JPH0515521U - Image Rigidation Mixer - Google Patents

Abstract

(57) [Abstract] [Purpose] To absorb a change in the phase of a 90 ° hybrid circuit due to a mixer matching circuit and a frequency, and to effectively suppress an image signal with a simple configuration by omitting a mixer and a filter. [Structure] The RF signal is distributed by the in-phase distributor 4, and
One is passed through the conditional phase shifter 10 and again synthesized by the 90 ° hybrid 2. Condition The phase shifter is -90 °, + 90 ° depending on the level of the input signal frequency based on the LO frequency.
Give a phase shift of. Therefore, the designated frequency and the image frequency corresponding to the height of the LO signal have opposite phases, and the 90 ° hybrid 2 performs image suppression synthesis. [Effect] The number of components can be reduced, and it is possible to cope with the phase shift.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an image reduction mixer used in a receiver of a heterodyne type wireless communication device.

[0002]

[Prior Art]

 A conventional image rejection mixer has a configuration as shown in Fig. 7, for example, which makes a 90 ° phase difference between RF signals by 90 ° HYBRID, mixes them, and then synthesizes them again by 90 ° HYBRID. The image was suppressed in each of USB, LSB, and USB. FIG. 7 is a block diagram of the image rejection mixer. 1 is an RF signal input unit, 2 is 90 ° HYBRID, 3 is a mixer for mixing LO and RF, 4 is a 0 ° distributor for dividing the LO output into two, and 5 is The LO signal input section 6 is 90 ° HYBRID, 7 is LPF, and 8 is IF output section.

Next, the outline of the operation will be described with reference to FIG. When the designated reception signal RF is input to the reception input section 1, this RF signal is distributed by the 90 ° distributor 2 and is also input to the mixer 3 together with the local oscillator output signal LO distributed by the 0 ° distributor 4. To be done. In the mixer, the LO and RF signals are mixed, and the sum and difference components of both are output together with the LO, but the low pass filter 7 outputs only the difference component of both as the intermediate frequency signal IF. At this time, the phase relationship between the intermediate frequency signals IF1 and IF2 output from the respective mixers is as shown in FIG. 8a because of the 90 ° distributor 2. Further, when the image signal RF 'is input to the reception input section 1, the output of the 90 ° distributor 2 is shifted by 180 °, so the relationship between the outputs IF1' and IF2 'of the respective mixers is as shown in FIG. 8b. .. Therefore, the outputs phase-shifted and combined by the 90 ° combiner 6 are strengthened or weakened depending on the phase relationship of each IF. For example, in the case of the phase relationship of FIG. Image strengthening, and USBIF output unit weakening each other and image rejection.

[0004]

[Problems to be solved by the device]

 The conventional image rejection mixer is configured as described above, but the types of 90 ° hybrids 2 and 6 are different. That is, the 90 ° combiner 6 can use a lumped element for the IF frequency band, and the frequency is constant, but the 90 ° distributor 2 is used at any assigned RF frequency, so the frequency is constant. Not constant. Further, when the RF band used has a high frequency, the lumped element cannot be used, and in this case, it is usually constituted by a pattern using a distributed constant such as a branch line as shown in FIG. However, it is difficult to use as a 90 ° hybrid in a wide range because the pattern length that gives an appropriate amount of phase shift changes depending on the wavelength. Furthermore, the IF output phase difference between mixers changes depending on the conditions of the matching circuit of mixer 3. There is a problem of doing.

The present invention was made in order to solve the above-mentioned problems, and the phase change of the 90 ° distributor 2 in the RF band is corrected by the 90 ° combiner 6 in the IF band. Is.

[0006]

[Means for Solving the Problems]

 The image rejection mixer according to the present invention is a 90 ° combiner in the IF band which is variable in phase by a constant impedance symmetric lattice circuit.

[0007]

[Action]

 The constant impedance symmetric lattice circuit according to the present invention operates as an IF band phase shifter and operates a 90 ° combiner as an arbitrary phase combiner.

[0008]

【Example】

 Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an image rejection mixer using a constant impedance symmetric lattice circuit as a phase shifter. In FIG. 1, 1 is an RF signal input unit, 2 is 90 ° HYBRID, 3 is a mixer for mixing LO and RF, 4 is a 0 ° distributor that divides the LO output into two, 5 is an LO signal input unit, and 7 is A low-pass filter, 9 is a variable phase synthesizer using a symmetrical impedance symmetric lattice circuit, and 8 is an IF signal output section.

Next, the operation and operation of the embodiment shown in FIG. 1 will be described. In the circuit of the present invention, a variable phase shifter in the IF band is used to correct the 90 ° distributor (hybrid) in the RF band. First, the variable phase shifter will be briefly described. This variable phase shifter has the characteristics as shown in Fig. 2, and the amount of phase shift differs depending on the frequency. It can be adjusted so that the phase amount can be regarded as constant. FIG. 2 shows that the phase shift amount θ is given in the IF band.

The operation will be described below in comparison with the case of the conventional configuration. In the conventional mixer shown in FIG. 7, the phase of each mixer output must be shifted by 90 ° in order to suppress the image output signal. That is, IF signals IF1 and IF2 output to the respective mixers when a designated reception frequency RF is input to the RF signal input terminal 1 and IF1 'and IF2' output IF output signals when the image frequency RF 'is input. Then, the phase relationship between them is as shown in a and b of FIG.

However, when the RF signal has a high frequency and the 90 ° hybrid 2 is a distributed constant line such as a branch line as shown in FIG. 9, in order to obtain a 90 ° phase difference, each side length Must be 1/4 of the wavelength, and the phase difference will change as the frequency changes. Further, depending on the conditions of the matching circuit used in the mixer, the output phase between the mixers is different, and the phase relationship between IF1 and IF2 deviates from 90 °.

Assuming that the phase difference between IF1 and IF2 is θ, the waveform output to the IF output terminal 8 when the conventional 90 ° hybrid 6 is used is composed by being shifted by 90 ° −θ °. The output is as shown in FIGS. 10b and 10c.

On the other hand, if a phase shifter that gives a phase difference of θ as shown in FIG. 2 is used, the combined output will be as shown in FIG. 3, and the image output will be suppressed.

Example 2. Although the variable phase shifter is adopted in the IF band in the above embodiment to suppress the image, the same effect can be obtained even if it is adopted in the RF band as a variable phase shifter that changes the sign of the phase given depending on the frequency condition. The effect is obtained, and in this case the image signal is suppressed in the RF band, so only one mixer and filter are required, and the secondary effect that the IF band combiner can be omitted is also expected. it can. FIG. 4 is a block diagram showing this structure, which will be described below.

In FIG. 4, the RF signal input from the RF signal input unit 1 is in-phase distributed by the in-phase distributor 4, one of which remains as it is, and the other of which passes through the conditional phase shifter 10 and then 90 °. After being combined by the hybrid, it is combined with the LO output in the mixer 3, passes through the low pass filter 7, and is taken out as an IF signal from the IF signal output terminal 8. In the configuration of this figure, when the image frequency is input, the 90 ° hybrid 2 cancels each other out, and they are not input to the mixer 3. However, the conditional phase shifter 10 has this function.

The characteristics of the conditional phase shifter 10 are shown in FIG. This shows a capacitive property in which the phase is delayed with respect to a certain reference frequency (L O frequency in this case), and an inductive property with which the phase is advanced in a low frequency. FIG. 5 shows the case where the phase shifts of + 90 ° and −90 ° are obtained at the frequencies RF and RF ′, which are separated from the LO frequency by IF.

Therefore, when the RF signal is input in FIG. 4, the outputs of the 90 ° hybrid 2 are in-phase combined and reinforce each other, but when the RF ′ signal is input, the phases are 180 ° different and thus cancel each other out. We will weaken each other.

The conditional phase shifter exhibiting such an operation can be realized by using a short stub, and can also be realized by a symmetric lattice circuit as shown in FIG. 6 (or a modification thereof).

[0019]

[Effect of the device]

 As described above, according to the present invention, since the variable phase shifter is used, the following effects and advantages can be obtained. (1) It is possible to absorb the phase shift when the RF frequency is different. (2) The phase component changed depending on the matching condition of the mixer circuit can be absorbed.

Further, as another embodiment of the present invention, the use of the conditional phase shifter in the RF band has the following advantages. (1) Only one mixer and one low pass filter are required. (2) The IF band combiner is not required. (3) Since the image signal is suppressed before the mixer input, the phase shift of the matching circuit can be ignored.

[Brief description of drawings]

FIG. 1 is a block diagram of an image rejection mixer according to the present invention.

FIG. 2 is a diagram showing a characteristic example of a phase shifter used in the present invention.

FIG. 3 is a diagram showing image suppression according to the present invention.

FIG. 4 is a block diagram showing another embodiment of the present invention.

FIG. 5 is a diagram showing characteristics of a phase shifter used in another embodiment of the present invention.

FIG. 6 is a structural example of a phase shifter used in another embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a conventional image rejection mixer.

FIG. 8 is a diagram showing an operation of a conventional image rejection mixer.

FIG. 9 is a diagram showing an example of a pattern used for a high frequency hybrid in a conventional image rejection mixer.

FIG. 10 is a diagram showing a state when the image rejection mixer cannot successfully suppress an image.

[Explanation of symbols]

 1 RF signal input unit 2 90 ° hybrid (RF band) 3 Mixer 4 In-phase distributor 5 LO signal input unit 6 90 ° hybrid (IF band) 7 Low pass filter 8 IF signal output unit 9 Phase shifter 10 Conditional shifter Phaser 11 branch line pattern

Claims (1)

[Scope of utility model registration request] 1. A power combiner for obtaining an arbitrary amount of phase shift is configured in an intermediate frequency band by combining a phase shifter and a combiner using a constant resistance symmetric lattice circuit exhibiting a constant impedance regardless of frequency. An image rejection mixer using a radio frequency band power divider that provides a phase difference.