Impedance converter and distributor

Abstract

To provide an impedance converter capable of obtaining satisfactory characteristics in a wide band.SOLUTION: With the impedance converter 1 in which the low-band impedance converting circuit 12 and the high-band impedance converting circuit 11 are connected in parallel between the input terminal IN and the output terminal OUT, and with a circuit configuration in which the phase of the pass characteristic of the high-pass filter formed by the high-band impedance converting circuit 11 is delayed with respect to the phase of the pass characteristic of the low-pass filter formed by the low-band impedance converting circuit 12, the phases of the pass characteristics can be matched when the frequency bands are combined. As a result, an impedance converter having favorable impedance conversion performance in a wide band is realized.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an impedance converter that can operate in a desired wide band, and a splitter to which the impedance converter of the present invention is applied, and relates to a wideband impedance converter and splitter used in, for example, equipment and systems for transmitting television broadcast signals. [Background technology]

[0002] If there is a difference in impedance between the connected devices or circuits, reflections occur at the connection point, resulting in signal loss. An impedance converter has the function of matching impedance, allowing signals to be transmitted between the connected devices or circuits without signal loss. Impedance matching can be achieved using impedance conversion circuits that use high-frequency transformers, impedance conversion circuits that use resistors, or impedance conversion circuits that use distributed constant lines. A conventional impedance conversion circuit 100 using a high-frequency transformer is shown in Fig. 25. The impedance conversion circuit 100 shown in Fig. 25 is composed of a matching transformer Ta having one end connected to a terminal 101 of impedance Za and the other end connected to ground, and a terminal 102 of impedance Zb connected to a tap of the matching transformer Ta. The matching transformer Ta is composed of a winding wound around a ferrite core, with the number of turns up to the tap being n1 and the number of turns from the tap being n2, resulting in a winding ratio n of n2 / n1. If the impedance seen from the tap of the matching transformer Ta to the terminal 101 in the impedance conversion circuit 100 is Zo, then Zo=n2·Za The condition for impedance matching between the terminal 101 and the terminal 102 is as follows: Zo=Zb Therefore, Zo=n2·Za=Zb And n=√(Zb / Za) That is, by setting the turns ratio n of the matching transformer Ta to √(Zb / Za), impedance matching can be achieved between the terminal 101 with impedance Za and the terminal 102 with impedance Zb. Note that the condition of the impedance conversion circuit 100 shown in FIG. 25 is that Za>Zb. The impedance conversion circuit 100 using a high-frequency transformer makes use of the properties of a ferrite core, which is a magnetic material, to obtain low-loss and stable impedance conversion performance over a wide frequency band of approximately 10 MHz to 1 GHz.

[0003] 26 shows a circuit diagram of a conventional impedance conversion circuit 200 using resistors. The impedance conversion circuit 200 shown in FIG. 26 is configured by connecting two resistors Ra and Rb in series. That is, one end of the resistor Ra is connected to a terminal 201 with an impedance Za, the connection point between the other end of the resistor Ra and one end of the resistor Rb is connected to a terminal 202 with an impedance Zb, and the other end of the resistor Rb is connected to the ground. The two resistors Ra and Rb for impedance matching the terminals 201 and 202 are Ra = √Za(Za-Zb) Rb=Zb√Za / (Za-Zb) It should be noted that the impedance conversion circuit 200 shown in FIG. 26 is required to satisfy the condition Za>Zb. The impedance conversion circuit 200 using resistors can perform stable impedance conversion over a wider frequency band than the impedance conversion circuit 100 using a high-frequency transformer, which is approximately 10 MHz to 3 GHz. However, since the circuit configuration using resistors Ra and Rb also functions as an attenuator, a certain amount of attenuation occurs in the pass characteristics.

[0004] Furthermore, a circuit of a conventional impedance conversion circuit 300 using a distributed constant line is shown in Fig. 27. As shown in Fig. 27, the impedance conversion circuit 300 is configured with a distributed constant line Wc having an impedance Zc, with a terminal 301 having an impedance Za connected to one end of the distributed constant line Wc and a terminal 302 having an impedance Zb connected to the other end of the distributed constant line Wc. The distributed constant line Wc has an electrical length of λ / 4, where λ is the wavelength of the frequency used, Zc=√(Za×Zb) By doing so, impedance matching can be achieved. The impedance conversion circuit 300 using a distributed constant line can perform good impedance conversion even at high frequencies of 3 GHz or higher, compared to the impedance conversion circuit 100 using a high-frequency transformer and the impedance conversion circuit 200 using a resistor. However, the frequency band in which impedance conversion can be performed is the frequency band in which the impedance of the distributed constant line Wc exhibits Zc, which is a narrow band.

[0005] Impedance conversion circuits using matching elements such as inductors and capacitors have also been proposed. Circuit diagrams of an impedance conversion circuit 400 using matching elements are shown in Figures 28(a) and 28(b). The impedance conversion circuit 400-1 shown in Figure 28(a) is a low-pass filter type impedance converter, and is configured by connecting an inductor La between a terminal 401 of impedance Za and a terminal 402 of impedance Zb, and connecting a capacitor Ca between the terminal 401 and ground. Furthermore, the impedance conversion circuit 400-2 shown in FIG. 28(b) is a high-pass filter type impedance converter, and is configured such that a capacitor Cb is connected between a terminal 403 of impedance Za and a terminal 404 of impedance Zb, and an inductor Lb is connected between the terminal 403 and earth. Both impedance conversion circuits 400-1 and 400-2 using matching elements can perform good impedance conversion in a frequency range of approximately 10 MHz to 3 GHz. However, the frequency band in which good impedance conversion can be performed is a narrow frequency band in which capacitors Ca and Cb and inductors La and Lb exhibit a predetermined impedance, similar to impedance conversion circuit 300 using distributed constant lines. Furthermore, since the circuit configuration of impedance conversion circuit 400-1 functions as a low-pass filter circuit and impedance conversion circuit 400-2 functions as a high-pass filter circuit, a filter characteristic appears in the pass characteristics.

[0006] Patent Document 1 discloses a conventional in-building community viewing device that branches and distributes transmission signals from CATV stations within a building, apartment building, or other building. In this in-building community viewing device, the frequency band of BS / CS broadcast intermediate frequency signals is set to 1030 MHz to 3224 MHz to accommodate 4K / 8K broadcasting, which provides ultra-high-definition images that exceed current high-definition television signals. The frequency band of CATV upstream signals is set to 10 MHz to 55 MHz or 60 MHz, the frequency band of CATV downstream signals is set to 70 MHz to 770 MHz or 962 MHz, and the frequency band of terrestrial digital broadcast signals is set to 470 MHz to 710 MHz. Thus, the transmission frequency band of television broadcast signals is an extremely wide frequency band, ranging up to a maximum of 10 MHz to 3224 MHz. Therefore, it is desirable to perform wideband, low-loss impedance matching for impedance matching in television broadcast signal transmission equipment and systems. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-25266 Summary of the Invention [Problem to be solved by the invention]

[0008] In a conventional impedance conversion circuit 100 using a high-frequency transformer, stable impedance conversion performance with low loss can be obtained over a wide frequency range from the low frequency of 10 MHz. However, in the high frequency range of 1 GHz or higher, the magnetic loss of the ferrite core and the stray capacitance between the windings cannot be ignored, and the transmission loss increases as the frequency increases. Furthermore, in the conventional impedance conversion circuit 200 using resistors, stable impedance conversion performance can be obtained over a wide frequency band of 10 MHz to 3224 MHz, but since the circuit configuration using resistors functions as an attenuator, a certain amount of attenuation occurs in the pass characteristics. Furthermore, in the conventional impedance conversion circuit 300 using a distributed constant line, stable impedance conversion performance can be obtained at 3224 MHz, but it is difficult to obtain good impedance conversion performance at 10 MHz, which is considered to be a low frequency range. Furthermore, in the impedance conversion circuits 400-1, 400-2 using matching elements of an inductor and a capacitor, stable impedance conversion performance can be obtained in a narrow band of frequencies set as the operating frequencies within the frequency band range of 10 MHz to 3224 MHz, but it is considered difficult to obtain stable impedance conversion performance over the wide frequency band of 10 MHz to 3224 MHz. As described above, it has been difficult to obtain an impedance converter that can provide low-loss, wide-band, stable impedance conversion performance in the frequency band of 10 MHz to 3224 MHz.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an impedance converter that can obtain good characteristics with low loss over a wide band. Another object of the present invention is to provide a divider to which the impedance converter according to the present invention is applied. [Means for solving the problem]

[0010] The impedance converter of the present invention, which can achieve the above object, is an impedance converter in which a low-frequency impedance conversion circuit and a high-frequency impedance conversion circuit are connected in parallel between an input terminal and an output terminal, and the low-frequency impedance conversion circuit is an impedance conversion circuit using a high-frequency transformer and has a circuit configuration that functions equivalently as a low-pass filter between the input terminal and the output terminal, and the high-frequency impedance conversion circuit is a series-connected circuit of a distributed constant line and a capacitor and has a circuit configuration that functions equivalently as a high-pass filter between the input terminal and the output terminal, and is mainly characterized in that the high-frequency impedance conversion circuit is configured so that the phase of the pass characteristic of the high-pass filter lags the phase of the pass characteristic of the low-pass filter, thereby matching the phases of the pass characteristics of the low-pass filter and the high-pass filter, and the outputs of the low-pass filter and the high-pass filter are frequency band combined and the cutoff frequencies of the low-pass filter and the high-pass filter are approximately the same. Another impedance converter of the present invention that can achieve the above object is an impedance converter in which a low-pass filter circuit and a high-pass impedance conversion circuit are connected in parallel between an input terminal and an output terminal, the low-pass filter circuit being a low-pass filter between the input terminal and the output terminal, and the high-pass impedance conversion circuit being a series-connected circuit of a distributed constant line and a capacitor, and having a circuit configuration that functions equivalently as a high-pass filter between the input terminal and the output terminal, and is mainly characterized in that the high-pass filter is configured so that the phase of the pass characteristic of the high-pass filter lags the phase of the pass characteristic of the low-pass filter, thereby matching the phases of the pass characteristics of the low-pass filter and the high-pass filter, the outputs of the low-pass filter and the high-pass filter are frequency band combined, and the cutoff frequencies of the low-pass filter and the high-pass filter are approximately the same.

[0011] In the impedance converter of the present invention described above, when the low-pass filter functions equivalently as a 4n-1 (n=1, 2, 3, . . .)-stage T-type low-pass filter, the high-frequency impedance conversion circuit may be configured so that the high-pass filter functions equivalently as a 3-stage π-type high-pass filter, thereby matching the phases of the pass characteristics of the low-pass filter and the high-pass filter and performing frequency synthesis. Furthermore, in the impedance converter of the present invention described above, when the low-pass filter functions as an equivalent 4n+1 (n=1, 2, 3, . . .) stage T-type low-pass filter, the high-frequency impedance conversion circuit may be configured so that the high-pass filter functions as an equivalent 4n+3 (n=1, 2, 3, . . .) stage π-type high-pass filter, thereby matching the phases of the pass characteristics of the low-pass filter and the high-pass filter and combining the frequency bands. Furthermore, in the impedance converter of the present invention described above, when the low-pass filter functions as an equivalent 4n+3 (n=1, 2, 3, . . .) stage T-type low-pass filter, the high-frequency impedance conversion circuit may be configured so that the high-pass filter functions as an equivalent 4n+1 (n=1, 2, 3, . . . ) stage π-type high-pass filter, thereby matching the phases of the pass characteristics of the low-pass filter and the high-pass filter and combining the frequency bands. Furthermore, in the impedance converter of the present invention described above, a usable frequency band of 10 MHz to 3224 MHz can be obtained. Furthermore, in the impedance converter of the present invention described above, a usable frequency band of 470 MHz to 3224 MHz can be obtained.

[0012] Yet another impedance converter of the present invention that can achieve the above object is an impedance converter in which a low-frequency impedance conversion circuit and a high-frequency impedance conversion circuit are connected in parallel between an input terminal and an output terminal, and a predetermined frequency band including an unused frequency band is set as a usable frequency band, the low-frequency impedance conversion circuit is an impedance conversion circuit using a high-frequency transformer, and has a circuit configuration that functions equivalently as a low-pass filter between the input terminal and the output terminal; and the high-frequency impedance conversion circuit is a series connection circuit of a high-pass filter circuit and a distributed constant line, and has a circuit configuration that functions equivalently as a high-pass filter between the input terminal and the output terminal, and the cutoff frequencies that are approximately matched between the low-pass filter and the high-pass filter are set as predetermined frequencies in the unused frequency band, and the outputs of the low-pass filter and the high-pass filter are frequency-combined when the pass characteristics of the low-pass filter and the high-pass filter are in a phase mismatch state. The branching device of the present invention that can achieve the above object is mainly characterized in that it is configured by connecting the impedance converter of the present invention described above to a distribution transformer. [Effects of the Invention]

[0013] The impedance converter of the present invention is an impedance converter in which a low-pass impedance conversion circuit and a high-pass impedance conversion circuit are connected in parallel between an input terminal and an output terminal, and is configured so that the phase of the pass characteristic of the high-pass filter formed by the high-pass impedance conversion circuit is delayed relative to the phase of the pass characteristic of the low-pass filter formed by the low-pass impedance conversion circuit, thereby making it possible to match the phase of the pass characteristic when combining frequency bands.This makes it possible to realize an impedance converter with excellent impedance conversion performance over a wide frequency band from 10 MHz to 3224 MHz. In the impedance converter of the present invention, the low-pass impedance conversion circuit functions equivalently as a low-pass filter, and the high-pass impedance conversion circuit functions equivalently as a high-pass filter, so that the low-pass filter and the high-pass filter function as a branching / mixing filter. Furthermore, the circuit is configured to delay the phase of the pass characteristic of the high-pass filter relative to the phase of the pass characteristic of the low-pass filter. This makes it possible to match the phase of the pass characteristic when combining frequency bands of the branching / mixing filter, thereby achieving good impedance conversion performance over a wide band. In the impedance converter of the present invention, the low-frequency impedance conversion circuit may be replaced with a low-pass filter circuit, thereby realizing an impedance converter with good impedance conversion performance in the frequency band of 470 MHz to 3224 MHz. In the impedance converter of the present invention, a predetermined frequency band including an unused frequency band is set as the used frequency band, the cutoff frequencies of the low-pass filter and the high-pass filter are set to frequencies in the unused frequency band, and the pass characteristics of the low-pass filter and the high-pass filter are mismatched in phase. In this case, an impedance converter is realized that has good impedance conversion performance in the low frequency range up to the unused frequency band and in the high frequency range from the unused frequency band. Furthermore, a divider to which the impedance converter according to the present invention is applied can be a divider that can obtain good division performance over a wide band. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a circuit diagram illustrating a configuration of an impedance converter according to a first embodiment of the present invention. [Figure 2] 4 is a graph showing frequency characteristics of S parameters of the impedance converter according to the first embodiment of the present invention. [Figure 3] 1A and 1B are diagrams illustrating a low-frequency impedance conversion circuit and an equivalent circuit of an impedance converter according to a first embodiment of the present invention. [Figure 4] 1A and 1B are diagrams illustrating a high-frequency impedance conversion circuit and an equivalent circuit of an impedance converter according to a first embodiment of the present invention. [Figure 5] 1 is a circuit diagram showing the configuration of an equivalent branching / mixing filter of an impedance converter according to a first embodiment of the present invention. [Figure 6] 10 is a graph showing the phase of the passband characteristics with respect to frequency in a branching / mixing filter. [Figure 7] 10 is a graph showing pass characteristics versus frequency in a branching / mixing filter. [Figure 8] 10 is a graph showing the phase of the pass characteristic versus frequency when the phase of a high-pass filter in the demultiplexing / mixing filter is delayed. [Figure 9] 10 is a graph showing pass characteristics versus frequency when the phase of a high-pass filter in a demultiplexing / mixing filter is delayed. [Figure 10] 4 is a graph showing the phase of the passband characteristics versus frequency in an equivalent branching / mixing filter of the impedance converter according to the first embodiment of the present invention. [Figure 11] 4 is a graph showing the pass characteristics versus frequency of an equivalent branching / mixing filter of the impedance converter according to the first embodiment of the present invention. [Figure 12] FIG. 10 is a circuit diagram illustrating a configuration of an impedance converter according to a second embodiment of the present invention. [Figure 13] 10 is a graph showing the pass characteristic versus frequency in the impedance converter according to the second embodiment of the present invention. [Figure 14] 10 is a graph showing frequency characteristics of S parameters of the impedance converter according to the second embodiment of the present invention. [Figure 15] FIG. 10 is a circuit diagram illustrating a configuration of an impedance converter according to a third embodiment of the present invention. [Figure 16] 10 is a graph showing frequency characteristics of S parameters of the impedance converter according to the third embodiment of the present invention. [Figure 17] FIG. 1 is a circuit diagram showing the configuration of a conventional divider using a high-frequency transformer. [Figure 18] 1 is a circuit diagram showing the configuration of a divider according to a first embodiment of the present invention, which uses an impedance converter. [Figure 19] 4 is a graph showing frequency characteristics of S parameters of the divider according to the first embodiment using the impedance converter of the present invention. [Figure 20] 10 is a graph showing other frequency characteristics of the S parameters of the divider according to the first embodiment using the impedance converter of the present invention. [Figure 21] 1 is a circuit diagram showing an equivalent circuit of a distribution transformer of a divider according to a first embodiment of the present invention, which uses an impedance converter. [Figure 22] 22 is a graph showing frequency characteristics of S parameters when the equivalent circuit of the distribution transformer of the divider according to the first embodiment using the impedance converter of the present invention is the equivalent circuit shown in FIG. 21. [Figure 23] FIG. 10 is a circuit diagram showing the configuration of a divider according to a second embodiment of the present invention, which uses an impedance converter. [Figure 24] 10 is a graph showing frequency characteristics of S parameters of a divider according to a second embodiment of the present invention, which uses an impedance converter. [Figure 25] FIG. 1 is a circuit diagram showing the configuration of a conventional impedance conversion circuit using a high-frequency transformer. [Figure 26] FIG. 1 is a circuit diagram showing a configuration of a conventional impedance conversion circuit using resistors. [Figure 27] FIG. 1 is a circuit diagram showing the configuration of a conventional impedance conversion circuit using a distributed constant line. [Figure 28] FIG. 1 is a circuit diagram showing a configuration of an impedance conversion circuit using a matching element. DETAILED DESCRIPTION OF THE INVENTION

[0015] <Impedance converter according to the first embodiment of the present invention> A circuit diagram showing the configuration of an impedance converter 1 according to a first embodiment of the present invention is shown in Fig. 1. The impedance converter 1 according to the first embodiment of the present invention shown in Fig. 1 is an impedance converter 1 that is operable over a wide band and is made up of a high-frequency impedance conversion circuit 11 and a low-frequency impedance conversion circuit 12. 1, in the impedance converter 1 according to the first embodiment of the present invention, if the impedance of the input terminal IN is Zi, Zi is set to, for example, 75 Ω, and if the impedance of the output terminal OUT is Zo, Zo is set to, for example, 50 Ω. A high-frequency impedance conversion circuit 11 and a low-frequency impedance conversion circuit 12 are connected in parallel between the input terminal IN and the output terminal OUT. The operating frequency band of the impedance converter 1 according to the first embodiment of the present invention is at least 10 MHz to 3224 MHz.

[0016] The high-frequency impedance conversion circuit 11 is a series circuit connected between the input terminal IN and the output terminal OUT, with one end of a capacitor C1 connected to the input terminal IN and the other end of a distributed constant line W1 of impedance Z1 connected to the first output terminal OUT1. The low-frequency impedance conversion circuit 12 has one end of an inductor L1 connected to the input terminal IN, and the other end of a matching transformer T1, which has a ferrite core wrapped in an insulated wire and the other end grounded, connected to the other end. Furthermore, one end of an inductor L2, which has the other end connected to the output terminal OUT, is connected to a tap of the matching transformer T1. One end of a capacitor C2, the other end of which is grounded, is connected to the tap of the matching transformer T1. The capacitor C2 may be connected between the junction of the other end of the inductor L1 and the matching transformer T1 and the ground. In this way, the low-frequency impedance conversion circuit 12 performs impedance conversion between the impedance Zi of the input terminal IN and the impedance Zo of the output terminal OUT by connecting the tap of the matching transformer T1 to the output terminal OUT.

[0017] In the impedance converter 1 according to the first embodiment of the present invention, the low-frequency impedance conversion circuit 12 functions as an equivalent three-stage T-type low-pass filter due to the leakage inductance generated in the matching transformer T1, inductors L1 and L2, and capacitor C2, as will be described later. This allows the low-frequency impedance conversion circuit 12 to function as a low-pass filter when combining frequency bands. The high-frequency impedance conversion circuit 11 is configured to function equivalently as a high-pass filter, as will be described later. At the cutoff frequency of this high-pass filter, the distributed constant line W1 is considered a circuit pattern. Furthermore, because the high-pass filter shares some of the elements that form the low-pass filter, the high-frequency impedance conversion circuit 11 between the input terminal IN and the output terminal OUT equivalently forms a π-type three-stage high-pass filter with the inductor L1, leakage inductance, capacitors C1 and C2, and inductor L2. The high-frequency impedance conversion circuit 11 performs impedance conversion using the distributed constant line W1 as one of the matching elements in addition to the inductor L1, leakage inductance, inductor L2, and capacitors C1 and C2. As described above, the low-pass impedance conversion circuit 12 forms an equivalent three-stage T-type low-pass filter, and the high-pass impedance conversion circuit 11 forms an equivalent three-stage π-type high-pass filter. This allows the phase of the pass characteristic of the high-pass filter to lag behind the phase of the pass characteristic of the low-pass filter formed by the low-pass impedance conversion circuit 12, making it possible to match the phase of the pass characteristic when combining frequency bands. The circuit constants are adjusted so that the cutoff frequency of the low-pass filter and the cutoff frequency of the high-pass filter match.

[0018] The frequency characteristics of the S parameters of the impedance converter 1 according to the first embodiment of the present invention are shown in Fig. 2. In Fig. 2, the horizontal axis represents frequency [GHz] and the vertical axis represents absolute value (magnitude) [dB]. 2, the pass characteristic |S21| between the input terminal IN and the first output terminal OUT1 is a good frequency characteristic that maintains approximately 0 dB over the range of 10 MHz to 3224 MHz. Furthermore, the reflection characteristic |S11| of the input terminal IN and the reflection characteristic |S22| of the output terminal OUT have almost the same frequency characteristic, and are approximately −35 dB or less over the range of 10 MHz to 3224 MHz, which is a good frequency characteristic. As such, the impedance converter 1 of the first embodiment of the present invention has a usable frequency band of at least 10 MHz to 3224 MHz.

[0019] <Equivalent circuit of the impedance converter according to the first embodiment of the present invention> Here, it will be explained that in the impedance converter 1 according to the first embodiment of the present invention, the high-frequency impedance conversion circuit 11 functions equivalently as a high-pass filter, and the low-frequency impedance conversion circuit 12 functions equivalently as a low-pass filter. FIG. 3(a) shows a circuit diagram of the low-frequency impedance conversion circuit 12, and FIG. 3(b) shows an equivalent circuit diagram of the low-frequency impedance conversion circuit 12. The low-frequency impedance conversion circuit 12 shown in Fig. 3(a) is a circuit diagram that takes into account the leakage inductance of the matching transformer T1. That is, the inductor Lo1 between the input terminal IN and one end of the matching transformer T1 is an inductor consisting of inductor L1 and leakage inductance. As a result, as shown in the equivalent circuit of the low-frequency impedance conversion circuit 12 shown in Fig. 3(b), the low-frequency impedance conversion circuit 12 functions as a three-stage T-type low-pass filter consisting of a series-connected circuit of inductor Lo1 and inductor L2 connected between the input terminal IN and the output terminal OUT, and a capacitor C2 connected between the junction point between inductor Lo1 and inductor L2 and ground.

[0020] Next, FIG. 4(a) shows an equivalent circuit diagram of the high-frequency impedance conversion circuit 11. In the equivalent circuit of the high-frequency impedance conversion circuit 11 shown in FIG. 4(a), the high-frequency impedance conversion circuit 11 functions as a high-pass filter. At the cutoff frequency of this high-pass filter, the distributed constant line W1 is considered a circuit pattern. Furthermore, because the high-pass filter shares some of the elements of the low-frequency impedance conversion circuit 12, the high-frequency impedance conversion circuit 11 is equivalently configured as shown in FIG. 4(a) to include a series connection of inductor Lo1 and inductor L2 connected between the input terminal IN and the output terminal OUT, a capacitor C2 connected between the junction of inductor Lo1 and inductor L2 and ground, and a capacitor C1 connected between the input terminal IN and the output terminal OUT. In this circuit configuration, the operating frequency band of the high-frequency impedance conversion circuit 11 is approximately 1000 MHz to 3224 MHz, and therefore, capacitor C2 is shorted in this operating frequency band. In other words, because the junction of inductor Lo1 and inductor L2 is grounded, the high-frequency impedance conversion circuit 11 functions as a π-type three-stage high-pass filter, as shown in FIG. 4(b).

[0021] The impedance converter 1 of the first embodiment of the present invention is configured by connecting the equivalent low-frequency impedance conversion circuit 12 shown in Figure 3(b) and the equivalent high-frequency impedance conversion circuit 11 shown in Figure 4(b) in parallel between the input terminal IN and the output terminal OUT. That is, the equivalent circuit of the impedance converter 1 of the first embodiment of the present invention is as shown in Figure 5(a). As shown in Figure 5(a), the impedance converter 1 of the first embodiment is composed of a branching / mixing filter 14, which is configured by connecting in parallel a T-type three-stage low-pass filter in which the low-frequency impedance conversion circuit 12 functions and a π-type three-stage high-pass filter in which the high-frequency impedance conversion circuit 11 functions. Here, in the high frequency range of approximately 1000 MHz to 3224 MHz, the impedance of capacitor C2 in the demultiplexing / mixing filter 14 shown in Fig. 5(a) becomes low and enters a short-circuit state, so that the demultiplexing / mixing filter 14 becomes the equivalent circuit shown in Fig. 5(b) similar to the equivalent circuit shown in Fig. 4(b), and functions as a π-type three-stage high-pass filter. Also, in the low frequency range of approximately 10 MHz to 1000 MHz, the impedance of capacitor C1 in the demultiplexing / mixing filter 14 shown in Fig. 5(a) becomes high and enters an open state, so that the demultiplexing / mixing filter 14 becomes the equivalent circuit shown in Fig. 5(c) similar to the equivalent circuit shown in Fig. 3(b), and functions as a T-type three-stage low-pass filter.

[0022] As described above, in the impedance converter 1 of the first embodiment of the present invention, an output obtained by combining frequency bands of a low-pass filter equivalently formed by the low-pass impedance conversion circuit 12 and a high-pass filter equivalently formed by the high-pass impedance conversion circuit 11 through the demultiplexing / mixing filter 14 is output from the output terminal OUT. In the impedance converter 1 of the first embodiment of the present invention, the low-pass filter equivalently formed by the low-pass impedance conversion circuit 12 is a three-stage T-type low-pass filter, and the high-pass filter equivalently formed by the high-pass impedance conversion circuit 11 is a three-stage π-type high-pass filter. As a result, the impedance converter 1 of the first embodiment of the present invention exhibits good S-parameter frequency characteristics as shown in FIG. 2.

[0023] <Phase matching of pass characteristics> The impedance converter 1 according to the first embodiment of the present invention will be described as being able to match the phase of the passband characteristics when combining frequency bands without adding a phase correction circuit as in the conventional case. Conventionally, to combine two frequency bands, a branching / mixing circuit configured with a low-pass filter and a high-pass filter that can pass and attenuate each frequency band is used. In the impedance converter 1 of the first embodiment of the present invention, the circuit constants of the high-pass impedance conversion circuit 11 and the low-pass impedance conversion circuit 12 are adjusted so that the cutoff frequencies of the low-pass filter and the high-pass filter match. The cutoff frequency is set to, for example, 1 GHz. Furthermore, when combining frequency bands, it is necessary to match the phase of the pass characteristics of each filter at the cutoff frequency. FIG. 6 shows a graph of the phase of the pass characteristics versus frequency for the demultiplexing / mixing filter 14, and FIG. 7 shows the pass characteristics versus frequency for the demultiplexing / mixing filter 14. In FIG. 6, the phase of the pass characteristics of the low-pass filter is indicated as PL1, the phase of the pass characteristics of the high-pass filter is indicated as PH1, and the phase of the pass characteristics after demultiplexing / mixing is indicated as PD1. Also, in FIG. 7, the cutoff frequencies of the low-pass filter and high-pass filter are set to 1 GHz, the pass characteristics of the low-pass filter are indicated as SL1, the pass characteristics of the high-pass filter are indicated as SH1, and the phase of the pass characteristics after demultiplexing / mixing is indicated as SD1. If the phases of the pass characteristics are not matched, a notch characteristic will occur at 1 GHz (the cutoff frequency), as shown in FIGS. 6 and 7. To match the phase of the pass characteristics, a phase correction circuit is used to adjust the phase of the pass characteristics of the high-pass filter, thereby achieving phase matching of the pass characteristics.

[0024] Referring to FIG. 6, the phase of the high-pass filter leads the phase of the low-pass filter by 90 degrees. Phase mismatch between the low-pass filter and the high-pass filter at the 1 GHz cutoff frequency affects the attenuation of the passband characteristics. Therefore, a phase correction circuit (not shown) is used to shift the phase of the high-pass filter's passband characteristics by 180 degrees. FIG. 8 shows a graph of the phase of the passband characteristics versus frequency in the demultiplexer / mixer circuit when the phase of the high-pass filter's passband characteristics is shifted by 180 degrees, and FIG. 9 shows the passband characteristics versus frequency in the demultiplexer / mixer circuit. Referring to FIG. 8, it can be seen that the phase PH1 of the high-pass filter's passband characteristics lags the phase PL1 of the low-pass filter's passband characteristics by 90 degrees, and the phase PD1 of the demultiplexer / mixer passband characteristics is matched. Furthermore, referring to FIG. 9, it can be seen that the cutoff frequencies of the low-pass filter and high-pass filter are set to 1 GHz, and no notch occurs at 1 GHz in the phase SD1 of the demultiplexer / mixer passband characteristics. This is because the phase PD1 of the demultiplexer / mixer passband characteristics is matched. In this way, conventionally, in a demultiplexing / mixing circuit, a phase correction circuit is added to match the phase of the pass characteristics of the cutoff frequency, thereby synthesizing frequency bands.

[0025] As explained above, in a demultiplexing mixer circuit, if the phase of the high-pass filter's pass characteristic is ahead of the phase of the low-pass filter's pass characteristic at the cutoff frequency of the low-pass filter and high-pass filter, the pass characteristics will be mismatched, and if it is behind, they will be matched. The phase will change by 90 degrees per element that makes up the filter. In the branching / mixing filter 14 of the impedance converter 1 according to the first embodiment of the present invention, the circuit configuration of the high-pass filter equivalently formed by the high-pass impedance conversion circuit 11 is affected by the inductors Lo1 and L2 of the low-pass impedance conversion circuit 12, as described above, and is therefore equivalent to a π-type three-stage high-pass filter, as shown in FIG. 4(b). Because the high-pass filter equivalently formed by the high-pass impedance conversion circuit 11 has three elements, the phase shift is 3 × 90 degrees = 270 degrees = −90 degrees. This results in a 90-degree delay, and the phase of the pass characteristic of the high-pass filter is matched without using a phase shift circuit. FIG. 10 shows a graph of the phase of the pass characteristic versus frequency for the branching / mixing filter 14 of the impedance converter 1 according to the first embodiment of the present invention, and FIG. 11 shows the pass characteristic versus frequency for the branching / mixing filter 14. 10, it can be seen that the phase PH1 of the high-pass filter bandpass characteristic lags 90 degrees behind the phase PL1 of the low-pass filter bandpass characteristic, and the phases of the demultiplexed and mixed bandpass characteristic PD1 are matched. Also, with reference to FIG. 11, it can be seen that the cutoff frequency of the low-pass filter and high-pass filter is set to 1 GHz, and no notch occurs at 1 GHz in the phase SD1 of the demultiplexed and mixed bandpass characteristic. This is because the phases of the demultiplexed and mixed bandpass characteristic PD1 are matched. In this way, in the demultiplexing / mixing filter 14 of the impedance converter 1 according to the first embodiment of the present invention, the phases of the pass characteristics of the cutoff frequencies are matched and the frequency bands are combined without adding a phase correction circuit.

[0026] <Conditions for achieving phase matching in the impedance converter according to the first embodiment of the present invention> The impedance converter 1 of the first embodiment of the present invention described above is configured so that the phase of the pass characteristic of the high-pass filter formed by the high-pass impedance conversion circuit 11 is delayed relative to the phase of the pass characteristic of the low-pass filter formed by the high-pass impedance conversion circuit 11. As a result, the phases of the pass characteristics of the low-pass filter and the high-pass filter are matched and the frequency bands are combined. When the low-pass filter formed by the low-pass impedance conversion circuit 12 functions equivalently as a 4n-1 (n=1, 2, 3, . . .)-stage T-type low-pass filter, the high-pass impedance conversion circuit 11 is configured so that the high-pass filter formed by the high-pass impedance conversion circuit 11 functions equivalently as a three-stage π-type high-pass filter. As a result, the phase of the pass characteristic of the high-pass filter lags behind the phase of the pass characteristic of the low-pass filter, and the phases of the pass characteristics of the low-pass filter and high-pass filter are matched, resulting in frequency band synthesis. Furthermore, when the low-pass filter functions equivalently as a 4n+1 (n=1, 2, 3...) stage T-type low-pass filter, the high-pass filter is configured to function equivalently as a 4n+3 (n=1, 2, 3...) stage π-type high-pass filter. As a result, the phase of the pass characteristic of the high-pass filter lags behind the phase of the pass characteristic of the low-pass filter, and the phases of the pass characteristics of the low-pass filter and high-pass filter are matched, allowing frequency bands to be synthesized. Furthermore, when the low-pass filter functions equivalently as a 4n+3 (n=1, 2, 3...) stage T-type low-pass filter, the high-pass filter is configured to function equivalently as a 4n+1 (n=1, 2, 3...) stage π-type high-pass filter. As a result, the phase of the pass characteristic of the high-pass filter lags behind the phase of the pass characteristic of the low-pass filter, and the phases of the pass characteristics of the low-pass filter and high-pass filter are matched, resulting in frequency band synthesis.

[0027] <Impedance converter according to a second embodiment of the present invention> A circuit diagram showing the configuration of an impedance converter 2 according to a second embodiment of the present invention is shown in Fig. 12. The impedance converter 2 according to the second embodiment of the present invention shown in Fig. 12 is a wideband impedance converter 2 made up of a high-frequency impedance conversion circuit 21 and a low-frequency impedance conversion circuit 12. As shown in FIG. 12 , in the impedance converter 2 according to the second embodiment of the present invention, Zi denotes the impedance of the input terminal IN, which is set to, for example, 75 Ω, and Zo denotes the impedance of the output terminal OUT, which is set to, for example, 50 Ω. A high-frequency impedance conversion circuit 21 and a low-frequency impedance conversion circuit 12 are connected in parallel between the input terminal IN and the output terminal OUT. The low-frequency impedance conversion circuit 12 is the same as the low-frequency impedance conversion circuit 12 of the impedance converter 1 according to the first embodiment of the present invention. In the impedance converter 2 according to the second embodiment of the present invention, within the 10 MHz to 3224 MHz band, the frequency bands of 770 MHz to 1030 MHz and 962 MHz to 1030 MHz are unused bands. In the impedance converter 2 according to the second embodiment of the present invention, the used frequency band is divided into a low band from 10 MHz to a predetermined lower limit frequency of the unused band, and a high band from a predetermined upper limit frequency of the unused band to 3224 MHz.

[0028] The high-frequency impedance conversion circuit 21 is composed of capacitors C3 and C4 connected in series between the input terminal IN and the output terminal OUT, a distributed constant line W2, and an inductor L3 connected at one end between the junction of the capacitors C3 and C4 and ground. In this case, a high-pass filter is formed by the series-connected capacitors C4 and C5, and the inductor L3 connected between the junction of the capacitor C4 and ground. The low-frequency impedance conversion circuit 12 is the same as the low-frequency impedance conversion circuit 12 in the impedance converter 1 of the first embodiment, and therefore its description will be omitted. However, the low-frequency impedance conversion circuit 12 performs impedance conversion between the impedance Zi of the input terminal IN and the impedance Zo of the output terminal OUT by connecting the tap of the matching transformer T1 to the output terminal OUT.

[0029] As described above, in the impedance converter 2 of the second embodiment of the present invention, the low-frequency impedance conversion circuit 12 functions as an equivalent three-stage T-type low-pass filter using the leakage inductance generated in the matching transformer T1, inductor L1, and L2 and capacitor C2, and is made to function as a low-pass filter when combining frequency bands. The high-frequency impedance conversion circuit 21 is configured to function equivalently as a high-pass filter. At the cutoff frequency of this high-pass filter, the distributed constant line W2 is considered a circuit pattern. Furthermore, because the high-pass filter shares some of the elements forming the low-pass filter, the high-frequency impedance conversion circuit 21 between the input terminal IN and the output terminal OUT equivalently forms a π-type five-stage high-pass filter with the inductor L1, leakage inductance, capacitors C2, C3, and C4, and inductors L2 and L3. In this way, the high-frequency impedance conversion circuit 21 functions as a high-pass filter during frequency band synthesis. The high-frequency impedance conversion circuit 21 performs impedance conversion using the inductor L1, leakage inductance, inductors L2 and L3, and capacitors C2, C3, and C4, as well as the distributed constant line W2, as one of the matching elements.

[0030] In this way, the low-pass impedance conversion circuit 12 forms an equivalent three-stage T-type low-pass filter, and the high-pass impedance conversion circuit 21 forms an equivalent five-stage π-type high-pass filter. In this case, since the high-pass filter has five elements, the phase shift is 5 × 90 degrees = 450 degrees = +90 degrees. As a result, the phase of the pass characteristic of the high-pass filter formed by the high-pass impedance conversion circuit 21 leads the phase of the pass characteristic of the low-pass filter formed by the low-pass impedance conversion circuit 12. This results in a phase mismatch of the pass characteristics when the frequency bands are combined in a demultiplexing / mixing filter composed of the low-pass filter and the high-pass filter. In this case, the circuit constants are adjusted so that the cutoff frequencies of the low-pass filter and the high-pass filter are a desired frequency in an unused band, for example, 850 MHz. Note that, since the phases of the pass characteristics of the impedance converter 2 of the second embodiment of the present invention are mismatched, a steep attenuation waveform is generated at the cutoff frequency, but good impedance conversion performance is achieved over a wide band at other frequencies. As described above, in the impedance converter 2 according to the second embodiment of the present invention, the circuit configuration and number of stages of the low-pass filter and the high-pass filter can be configured without being restricted by the condition for matching the phases of the pass characteristics. The circuit constants are adjusted so that the cutoff frequencies of the low-pass filter and the high-pass filter match.

[0031] The pass characteristics of the S parameters of the impedance converter 2 according to the second embodiment of the present invention versus frequency are shown in Fig. 13. In Fig. 13, the horizontal axis represents frequency [GHz], and the vertical axis represents absolute value (magnitude) [dB]. 13, the pass characteristic |S21| between the input terminal IN and the output terminal OUT has good frequency characteristics with almost no loss except for the frequency characteristic around 850 MHz among 10 MHz to 3224 MHz. It can also be seen that the pass characteristic |S21| has a notch shape with a steep attenuation waveform at the cutoff frequency of 850 MHz. Next, the frequency characteristics of the S parameters of the impedance converter 2 according to the second embodiment of the present invention are shown in Fig. 14. The horizontal axis of Fig. 14 is frequency [GHz], and the vertical axis is absolute value (magnitude) [dB]. 14, the passband characteristic |S21| between the input terminal IN and the output terminal OUT has good frequency characteristics with almost no loss in the low frequency range from 10 MHz to less than 850 MHz, and in the high frequency range from above 850 MHz to 3224 MHz. Furthermore, the reflection characteristic |S11| of the input terminal IN and the reflection characteristic |S22| of the output terminal OUT have similar frequency characteristics, and are approximately -35 dB or less in the range from 10 MHz to 3224 MHz except for the band around 850 MHz, which is good frequency characteristics. In the impedance converter 2 of the second embodiment of the present invention, within the band of 10 MHz to 3224 MHz, the band of 770 MHz to 1030 MHz is an unused band, and the impedance converter 2 of the second embodiment of the present invention is an impedance converter that operates well in the usable frequency band, which is the frequency band from 10 MHz to a predetermined unused lower limit frequency, and from a predetermined upper limit frequency of the unused band to 3224 MHz.

[0032] In the impedance converter 2 according to the second embodiment of the present invention, a low-pass filter formed by the low-pass impedance conversion circuit 12 and a high-pass filter formed by the high-pass impedance conversion circuit 21 are connected in parallel between the input terminal IN and the output terminal OUT to form a branching / mixing filter. The cutoff frequencies of the low-pass filter formed by the low-pass impedance conversion circuit 12 and the high-pass filter formed by the high-pass impedance conversion circuit 21 are the same, and a frequency band is synthesized in a low band from 10 MHz to approximately the cutoff frequency and a high band from approximately the cutoff frequency to 3224 MHz. Note that the phase of the pass characteristics is mismatched in the 10 MHz to 3224 MHz band. In this case, the cutoff frequency can be set to a predetermined frequency in an unused band. For example, if the cutoff frequency is set to 850 MHz, the frequency characteristics of the S parameters will be good in the low frequency band from 10 MHz to less than 850 MHz and in the high frequency band from frequencies above 850 MHz to 3224 MHz.

[0033] <Impedance converter according to a third embodiment of the present invention> As mentioned above, the transmission frequency band of television broadcast signals is a maximum of 10 MHz to 3224 MHz, but when transmitting terrestrial digital broadcast signals and BS / CS broadcast intermediate frequency signals compatible with 4K8K broadcasting without the need for transmission of CATV signals, the transmission frequency band is 470 MHz to 3224 MHz. The impedance converter 3 of the third embodiment of the present invention is an impedance converter 3 that uses at least a frequency band of 470 MHz to 3224 MHz. 15 is a circuit diagram showing the configuration of an impedance converter 3 according to a third embodiment of the present invention. The impedance converter 3 according to the third embodiment of the present invention shown in FIG. 15 is a wideband impedance converter 1 made up of a high-frequency impedance conversion circuit 11 and a low-pass filter circuit 32. 15, in the impedance converter 1 of the first embodiment of the present invention, if the impedance of the input terminal IN is Zi, Zi is set to, for example, 75 Ω, and if the impedance of the output terminal OUT is Zo, Zo is set to, for example, 50 Ω. A high-frequency impedance conversion circuit 11 and a low-pass filter circuit 32 are connected in parallel between the input terminal IN and the output terminal OUT. The impedance converter 3 of the third embodiment of the present invention is suitable for signal transmission in a frequency band equal to or higher than the frequencies of terrestrial digital broadcasting, and uses a frequency band of at least 470 MHz to 3224 MHz.

[0034] The high-frequency impedance conversion circuit 11 is the same as the high-frequency impedance conversion circuit 11 of the impedance converter 1 of the first embodiment, and is a series circuit connected between the input terminal IN and the output terminal OUT, with one end of a capacitor C1 connected to the input terminal IN and the other end of a distributed constant line W1 of impedance Z1 connected to the first output terminal OUT1. The high-frequency impedance conversion circuit 11 is similar to the high-frequency impedance conversion circuit 11 of the impedance converter 1 of the first embodiment, and because some of the elements in the low-pass filter circuit 32 are shared, in the high-frequency impedance conversion circuit 11 between the input terminal IN and the output terminal OUT, inductors L4, L5 and capacitors C1, C5 equivalently form a π-type three-stage high-pass filter. In addition to these inductors L4, L5 and capacitors C1, C5, the high-frequency impedance conversion circuit 11 also uses the distributed constant line W1 as one of the matching elements to perform impedance conversion. The low-pass filter circuit 32 is composed of a series circuit of an inductor L4 having one end connected to the input terminal IN and an inductor L5 having the other end connected to the output terminal OUT, and a capacitor C5 connected between the junction of inductors L4 and L5 and ground. That is, the low-pass filter circuit 32 is a three-stage T-type low-pass filter made up of inductors L4, L5, and capacitor C5.

[0035] In this way, a three-stage T-type low-pass filter is formed in the low-pass filter circuit 32, and an equivalent three-stage π-type high-pass filter is formed in the high-frequency impedance conversion circuit 11. This allows the phase of the pass characteristic of the high-pass filter to be delayed relative to the phase of the pass characteristic of the low-pass filter circuit 32, thereby enabling the phases of the pass characteristics to be matched when frequency bands are combined. The circuit constants are adjusted so that the cutoff frequency of the low-pass filter matches the cutoff frequency of the high-pass filter.

[0036] The frequency characteristics of the S parameters of the impedance converter 3 according to the third embodiment of the present invention are shown in Fig. 16. In Fig. 16, the horizontal axis represents frequency [GHz], and the vertical axis represents absolute value (magnitude) [dB]. 16, the pass characteristic |S21| between the input terminal IN and the output terminal OUT has good frequency characteristics with almost no loss from 470 MHz to 3224 MHz. Furthermore, the reflection characteristic |S11| of the input terminal IN and the reflection characteristic |S22| of the output terminal OUT have similar frequency characteristics, and are approximately −30 dB or less from 470 MHz to 3224 MHz, which are good frequency characteristics. Thus, the operating frequency band of the impedance converter 3 of the third embodiment of the present invention is at least 470 MHz to 3224 MHz. To achieve the above performance using an impedance conversion circuit with distributed constant lines, it would be possible to use seven stages of distributed constant lines, but forming the circuit board would require a very large circuit pattern area.In contrast, the impedance converter 3 of the third embodiment of the present invention has a very simple circuit configuration, yet is able to achieve performance equivalent to that of an impedance conversion circuit with seven stages of distributed constant lines, making it possible to achieve both a compact circuit board and wideband impedance conversion performance. In the impedance converter 3 of the third embodiment, the use of the low-pass filter circuit 32 eliminates the need for the matching transformer T1. However, since the low-pass filter circuit 32 does not perform impedance conversion, impedance conversion is not performed in the frequency band of 470 MHz or less. In this case, since the frequency band of 470 MHz or less is not the operating frequency band, impedance mismatch may occur in the frequency band of 470 MHz or less.

[0037] <Distributor according to the first embodiment of the present invention> The impedance converter according to the embodiment of the present invention described above can be applied to a divider. When the impedance converter according to the embodiment of the present invention is applied to a divider, a divider that can achieve good division performance over a wide band can be provided. FIG. 17 shows a circuit diagram of a conventional divider 400 using a high-frequency transformer. The divider 400 using a high-frequency transformer is composed of two high-frequency transformers: a matching transformer P and a distribution transformer S. The matching transformer P functions to convert the signal impedance, while the distribution transformer S functions to distribute the signal power. A resistor R is connected between the first output terminal OUT1 and the second output terminal OUT2. The resistor R provides isolation between the first output terminal OUT1 and the second output terminal OUT2. If the input terminal IN, the first output terminal OUT1, and the second output terminal OUT2 all have the same impedance Za, and Za is, for example, 75 Ω, the matching transformer P converts the impedance of the input signal from 75 Ω to 37.5 Ω. The distribution transformer S then divides the signal into two and converts the impedance from 37.5 Ω to 75 Ω, outputting the signal from the first output terminal OUT1 and the second output terminal OUT2, respectively.

[0038] The divider 400 using the high-frequency transformer shown in Fig. 17 can achieve stable division performance over a wide frequency range, from a low frequency of 10 MHz. However, in the high frequency band above 1000 MHz, magnetic loss in the ferrite core and stray capacitance between windings become significant, and division loss increases as the frequency increases. Furthermore, these losses are particularly influenced by the matching transformer P. Therefore, by using the impedance converter 1 of the first embodiment of the present invention, which can achieve stable impedance conversion with low loss over a wide frequency band from 10 MHz to 3224 MHz, instead of the matching transformer P, a divider can be achieved that can achieve good division performance over the operating frequency band of 10 MHz to 3224 MHz.

[0039] FIG. 18 is a circuit diagram showing the configuration of a divider 50 according to a first embodiment of the present invention, to which the impedance converter 1 according to the first embodiment of the present invention is applied. The divider 50 according to the first embodiment of the present invention shown in FIG. 18 has a circuit configuration including an impedance converter 4, which is the impedance converter 1 according to the first embodiment of the present invention, one end of which is connected to an input terminal IN, and a distribution transformer S. Specifically, the other end of the impedance converter 4 is connected to the center tap of the distribution transformer S, and the outputs of the distribution transformer S are connected to the first output terminal OUT1 and the second output terminal OUT2, respectively. In addition, a resistor R is connected between the first output terminal OUT1 and the second output terminal OUT2. The resistor R is used for isolation between the first output terminal OUT1 and the second output terminal OUT2. The divider 50 according to the first embodiment of the present invention is a wideband equal divider with a division ratio of 1:1 and a division number of 2. As shown in FIG. 18, a divider 50 according to a first embodiment of the present invention includes an input terminal IN and two output terminals, a first output terminal OUT1 and a second output terminal OUT2, with the first output terminal OUT1 and the second output terminal OUT2 serving as divided outputs. Assume that the impedance Zi of the input terminal IN, the impedance Zo1 of the first output terminal OUT1, and the impedance Zo2 of the second output terminal OUT2 are all the same, e.g., 75 Ω. If the impedance converter 4 has the same circuit configuration as the impedance converter 1 according to the first embodiment of the present invention, the impedance Z1 of the distributed constant line W1 is changed and the turns ratio of the matching transformer T1 is changed, so that the impedance of the signal input to the impedance converter 4 is converted from 75 Ω to 37.5 Ω. The operating frequency band of the divider 50 according to the first embodiment of the present invention is at least 10 MHz to 3224 MHz.

[0040] 19 shows the frequency characteristics of the S parameters of divider 50 of the first embodiment of the present invention when impedance converter 1 of the first embodiment of the present invention is used as impedance converter 4 of divider 50 of the first embodiment of the present invention. In Fig. 19, the horizontal axis is frequency [GHz] and the vertical axis is absolute value (magnitude) [dB]. 19, the passband characteristic |S21| between the input terminal IN and the first output terminal OUT1 and the passband characteristic |S31| between the second output terminal OUT2 are nearly identical in frequency characteristics, maintaining a good frequency characteristic of approximately -3 dB from 10 MHz to 3224 MHz. Furthermore, the reflection characteristic |S11| of the input terminal IN is approximately -25 dB or less from 10 MHz to 3224 MHz. The reflection characteristic |S22| of the first output terminal OUT1 and the reflection characteristic |S33| of the second output terminal OUT2 are nearly identical in frequency characteristics, maintaining a good frequency characteristic of approximately -30 dB or less from 10 MHz to 3224 MHz. Furthermore, the isolation characteristic |S32| between the first output terminal OUT1 and the second output terminal OUT2 is approximately -30 dB or less from 10 MHz to 3224 MHz, maintaining a good frequency characteristic. As described above, the divider 50 of the first embodiment of the present invention is a divider with good division performance at least in the wide band from 10 MHz to 3224 MHz.

[0041] In the divider 50 of the first embodiment of the present invention, the matching transformer P is replaced with the impedance converter 1 of the first embodiment of the present invention. However, the matching transformer P can also be replaced with the impedance converter 2 of the second embodiment of the present invention or the impedance converter 3 of the third embodiment of the present invention. That is, by using the impedance converter 2 of the second embodiment of the present invention, which can achieve low-loss and stable impedance conversion in a wide frequency band from 10 MHz to a predetermined lower-limit frequency of an unused band, and from a predetermined upper-limit frequency of the unused band to 3224 MHz, instead of the matching transformer P, a divider 50 can be realized that can achieve good division performance in the used frequency band from 10 MHz to a predetermined lower-limit frequency of an unused band, and from a predetermined upper-limit frequency of the unused band to 3224 MHz. Furthermore, by using the impedance converter 3 of the third embodiment of the present invention, which can achieve low-loss and stable impedance conversion in a wide frequency band from 470 MHz to 3224 MHz, instead of the matching transformer P, a divider 50 can be realized that can achieve good division performance in the used frequency band from 470 MHz to 3224 MHz.

[0042] <Distributor according to the second embodiment of the present invention> It has been confirmed that in the divider 50 of the first embodiment of the present invention shown in Fig. 18, depending on the dividing transformer S used, the frequency characteristics of the S parameters may become those shown in Fig. 20. In Fig. 20, the horizontal axis is frequency [GHz] and the vertical axis is absolute value (magnitude) [dB]. Referring to Figure 20, the passband characteristic |S21| between the input terminal IN and the first output terminal OUT1 and the passband characteristic |S31| between the input terminal IN and the second output terminal OUT2 have almost the same frequency characteristics, maintaining a good frequency characteristic of approximately -3 dB from 10 MHz to 3224 MHz. The reflection characteristic |S11| of the input terminal IN is also good, being approximately -25 dB or less from 10 MHz to 3224 MHz. However, the reflection characteristic |S22| of the first output terminal OUT1 and the reflection characteristic |S33| of the second output terminal OUT2 have almost the same frequency characteristics, but degrades to approximately -15 dB or less from 10 MHz to 3224 MHz. Furthermore, the isolation characteristic |S32| between the first output terminal OUT1 and the second output terminal OUT2 also degrades to approximately -15 dB or less from 10 MHz to 3224 MHz.

[0043] Therefore, the causes of deterioration in the reflection characteristic |S22| of the first output terminal OUT1, the reflection characteristic |S33| of the second output terminal OUT2, and the isolation characteristic |S32| between the first output terminal OUT1 and the second output terminal OUT2 will be considered. The electrical characteristics of the distribution transformer S of the distributor 50 of the first embodiment may differ depending on the coil winding method. Therefore, we analyzed the distribution transformer S used to show the frequency characteristics of the S parameters shown in Figure 20. Through the analysis, we found that, like the distribution transformer S shown in Figure 21, a resistance component RL that functions in a low frequency range of approximately 1 GHz or less and a resistance component RH that functions in a high frequency range of approximately 1 GHz or more are equivalently generated between the distribution output terminals. In Figure 21, to show that equivalent resistance components are generated in the low frequency range and the high frequency range, an inductor LL is connected in series with the resistance component RL that functions in the low frequency range, and a capacitor CH is connected in series with the resistance component RH that functions in the high frequency range.

[0044] Next, let us consider the resistance components RL and RH generated in the distribution transformer S. In the distributor 50 of the first embodiment shown in Fig. 18, when the resistance components RL and RH like those of the distribution transformer S shown in Fig. 21 are generated in the distribution transformer S, and the resistance R is removed, the frequency characteristics become those shown in Fig. 22. In Fig. 22, the horizontal axis is frequency [GHz] and the vertical axis is absolute value (magnitude) [dB]. 22, the pass characteristic |S21| between the input terminal IN and the first output terminal OUT1 and the pass characteristic |S31| between the input terminal IN and the second output terminal OUT2 have substantially similar frequency characteristics, maintaining a good frequency characteristic of approximately -3 dB from 10 MHz to 3224 MHz. Furthermore, the reflection characteristic |S11| of the input terminal IN is approximately -25 dB or less from 10 MHz to 3224 MHz, maintaining a good characteristic. However, the reflection characteristic |S22| of the first output terminal OUT1 and the reflection characteristic |S33| of the second output terminal OUT2 have substantially similar frequency characteristics, maintaining a good characteristic of approximately -25 dB or less in the low-frequency band of approximately 500 MHz or less from 10 MHz to 3224 MHz, but degrading to approximately -15 dB or less as the frequency increases. Furthermore, the isolation characteristic |S32| between the first output terminal OUT1 and the second output terminal OUT2 is also considered to be good in the low frequency band of approximately 800 MHz or less in the 10 MHz to 3224 MHz range, but deteriorates to approximately -15 dB or less as the frequency increases. Therefore, considering the frequency characteristics of Fig. 20 and Fig. 22, it can be seen that in the divider 50 of the first embodiment shown in Fig. 18, the isolation resistor R can be replaced with a resistance component RL in the low frequency range, but the resistance value of the resistance component RH deviates from the optimum resistance value for isolation in the high frequency range. Therefore, in order to obtain a divider with good performance characteristics even if the coil winding method is different, it is necessary to minimize the influence of the resistance component RH.

[0045] FIG. 23 shows a circuit diagram illustrating the configuration of a divider 60 according to a second embodiment of the present invention, which can achieve good performance characteristics even when the coil winding method is different. The divider 60 according to the second embodiment of the present invention shown in FIG. 23 has a circuit configuration including an impedance converter 4 (the impedance converter 1 according to the first embodiment of the present invention) connected at one end to the input terminal IN, and a distribution transformer S2. The other end of the impedance converter 4 is connected to the center tap of the distribution transformer S2, and the outputs of the distribution transformer S2 are connected to the first output terminal OUT1 and the second output terminal OUT2, respectively. A series circuit in which a resistor R2 and a capacitor C6 are connected in series is also connected between the first output terminal OUT1 and the second output terminal OUT2. The divider 60 according to the second embodiment of the present invention is a wideband equal divider with a division ratio of 1:1 and a division number of 2. As shown in FIG. 23, a divider 60 according to the second embodiment, with a division ratio of 2, includes an input terminal IN and two output terminals OUT1 and OUT2, with the first output terminal OUT1 and the second output terminal OUT2 serving as divided outputs. Assume that the impedance Zi of the input terminal IN, the impedance Zo1 of the first output terminal OUT1, and the impedance Zo2 of the second output terminal OUT2 are all the same, e.g., 75 Ω. If the impedance converter 4 has the same circuit configuration as the impedance converter 1 according to the first embodiment of the present invention, the impedance Z1 of the distributed constant line W1 is changed and the number of turns of the matching transformer T1 is changed, so that the impedance of the signal input to the impedance converter 4 is converted from 75 Ω to 37.5 Ω. The operating frequency band of the divider 60 according to the second embodiment of the present invention is at least 10 MHz to 3224 MHz.

[0046] An impedance converter 4 and a distribution transformer S2 are connected in series between the input terminal IN and the first and second output terminals OUT1 and OUT2. A resistor R2 and a capacitor C6 are connected in series between the first and second output terminals OUT1 and OUT2. Because the resistor R2 functions only in the high frequency range due to the capacitor C6, the resistor R2 is connected in parallel with the high frequency resistance component RH generated in the distribution transformer S2 without interfering with the low frequency resistance component RL generated in the distribution transformer S2. As a result, the combined resistance of the resistor R2 and the resistance component RH serves as an isolation resistor, and the resistance value of the combined resistance is optimized for isolation, enabling excellent performance characteristics even in the high frequency range. As a result, the operating frequency band of the divider 60 of the second embodiment of the present invention is at least 10 MHz to 3224 MHz. The frequency characteristics of the S parameters of the divider 60 according to the second embodiment of the present invention are shown in Fig. 24. In Fig. 24, the horizontal axis represents frequency [GHz], and the vertical axis represents absolute value (magnitude) [dB]. Referring to Figure 24, the pass characteristic |S21| between the input terminal IN and the first output terminal OUT1 and the pass characteristic |S31| between the second output terminal OUT2 have nearly the same frequency characteristics, maintaining approximately -3 dB from 10 MHz to 3224 MHz, providing good frequency characteristics. The reflection characteristic |S11| of the input terminal IN is approximately -25 dB or less from 10 MHz to 3224 MHz, providing good frequency characteristics. The reflection characteristic |S22| of the first output terminal OUT1 and the reflection characteristic |S33| of the second output terminal OUT2 have nearly the same frequency characteristics, maintaining approximately -25 dB or less from 10 MHz to 3224 MHz, providing good frequency characteristics. Furthermore, the isolation characteristic |S32| between the first output terminal OUT1 and the second output terminal OUT2 is approximately -25 dB or less from 10 MHz to 3224 MHz, providing good frequency characteristics. In this way, even if a resistance component RL that functions in the low frequency range and a resistance component RH that functions in the high frequency range are equivalently generated between the distribution output terminals in the distribution transformer S2, the frequency characteristics of the S parameters can be improved in the distributor 60 of the second embodiment of the present invention.

[0047] In the divider 60 of the second embodiment of the present invention, the impedance converter 1 of the first embodiment of the present invention is used instead of the matching transformer P. However, the impedance converter 2 of the second embodiment of the present invention or the impedance converter 3 of the third embodiment of the present invention can be used instead of the matching transformer P. That is, by using the impedance converter 2 of the second embodiment of the present invention, which can achieve low-loss and stable impedance conversion in a wide frequency band from 10 MHz to a predetermined lower-limit frequency of an unused band, and from a predetermined upper-limit frequency of the unused band to a high frequency band from 3224 MHz, instead of the matching transformer P, a divider 60 can be realized that can achieve good division performance in the used frequency band from 10 MHz to a predetermined lower-limit frequency of an unused band, and from a predetermined upper-limit frequency of the unused band to 3224 MHz. Furthermore, by using the impedance converter 3 of the third embodiment of the present invention, which can achieve low-loss and stable impedance conversion in a wide frequency band from 470 MHz to 3224 MHz, instead of the matching transformer P, a divider 60 can be realized that can achieve good division performance in the used frequency band from 470 MHz to 3224 MHz. [Industrial Applicability]

[0048] The impedance converter of the first embodiment of the present invention described above is configured to delay the phase of the pass characteristic of the high-pass filter formed by the high-pass impedance conversion circuit relative to the phase of the pass characteristic of the low-pass filter formed by the low-pass impedance conversion circuit. This matches the phases of the pass characteristics of the low-pass filter and the high-pass filter, making it possible to match the phases of the pass characteristics of the low-pass filter and the high-pass filter when combining frequency bands. Furthermore, in the impedance converter of the third embodiment of the present invention, the low-pass impedance conversion circuit is replaced with a low-pass filter circuit. In this case, too, the phases of the pass characteristics of the low-pass filter and the high-pass filter formed by the low-pass filter circuit are matched, making it possible to match the phases of the pass characteristics of the low-pass filter and the high-pass filter when combining frequency bands. In this case, when the low-pass filter formed by the low-pass impedance conversion circuit or the low-pass filter circuit functions equivalently as a 4n-1 (n=1, 2, 3, . . .)-stage T-type low-pass filter, the high-pass filter formed by the high-pass impedance conversion circuit is configured so that it functions equivalently as a three-stage π-type high-pass filter. This causes the phase of the pass characteristic of the high-pass filter to lag behind the phase of the pass characteristic of the low-pass filter, making it possible to match the phases of the pass characteristics of the low-pass filter and high-pass filter when combining frequency bands. Furthermore, in the impedance converters of the first and third embodiments of the present invention, when the low-pass filter functions equivalently as a 4n+1 (n=1, 2, 3...) stage T-type low-pass filter, the high-pass filter is configured to function equivalently as a 4n+3 (n=1, 2, 3...) stage π-type high-pass filter. This causes the phase of the pass characteristic of the high-pass filter to lag behind the pass characteristic phase of the low-pass filter, making it possible to match the phases of the pass characteristics of the low-pass filter and high-pass filter when combining frequency bands. Furthermore, when the low-pass filter functions equivalently as a 4n+3 (n = 1, 2, 3...) stage T-type low-pass filter, the high-pass filter is configured to function equivalently as a 4n+1 (n = 1, 2, 3...) stage π-type high-pass filter. This causes the phase of the pass characteristic of the high-pass filter to lag behind the phase of the pass characteristic of the low-pass filter, making it possible to match the phases of the pass characteristics of the low-pass filter and high-pass filter when combining frequency bands.

[0049] The impedance converters of the first and third embodiments of the present invention described above form equivalent wavelength-branching / mixing filters, and in the wavelength-branching / mixing filters, the phases of the pass characteristics of the cutoff frequencies are matched without adding a phase correction circuit, and frequency bands are combined. The operating frequency band of the impedance converter according to the first embodiment of the present invention is 10 MHz to 3224 MHz. Thus, the impedance converter according to the first embodiment of the present invention is compatible with television broadcast signals having a frequency band of 10 MHz to 55 MHz or 60 MHz for CATV upstream signals, a frequency band of 70 MHz to 770 MHz or 962 MHz for CATV downstream signals, a frequency band of 470 MHz to 710 MHz for terrestrial digital broadcast signals, and a frequency band of 1030 MHz to 3224 MHz for BS / CS broadcast intermediate frequency signals compatible with 4K8K broadcasts. In the impedance converter according to the second embodiment of the present invention, in the 10 MHz to 3224 MHz band, the frequency bands of 770 MHz to 1030 MHz or 962 MHz to 1030 MHz are unused bands, and the frequency bands actually used are the low band of 10 MHz to 770 MHz (962 MHz) and the high band of 1030 MHz to 3224 MHz. That is, the impedance converter according to the second embodiment of the present invention is required to operate at least in the low band of 10 MHz to 770 MHz and the high band of 1030 MHz to 3224 MHz. In the impedance converter according to the second embodiment of the present invention, the phase of the pass characteristics is mismatched in the used frequency band of 10 MHz to 3224 MHz, but the converter operates well in the low band from 10 MHz to a predetermined lower limit frequency of the unused band and in the high band from a predetermined upper limit frequency of the unused band to 3224 MHz. That is, the used frequency band of the impedance converter according to the second embodiment of the present invention is substantially 10 MHz to 3224 MHz.

[0050] The divider of the embodiment of the present invention is a divider to which an impedance converter according to the embodiment of the present invention is applied, and is a divider that can obtain good division performance over a wide band. Similarly, the divider of the second embodiment of the present invention is a divider to which an impedance converter according to the embodiment of the present invention is applied, and is a divider that can obtain good division performance over a wide band. Furthermore, the divider of the second embodiment of the present invention can obtain good frequency characteristics even if a resistive component that functions in a low frequency range and a resistive component that functions in a high frequency range are equivalently generated between the distribution output terminals in the distribution transformer. [Explanation of symbols]

[0051] 1 impedance converter, 2 impedance converter, 3 impedance converter, 4 impedance converter, 11 high-frequency impedance conversion circuit, 12 low-frequency impedance conversion circuit, 14 branching / mixing filter, 21 high-frequency impedance conversion circuit, 32 low-pass filter circuit, 50 divider, 60 divider, 100 impedance conversion circuit, 200 impedance conversion circuit, 300 impedance conversion circuit, 400 impedance conversion circuit, 400 divider, P matching transformer, S distribution transformer, S2 distribution transformer, T1 matching transformer, Ta matching transformer, W1 distributed constant line, W2 distributed constant line, Wc distributed constant line

Claims

1. An impedance converter in which a low-frequency impedance conversion circuit and a high-frequency impedance conversion circuit are connected in parallel between an input terminal and an output terminal, the low-frequency impedance conversion circuit is an impedance conversion circuit using a high-frequency transformer, and has a circuit configuration that functions equivalently as a low-pass filter between the input terminal and the output terminal; the high-frequency impedance conversion circuit is a series-connected circuit of a distributed constant line and a capacitor, and has a circuit configuration that functions equivalently as a high-pass filter between the input terminal and the output terminal; the high-pass impedance conversion circuit is configured so that the phase of the pass characteristic of the high-pass filter lags behind the phase of the pass characteristic of the low-pass filter, thereby matching the phases of the pass characteristics of the low-pass filter and the high-pass filter, synthesizing the outputs of the low-pass filter and the high-pass filter in frequency bands, and substantially matching the cutoff frequencies of the low-pass filter and the high-pass filter.

2. An impedance converter in which a low-pass filter circuit and a high-frequency impedance conversion circuit are connected in parallel between an input terminal and an output terminal, the low-pass filter circuit serving as a low-pass filter between the input terminal and the output terminal; the high-frequency impedance conversion circuit is a series-connected circuit of a distributed constant line and a capacitor, and has a circuit configuration that functions equivalently as a high-pass filter between the input terminal and the output terminal; the high-pass impedance conversion circuit is configured so that the phase of the pass characteristic of the high-pass filter lags behind the phase of the pass characteristic of the low-pass filter, thereby matching the phases of the pass characteristics of the low-pass filter and the high-pass filter, synthesizing the outputs of the low-pass filter and the high-pass filter in frequency bands, and substantially matching the cutoff frequencies of the low-pass filter and the high-pass filter.

3. 3. The impedance converter according to claim 1, wherein the high-frequency impedance conversion circuit is configured so that when the low-pass filter functions equivalently as a 4n-1 (n=1, 2, 3, ...)-stage T-type low-pass filter, the high-pass filter functions equivalently as a 3-stage π-type high-pass filter, thereby matching the phases of the pass characteristics of the low-pass filter and the high-pass filter and synthesizing the frequencies.

4. 3. The impedance converter according to claim 1, wherein the high-frequency impedance conversion circuit is configured so that when the low-pass filter functions equivalently as a 4n+1 (n=1, 2, 3, . . .) stage T-type low-pass filter, the high-pass filter functions equivalently as a 4n+3 (n=1, 2, 3, . . .) stage π-type high-pass filter, thereby matching the phases of the pass characteristics of the low-pass filter and the high-pass filter and combining the frequency bands.

5. 3. The impedance converter according to claim 1, wherein the high-frequency impedance conversion circuit is configured so that when the low-pass filter functions equivalently as a 4n+3 (n=1, 2, 3, . . .) stage T-type low-pass filter, the high-pass filter functions equivalently as a 4n+1 (n=1, 2, 3, . . .) stage π-type high-pass filter, thereby matching the phases of the pass characteristics of the low-pass filter and the high-pass filter and combining the frequency bands.

6. 2. The impedance converter according to claim 1, wherein a frequency band of 10 MHz to 3224 MHz is obtained as a usable frequency band.

7. 3. The impedance conversion circuit according to claim 2, wherein a frequency band of 470 MHz to 3224 MHz is obtained as a usable frequency band.

8. an impedance converter in which a low-frequency impedance conversion circuit and a high-frequency impedance conversion circuit are connected in parallel between an input terminal and an output terminal, and a predetermined frequency band including an unused frequency band is set as a usable frequency band; the low-frequency impedance conversion circuit is an impedance conversion circuit using a high-frequency transformer, and has a circuit configuration that functions equivalently as a low-pass filter between the input terminal and the output terminal; the high-frequency impedance conversion circuit being a series-connected circuit of a high-pass filter circuit and a distributed constant line, and having a circuit configuration that functions equivalently as a high-pass filter between the input terminal and the output terminal; the cutoff frequency of the low-pass filter and the high-pass filter that are approximately matched is a predetermined frequency in the unused frequency band, and the outputs of the low-pass filter and the high-pass filter are frequency-combined when the pass characteristics of the low-pass filter and the high-pass filter are in a phase mismatch state.

9. 9. A divider comprising an impedance converter according to claim 1, 2 or 8 connected to a distribution transformer.

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