JP3170334B2 - High frequency transformer and mixer using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency transformer and a mixer using the same. C. To a mixer that can operate stably from high to high frequencies, and a mixer that can eliminate a common mode choke from the input section and can eliminate an increase in input impedance due to the inductance of the choke in the RF port even if a common mode choke is provided. .

[0002]

2. Description of the Related Art As balanced high-frequency mixers, there are a single balanced mixer ( SBM ) and a double balanced mixer (DBM), and these mixers include a diode and a transformer. In particular, recently, for reasons such as downsizing of a mixer, a microstrip line is formed on a printed circuit board without using a high-frequency core for the transformer, and the microstrip line is used as a transformer. There is provided a coaxial cable having no sheath, which is soldered and used as a transformer.

For example, as shown in FIG. 7A, an SBM is formed on a printed circuit board by strip lines 21a and 21b.
(First and second strip lines) are formed on one straight line with a pattern non-formation part interposed between opposing ends, and a third strip line 22 is formed from the pattern non-formation part by both strip lines 21a. , 21b. In this way, each strip line is formed so as to be entirely T-shaped. Stripline 2
The base of the T-shaped 2 is branched into two branches, and the branches (a balun is formed by the inductance of both branches) 23a, 2
The tip of 3b is connected to the T-shaped inner ends of the strip lines 21a and 21b. Also, stripline 2
The length of 1a, 21b is set to 1/4 of the wavelength λ of the specific frequency, and the characteristic impedance of the strip lines 21a , 21b, 22 and the characteristic impedance (usually 50Ω) on the IF output side are matched. .

[0004] Strip lines 21a, 21b
, Two diodes D ₂₁ ,
A series circuit of D ₂₂ are connected, both diodes _D 21, D
_An RF input terminal 24 is drawn out from between them. A coaxial cable 25 having the same length as that of the strip line 21a and having no insulation jacket is soldered on the strip line 21a, and the T-shaped inner end of the center conductor of the coaxial cable 25 is connected to the T-shaped inner end of the strip line 21b. It is connected. Also, a station is located at the T-shaped outer end of the center conductor of the
Part oscillator (hereinafter, referred to as "local oscillator") Ru Tei one terminal connected to 26. The other end of the local oscillator 26 and the T-shaped outer ends of the strip lines 21a and 21b are connected to the ground on the back surface of the printed circuit board via through holes (not shown), for example. Incidentally, FIG. 7 (B) is an equivalent circuit diagram of the mixer, in inductance L _A COAX 25 on the strip line 21a in FIG. 7 (A), (also acts as a common mode choke) balun 23
a, it is shown the inductance _{L B} by 23b.

In such an SBM, for example, C.
When converting a 1.5 GHz RF signal into a 2 GHz IF signal, the local signal of the local oscillator 25 is 2-3.5 GHz.
Is set to This local signal is applied to the diode group D ₂₁ ,
The D ₂₂ was switched, the local signal and the RF input is mixed, branched 23a, via a common mode impedance formed by 23b outputs the IF signal from the terminal 24. The microstrip line 21b on the side where the coaxial cable 25 is not joined is used as a dummy for balancing with the microstrip line 21a. By the way, SBM as described above
Although the input impedance can be kept low,
Since the port and the local port are connected via the diodes D ₂₁ and D ₂₂ , the isolation is insufficient and the insertion loss is large, and the leakage of the RF signal and the local signal causes the DBM described below. There is a disadvantage that it becomes larger than that.

FIG. 8A is an equivalent circuit diagram of the DBM.
Although illustration of the pattern and the like on the printed board is omitted, the transformers 31 and 32 (inductance L
₁ , L ₂ ) and the common mode choke 33 (inductance L ₃ ) are formed by microstrip lines formed on the printed circuit board surface. In FIG. (A), the common mode choke 33 of the local signal is a local oscillator 34 side, D ₁ of the diode group 35 through a transformer 31 and 32, D ₂
Alternatively, D ₃ and D ₄ are switched, and the RF signal input from the terminal 37 is mixed with the local signal.
The mixed signal is output as an IF signal from a terminal 38 via a transformer 36 for balanced / unbalanced conversion.

[0007] For example, D. C. When converting an RF input of 1.5 GHz to 2 GHz, the output of the local oscillator 34 is 2 to
Is set to 3.5 GHz, the local oscillator signal is L ₁ and L _2, L
The switching of the diode group 35 is performed via ₃ , and two balanced signals (mixed signals) are output from the diode group 35, converted by the balanced / unbalanced conversion transformer 36 and output as IF signals. By the way, when the diode is viewed from the RF input side, the inductance L ₃ of the common mode choke 33 is directly seen through the transformers 31 and 32. Therefore, RF
There are inconveniences such as an increase in the input impedance of the terminal 37, an increase in insertion loss and distortion, and an increase in input return loss.

[0008] When there is no common-mode choke 33, as shown in FIG. 8 (B), effect of the source resistance 39 of the local oscillator 34 is increased, the inductance _{L 2} and _{L 3} of the transformer 31, 32 Imbalance occurs in the path of
A stable IF output cannot be obtained. Therefore, the common mode choke 3 3 for the balance of the path was hitherto essential.

[0009]

SUMMARY OF THE INVENTION The present invention has been proposed in order to solve the above-mentioned problems. C. Together to provide a high frequency transformer for a high frequency range to a stable operation from, (2) and this to remove the common mode choke from the input unit are possible, be provided with a common-mode choke, RF by said choke inductance It can be eliminated to increase the input impedance of the terminal, low insertion loss, and an object thereof is to provide a wideband mixer of low distortion.

[0010]

SUMMARY OF THE INVENTION A high frequency transformer according to the present invention has a substantially U-shaped pattern formed on a printed circuit board surface, the pattern comprising two strip lines and a pattern for short-circuiting one end of both strip lines. A conductive wire having substantially the same length as the line length is provided on each of the strip lines in an insulated manner on each of the strip lines, and the U-shaped leading ends of the conductive wires are short-circuited . An end opposite to the U-shaped front end side is a first port, and the U-shaped front ends of both strip lines are a second port.

Also, the mixer (DBM) of the present invention has a configuration in which a local oscillator is connected between both terminals of the first port, and two diodes in series connection circuit of two diodes are connected between both terminals of the second port. A pair of diode switches connected in opposite directions are connected to each other, and this is used as an IF output terminal. A third port is formed in a short-circuit pattern portion of the two strip lines of the U-shaped pattern, and this is used as an RF input terminal. It is characterized in that each characteristic impedance of the strip line is configured to be twice the characteristic impedance of the RF input system.

The basic operation of the present invention will be described below. In the high-frequency transformer of the present invention, the two strip lines constituting the substantially U-shaped pattern may not be parallel, but are usually parallel in consideration of the convenience in pattern design. In addition, as long as the conductor provided on the strip line is insulated from the strip line, various conductors such as cords can be used. However, in consideration of the easiness of joining to the strip line, an insulating jacket is provided. A coaxial cable with no (exposed outer conductor) is preferably used. In this case, the coaxial cables are respectively joined on the two strip lines by soldering or the like.

In the high-frequency transformer as described above, the first port and the second port are used as either input ports or output ports. Further, a terminal corresponding to the center tap of the transformer can be taken out as a third port from the short-circuit pattern portion of the U-shaped pattern or from the short-circuited end formed on the U-shaped tip side of the conductor. Such a port is used for both input and output as well as the first and second ports. Further, both strip lines may be formed so that the characteristic impedance matches the characteristic impedance of the input / output system. In this case, when the transformer is viewed from the second and third ports, since the two strip lines are connected in parallel, the characteristic impedance of the strip line is twice the characteristic impedance of the input / output system.

Further, the short-circuit pattern portion can be formed as a capacitor. For example, in the case where a third port is formed in a short-circuit pattern portion, when a filter in which an inductor and a capacitor are patterned on a printed circuit board is connected to the third port, the capacitor pattern formed in the short-circuit portion is connected to the filter. It can also be used as a final capacitor. The length of the strip line is appropriately determined in consideration of the frequency to be handled. For example, the length of the inside and outside of a quarter of the wavelength λ of the maximum frequency of the signal to be handled can be determined as a guide. However, if the length of the strip line is too long, the coupling of the transformer in a low frequency range is considered to be good. However, resonance may occur in a high frequency range. Therefore, the length of the strip line is usually set as long as possible without causing resonance at the maximum frequency.

Further, in the mixer of the present invention, a local oscillator is connected to the first port, and the above-mentioned diode group (2 connected between both terminals of the second port) is provided next to the second port. The connection point of each diode of the set of two-diode serial connection circuit is an IF output terminal). Also,
The third port is an RF input terminal. Usually, the characteristic impedance of the two strip lines constituting the U-shaped pattern and the characteristic impedance of the system are matched by appropriately designing the width and the like of both strip lines as described above. In the above DBM, a common mode choke is usually provided between the power supply side and the transformer. However, the common mode choke may be formed of, for example, a coaxial cable, or may be formed in a pattern on a printed circuit board.

The high-frequency transformer of the present invention can be used as a balanced / unbalanced conversion transformer provided at the subsequent stage of the diode group. In this case, for example, a coaxial cable (center conductor) is used as the conductor of the transformer, and a short-circuited portion between two U-shaped ends of the center conductor is grounded.
The U-shaped ends of both strip lines constituting the U-shaped pattern are connected to the diode group side, and both center conductors on the short-circuit pattern side of the two coaxial cables joined on both strip lines can be used as IF ports.

In the transformer of the present invention, since the U-shaped tip of the center conductor of the coaxial cable joined on the stripline is short-circuited, the DB of the present invention using the transformer is used.
In M, the primary side does not need to be grounded as viewed from the local oscillator (see FIG. 8A). Therefore, even if a common mode choke is provided on the local oscillator side, the inductance of the choke viewed from the RF port can be ignored, and a wideband mixer with low insertion loss and low distortion is provided.

[0018]

FIG. 1A is a diagram showing a surface pattern of a printed circuit board showing one embodiment of a high-frequency transformer according to the present invention. The back surface of the printed circuit board is a ground plane. In FIG. 1A, a U-shaped pattern 1 (shown by oblique lines) is formed on a printed circuit board, and two U-shaped strip lines 1a and 1b (formed in parallel in the same drawing). ) Is short-circuited at one end by the short-circuit pattern 1c. Further, coaxial cables 2a and 2b having substantially the same length as the line length are joined to the strip lines 1a and 1b. These cables 2a, 2b do not have an insulating jacket, and the outer conductors are directly connected to the strip lines 1a, 1b.
Soldered above. In this embodiment, the center conductors of the coaxial cables 2a and 2b are used as the conductors provided on the strip lines 1a and 1b, and the center conductors are insulated by insulators between the coaxial cables 2a and 2b.

The ends of the center conductors of the coaxial cables 2a and 2b opposite to the short-circuit pattern 1c ( the ends of the U-shaped ends ) are short-circuited by short-circuit pieces 6, and a pair of short-circuit ends are formed from the ends on the short-circuit pattern 1c side. Terminals 3a and 3b are drawn out as first ports. Terminals 4a and 4b are drawn out from the U-shaped ends of the strip lines 1a and 1b, respectively, and these terminals form a second port. A terminal 5a (third port) is drawn from the short-circuit pattern 1c side of the U-shaped pattern 1. In addition, instead of short-circuiting the center conductors of the coaxial cables 2a and 2b with the short-circuiting pieces 6, the center conductors are grounded 7a and 7b for ease of manufacture.
b may be grounded. Also in the following embodiments, it is possible to appropriately replace the short-circuit piece 6 with the grounds 7a and 7b.

If the length of the strip lines 2a, 2b is too short, the coupling will be insufficient. If the length is too long, the coupling can be ensured in a low frequency range, but resonate in a high frequency range. Therefore, the lengths of the lines 1a and 1b are determined as long as possible without causing resonance even at the highest frequency handled by the transformer. For example, a quarter of the wavelength of the highest frequency specific frequency
It is determined based on the inside and outside. In addition, the above strip line 1
The characteristic impedance of the lines 1a, 1b
By appropriately determining the width, thickness, length, etc., the impedance is made twice as large as a predetermined impedance (usually, for example, the characteristic impedance of the third port) to achieve matching. In the above transformer, any of the first to third ports can be used as an input port or an output port. For example, when the transformer is used for a DBM, the first port is used as described later. Is a local oscillation input port, the second port is an IF output port, and the third port is an RF input port. FIG. 1B shows an equivalent circuit diagram of the high frequency transformer shown in FIG. 1A for reference.

[0021] FIG. 2 is a diagram showing a basic circuit configuration of the DBM was configured with transformer of FIG. 1 (A), the first port (terminal 3a, 3b) local oscillator 11 is connected to, Second
(Terminals 4a and 4b) are provided with a switching diode group 12 . This diode group 12
A pair of two diodes (D ₁ , D ₂ and D ₃ , D ₄ ) connected in series in the same direction are connected in parallel in opposite directions between both terminals of the second port of the transformer 10 . ,
Both sets of this diode (D ₁ , D ₂ and D ₃ , D ₄ )
The IF output port is drawn out from the connection point. The third port (terminal 5) is an RF input port. In FIG. 2, when the strip lines 1a and 1b are viewed from the RF input terminal, the lines 1a and 1b can be viewed as a parallel circuit. Therefore, when the characteristic impedance of the RF input system is, for example, 50Ω, both the strip lines 1a and 1b are used. , 1b have a characteristic impedance of 100Ω.

FIG. 3 shows a case where a low-pass filter circuit is formed on the RF input side of the transformer 10 by patterning.
4 are formed. It is a filter to form a capacitor and inductance on the printed circuit board, generally but that have been made, in the present invention short-circuit pattern 1
When the filter capacitor 1c 'is provided in the portion c,
It is also possible to form a filter circuit with high matching on only one surface of the printed circuit board.

FIG. 4 shows a case where a common mode choke 15 composed of a coaxial cable is provided between the local oscillator and the transformer. For example, if the local signal is a coaxial cable 1
Due to the common mode voltage due to the capacitance between the center conductors a and 1b and the ground, there is a difference between the current for switching the diodes D ₁ and D ₂ and the current for switching the diodes D ₃ and D _4. In such a case, the common mode choke 15 is used. By using the choke 15, the diodes D ₁ and D ₂ and the diodes D ₃ and D ₄
And the switching current can be balanced, and a balanced IF output can be obtained. As shown in the figure, the toroidal beads 16 can be attached to the common mode choke 15 to further increase the common mode inductance.

FIG. 5 is a diagram showing an embodiment in which the above-described mixer is extended for a wide band. In the figure,
Capacitor 13 and inductance 14 on RF input side
A low-pass filter as shown in FIG. 3 is formed, and a capacitor 1c 'is formed in the short-circuit pattern 1c. A choke 15 ′ for dummy which is the same as the common mode choke 15 shown in FIG. 4 is connected in parallel with the local oscillator 11. In this case, the center conductor of the coaxial cable 2b connected to the outer conductor of the common mode choke 15 is the center conductor of the common mode choke 15 '.
The center conductor of the coaxial cable 2a connected to the center conductor of the common mode choke 15 is the common mode choke 1
5 'are connected to the outer conductors, respectively, and a high balance (symmetry) is maintained on the local oscillator 11 side. Incidentally, toroidal beads 16 may be attached to the common mode choke 15 'in order to further improve the balance.

On the output side of the diode group 12 , a transformer 10 'of the same type as the transformer shown in FIG. 1 is formed. The output terminal of the diode group 12 is a transformer 10 '.
Stripline 1a of ', 1b' are connected to the U-shaped leading end of the short circuit portion 2c of the U-shaped leading end of the coaxial cable 2a ', 2b' is connected to ground. The transformer 10 ′ is used for balanced / unbalanced conversion, and performs balanced / unbalanced conversion by inverting one phase of two balanced outputs from the diode group 12 . Further, the first port "(in the figure the toroidal bead 16 'is attached) similar to the choke 15 and common mode choke 15 is connected, IF signal the choke 1
It is output from the 5 ″ output terminal.

FIG. 6 is a circuit diagram showing another embodiment in which the mixer shown in FIG. 4 is extended for a wide band. In the figure, an attenuator 17 is connected to the output side of the diode group 12.
(Consisting of two sets of resistor groups consisting of R _{1 to} R ₃ ). This attenuator 17 also operates as a balanced / unbalanced converter, so that one of the lines drawn from both output terminals of the diode group 12 is 1/1 / the wavelength of the specific frequency (frequency after conversion) more than the other. It is 2 minutes longer. The two balanced outputs from the diode group 12 are converted into unbalanced outputs by the balance / unbalance conversion action of the attenuator 17 and output from the IF terminal 19 via the pattern 18 for matching with the next stage. Note that the high frequency transformer of the present invention is not limited to DBM,
It can also be used for BM. In this case, one of the U-shaped strip lines is used as a dummy.

[0027]

According to the high frequency transformer of the present invention, a conductor is provided on two strip lines of a U-shaped pattern in a state insulated from the strip line, and the U-shaped tip of the conductor is short-circuited. Since the length of the strip line is appropriately determined, an ideal broadband transformer can be formed on a printed circuit board. If the short-circuit pattern portion of the U-shaped pattern is formed in a desired shape, the short-circuit pattern portion can be used as a capacitor pattern of a filter circuit. Further, in the mixer of the present invention, the short-circuited portion of the U-shaped pattern of the transformer is an RF input, and the tip of the U-shaped pattern of the conductive wire is an IF input, and the U-shaped of the two conductive wires provided on the strip line in an insulated state. A local oscillator was connected to each terminal on the short-circuit pattern side. Therefore, the primary side of the transformer viewed from the local oscillator is short-circuited at the end of the center conductor of the coaxial cable and is not grounded. Therefore, even if a common mode choke is provided on the local oscillator side, the local oscillator on the RF input side. No side impedance is visible.

[Brief description of the drawings]

FIG. 1A is a circuit diagram showing an embodiment of a transformer according to the present invention, and FIG. 1B is an equivalent circuit diagram of FIG. 1A.

FIG. 2 is a diagram showing a basic configuration of a mixer of the present invention.

FIG. 3 is a diagram showing an embodiment in which a pattern-formed filter circuit is connected to the RF terminal of the mixer of the present invention.

FIG. 4 is a diagram showing an embodiment in which a common mode choke is connected to the local oscillator side of the mixer of the present invention.

FIG. 5 is a circuit diagram showing an embodiment when the mixer of the present invention is extended to a wide band.

FIG. 6 is a circuit diagram showing another embodiment when the mixer of the present invention is extended to a wide band.

FIG. 7A is a circuit diagram of a conventional SBM, and FIG. 7B is an equivalent circuit diagram of FIG.

8 (A) is a circuit diagram of a conventional DBM, and FIG. 8 (B) is an equivalent circuit diagram of FIG. 8 (A).

[Explanation of symbols]

1 U-shaped pattern 1a, 1b Strip line 1c Short-circuit pattern 2a, 2b Coaxial cable (conductor) 3a, 3b First port (local signal terminal) 4a, 4b Second port (IF output terminal) 5 Third port ( (RF input terminal) 6 Short-circuit piece of coaxial cable center conductor 7a, 7b Grounding of coaxial cable center conductor 10 Transformer 12 Diode group for switching

Claims (3)

(57) [Claims] 1. A high-frequency transformer formed on a printed circuit board with a substantially U-shaped pattern comprising two strip lines and a pattern for short-circuiting one end of both strip lines. A conductor having substantially the same length as the line length is provided on each of the strip lines in an insulated manner , and the ends of the U-shaped ends of the two conductors are short-circuited. A high frequency transformer characterized in that the end opposite to the above is a first port, and the U-shaped ends of both strip lines are a second port. 2. A local oscillation circuit between two terminals of the first port.
And a diode switch in which two sets of a series connection circuit of two diodes are connected in opposite directions between both terminals of the second port, and this is used as an IF output terminal. A third port is formed in the short-circuit pattern portion of the strip line, and this is used as an RF input terminal;
2. The mixer using a high-frequency transformer according to claim 1, wherein each characteristic impedance of both of the strip lines is configured to be twice the characteristic impedance of the RF input system. 3. The high-frequency transformer according to claim 1, wherein the U-shaped front ends of the short-circuited conductors are grounded.