JP3042184B2 - Image rejection mixer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image rejection mixer for a down converter used in a receiver such as a radio communication device.

[0002]

2. Description of the Related Art In recent years, an image rejection mixer is a receiver of only a single frequency, a frequency conversion circuit of a single superheterodyne receiver, and is often used when an IF signal is low and an image signal cannot be attenuated by an RF input filter. Have been.

Hereinafter, a conventional image rejection mixer will be described. FIG. 4 shows a block connection of a conventional image rejection mixer. In FIG. 4, reference numeral 1 denotes an in-phase two-way divider, which distributes an RF input signal in-phase and sends out the same to two mixer circuits 2a and 2b. Reference numeral 4 denotes a local signal oscillator, which divides the output into two by a 90-degree hybrid 3 and sends it to the mixers 2a and 2b. The two mixer outputs 5 are 90-degree hybrid combiners in the IF band, which combine the outputs of the mixers 2a and 2b. Reference numeral 6 denotes an IF output terminal which can obtain an IF output when the local frequency is higher than the RF frequency. 7 is an IF output terminal, and IF output terminal 6
IF when local frequency is lower than RF frequency
The output is obtained.

The operation of the image rejection mixer configured as described above will be described below.

First, consider the case where the local signal is lower than the RF signal. The RF signal which is the input signal is in-phase 2
The signal is distributed by the distributor 1 and sent to the two mixers 2a and 2b. A local signal output from a local signal oscillator 4 as a local signal source is sent to a 90-degree hybrid 3, and an in-phase output and a 90-degree phase difference output are output to two mixers 2a,
2b. Then, the IF of the two mixers 2a and 2b
As the output, IF outputs having a phase difference of 90 degrees are obtained. The IF outputs having different phases by 90 degrees are further added to the 90
When the signals are combined by the hybrid 5, the combined signals of the IF outputs of the two mixers 2a and 2b are output to the 90-degree phase difference output of the hybrid 90 in the IF band with the same phase as the local signal. On the other hand, the in-phase output of the in-phase IF signal of the mixer output and the 90-degree phase difference output of the local signal are further added to the I-phase output.
In the F-band hybrid, if a phase difference of 90 degrees is received and a phase difference of 180 degrees is generated in total, IF outputs are generated, so that the IF outputs cancel each other and no IF output is generated. When the local signal is higher than the RF frequency, the IF signal output of the IF band hybrid 5 is reversed, and is not output to the 90-degree phase difference output terminal, but is output from the in-phase output terminal. That is, the IF output terminal 6 or 7 from which the IF output signal is obtained is determined depending on whether the local signal is located above or below the RF signal. In that case, the image signal is not output to the IF output terminal 6 or 7 and operates as an image rejection mixer.

[0006]

However, in the above-described conventional configuration, when the IF frequency becomes low, a 90 ° hybrid in the IF band cannot be formed by a hybrid circuit using a 波長 wavelength line. I have to do it. Therefore, there is a problem that the entire circuit becomes large and cannot be miniaturized.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a small-sized image rejection mixer.

[0008]

SUMMARY OF THE INVENTION The present invention in order to achieve this object, in view of the miniaturization of the hybrid circuit of the IF band, a distributor for 2 distributes the RF signal in phase, the local signal
90 degrees 2 for local signals that distributes signals by 90 degrees phase difference
A splitter and a 90-degree two-way splitter for the RF signal and the local signal
Frequency of the RF signal and half the frequency of the local signal.
It is composed of parallel coupled lines corresponding to 1/4 wavelength of
Input signal and local signal from isolation terminal
The two 90-degree phase difference output terminals on the output side
First and second mixers configured by inputting as a mixer
And the IF frequency is cut off at the first and second mixer outputs.
Two sets of resistance / capacitance times connected in series to obtain the wave number
Path and the connection point of resistance and capacitance of the resistance / capacitance circuit.
Each of the connected load resistors and one of the load resistors
And an IF output terminal for suppressing the image signal . The number of components is reduced by using a harmonic mixer as the mixer and sharing the RF signal and the local signal distributor with a 90-degree hybrid circuit formed of parallel coupling lines .
Has a configuration in which the small-type.

[0009]

According to the present invention, the two mixers I
A 90-degree hybrid in the IF band for synthesizing the F output, without using a conventional hybrid coil, selects a resistance value and a capacitance value that are cutoff frequencies at the IF frequency for two mixer outputs, and sets two pairs of the resistance and the capacitance. A resistor and a capacitor are connected in reverse to the outputs of the two mixers, and a load resistor corresponding to the output impedance is connected to a point where the two sets of the resistor and the capacitor are connected in series. The phase difference between the outputs is set to have a phase difference of 90 degrees in the IF frequency band, and the IF output is taken out from one of the two IF output terminals with high impedance. Therefore, the 90-degree hybrid in the IF band can use the resistance and capacitance of chip components without using a hybrid coil as in the related art, so that when a circuit is configured on a printed circuit board, automatic mounting becomes possible. Occupies a small area, and a small-sized image rejection mixer can be realized. Further, the mixer is a harmonic mixer, and the distributor for the RF signal and the local signal is constituted by a parallel coupling line.
By reducing the number of parts by using a hybrid circuit, the size can be further reduced.

[0010]

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an image rejection mixer according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an in-phase two-way splitter for RF signals;
Is a mixer circuit. 3 is a 90 degree hybrid circuit,
The signal from the local signal oscillator 4 is supplied to the two mixer circuits 22 and 23 with a phase difference of 90 degrees. On the output side of the mixer circuits 22 and 23, a capacitor 11 having a cut-off frequency of the IF frequency and a resistor 10 are connected in series to the respective mixer circuits 22 and 2.
3, a load resistor 12 corresponding to the output impedance is connected to the series connection point of the resistor 10 and the capacitor 11, and the connection point is connected to the output terminal 8 of the image rejection mixer.
And 9.

The operation of the thus configured image rejection mixer will be described below.

First, consider the case where the local signal is lower than the RF signal. The RF signal is split by the in-phase two splitter 1 and sent to two mixer circuits 22 and 23. on the other hand,
The local signal output from the local signal oscillator 4 is also
Once sent to the 90-degree hybrid 3, the in-phase output and 9
Two mixer circuits 2 distributed to outputs having different phases by 0 degrees
2, 23. Then, two mixer circuits 22,
After the mixing of 23, the IF output is obtained with an IF output having a phase difference of 90 degrees. The output signal from the mixer circuit 22 is output to the IF output terminal 8 after being subjected to a 90-degree phase shift by the capacitor 11, and the mixer output of the mixer circuit 23 uses a 90-degree phase difference output signal as a local signal. Therefore, the IF output signal is output after being subjected to a phase shift of 90 degrees, and a composite output thereof is obtained. On the other hand, when an image signal is input, the two mixer circuits 22 and 2
The IF output of No. 3 has a phase relationship opposite to the normal IF frequency, and is output from the IF output terminal 9 as an IF signal.

That is, by setting the local frequency above or below the RF frequency, an IF output terminal from which an IF output signal is obtained is determined, and the other end becomes an image signal output, and operates as an image rejection mixer.

As described above, according to the present embodiment, a 90-degree hybrid in the IF band for synthesizing the IF outputs of the two mixers is output to the two mixer outputs at the IF frequency without using a conventional hybrid coil. A resistance value and a capacitance value are selected so as to have a cutoff frequency, and two resistors 10 and 11 connected in series are connected to the outputs of two mixer circuits 22 and 23 by inverting the resistance 10 and the capacitance 11 respectively. , And a load resistor 12 corresponding to the output impedance is connected to the point where the two sets of the resistor 10 and the capacitor 11 are connected in series. Thus, a signal in which the image frequency is suppressed can be obtained. Therefore, since the resistance and capacitance of the chip components can be used, the circuit can be automatically mounted when a circuit is formed on a printed circuit board, and a small image rejection mixer with a reduced area occupied by the circuit can be realized.

In the above description, the configuration has been described in which the RF frequency is distributed in phase, the local signal is distributed with a phase difference of 90 degrees, and is input to the two mixers. It goes without saying that the same operation is performed even if the signal is distributed in phase and input to the mixer. Further, even when the local signal uses a half frequency and the mixer is constituted by a harmonic mixer, the RF signal is transmitted by 90%.
The same operation can be performed by inputting the harmonic phase difference to the harmonic mixer.

(Embodiment 2) Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a circuit diagram of an image rejection mixer according to a second embodiment of the present invention.

In FIG. 2, the output circuit of an image rejection mixer composed of a resistor 10, a capacitor 11, and a load resistor 12 is the same as the configuration of FIG. 1 in that the output frequency of the local signal oscillator 4 is set to (R
(F frequency) + (IF frequency) or (RF frequency)-
The difference is that the harmonic mixer is と し た of the (IF frequency), and the distributor for the RF signal and the local signal is shared by the 90-degree hybrid 17 constituted by parallel coupling lines. The capacitor 13 is a DC cut element, and the inductance 14 is a DC return element.

The operation of the image rejection mixer configured as described above will be described below.

First, by using a parallel coupling line composed of a half of the local frequency and a quarter wavelength of an almost intermediate frequency of the RF frequency as the 90-degree hybrid circuit 17, the local signal of the half is reduced to 90%. Are input to the mixer diodes 15 and 16 with a phase difference of degrees and operate as a local signal having a frequency twice that of the mixer diodes 15 and 16.
This means that the signal is input with a phase difference of 0 degrees, and the signal is harmonic-mixed with the RF signal having a phase difference of 90 degrees input from the other end of the 90-degree hybrid, and operates as an image rejection mixer. Thus, when this circuit is configured on a printed circuit board, the number of components is reduced, so that the occupied area can be reduced, and a small-sized image rejection mixer can be provided.

Incidentally, the 90-degree hybrid circuit 17 shown in FIG. 2 can be specifically constituted by a parallel coupling line 18 using a multilayer substrate as shown in FIG. FIG. 3B is a cross-sectional view taken along line XX of FIG.
The terminals B, C and D correspond to the terminals A, B, C and D in FIG.

In FIG. 3, a parallel coupling line 18 is coupled between upper and lower lines via a dielectric 19 to form a 90-degree hybrid. The degree of coupling is determined by the width of the line and the thickness of the dielectric 19 between the lines. Here, the dielectric width between the line width and between the lines and between the line and the upper and lower ground substrates is set so that the coupling degree becomes 0.5 at the local frequency and the RF frequency.
And the coupling line length is １ ／ of the local frequency.
And a line length of 1/4 wavelength of a frequency almost intermediate between the RF frequency and a mixer circuit and a separate substrate. By changing this hybrid substrate according to the frequency band, a mixer of a different frequency can be easily formed. Can be configured. Further, it is necessary to increase the accuracy of the thickness and pattern width of the substrate constituting the hybrid circuit as compared with a normal printed circuit board. Therefore, by separating the mixer circuit from the circuit board, the mixer circuit can be configured with the accuracy of a normal printed circuit board, and the unit cost of the circuit board can be reduced.

[0024]

As described above, according to the present invention, the RF signal is in phase.
And a local signal with a 90 degree phase difference
A 90-degree two-way splitter for local signals for splitting into two, and the RF
90 degree splitter for signal and local signal
に wavelength of the middle frequency
RF signal and local signal
Is input from the isolation terminal and the output side is about 90 degrees
Input the phase difference output terminal as two harmonic mixers
First and second mixers configured as described above, and the first and second mixers
To the mixer output so that the IF frequency becomes the cutoff frequency.
Two connected resistor / capacitor circuits and the resistor / capacitor circuit
Load resistance connected to the connection point of the resistance and capacitance of the path
And an IF in which an image signal is suppressed to one of the load resistors.
An image rejection mixer provided with an output terminal is configured. The mixer is a harmonic mixer, and R
By the structure shared by 90-degree hybrid circuit which is constituted by parallel coupled line a distributor of F signal and the local signal, but can realize image rejection mixer of the small image rejection mixer.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of an image rejection mixer according to a second embodiment of the present invention.

FIG. 3 is a pattern and side sectional view of a main part of the image rejection mixer.

FIG. 4 is a block diagram of a conventional image rejection mixer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 In-phase 2 splitter 2, 22, 23 Mixer circuit 3 90 degree hybrid circuit 4 Local signal oscillator 12 Load resistance 15, 16 Mixer diode 17 90 degree hybrid parallel coupling line

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03D ⁷ /14-7/18 H03H 11/16-11/18

Claims (2)

(57) [Claims] A splitter for splitting an RF signal into two in-phase ;
Local local signal signal 2 distributed at 90 degree phase difference
90-degree splitter for the RF signal and the local signal 9
The 0 degree 2-divider is almost equal to 1/2 of the RF signal and the local signal.
It is composed of a parallel coupling line corresponding to １ ／ wavelength of the intermediate frequency.
To isolate RF and local signals
And a 90 ° phase difference output terminal on the output side.
First and second mixers configured to be input as a harmonic mixer, and two sets of resistors connected in series to the first and second mixer outputs so that the IF frequency becomes a cutoff frequency.
An image rejection mixer comprising: a capacitance circuit; a load resistance connected to a connection point between the resistance and the capacitance of the resistance / capacitance circuit; and an IF output terminal for suppressing an image signal on one of the load resistances. 2. The parallel coupling line according to claim 1 , wherein
It is composed of a separate substrate from the mixer, and is actually mounted on the first and second mixers.
The image rejection mixer according to claim 1, wherein the mixer is mounted .