JPH06283936A - Image rejection mixer - Google Patents

Abstract

PURPOSE:To construct the mixer part of an image rejection mixer by a monolithic microwave integrated circuit consisting of a general-purpose circuit which suppresses the output leakage of the local oscillation signal and also reduces the dependency of frequency. CONSTITUTION:A 180 deg.C-phase shifter applying a strip line 90 is provided on one of outputs of two FET mixers 52 and 62. Thus the phase of the local oscillation signal leaked out to the output is shifted. Then both outputs are transmitted through the HPF 91 and 92 and then connected to each other via a resistance 93. Thus the leakage of the local oscillation signal is synthesized and canceled. In such a constitution, the leakage of the local oscillation signal can be suppressed to the output without affecting the necessary signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency converter,
In particular, the present invention relates to an image rejection mixer used in a receiver for a microwave wireless communication device.

[0002]

2. Description of the Related Art A conventional image rejection mixer will be described with reference to FIG. The image rejection mixer is the first that uses two mixer diodes.
And second single balance type mixers 51 and 61. The input signal supplied to the first input terminal 1 is 90 °
It is added to the first and second mixers 51, 61 via the hybrid circuit (90 ° HYB) 4. On the other hand, the local oscillation signal is transmitted from the second input terminal 2 through the in-phase hybrid (0 °
HYB) 7 to the first and second mixers 51, 61. The signals frequency-converted by the first and second mixers 51 and 61 (mixed signals) are combined by the 90 ° hybrid 9 through the first and second low-pass filters 81 and 82, respectively. , Output terminal 3
The 90 ° hybrid circuit 4 and the first and second mixers 51 and 61, the in-phase hybrid 7 and the first and second low-pass filters 81 and 82, which are output as output signals (shown by one point in FIG. 2). The portion surrounded by the chain line) is composed of the microwave integrated circuit 10. Here, the first and second mixers 51 and 61 and the part of the in-phase hybrid 7 are called a mixer section.

With the demand for miniaturization of receivers, gallium arsenide field effect transistors (FETs) are used in place of mixer diodes, and monolithic microwave integrated circuits are also used for the above mixers ( See, for example, JP-A-62-188509).

An example thereof is shown in FIG. As shown in FIG. 3, FET mixers 52 and 62 are used instead of the single balance type mixers 51 and 61 shown in FIG.
Monolithic microwave integrated circuit 20 with one mixer section
The image rejection mixer can be miniaturized.

[0005]

Problems to be Solved by the Invention As shown in FIG.
In the conventional image rejection mixer in which the mixer section is composed of a monolithic microwave integrated circuit, the leakage of the local oscillation signal to the output becomes a problem. In order to prevent the leakage of the local oscillation signal, when the low-pass filter is provided at the two outputs of the monolithic microwave integrated circuit 20, the size of the image rejection mixer is such that a diode is used for the mixer. The difference is almost the same, and the advantage of using a monolithic microwave integrated circuit is lost.

Consider the provision of a low pass filter inside the monolithic microwave integrated circuit 20. When a Butterworth type low pass filter having a signal frequency of several GHz and an output frequency of several hundred MHz is used as the low pass filter, an inductance of several tens nH is required. It is difficult to realize a low-pass filter having an inductance having such a large value in a monolithic microwave integrated circuit.

Therefore, an object of the present invention is to provide an image rejection mixer capable of suppressing the leakage of the output of the local oscillation signal and realizing the mixer section in the monolithic microwave integrated circuit.

[0008]

To achieve the above object, an image rejection mixer of the present invention divides an input signal into first and second branched input signals having a 90 ° phase difference from each other. A circuit and a local oscillation signal connected to the branch circuit, and the first and second branched input signals and the local oscillation signal are mixed, respectively, and the first and second mixed signals are output. An image rectifier having a mixer section including first and second mixers, and a combining circuit connected to the mixer section for combining the first and second mixed signals and outputting the combined signal as an output signal. In the operation mixer, the mixer section is integrated into a monolithic microwave integrated circuit, and one of the outputs of the first and second mixers in the monolithic microwave integrated circuit is connected to the frequency of the local oscillation signal. And a first high-pass filter connected to the output of this strip line, and a second line connected to the other of the outputs of the first and second mixers. And a resistor connecting the outputs of the first and second high-pass filters.

[0009]

The image rejection mixer of the present invention is provided with the first and second high-pass filters at the outputs of the first and second mixers of the monolithic microwave integrated circuit, respectively. The output of the high-pass filter 2 is connected by a terminating resistor. The local oscillation signal is distributed by the in-phase hybrid, and the distributed local oscillation signals are respectively supplied to the mixer sections, so that the phases of the local oscillation signals leaking to the output are also in phase. Therefore, by shifting the phase of the local oscillation signal output from one of the first and second mixers by 180 ° on the strip line, it is combined by the resistors through the first and second high-pass filters. , Cancel the local oscillation signal. On the other hand, the required signal (intermediate frequency signal) does not pass through the first and second high-pass filters, so it is output as it is. Therefore, this circuit does not affect the required signal.

Considering the first and second high-pass filters for the above-mentioned frequencies, each of the first and second high-pass filters has an inductance of several nH and a number of nH. It can be realized by the capacitance of pF. Therefore, the mixer unit can be realized in the monolithic microwave integrated circuit.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, an image rejection mixer according to an embodiment of the present invention includes a first input terminal 1 to which an input signal is supplied and a second input terminal 1 to which a local oscillation signal from a local oscillator 100 is supplied. Input terminal 2 and an output terminal 3 for outputting an output signal. The first input terminal 1 is 90
° Connected to Hybrid 4. The 90 ° hybrid 4 inputs the input signals from the first input terminal 1 to each other by 90 °.
It is distributed to the first and second branched input signals having a phase difference. The first and second branched input signals are supplied to the first and second FET mixers 52 and 62, respectively.

On the other hand, the second input terminal 2 is connected to the in-phase hybrid 7. The in-phase hybrid 7 branches the local oscillation signal from the second input terminal 2 into first and second branched local oscillation signals in phase with each other. The first and second branched local oscillation signals are supplied to the first and second FET mixers 52 and 62, respectively. First FET mixer 52
Outputs the first mixed signal by mixing the first branched input signal and the first branched local oscillation signal. Similarly, the second FET mixer 52 mixes the second branched input signal and the second branched local oscillation signal to generate a second mixed signal.
The mixed signal of is output.

The first mixed signal is connected via stripline 90 to the first input of a 90 ° hybrid 9. The strip line 90 works to shift the phase of the local oscillation signal by 180 °. On the other hand, the second mixed signal is directly connected to the second input of the 90 ° hybrid 9. Further, the first and second inputs of the 90 ° hybrid 9 are connected to the resistor 93 via the first and second high pass filters 91 and 92, respectively.

According to this structure, the leakage signal of the first branched local oscillation signal passes through the first high-pass filter 91 and is consumed by the resistor 93, and the leakage signal of the second branched local oscillation signal is consumed. The leakage signal passes through the second high pass filter 92 and is consumed by the resistor 93. On the other hand, the required signal (intermediate frequency signal) included in the first and second mixed signals is 90
Combined by the hybrid 9 and the combined signal is supplied to the output terminal 3 as an output signal.

Under general usage conditions, the order of the frequency of the required signal and the frequency of the local oscillation signal differs by one digit or more. Therefore, the first and second high pass filters 91, 9
Each of the two types can cover the required frequency band with one type.

The phase shifter using the strip line 90 ideally needs to shift the phase of the local oscillation signal by 180 °. However, the local oscillation signal
And a resistor 93 through the second high-pass filters 91 and 92.
Since it is consumed in the strip line 90, the sensitivity to the length of the strip line 90 is weak, and the strip line 9
0 can cover several GHz band.

In the above embodiment, field effect transistors are used as the first and second mixers 52 and 62 which are frequency conversion elements, but a single balance type mixer is incorporated in a monolithic integrated circuit by a Schottky diode and a balun. It may be configured. In the above embodiment, the outputs of the first and second high pass filters 91 and 92 are commonly connected to the resistor 93 in order to suppress the local oscillation signal. Even if the outputs of the high-pass filters 91 and 92 are separately connected to the first and second terminating resistors,
It is possible to suppress the local oscillation signal. Furthermore, the local oscillation signal can be canceled by simply substituting the first and second high-pass filters with the first and second capacitors. However, in that case, the local oscillation signal suppression ratio and the loss of the required signal are both deteriorated as compared with the case where the first and second high-pass filters are used.

[0019]

As is apparent from the above description, according to the present invention, the leakage of the local oscillation signal is combined and canceled by the phase shifter by the strip line, the high-pass filter and the terminating resistor. Leakage of the local oscillation signal to the output can be suppressed. Moreover, since the mixer unit can be configured by a monolithic microwave integrated circuit, the integrated circuit can be miniaturized while maintaining the versatility of the integrated circuit, which leads to cost reduction.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an image rejection mixer according to an exemplary embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional image rejection mixer.

FIG. 3 is a circuit diagram showing a configuration of a conventional image rejection mixer in which a mixer unit is configured by a monolithic microwave integrated circuit.

[Explanation of symbols]

 1 1st input terminal 2 2nd input terminal 3 Output terminal 4 90 ° hybrid (90 ° HYB) 7 In-phase hybrid (0 ° HYB) 9 90 ° hybrid (90 ° HYB) 10 Microwave integrated circuit 20 Monolithic microwave Integrated circuit 51 Single-balance type mixer 52 FET mixer 61 Single-balance type mixer 62 FET mixer 81 Low-pass filter 82 Low-pass filter 90 Stripline 180 ° phase shifter 91 High-pass filter 92 High-pass filter Pass filter 93 Resistance 100 Local oscillator

Claims (5)

[Claims] 1. A branch circuit for distributing an input signal into first and second branched input signals having a phase difference of 90 ° from each other,
A second oscillator connected to the branch circuit, supplied with a local oscillation signal, mixing the first and second branched input signals with the local oscillation signal, and outputting a first mixed signal An image rig having a mixer section including first and second mixers, and a combining circuit that is connected to the mixer section and that combines the first and second mixed signals and outputs the combined signal as an output signal. In the operation mixer, the mixer unit is integrated into a monolithic microwave integrated circuit, and one of the outputs of the first and second mixers in the monolithic microwave integrated circuit is 180 ° relative to the frequency of the local oscillation signal. A stripline having a phase difference, a first high-pass filter connected to the output of the stripline, and the other of the outputs of the first and second mixers. Image rejection mixer, characterized in that it comprises a second high pass filtering unit, and a resistor connected between the output of said first and said second high pass filtering unit. 2. Each of the branching circuit and the synthesizing circuit,
The image rejection mixer according to claim 1, which is configured by a 90 ° hybrid circuit. 3. The mixer section has an in-phase hybrid that divides the local oscillation signal into first and second branched local oscillation signals that are in phase with each other, and outputs the first and second branched local oscillation signals. The image rejection mixer according to claim 1, wherein the image rejection mixer is supplied to the first and second mixers, respectively. 4. The first and second resistors instead of the resistor.
2. The image rejection mixer according to claim 1, wherein the first and second terminating resistors are respectively connected to the outputs of the high pass filter of FIG. 5. The image rejection mixer according to claim 1, wherein first and second capacitors are used instead of the first and second high pass filters.