesized wave becomes as follows.
When this phase φ becomes “0 degree” or “multiple of 360 degrees”, the in-phase synthesis is performed so that a maximum power may be extracted. If it is a “180 degrees+multiple of 360 degrees”, it is suppressed by the opposite phase synthesis.
(The Case of Fourth-Order Harmonic Mixer)
It is understood that the RF signal components of the desired wave have A=4, B=1, and φ=360 degrees, and are synthesized in phase, while image frequencies have A=4, B=−1, and φ=180 degrees, and are synthesized in opposite phase, which operates as an image rejection mixer.
Further, as an example of the harmonic components that are output at the vicinity of the desired wave, components of relatively low order and relatively high output level such as 2LO+IF (=180 degrees), 2LO−3IF (=180 degrees), 3LO+4IF (=540 degrees), 3LO−4IF (=−180 degrees), 4LO+3IF (=540 degrees), and 5LO+2IF (540 degrees) are also synthesized in opposite phase and may be suppressed in theory.
In addition, the effect is also the same as that in Embodiment 1. A spurious component appearing at the vicinity of the desired wave depends on a selection method of the LO signal frequency and the IF signal frequency. Therefore, if Embodiment 1 or Embodiment 2 is selected in accordance with the spurious component to be suppressed, higher effect may be obtained.
Although the case of the transmission system is described above, the case of the reception system also has the same effect.
An operation of the image rejection mixer according to Embodiment 3 is similar to that illustrated in Embodiments 1 and 2. When described in accordance with Embodiment 1, the phase φ of the wave synthesized by the 90-degree RF synthesis distributor 6 becomes as follows.
When this phase φ becomes “0 degree” or “multiple of 360 degrees”, the in-phase synthesis is performed so that a maximum power may be extracted. If it is a “180 degrees+multiple of 360 degrees”, it is suppressed by the opposite phase synthesis.
In this way, according to this structure, as to multiple of the fourth order, there is an effect of allowing image rejection function to remain while suppressing in theory undesired waves generated by a combination of the LO frequency and the IF frequency to be φ=180+360n illustrated in the equation (4). The mixer uses the 4n-th order of the LO, and hence even if the LO has a difference of 90 degrees, a phase difference of the 4n-th order LO component in the two mixers becomes 360×n=0 degree. Therefore, the desired wave and the image wave may operate similarly to those in the conventional example.
Although the case of the transmission system is described above, the case of the reception system also has the same effect.
An operation of the image rejection mixer according to Embodiment 4 is similar to that illustrated in Embodiments 1 to 3. When described in accordance with Embodiment 1, the phase φ of the wave synthesized by the 90-degree RF synthesis distributor 6 becomes as follows.
When this phase φ becomes “0 degree” or “multiple of 360 degrees”, the in-phase synthesis is performed so that a maximum power may be extracted. If it is a “180 degrees+multiple of 360 degrees”, it is suppressed by the opposite phase synthesis.
Although the case of the transmission system is described above, the case of the reception system also has the same effect.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/069246 | 10/2/2007 | WO | 00 | 2/12/2010 |
