JPH0642615B2 - Frequency converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The IF branched into a phase difference of 90 ° by the first 90 ° hybrid.
The signal input is connected to the first and second diode mixers and the third and fourth diode mixers.
In addition to the diode mixer of, the local signal input branched to the phase difference of 90 ° by the second 90 ° hybrid is respectively -90 ° and -180 ° via the third and fourth 90 ° hybrids.
The signal of -90 ° phase is applied to the second and fourth diode mixers, and the signal of -180 ° phase is applied to the first and second λ / 8 lines respectively. , In addition to the third diode mixer, the generated signals are combined again with the phases of −90 ° and −180 ° via the third and fourth hybrids to obtain a sum having a phase difference of 90 °. Frequency or difference frequency signal is obtained and this is the fifth 90 °
By synthesizing with a phase difference of 90 ° through the hybrid, a frequency conversion output of the sum frequency or the difference frequency in which both the local leak and the image signal are suppressed is obtained.

[Industrial application field]

The present invention relates to a frequency converter in a radio frequency band, and more particularly to a frequency converter capable of suppressing local leak and suppressing an image signal at the same time.

For the purpose of input / output conversion between the microwave signal and the intermediate frequency signal, the local oscillation output and the intermediate frequency input are mixed,
A frequency converter that obtains a frequency converted output is used. In such a frequency converter, in order to reduce reception interference, it is desired that the leakage of the local oscillation output to the frequency conversion output side is small and the image frequency signal is sufficiently suppressed.

[Conventional technology]

Conventionally, as the frequency converter, one having a configuration shown in FIG. 8 for suppressing local leak and one having a configuration shown in FIG. 9 for suppressing image are known.

In FIG. 8, reference numerals 1 and 2 denote hybrids (H), and 3 and 4 denote mixers. The local signal input is branched through the hybrid _{1 with} a phase difference of -φ ₁ and supplied to the mixers 3 and 4. At the same time, the mixers 3 and 4 are supplied with an intermediate frequency (IF) input with a phase difference of −π, and the outputs of both mixers 3 and 4 are supplied with a phase difference of − (π−φ ₁ ) in the hybrid 2. By synthesizing in this way, the frequency converted output in which the local leak is suppressed can be obtained in the output of the hybrid 2. Note that such a frequency converter is disclosed in
It is described in detail in Japanese Patent Publication No. 58-173906.

In FIG. 9, 5 and 6 are hybrids (H), 7, and 8.
Is a diode, and 9 is a λ / 8 (λ is a local signal wavelength) line, and an IF input is branched by a hybrid 6 with a phase difference of 90 ° and applied to frequency conversion diodes 7 and 8, respectively. On the other hand, the local input is 90 ° after passing through hybrid 5.
Are branched with a phase difference of 1
/ 8 line 9 with a delay of π / 4 and diodes 7, 8
Add to. As a result, a frequency conversion output in which the image signal is suppressed can be obtained from the other terminal of the hybrid 5. Note that such a frequency converter is disclosed in
It is described in detail in Japanese Patent Publication No. 57-107617.

[Problems to be solved by the invention]

The conventional frequency converter shown in FIG. 8 can suppress the local leak, but cannot suppress the image, and the necessary signal and the image signal are output at the same level. There is a problem that a narrow band wave filter is required after the frequency converter.

Further, the conventional frequency converter shown in FIG. 9 has a problem that the isolation between the input and output signals is poor and the local oscillation signal leaks to the frequency conversion output.

[Means for solving problems]

In order to solve the problems of the prior art, the frequency converter of the present invention has a principle configuration as shown in FIG.

101 is a 90 ° hybrid, which allows input of signals such as IF 9
Two outputs are produced by branching with a phase difference of 0 °.

102 is a 90 ° hybrid which produces two outputs by phasing the signal input of the local oscillator to 90 °.

109 and 110 are 90 ° hybrids respectively. One of the signals branched by the hybrid 101 is a non-linear element 103,1.
04 and λ / 8 line 105, 106, the other is a non-linear element 10
The local signals, which are respectively branched via the hybrid circuit 102, are input to one of the terminals having isolation characteristics.

111 is a 90 ° hybrid, and hybrid 109,110
The respective outputs of the other terminal having the isolation characteristic of are combined with a phase difference of 90 °.

[Action]

The hybrid 101 branches the IF signal input with a phase difference of about 90 ° and inputs it to the diodes 103, 104 and 107, 108, and the hybrid 102 branches the local signal input with a phase difference of about 90 ° and inputs it to the hybrids 109, 110, and the hybrid 10
At 9,110, local signal input is branched at −90 ° and −180 ° phases, and signals at −90 ° phase are diode 107,10.
In addition to 8, add a signal of −180 ° phase to λ / 8 line
After passing through 105 and 106, the phase is shifted by 45 ° and added to the diodes 103 and 104. As a result, the sum frequency signal and the difference frequency signal generated in the diodes 107 and 108 and the sum frequency signal and the difference frequency signal generated in the diodes 103 and 104 and phase-shifted by 45 ° in the λ / 8 lines 105 and 106 are -90 in the hybrid 109 and 110. The signals of the sum frequency and the signal of the difference frequency are canceled in the opposite phase, and the other signals are combined in the same phase. Since the signals of the sum frequency or the difference frequency combined in the same phase have a phase difference of 90 °, by combining them with the phase difference of 90 ° through the hybrid 111, the sum frequency or the suppressed sum frequency A frequency conversion output consisting of the difference frequency is obtained. At this time, the local leaks generated in hybrids 109 and 110 are
At 11, the signals are combined in the opposite phase with a phase difference of 90 °, and the frequency converted output in which the local leak is suppressed is obtained.

〔Example〕

FIG. 2 shows an embodiment of the present invention.
15 is a 90 ° hybrid (H), 16 to 19 are diodes, 2
Reference numerals 0 and 21 are λ / 8 (λ is a local signal wavelength) lines. In FIG. 2, diodes 16 and 17, 18 and 19 are connected to hybrids 13 and 14 in opposite directions.

FIG. 3 shows the phase relationship of the hybrid input / output signals used in the present invention. The input signal at the terminal a is branched to the terminals c and d at the phases of -90 ° and -180 °, respectively. , The input signal of terminal b is -180 °, -90 respectively
It is branched to terminals c and d in the phase of °. The terminals c and d have mutual isolation characteristics. Further, when the terminals c and d are used as input terminals, the terminals c and d operate reversibly, and outputs are produced at the terminals c and d in the same phase relationship as described above.

A local signal ω _L from a local oscillator not shown in FIG. Goes through the hybrid 12 and follows the phase relationship of FIG.
The outputs are branched by the phases of 90 ° and -180 ° and are input to the hybrids 13 and 14, respectively. This local signal passes through the hybrids 13 and 14 and causes a local leak at the other terminal having the isolation characteristic, but these signals are applied to both inputs of the hybrid 15 and are -90 ° and -180 °, respectively. It is transmitted to the output terminal in the phase of ° and synthesized in the opposite phase. Therefore, in the circuit of FIG. 2, the local leak at the output is eliminated.

On the other hand, the intermediate frequency (IF) signal ω _IF (indicated by ↑) is similarly branched through the hybrid 11 in the phases of −90 ° and −180 °, and further through the T branch to the diodes 16, 17 respectively.
And added to 18,19. In the diode 16, the local signal of −180 ° phase of the hybrid 13 is transmitted through the λ / 8 line 20.
In addition, a 45 ° phase change is applied to the diode
A local signal having a phase of −90 ° of hybrid 13 is applied to 17. Similarly, the local signal of −180 ° phase of the hybrid 14 is further fed to the diode 18 by the λ / 8 line 21.
The phase change of 5 ° is applied, and the diode 19 is applied with the local signal of the hybrid 14 having a phase of -90 °. Each of the diodes 16 to 19 operates as a mixer and mixes both applied signals to generate a frequency conversion output.

The first harmonic component i (t) of the signal output current in each diode in this case is expressed by the following equation.

Where ω _L = 2π _LO (where _LO is the frequency of the local signal) ω _IF = 2π _IF (where _IF is the frequency of the IF signal) φ _L : Phase of the local signal φ _IF : Phase of the IF signal In equation (1), gm cos (ω _L + Φ _L ) represents the first harmonic component of the conductance of the mixer diode excited by the local signal, and E _IF cos (ω _IF + φ _IF ) is the IF signal voltage generated in the diode. It is known from the equation (1) that a signal of the sum frequency of the intermediate frequency signal and the local signal (ω _L + ω _IF ) and a signal of the difference frequency (ω _L −ω _IF ) are generated as a result of the frequency conversion. Figure 4
It is a diagram schematically showing the frequency spectrum of each signal in the equation (1).

The sum frequency signal (ω _L + ω _IF ) generated in this way And the difference frequency signal (ω _L −ω _LF ) And occur in a phase relationship as shown in FIG. The signals generated in the diodes 17 and 19 remain unchanged and the diodes 16 and 18
The signal generated at 1 is subjected to a phase change of 45 ° via the λ / 8 line and is added to the hybrids 13 and 14, respectively, and outputs are produced according to the phase relationship shown in FIG. At this time, as shown in FIG. 2, the signals of the difference frequency are canceled out in the opposite phase,
The sum frequency signals are combined in phase. The sum frequency signal of hybrid 13 and the sum frequency signal of hybrid 14 are 90 °
There is a phase difference between the two signals, and these signals are transmitted through the hybrid 15 at the phases of −90 ° and −180 °, respectively, and are combined in the same phase to produce an output. FIG. 5 shows the direction of each signal vector in this case.

In the case of the embodiment shown in FIG. 2, a frequency conversion output in which both the local leak and the image signal are suppressed by setting the sum frequency of the local signal and the IF signal as the desired signal and the difference frequency as the image signal. Can be obtained.

FIG. 6 shows another embodiment of the present invention, in which the same parts as in FIG.
2,23 are diodes.

The embodiment shown in FIG. 6 differs from the embodiment shown in FIG. 2 only in that the diodes 22, 23 are oriented in the same direction as the diodes 16, 17, respectively. As a result, in the embodiment shown in FIG. 6, the signals of the sum frequency and the signals of the difference frequency generated in the diodes 22 and 23 are in opposite phase to those in the case of FIG. 2, and the hybrid 13, At the output of 14, the sum frequency signal is canceled out as an opposite phase, and the difference frequency signal is combined in phase. There is a 90 ° phase difference between the difference frequency signal of the hybrid 13 and the difference frequency signal of the hybrid 14, and both signals are combined in phase via the hybrid 15 to obtain an output. FIG. 7 shows the frequency spectrum of each signal in this case.

In the case of the embodiment shown in FIG. 6, the frequency conversion output in which both the local leak and the image signal are suppressed by setting the difference frequency between the local signal and the IF signal as the desired signal and the sum frequency as the image signal. Can be obtained.

〔The invention's effect〕

As described above, according to the present invention, it is possible to realize a frequency converter that has good isolation between input and output, suppresses local leaks, and simultaneously suppresses image signals. Therefore, in the frequency converter of the present invention, it is not necessary to provide a narrow band wave filter for removing the image signal in the subsequent stage.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention, FIG. 2 is a diagram showing an embodiment of the present invention, FIG. 3 is a diagram showing a phase relationship in a 90 ° hybrid, and FIG. 4 is a diagram showing FIG. FIG. 5 is a diagram showing a frequency spectrum in the embodiment, FIG. 5 is a diagram showing directions of respective signal vectors, FIG. 6 is a diagram showing another embodiment of the present invention, and FIG. 7 is a frequency spectrum in the embodiment of FIG. FIG. 8, FIG. 8 and FIG. 9 are diagrams showing a conventional frequency converter. 11-15… 90 ° hybrid (H), 16-19,22,23… diode, 20,21… λ / 8 line

Claims (1)

[Claims] 1. A 90 ° hybrid (101) for branching a signal input with a phase difference of 90 °, a 90 ° hybrid (102) for branching a local input with a phase difference of 90 °, and one of the branched signals. Is the non-linear element (103,104) and λ
/ 8 (λ is a local signal wavelength) line (105, 106) and the other is input through a non-linear element (107, 108) and one of the terminals having the isolation characteristic of the branched local signal. A 90 ° hybrid (109,110) that is input to the 90 ° hybrid (109,110) and the output of the other terminal having the isolation characteristic of the hybrid (109,110) are combined with a 90 ° phase difference to generate a frequency conversion output. 111)
A frequency converter characterized by comprising: