JP2008061082A - Balancing filter circuit and high frequency device fabricated thereby - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve difficulties in fabricating a small, high performance balun built-in filter circuit due to many devices in a balance-unbalance conversion circuit component. <P>SOLUTION: This circuit includes two functions, band-pass filter and balance-unbalance conversion circuit, which have characteristics for transmitting signals in a specific band (2.4 GHz band) and attenuating them in low-pass and high-pass filters of adjacent bands (band of 1.9 GHz or less and band of approx. 3.6 GHz or more). First and second attenuation circuits 10, 20, which attenuate signal components in adjacent frequency bands of the passing band, are connected to a signal path for an unbalanced I/O terminal and a first connection line CL1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes first and second coupling lines that are electromagnetically coupled to each other, and a filter circuit having a function of a so-called balun (balanced and unbalanced conversion circuit) and a function of a plurality of band-pass filters (hereinafter referred to as a “band” filter). (Referred to as a balance filter circuit).

There are various types of balanced filter circuits using a coupled line, and each includes an attenuation circuit that attenuates the signal level of the adjacent frequency band in the low pass band.
For example, a filter having a characteristic of passing a 2.4 GHz band signal and attenuating a frequency band of a radio wave of another communication system adjacent to the 1.9 GHz band and having a balun function is formed by laminating a dielectric layer at a low temperature. A filter circuit having an integrated structure using a firing technique is known (for example, see Patent Document 1).

This Patent Document 1 discloses a multilayer dielectric filter using a low-temperature firing technique as a balance filter circuit. This is because the balanced / unbalanced conversion circuit and the filter circuit are in dielectric layers having different dielectric constants. Since it is configured and laminated on the upper part and the lower part, there is a limit to miniaturization of the shape and dimension.
In addition, when an inductor and a capacitor are arranged on the balanced input / output terminal side of the balanced / unbalanced conversion circuit, it is necessary to arrange them mirror-symmetrically in consideration of high frequency characteristics, which is a limitation in layout. Further, the level balance of the signal output from the balanced input / output terminal is poor, and trimming in the selection process is required. In addition, since more inductors and capacitors are required than when the inductors and capacitors are arranged on the balanced input / output terminal side, it is disadvantageous for miniaturization and the frequency characteristics deteriorate due to variations in the elements.
Further, the wavelength shortening capacitor connected to the normal edge coupling line is configured separately from the capacitor of the resonance circuit forming the attenuation pole. For this reason, if the manufacturing accuracy of the capacitor varies, there is a problem that the pass band is affected by the attenuation characteristics on both sides and the bandwidth becomes narrow.
JP 2003-087008 A

  In view of the above, the present invention attenuates other signals present on the low band side of the pass band and harmonic signals in the high band side pass band, and obtains a predetermined pass band characteristic even if the elements vary. That is.

  The balance filter circuit of the present invention has an unbalanced input / output terminal and first and second terminals, the first terminal being connected to the unbalanced input / output terminal, and a low pass band of an input signal. A first attenuation circuit having a first attenuation pole on the side, and third and fourth terminals, the third terminal being connected to the unbalanced input / output terminal, and the high band side of the passband And a second attenuation circuit having a second attenuation pole, a second terminal of the first attenuation circuit, and a fourth terminal of the second attenuation circuit. Bandpass filter, fifth and sixth input / output terminals for inputting / outputting balanced signal, at least part of which is arranged in parallel to the first coupling line, and electromagnetically deriving the signal in the passband Or a balanced signal input from the fifth and sixth input / output terminals is supplied to the first coupling line by electromagnetic coupling. And a second coupling line.

  A high-frequency device according to the present invention is a high-frequency device in which a balanced / unbalanced conversion circuit and a filter circuit are integrated by a coupling line formed on an insulator substrate, and includes first and second terminals. 1 terminal is connected to the unbalanced input / output terminal, has a first attenuation circuit having a first attenuation pole on the lower side of the pass band of the input signal, and third and fourth terminals, 3 terminal is connected to the unbalanced input / output terminal, a second attenuation circuit having a second attenuation pole on the high band side of the pass band, a second terminal of the first attenuation circuit, and the second terminal And a balanced / unbalanced conversion circuit comprising a coupled line connected to the fourth terminal of the second attenuation circuit.

A signal input from the unbalanced input / output terminal is converted into a balanced signal through the first attenuation circuit, the second attenuation circuit, the band pass filter, and the balanced unbalanced conversion unit, and is output from the balanced input / output terminal. . At this time, the constant is set so that the impedance of the LC parallel resonant circuit is low at the frequency of the pass band of the LC parallel resonant circuit constituting the band pass filter.
At this passband frequency, the impedance of the LC series resonance circuit having an attenuation pole in the adjacent frequency region on the lower side of the passband is high, but is low in the adjacent frequency region of the passband. In addition, the impedance of the LC parallel resonant circuit having an attenuation pole in the adjacent frequency region on the high frequency side is low in the passband frequency but high in the high frequency adjacent frequency region in the passband. As a result, it is possible to obtain a passband filter characteristic having attenuation poles in the low frequency band and high frequency adjacent frequency bands.

Further, the input signal is balanced and unbalanced by the first and second coupled lines. At this time, the first and second coupled lines are bent so that both ends of the coupled line are close to the output path of the balanced signal. Therefore, balanced / unbalanced conversion is performed without being affected by the parasitic inductance.
On the other hand, after a balanced signal is supplied from the balanced input / output terminal and filtered, the unbalanced signal can be derived from the unbalanced input / output terminal.

  The balanced filter circuit of the present invention and the high-frequency device using the balanced filter circuit, while realizing an input / output type that is unbalanced-balanced or balanced-unbalanced in consideration of the connection of a high-frequency amplifier circuit, etc. It is possible to configure a filter circuit that attenuates harmonic components and the like in the passband, effectively reduces the size, and is resistant to manufacturing variations.

  FIG. 1 shows a circuit diagram of a balance filter circuit (or a filter circuit) according to an embodiment of the present invention. This balance filter circuit is a high-frequency component that is placed between the antenna and the IC circuit (differential-type microwave amplifier circuit, etc.) constituting the microwave circuit part of a wireless data communication device such as WLAN (Wireless LAN) or Bluetooth. Used. As the input / output terminals of the balanced filter circuit 1, an unbalanced input / output terminal Tu and balanced input / output terminals Tb1 and Tb2 are configured. The signal input is input from one of the terminals, and the signal is derived from the other terminal. To do.

For example, when a signal is input from the unbalanced input / output terminal Tu11 and an output signal is derived from the balanced input / output terminals Tb1 and Tb2, an unbalanced input-balanced output filter circuit is configured. When a signal is input from the balanced input / output terminals Tb1 and Tb2 and derived from the unbalanced input / output terminal Tu, a balanced input / unbalanced output filter circuit is configured.
In other words, since the input terminal is adapted to the input format of the input signal, it can be either an unbalanced input terminal or a balanced input / output terminal. Is set.

  The filter circuit (balance filter circuit) 1 includes a first attenuation circuit 10, a second attenuation circuit 20, a coupled line unit 30, and an impedance matching (conversion) unit 40. Among these, the coupled line portion 30 is configured to output a microstrip line (also referred to as a coupled line), and the planar layout is referred to as so-called edge coupling or lateral coupling formed from the same conductive layer, for example, as described later. There are two embodiments: a type that is connected, and a type that is electromagnetically coupled with a dielectric layer sandwiched between different conductive layers, so-called broadside coupling or longitudinal coupling. Both types have the same basic equivalent circuit configuration except for the structure of the coupling lines CL1 and CL2.

The first attenuation circuit 10 is composed of an LC series resonance circuit and is generally called a trap circuit. This LC series resonance circuit is composed of, for example, elements of an inductor L1 and a capacitor C1, and has a specific frequency, for example, near 1.9 GHz. It has an attenuation pole of resonance frequency.
As a specific example of the first attenuation circuit 10, one end of an inductor L1 is connected between an unbalanced input / output terminal Tu and a reference potential (ground potential: GND), and the other end is connected to one end of a capacitor C1. The other end of the capacitor C1 is connected to the ground.
Here, when the input signal is input to the first attenuation circuit 10 via the unbalanced input / output terminal Tu, it is an unbalanced input terminal, and conversely, the unbalanced input / output from the first attenuation circuit 10. When the output signal is derived via the terminal Tu, it becomes an unbalanced output terminal. The roles of these two terminals are collectively defined as an unbalanced input / output terminal Tu.

The second attenuation circuit 20 is a trap circuit composed of an LC parallel resonance circuit, and has a resonance frequency attenuation pole in the vicinity of 4.8 GHz, a frequency that is approximately twice the center frequency of the passband. This LC parallel resonant circuit includes an inductor L2 and a capacitor C2.
As a specific example of the second attenuation circuit 20, one end of the inductor L2 and one end of the capacitor C2 are connected to the unbalanced input / output terminal Tu, and the other end of the inductor L2 and the other end of the capacitor C2 are connected to one end of the coupling line CL1. The other end of the coupled line CL1 is connected to the ground.
The coupled line unit 30 includes a first coupled line CL1 and a second coupled line CL2. The first coupled line CL1 forms an LC parallel resonant circuit and is grounded. The coupling line CL1 is formed of, for example, a microstrip line, and a band path (band) that resonates in parallel at the center frequency of the above-described pass band, for example, 2.4 GHz, by setting the line length to λ / 4 (λ is a wavelength). ) Configure the filter. As shown in FIG. 1, no capacitor is connected between the coupling line CL1 and the ground, and the other end of CL1 is directly connected to the ground.

Although a wavelength shortening capacitor is not connected to the coupling line CL1, a capacitor is substituted by using a capacitance component of the LC parallel resonance circuit. Specifically, since the resonance frequency (attenuation pole) of the second attenuation circuit 20 is higher than the center frequency of the pass band, the impedance of the parallel resonator circuit is capacitive at the frequency of the pass band. Since this capacitive component is connected in series with the first coupled line CL1, the line length can be shortened.
Next, the second coupled line CL2 is formed of, for example, a microstrip line, arranged along the coupled line CL1, and connected between the two balanced input / output terminals Tb1 and Tb2.
The balanced input / output terminals Tb1 and Tb2 usually include a parasitic inductor and a parasitic resistance in a pattern layout, but they are very small. Therefore, in FIG. Only C3 is shown. Here, when the output signal is derived via the balanced input / output terminals Tb1 and Tb2, the balanced input / output terminals Tb1 and Tb2 are balanced output terminals. When the signal is input to the second coupled line via the line, it becomes a balanced input terminal. The roles of these two terminals are collectively defined as balanced input / output terminals Tb1 and Tb2.
In this embodiment, the unbalanced input / output terminal Tu of the first attenuation circuit 10 and the common connection terminal of the inductor L1 correspond to the first terminal, and the terminal connected to the ground of the capacitor C1 is the second terminal. It corresponds to. The inductor L2 and the capacitor C2 of the second attenuation circuit 20 are commonly connected, the terminal connected to the unbalanced input / output terminal Tu corresponds to the third terminal, and the first coupling line CL1, the inductor L2, and the capacitor C2 The commonly connected terminal corresponds to the fourth terminal. The balanced input / output terminals Tb1 and Tb2 of the second coupling line CL2 correspond to the fifth and sixth terminals.

Next, the operation of the balance filter circuit 1 of FIG. 1 will be described. For the sake of simplicity, a case will be described below where an input signal is input from the unbalanced input / output terminal Tu and the filtered signal is derived from the balanced input / output terminals Tb1 and Tb2. Of course, filter processing can be performed by reverse signal input and signal output.
When a high frequency signal of 2.4 GHz, for example, is input from the unbalanced input / output terminal Tu, the resonance frequency of the first attenuation circuit 10 is about 1.9 GHz, and thus the 2.4 GHz signal is not attenuated. However, other signals with a frequency of about 1.9 GHz coincide with the attenuation pole of the first attenuation circuit 10 and are attenuated here. As a result, interference by other signals on the low frequency side adjacent to the desired signal can be reduced.

Next, the signal in which the adjacent signal is attenuated by the first attenuation circuit 10 is supplied to the second attenuation circuit 20. Here, the second attenuation circuit 20 constitutes a trap composed of an LC parallel resonance circuit, and the trap center frequency is set to 4.8 GHz, which is about twice the center frequency of the pass band. As a result, the harmonic of 2.4 GHz is attenuated because it matches the frequency of the attenuation pole.
Accordingly, at the output of the second attenuation circuit 20, the 1.9 GHz and 4.8 GHz signals adjacent to the input signal are attenuated, and only the desired signal within the passband is output.
The signal that has passed through the second attenuation circuit 20 is supplied to the coupled line section 30, and a bandpass filter having a center frequency of 2.4 GHz is configured by the first coupled line CL1, and a frequency having a predetermined bandwidth is extracted.
The first and second coupling lines CL1 and CL2 are coupled, and the impedance is converted by the capacitor C3, so that signals having phases different from each other by 180 degrees are derived from the balanced input / output terminals Tb1 and Tb2.
That is, the unbalanced signal input from the unbalanced input / output terminal Tu is derived from the balanced input / output terminals Tb1 and Tb2 after the frequencies on the low band side and high band side of the pass band are attenuated.

Further, the signal input path described above can be reversed. For example, a balanced signal is input to the balanced input / output terminals Tb1 and Tb2, and is input to the second coupling line CL2. The second coupled line CL2 and the first coupled line CL1 are electromagnetically coupled, and only the passband frequency (signal) of the first coupled line CL1 is extracted. This extracted signal becomes an unbalanced signal, a signal having a frequency about twice the center frequency of the band of the second attenuation circuit 20 is attenuated, and further supplied to the first attenuation circuit, so that the low frequency of the pass band is obtained. The resonance frequency of about 1.9 GHz provided on the side is attenuated.
In this way, unnecessary signals are attenuated by the attenuation poles adjacent to the low band side and the high band side of the pass band, and only the band frequency is extracted, and the output signal is derived from the unbalanced input / output terminal Tu.
As described above, the balance filter circuit 1 can set the input and output according to the input format.

In addition, the balance filter circuit 1 can be combined to form filter circuits of various input and output formats.
As a specific example, two balance filter circuits 1 shown in FIG. 1 are used, and the balanced input / output terminals Tb1, Tb2 of the first balance filter and the balanced input / output terminals Tb1, Tb2 of the second balance filter are connected to each other. Thus, a filter circuit with unbalanced input and unbalanced output can be configured.
As another example, by connecting the unbalanced input / output terminal Tu of the first balance filter circuit and the unbalanced input / output terminal Tu of the second balance filter circuit to each other, a balanced input and balanced output filter circuit can be obtained. Can be configured.

Next, a pattern layout and a cross-sectional structure of the high frequency device 100 having the balance filter circuit of FIG. 1 will be described. In the pattern layout, with respect to the first coupling line CL1 and the second coupling line CL2, there are embodiments of a lateral coupling line (edge coupling) and a vertical coupling line, and the latter increases the area of the filter circuit.
FIG. 2 is a layout example of the high-frequency device 100 when the coupled lines are edge-coupled (laterally coupled).
As shown in FIG. 3, the lateral coupling type high-frequency device 100 shown in FIG. 2 has an insulating layer 142 formed on, for example, a semi-insulating semiconductor substrate or other substrate 140 having low conductivity, A ground (GND) plate 144 for supplying a reference potential (for example, ground potential GND) is formed. An interlayer dielectric layer 146 is formed on the ground plate 144, and an upper conductive layer that is a material of most filter circuit elements is formed on the interlayer dielectric layer 146.

The pattern layout diagram of the high-frequency device 100 has the configuration shown in FIG. In general, the constituent elements of the first attenuation circuit 110 and the second attenuation circuit 107 are arranged in the left region of the pattern layout diagram, and the elements constituting the coupled line portion 114 and the impedance matching unit are arranged in the right region.
In the pattern layout diagram of the high-frequency device 100, ground (GND) lines 101 are arranged on the outer periphery of the pattern layout diagram, and via holes 102 are provided at predetermined intervals of the ground lines 101, and a lower-layer ground (GND) is interposed therethrough. Connected to plate 144. Thereby, each passive element is surrounded by the ground line 101, the balance filter circuit 1 is electromagnetically shielded, and signal interference between elements is prevented. Since the ground line 101 lays out the input line (wiring) 103 and the output lines (wirings) 120 and 121 to the end of the substrate, the unbalanced input / output terminal 111 (Tu) and the balanced input / output terminals 116 (Tb1) and 117 are arranged. Only the terminal extraction region of (Tb2) is not formed.

A pattern layout diagram corresponding to the first attenuation circuit 110 will be described. One end of a spiral inductor 108 is connected to the unbalanced input / output terminal 111. The inductor 108 is formed of an upper conductive layer, and the other end near the center thereof is connected to the ground line 101 via a via hole 130B, a connection layer 135 made of a lower conductive layer, a via hole 130A, and a capacitor 109.
In the balance filter circuit 1, only the connection layer 135 is constituted by a lower conductive layer embedded in the interlayer dielectric layer 146, and all other circuit elements and wirings in the plan view of FIG. 2 are all in the interlayer dielectric layer 146. It is comprised from the upper conductive layer formed on the top.

The unbalanced input / output terminal 111 is connected to the second attenuation circuit 107. Specifically, the second attenuation circuit 107 is connected to one terminal near the center of the spiral inductor 105 and one terminal of the capacitor 106. Further, the unbalanced input / output terminal 111 is connected to a terminal near the center of the inductor 105 and connected to one terminal of the capacitor 106 via the via hole 131A, the connection layer 135A made of a lower conductive layer, and the via hole 131B. . Further, the other terminal of the inductor 105 is connected to the other terminal of the capacitor 106.
In the balance filter circuit 1, only the connection layers 135 and 135A are composed of a lower conductive layer embedded in the interlayer dielectric layer 146, and all other circuit elements and wirings in the plan view of FIG. The upper conductive layer is formed on the layer 146.

The output of the second attenuation circuit 107 is connected to the coupled line section 114, and the unbalanced signal is converted into a balanced signal and derived.
Specifically, the output of the second attenuation circuit 107 is connected to the end of the first coupling line 112 (CL1). The first coupled line 112 is configured by a distributed constant line that is partially bent, and the other end is connected to the ground line 101.
The effective joint portion of the second coupling line 113 (CL2) is arranged on the same plane in parallel along the inner periphery of the first coupling line 112, thereby enabling edge coupling (lateral coupling) to each other. ing.

Both ends of the effective coupling unit are connected to balanced input / output terminals 116 and 117 via balanced signal output lines 120 and 121, respectively. An impedance matching capacitor 115 is disposed between the output lines 120 and 121 for deriving a balanced signal.
In the layout pattern diagram of the high-frequency device 100 shown in FIG. 2, the second coupling line 113 and the impedance matching unit are mirror-symmetrically arranged at the center of the capacitor 115. Thus, consideration is given to avoiding large deviations in the characteristics of the two balanced signals whose output signal levels are uniform and whose phases are inverted. Note that all the capacitors 106, 109, and 115 are upper conductive layers and have a MIM (Metal Insulator Metal) structure.

  In FIG. 3, the connection layer 135 of the inductor 108 is formed of the same conductive layer as the connection layer 135 </ b> A below the second coupling line 113, but is not limited thereto, and is different from the second coupling line 113. The connection layer 135 may be formed from a conductive layer in a hierarchy. Thus, by using a lower conductive layer, the parasitic capacitance at the intersection of the inductor can be reduced, and high characteristics of the inductor can be obtained.

  In addition to the cross-sectional structure shown in FIGS. For example, as a modification of the coupled line portion 114 of the lateral coupled line in FIG. 2, the first coupled line 112 is formed in a straight line without bending, and a part of the second coupled line 113 is formed in this manner. A linear pattern is laid out parallel to the first coupling line 112, and a rectangular pattern is formed so as to be surrounded by an impedance matching capacitor. Then, a take-out line is connected from both ends of the capacitor and connected to the balanced input / output terminals 116 and 117. At this time, the layout of the first attenuation circuit 110 and the second attenuation circuit 107 is not limited, and may be arranged in the region shown in FIG.

  In addition, as an example of the longitudinally coupled line, the first coupled line 112 is laid out linearly on the interlayer dielectric layer 146, and a part of the second coupled line 113 is correspondingly disposed on the interlayer dielectric layer. It is embedded in 146 and laid out in a straight line parallel to the first coupling line 112, and a rectangular pattern is formed through an impedance matching capacitor. A wiring layer is connected to both ends of the capacitor, and an output terminal for deriving a balanced signal is connected. Also in this example, the first attenuation circuit and the second attenuation circuit may be laid out as shown in FIG.

FIG. 4 shows frequency characteristics of frequency-attenuation. In the graph showing the frequency characteristics, the horizontal axis indicates the frequency, the range of 0.00 GHz to 6.00 GHz is shown on the scale of 1 GHz step, while the vertical axis shows the amount of attenuation, 0.0 dB on the 10 dB step scale. To -60.0 dB.
A curve b shown in FIG. 4 shows a signal transmission characteristic (level L frequency characteristic) when routed from the unbalanced input / output terminal Tu (11, 111) to one balanced input / output terminal Tb1 (12, 116). a represents signal transmission characteristics when the other balanced input / output terminal Tb2 (13, 117) is routed from the unbalanced input / output terminal Tu (11, 111). A value obtained by combining the curve a and the curve b is a curve c, and balanced input / output terminals Tb1 (12, 116) and Tb2 (13) when a signal is input from the unbalanced input / output terminal Tu (11, 111). , 117) corresponding to the total output signal.

In the curve a, one parasitic trap exists at 1 GHz or less, but a 1.9 GHz trap of the resonance frequency of the first attenuation circuit 10 also exists, and the attenuation amount of the attenuation pole of 1.9 GHz is large. As described above, the trap due to the LC series resonance is generated by the inductor L1 and the capacitor C1 in FIG. 1, and is caused by the inductor 108 and the capacitor 109 in FIG. The attenuation of this trap is about -52 dB at the resonance frequency. Further, the trap on the high band side of the pass band is generated by the second attenuation circuit 20, and is specifically formed by parallel resonance of the inductor L2 and the capacitor C2. The parallel resonance frequency (attenuation pole) is about 4,4 GHz, and the attenuation at that frequency is −58 dB or more.
At this time, the signal loss taken out from each of the balanced input / output terminals Tb1 and Tb2 is about 4 dB in the range of the pass band of the center frequency 2.4 GHz.
A curve b is the amplitude level of the signal with respect to the frequency when a signal is input from the unbalanced input / output terminal Tu (11, 111) and the signal is extracted from the balanced input / output terminal Tb2 (13, 117). Same as curve a.
Curve c is the amplitude level with respect to frequency when curve a and curve b are combined. The transmission loss in the pass band of the curve c is about -2 dB, which is smaller than the reference value of -3 dB.

  Thus, the signal transmission loss in the signal pass band of 2.4 GHz band, the extreme attenuation frequency in the adjacent frequency band near 1.9 GHz, the low attenuation width of 1.5 GHz or less, the extreme attenuation frequency in the vicinity of 4.8 GHz, the attenuation The result is that the characteristics of the two balanced signals, such as width, are nearly identical. In addition, the attenuation pole can efficiently attenuate signal components and harmonic components in bands other than the passband used for wireless communication.

FIG. 5 shows a graph in which the frequency characteristics shown in FIG. 4 are partially enlarged. This frequency characteristic indicates the phase difference and attenuation of the output signal in the vicinity of the passband derived from the balanced input / output terminals Tb1 (12, 116) and Tb2 (13, 117).
In this enlarged view, the horizontal axis represents frequency and the range from 2.3 GHz to 2.6 GHz is shown. The right vertical axis indicates the phase, shows a range from 170 degrees to 190 degrees, the left vertical axis indicates the amount of attenuation, and indicates a range from 0.0 dB to -4.0 dB.
The phase difference between the output signals taken out from the balanced input / output terminals Tb1 (12, 116) and Tb2 (13, 117) increases linearly from the frequency 2.3 GHz to 2.42 GHz, and the phase difference in the frequency range. Is less than 1 degree. Further, in the frequency range from 2.42 GHz to 2.6 GHz, it decreases linearly in the range of 180 degrees and 179 degrees, and the difference is 0.5 degrees or less.

Further, the phase difference in the passband frequency range of about 2.4 GHz and 2.48 GHz is about 1.5 degrees.
Thus, the phase balance is in the range of a typical tolerance of 180 ± 10 degrees in the passband.
When the first coupled line CL1 and the second coupled line CL2 shown in FIG. 2 are bent, the level balance and phase balance of the balanced signals output from the balanced input / output terminals Tb1 and Tb2 are the results of electromagnetic field simulation. Therefore, it is equivalent to the case where the coupled line is a straight line.
Of course, when the first coupling line CL1 and the second coupling line CL2 are linearly arranged in parallel, the phase difference is further reduced.

Next, changes in electrical characteristics when elements used in the balance filter circuit 1 vary will be described.
FIG. 6 shows electrical characteristics related to the attenuation-frequency characteristics when the capacitance value varies.
Specifically, attenuation-frequency characteristics when the capacitance values of the capacitors C1 (109), C2 (106), and C3 (115) used in the balance filter circuit 1 or the high-frequency device 100 vary.
The horizontal axis indicates the frequency range of 0.00 GHz to 6.00 GHz, and the vertical axis indicates the attenuation range of 0.00 dB to −60.00 dB.

The electrical characteristic when the capacitance value varies + (plus) 10% is shown as curve a, the characteristic when there is no variation is curve b, and the characteristic when the variation is − (minus) 10% is shown as curve c. Show.
At this time, the change in the frequency of the attenuation pole lower than the pass band is about 0.2 GHz or less between the curves a, b, and c, and the change in the attenuation when changed is substantially the same. In addition, the attenuation in the region of about 1.3 GHz, which is lower than the attenuation pole, is −30 dB or less, and satisfies the reference value even if the capacitance value varies.
The frequency of the attenuation pole higher than the pass band is in the range from about 4.2 GHz of curve a to 4.6 GHz of curve c, and the corresponding attenuation amounts are about -59 dB and -57 dB. Further, the amount of attenuation in the vicinity of about 4.8 GHz higher than the frequency of the attenuation pole is in the range of about −35 dB to −39 dB, and the amount of attenuation is larger than the reference value of −30 dB.
When the capacitance value varies from −10% to + 10% in the pass band, the attenuation amount is −3 dB or less, and the attenuation amount is smaller than the reference value.

FIG. 7 shows an enlarged view of the attenuation amount-frequency characteristic shown in FIG. Specifically, an electrical characteristic diagram of the passband and its neighboring frequencies when the capacitance value varies is shown.
When the capacitance value varies by + 10%, the frequency characteristic is curve a, when the capacitance value does not vary, that is, when the capacitance value is the center value, curve b, and when the capacitance value varies by -10%, the characteristic is curve c. The phase characteristics corresponding to these are shown in curves a1, b1 and c1, respectively.
As shown by the curve a, when the capacitance value varies by + 10% with respect to the center value, the center frequency of the pass band is about 2.35 GHz. As a result, the attenuation is about 2.75 GHz which is the upper limit frequency of the pass band. However, the attenuation is about −3.0 dB or less than the reference value. Of course, the attenuation at the lower limit frequency of the passband at this time is about -2.1 dB, which is clearly less than the reference value.
The phase characteristic at this time is shown by a curve a1. The curve a1 increases linearly from 2.30 GHz to 2.34 GHz, and the amount of phase change is 1 degree or less. The phase abruptly changes in the negative direction around 2.34 GHz, but the amount is small, about 1 degree, and then decreases by 0.5 degrees or less in the range from 2.34 GHz to 2.60 GHz. Also, there is almost no phase change at the passband frequency.

As shown in the curve b, when the capacitance value does not vary with respect to the center value, the center frequency of the pass band is about 2.43 GHz, and as a result, the attenuation is about 2.40 GHz which is the lower limit frequency of the pass band. The attenuation is below -2.0 dB and below the reference value. Further, the attenuation at the upper limit frequency 2.475 GHz of the pass band at this time is about −2.0 dB, which is clearly less than the reference value.
The phase characteristic at this time is shown by a curve b1. The curve b1 increases linearly from 2.30 GHz to 2.42 GHz, and the amount of phase change is 0.5 degrees or less. The phase changes abruptly around 2.42 GHz, but the amount is about 1.5 degrees, and then decreases in the range from 2.43 GHz to 2.60 GHz. At this time, the change in phase attenuation is 0.5 degrees or less. Further, the phase change is the largest in the vicinity of 2.42 GHz, but the phase change is about 1.5 degrees or less in the passband.

As shown by the curve b, when the capacitance value varies by -10% with respect to the center value, the center frequency of the pass band is about 2.50 GHz, and as a result, the lower limit frequency of the pass band is about 2. Although the amount of attenuation increases at the unbalanced input / output terminal GHz, the amount of attenuation is less than about −3.0 dB and below the reference value. Of course, the attenuation at the upper limit frequency of the passband at this time is about -2.1 dB, which is clearly less than the reference value.
The phase characteristic at this time is shown by a curve c1. The curve c1 increases linearly from 2.30 GHz to 2.49 GHz, and the amount of phase change is 1 degree or less. The phase suddenly changes in the negative direction around 2.34 GHz, but the amount is about 2 degrees, and then decreases in the range of 2.51 GHz to 2.60 GHz, and the phase difference is less than 0.1 degree. . In the pass band, the phase change is 0.5 degrees or less and there is almost no phase change.

  Next, the electrical characteristics shown in FIGS. 4 to 7 are compared with the electrical characteristics of other balance filter circuits not shown. The characteristics of this comparative balance filter circuit are shown in FIGS. The circuit configuration of this balance filter circuit is that the second attenuation circuit is omitted as compared with the balance filter circuit 1 shown in FIG. 1, and the output of the first attenuation circuit and one terminal of the first coupling line CL1. A capacitor constituting a low-frequency cutoff circuit is connected between them, and a capacitor is connected between the common connection point of this capacitor and the first coupling line CL1 and the ground.

As shown in FIG. 8, in the above-described comparative balance filter circuit, a trap is formed at about 1.8 GHz on the low band side of the pass band, and no trap is formed on the high band side.
FIG. 9 shows the phase difference between the output terminals (Tb1 and Tb2) corresponding to FIG. The phase difference in the pass band is within 1 degree.

  As described above, the balance filter circuit 1 and the comparison balance filter circuit shown in FIG. 1 have an attenuation of -30 dB or more at 1.9 GHz and 4.8 GHz outside the passband when the elements do not vary. The phase difference within the pass band is also within the reference value.

Next, FIG. 10 shows electrical characteristics when the constituent elements of the comparative balance filter circuit vary.
A curve “a” shown in FIG. 10 shows characteristics when the capacitance value of the capacitor varies + 10% with respect to the center value. On the high band side of the pass band, the attenuation is about −3.4 dB, which is greater than the reference value. Further, when the capacitance value varies by -10% with respect to the center value, a curve c is shown, which is attenuated by about -3.4 dB on the lower side of the pass band, and the attenuation is larger than the reference value of -3.0 dB. Does not satisfy the standard value.

  Accordingly, the balance filter circuit 1 shown in FIG. 1 has an attenuation of the passband even when the capacitance value varies from −10% to + 10% or more with respect to the center value as compared with the comparative balance filter circuit shown in FIG. Is small.

As described above, an attenuation circuit is provided on the input side of the unbalanced input / output terminal to give the bandpass filter characteristics that attenuate the adjacent frequency bands on the low-pass and high-pass sides of the passband. Therefore, the degree of freedom of the arrangement is high and the entire area can be reduced.
By making the attenuation pole of the second attenuation circuit a harmonic of the pass band, the harmonic signal of the operating frequency can be attenuated.
Since the capacitor for shortening the wavelength of the coupled line is substituted with the capacitance component of the second attenuation circuit constituting the parallel resonant circuit, the number of elements can be reduced.
In addition, the circuit configuration is such that the number of capacitors constituting the filter is reduced, and even when the capacitors vary, a predetermined attenuation amount and phase amount can be secured.

It is a figure which shows the circuit structure of a balance filter circuit. It is a layout pattern figure of a high frequency device. FIG. 3 is a pattern cross-sectional view of the high frequency device shown in FIG. 2. It is a figure which shows the frequency characteristic of a balance filter circuit. It is an enlarged view of the pass band of the frequency characteristic shown in FIG. It is a frequency special figure when an element varies. It is an enlarged view of the pass band of FIG. It is a frequency characteristic figure of the balance filter circuit for comparison for comparing a characteristic. It is a figure which shows the phase characteristic of the balance filter circuit for a comparison for comparing a characteristic. It is a figure which shows the dispersion | variation characteristic of the balance filter circuit for a comparison for comparing a characteristic.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Balance filter circuit, 10, 110 ... 1st attenuation circuit, 20, 107 ... 2nd attenuation circuit, 30 ... Coupling line part, 40 ... Impedance matching (conversion) part, 100 ... High frequency apparatus, 101 ... Ground ( GND) line, 102 ... via hole, 103 ... input line (wiring), 105, 108, L1, L2 ... inductor, 106,109,115, C1, C2, C3 ... capacitor, 112,113, CL1, CL2 ... coupled line (Microstrip line), 111, Tu: unbalanced input / output terminals, 116, 117, Tb1, Tb2 ... balanced input / output terminals, 120, 121 ... output lines (wiring), 140 ... substrate, 142 ... insulating layer, 144 ... Ground (GND) plate, 146... Interlayer dielectric layer.

Claims (12)

Unbalanced input / output terminals;
A first attenuation circuit having first and second terminals, the first terminal being connected to the unbalanced input / output terminal, and having a first attenuation pole on the lower side of the passband of the input signal; ,
A second attenuation circuit having third and fourth terminals, the third terminal being connected to the unbalanced input / output terminal, and having a second attenuation pole on the high frequency side of the passband;
A band-pass filter connected to the second terminal of the first attenuation circuit and the fourth terminal of the second attenuation circuit and configured by a first coupled line;
It has fifth and sixth input / output terminals for inputting and outputting a balanced signal, and is arranged at least partially in parallel with the first coupling line, and electromagnetically couples to derive the signal in the passband or And a second coupling line that supplies balanced signals input from the fifth and sixth input / output terminals to the first coupling line by electromagnetic coupling. The balance filter circuit according to claim 1, wherein the frequency of the second attenuation pole of the second attenuation circuit is the same frequency as a harmonic of the center frequency of the passband. 2. The balanced filter circuit according to claim 1, wherein the electromagnetic coupling between the first and second coupling lines is horizontal coupling or vertical coupling. 2. The balanced filter circuit according to claim 1, wherein the first attenuation circuit is a series resonance circuit having an inductor and a capacitor, and the second attenuation circuit is a parallel resonance circuit having an inductor and a capacitor. The balance filter circuit according to claim 4, wherein the capacitor for shortening the wavelength of the first coupling line uses a capacitance component of the second attenuation circuit. The balance filter circuit according to claim 1, wherein the first and second attenuation circuits and the first and second coupled lines are formed on the same substrate. A high-frequency device in which a balanced / unbalanced conversion circuit and a filter circuit are integrated by a coupling line configured on an insulator substrate,
A first attenuation circuit having first and second terminals, the first terminal being connected to an unbalanced input / output terminal, and having a first attenuation pole on the lower side of the passband of the input signal;
A second attenuation circuit having third and fourth terminals, the third terminal being connected to the unbalanced input / output terminal, and having a second attenuation pole on the high frequency side of the passband;
A high-frequency device comprising: a second terminal of the first attenuation circuit; and a balanced / unbalanced conversion circuit comprising a coupled line connected to the fourth terminal of the second attenuation circuit. The high-frequency device according to claim 7, wherein the first and second attenuation circuits include an inductor and a capacitor, and the inductor and the capacitor are disposed on the unbalanced input / output terminal side. The high-frequency device according to claim 7, wherein a frequency of the second attenuation pole of the second attenuation circuit is the same frequency as a harmonic of the center frequency of the passband. The high-frequency device according to claim 7, wherein the coupled line of the balanced / unbalanced conversion circuit is a lateral coupling or a longitudinal coupling. The high-frequency device according to claim 7, wherein the first attenuation circuit is a series resonance circuit having an inductor and a capacitor, and the second attenuation circuit is a parallel resonance circuit having an inductor and a capacitor. The high-frequency device according to claim 11, wherein the capacitor for shortening the wavelength of the coupling line of the balanced / unbalanced conversion circuit uses a capacitance component of the second attenuation circuit.

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