JP2683432B2 - MIC type frequency converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention converts an RF signal in a microwave band into a UHF band (1 GHz).
The present invention relates to a MIC (MICROWAVE INTEGRATED CIRCUIT) type frequency converter (hereinafter referred to as MIC type mixer) used in a down converter for frequency conversion to the IF signal of the It was made for the purpose.

[Conventional technology]

FIG. 3 is a block diagram showing the configuration of a down-converter for converting a microwave signal in the 22 GHz band (hereinafter referred to as an RF signal) to an IF signal in the 1 GHz band, which is described in IEICE Technical Report MW88-28. In the figure, 1 is an RF signal input terminal, 2 is RF AM
P, 3 RF BPF, 4 mixer diode, 6 local oscillator (hereinafter referred to as LO), 5 LO BPF, 7 LO signal input terminal, 8 IF LPF, 9 IF signal output terminal . For convenience of explanation, RF BPF3, mixer diode 4, L
The O BPF5 and the IF LPF8 are collectively called a frequency converter (mixer) 10. Reference numeral 11 is an RF signal input terminal of the mixer 10.

In the figure, f ₁ is the RF signal frequency, f ₂ is the LO signal frequency, and f ₃
Is the IF signal frequency, and f ₄ is the image signal frequency of f ₁ .
And the relation that holds between these frequencies is f ₁ > f ₂ > f ₄
A »f _3, and is _{f 3 = f 1 -f 2 =} f 2 -f 4.

The primary function of the down converter and mixed by injecting the LO signal generated by the RF signal and LO6 inputted from the RF signal input terminal 1 to the mixer diode 4, the RF signal frequency f ₁ and LO
The frequency f ₃ of the difference from the frequency f _{2 of the} signal is obtained.

 The basic operation of each part will be described below.

RF AMP2 is intended to amplify the input RF signal, in the frequency band f ₁ of the RF signal, low noise, flatness of the predetermined gain is required. The output of RF AMP2 is supplied to the mixer diode (MIX DIODE) 4 via RF BPF3.

The RF BPF ₃ suppresses the image signal f ₄ with respect to the RF signal in the mixer diode 4, and at the same time, the RF BP is adjusted so that the energy of the LO signal f ₂ is sufficiently supplied to the diode 4.
The LO signal is suppressed so that the LO signal does not leak through F3. LO6 is the local signal oscillator, and the output L
The O signal is supplied to the mixer diode 4 via the LO signal input terminal 7 and LO BPF5.

LO BPF5 suppresses the unnecessary output wave from LO6, and at the same time suppresses the RF signal so that the energy of the RF signal does not leak to the outside via LO BPF3. The mixer diode 4 and the RF signal supplied via RF BPF3 and LO
BPF5 mixing the LO signal supplied through the, IF frequency f ₃ of the sum and difference of the signal frequency f ₂ of the frequency f ₁ and LO of the RF signal (= | f
₁ ± f ₂ |) is output.

Only the lower frequency component of the output of the mixer diode 4 is selected by the IF LPF8, and only f ₃ = | f ₁ −f ₂ | is taken out from the IF output terminal 9.

As described above, the microwave RF signal f ₁ is converted to the ₁ GHz band IF signal f ₃ in the down converter of FIG.

An equivalent circuit in the mixer 10 part is shown in FIG. In FIG. 4, 11 is the RF input terminal of the mixer, and 22 is the RF BPF3.
The microstrip line connecting the mixer diode 4 with the mixer diode 23, the input end of the mixer diode 4 is a 1/4 wavelength open line of the LO frequency provided so as to be short-circuited in the LO frequency band, and 24 is the LO BPF5 and the mixer. A microstrip line connecting the diode 4 and 25 is an IF LPF8 equivalent circuit. Further, 26 is a current feedback circuit for the mixer diode 4, 27 is a bias circuit for determining the operating point of the mixer diode 4, and these are composed of chip parts. It should be noted that all of the above components can be formed on the same Teflon substrate when the frequency band of the RF signal is near the 12 GHz band.

In FIG. 4, RF BPF3 and LO BPF5 are side-coupled BPFs composed of microstrip lines. The microstrip line 22 in FIG. 4 is RF
A length is usually selected so that the impedance on the microstrip line 22 side in the image signal frequency band of BPF3 is short-circuited or open when viewed from the mixer diode 4. Further, the length of the microstrip line 24 is selected so that the impedance on the side of the microstrip line 24 in the frequency band of the RF signal of LO BPF is short-circuited or open when viewed from the mixer diode 4. The conversion loss, which indicates the good performance of the mixer 10, depends largely on the characteristics of the RF BPF3, LO BPF5 and the length of the microstrip lines 22 and 24.Therefore, the combination of these components is important for realizing the circuit. It will be a point.

In FIG. 4, Z ₁₁ ,, Z ₁₂ ,, Z ₂₁ ,, Z ₃₁ ,, Z ₃₂ , Z ₃₃ , Z ₃₄ represent characteristic impedances of the respective microstrip lines, and l ₁₁ ,, l ₁₂ ,, l ₂₁ ,, l ₃₁ ,, l ₃₂ , l ₃₃ , and l ₃₄ indicate the electrical length of each microstrip line. Also, λ ₁ , λ ₂ ,
λ ₃ and λ ₄ indicate the wavelengths of the RF signal, LO signal, IF signal and image signal, respectively. Z _{11 to} Z ₃₄ and l _{11 to} l ₃₄ are often determined by experiments, but a rough guideline is
This is shown in the table in the figure. Z _L <50Ω, Z for Z _{11 to} Z ₃₄
Set ₀ ≈ 50Ω and Z _H > 50Ω.

As the RF BPF3 and LO BPF5, the microstrip line type described in FIG. 4 is easy to configure and the performance is stable. Therefore, the mixer 10 is a printed circuit board based on a dielectric such as Teflon. Widely used as the above component. As a result, the components shown in FIG.
All the MIC circuits can be configured on the same printed circuit board, and an inexpensive mixer can be realized.

[Problems to be solved by the invention]

However, the frequency of the RF signal and the frequency of the LO signal are 20 GHz.
When it gets higher near the band, the dielectric loss cannot be ignored, and in the case of BPF configured on a Teflon substrate, due to the nature of the material, B
Since the passing loss of PF becomes large,
As shown in, it is necessary to construct RF BPF and LO BPF using a dielectric resonator on an alumina ceramic substrate to obtain the required performance.

However, the BPF using an alumina ceramic substrate or a dielectric resonator is very expensive, and since it cannot be configured on a single substrate, the mixer and down converter itself become expensive, and they are not suitable for mass production. .

The present invention has been made to solve the problems of the conventional ones described above, and it is possible to realize a mixer that is inexpensive and has high mass productivity. It is also a down converter that is inexpensive, small, and stable in performance. The purpose is to realize a frequency converter.

[Means for solving the problem]

The MIC type frequency converter according to the present invention is a MIC type frequency converter in which a mixer section for inputting an RF signal and a local oscillation signal and outputting an IF signal is formed on the same printed circuit board. An amplifier for amplifying an RF signal, a first microstrip line for passing the RF signal output from the amplifier and suppressing an image signal, and a first microstrip line connected to both ends of the first microstrip line, respectively. 2nd, 3rd with shorted or opened tip
A high-pass filter or a band-rejection filter configured by a microstrip line of the fourth microstrip line, and a fourth microstrip line that passes the local oscillation signal and suppresses the RF signal output from the amplifier, and the fourth microstrip line. A low-pass filter or a band-rejection filter, which is connected to both ends of the strip line and has fifth and sixth microstrip lines whose ends are short-circuited or opened, the high-pass filter and the low-pass filter, respectively. Is connected to the RF signal by doubling the frequency of the local oscillation signal.
A mixer diode for mixing with a signal and an IF signal low-pass filter for receiving the output of the diode and outputting the IF signal are provided.

[Action]

In the MIC type frequency converter according to the present invention, by operating the mixer diode as a second harmonic mixer, the difference between the frequency of the LO signal and the frequency of the RF signal becomes large, and the out-of-band characteristics required for RF BPF, Since the LO signal and RF signal selectivity required for LO BPF is reduced, BP
The first microstrip line instead of F and the first microstrip line
High-pass filter or band-rejection filter, which is connected to both ends of the microstrip line and has a second and a third microstrip line whose ends are short-circuited or open, and a fourth
Low-pass filter or band rejection including a microstrip line and a fifth and sixth microstrip line which are respectively connected to both ends of the fourth microstrip line and whose ends are short-circuited or opened. A filter is used to achieve a predetermined performance as a mixer without increasing insertion loss.

Where RF HPF and LO LPF or RF BRF and LO BRF
Since the dielectric loss does not pose a problem in terms of transmission characteristics even if it is configured on a Teflon substrate, it can be inexpensively configured on a single Teflon substrate as a MIC type frequency converter.

〔Example〕

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

FIG. 1 shows a MIC type frequency converter according to an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 4 indicate the same elements. 33 LO, 40 with an oscillation output of the RF HPF, 35 is LO LPF, 36 is an RF signal f ₁ and half of the frequency f ₅ of the difference f ₂ of the frequency f ₃ of the IF signal (= f _2/2) Is a mixer including RF HPF33, LO LPF35, mixer diode 4 and IF LPF8.

Further, the reference numeral 2'is attached to RF AMP because the gain in the frequency band of the RF signal is increased from that of RF AMP2 in FIG. 3 in order to compensate the conversion loss of the mixer 40.

Next, the operation of each part in FIG. 1 will be described.

The RF AMP 2'amplifies the RF signal input from the RF signal input terminal 1. Since the conversion loss of the mixer 40 is actually larger than that of the mixer 10, the RF loss is equal to the difference in loss.
The gain is set larger than that of AMP2 in the frequency band of the RF signal. However, the increase in manufacturing cost due to this is small.

RF HPF 33 passes the RF signals f _1, and RF signals f ₁ and IF
Frequency f ₂ of the difference from the signal f ₃ {= frequency twice the LO signal f ₅ }
And the image frequency f ₄ for the RF signal f ₁ {= 2 × f ₅ −
It has a suppressing effect on f ₃ }.

Furthermore, LO LPF 35 passes the LO signal f _5, RF signal f ₁ and L
This is to suppress the frequency f ₂ which is twice the frequency of the O signal f ₅ .

The LO 36 oscillates at a frequency f ₅ that is half the frequency f _{2 that is} the difference between the RF signal f ₁ and the IF signal f ₃ , and supplies the LO signal to the mixer diode (MIX DIODE) 4 via the LO LPF 35. The mixer diode 4 has an LO due to the nonlinear characteristics of the mixer diode.
By generating a frequency twice as high as the signal f ₅ , that is, f ₂ , and mixing it with the RF signal frequency f ₁ , | f ₁ ± (2 × f ₅ ) | = | as in the case of FIG. The frequency f ₁ ± f ₂ |
The difference frequency | f ₁ −f ₂ | = f ₃
Only available as output.

By the above operation, the required function of the circuit of FIG. 1 matches that of the circuit of FIG.

An equivalent circuit for the mixer 40 is shown in FIG. The operation of each part will be described with reference to FIG. In the figure, Z _{11 to} Z ₃₄ , l ₁₁
~ L ₃₄ is a symbol having the same meaning as in FIG. 4. λ ₅ is LO36
Is the wavelength of the oscillation frequency f ₅ .

RF HPF 33 1/2 wavelength of the image signal when the distance corresponding to a quarter wavelength of the image signal of the microstrip line 22 'from the mixer diodes _{4 (= λ 4/4)} , which also is not possible to quarter wave A 1/4 wavelength open-ended line of the image signal is provided at the distance of 1/4, and a 1/4 wavelength open-ended line of the frequency of the image signal is further provided at a position of 1/4 wavelength of the image signal. Namely, In _{FIG, l 1 = λ 4/4} , l 2 = λ 4/4, l 3 =
Assuming that λ _4/4 , Z ₁ = Z _L , Z ₂ = Z _O , Z ₃ = Z as in the case of FIG.
Decide as _L. The pass characteristic of the RF HPF can be set as shown in FIG. 5, and when the RF HPF is seen from the mixer diode 4, a large attenuation amount close to a short circuit can be provided at the image frequency. This causes RF HPF to be R
Although the F signal f ₁ is passed, it has a suppression amount for the image frequency, and since it also has an suppression amount for f ₂ as shown in FIG. 5, it can be replaced with RF BPF3. . However, unlike RF BPF, the pass loss does not increase because the microstrip line serves as a transmission line for the frequency band of the RF signal.

Although FIG. 2 shows the case where the RF HPF 33 has two stages, it is also possible to repeatedly connect the same pattern with three stages, in which case the suppression amount increases in accordance with the number of stages. The 1/4 wavelength open line 21 having the LO frequency f ₅ is provided at the input end of the mixer diode 4 so as to be short-circuited at the frequency f ₅ .

On the other hand, the LO LPF35 is provided with a tip short-circuit line of 1/2 wavelength of the RF signal at a position of 1/4 wavelength or 1/2 wavelength of the RF signal from the mixer diode 4 via the microstrip line 23 '. Separate the 1/4 wavelength of the RF signal and provide a short-circuit line at the tip of the 1/2 wavelength of the RF signal. The LO LPF exhibits the pass characteristic as shown in FIG. 6, and when the LO LPF 35 is seen from the mixer diode 4 through the microstrip line 24, it is possible to provide the RF signal frequency with an attenuation amount which is almost open.

On the other hand, since the LO signal f ₅ has a frequency that is about 1/2 of the frequency f _{1 of the} RF signal, the transmission loss of the microstrip line is dominant in the pass loss in the LO LPF 35.
Small enough for practical use. As a result, the LO shown in FIG.
It can be replaced with BPF5.

Also, the RF HPF shows an HPF with a 1/4 wavelength open-ended line of 33 image frequencies, but it has a shape similar to that of the LO LPF35, and it may be a BRF for an image frequency with a 1/2 wavelength short-circuited line at the image frequency. , LO LPF35
The RF HPF 33 may have a shape similar to that of the RF HPF 33, and may be configured by a 1/4 wavelength open-ended line of the RF signal frequency.

Furthermore, as shown in other embodiments of FIGS. 7 and 8,
In the RF HPF33, select the frequency that gives the maximum suppression amount between the image frequency and twice the LO frequency, or LO
It is also possible to select the frequency that gives the maximum amount of suppression in the LPF35 between the RF signal frequency and twice the LO frequency.

All these modifications are carried out in the adjustment stage of the actual circuit.

As also shown in FIG. 2, the RF HPF 33 is connected to the first microstrip line and to both ends of the first microstrip line, respectively, and the tip ends of the second and third RF strips are opened. The LO LPF35 is composed of a microstrip line, and the LO LPF35 is connected to the fourth microstrip line and both ends of the fourth microstrip line, respectively, and the fifth and the sixth are short-circuited at their tips. , And the microstrip line can be easily formed on the same printed circuit board, so that the MIC type frequency converter can be realized at low cost.

Although the mixer diode is operated as a second-order harmonic mixer in the above-described embodiment, it may be operated as an n-th order (n is an integer of 2 or more) harmonic mixer, and the same effect as that of the above-described embodiment is obtained. Play.

〔The invention's effect〕

As described above, according to the present invention, in the MIC type frequency converter formed by forming the mixer section for inputting the RF signal and the local oscillation signal and outputting the IF signal on the same printed circuit board,
An amplifier that amplifies the input RF signal, a first microstrip line that passes an RF signal output from the amplifier and suppresses an image signal, and is connected to both ends of the first microstrip line, respectively. And a high-pass filter or band-rejection filter composed of second and third microstrip lines whose ends are short-circuited or open, and an RF signal output from the amplifier while passing the local oscillation signal. A fourth microstrip line for suppressing and fifth and sixth lines connected to both ends of the fourth microstrip line and having their ends short-circuited or opened.
A low-pass filter or a band-rejection filter constituted by a microstrip line, connected to the high-pass filter and the low-pass filter, and a mixer diode for doubling the frequency of the local oscillation signal and mixing with the RF signal, Since the output of the diode is input and the IF signal low-pass filter that outputs the IF signal is provided, the difference between the RF signal frequency and the LO signal frequency becomes large, and it is available at a high frequency of 20 GHz band. RF BPF and LO BPF that are difficult to configure with easy components
Instead of the first microstrip line and the first microstrip line,
High-pass filter or band-rejection filter, which is connected to both ends of the microstrip line and has a second and a third microstrip line whose ends are short-circuited or open, and a fourth
Low-pass filter or band-rejection composed of the fifth and sixth microstrip lines which are respectively connected to both ends of the fourth microstrip line and whose ends are short-circuited or opened. There is an effect that an inexpensive mixer can be configured by using a filter, and a down converter including the mixer can be configured at low cost.

[Brief description of the drawings]

1 is a block diagram of a down converter according to an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of a mixer according to an embodiment of the present invention, FIG. 3 is a block diagram of a conventional down converter, and FIG. An equivalent circuit diagram of a conventional mixer, FIG.
Explanatory diagram showing pass loss characteristics of RF HPF, Fig. 6 is LO LPF
FIG. 7 is an explanatory diagram showing a passage loss characteristic of a modification of RF HPF, and FIG. 8 is an explanatory diagram showing a passage loss characteristic of a modification of LO LPF. In the figure, 4 is a mixer diode, 33 is an RF HPF, 35
Is a LO LPF, and 36 is a local signal oscillator for operating the second harmonic mixer. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A MIC type frequency converter in which a mixer section for inputting an RF signal and a local oscillation signal and outputting an IF signal is formed on the same printed circuit board, and an amplifier for amplifying the inputted RF signal. And a first microstrip line that passes an RF signal output from the amplifier and suppresses an image signal,
Second ends connected to both ends of the first microstrip line and short-circuited or open at their ends,
A high-pass filter or a band-rejection filter configured by a third microstrip line; a fourth microstrip line that passes the local oscillation signal and suppresses an RF signal output by the amplifier; , A low-pass filter or a band-rejection filter, which is connected to both ends of the microstrip line and has fifth and sixth microstrip lines whose ends are short-circuited or open, and the high-pass filter and the low-pass filter. A mixer diode connected to the filter for doubling the frequency of the local oscillation signal and mixing with the RF signal; and an IF for inputting the output of the diode and outputting the IF signal.
MI characterized by having a signal low-pass filter
C type frequency converter.