JP2710154B2 - Phase shift element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a phase shift element used as a filter or a group delay equalizer. <Related Art> For example, in an IF stage of an FM tuner, a ceramic filter using a ceramic resonator and a group delay equalizer may be used in order to achieve no adjustment and high stability.
FIG. 13 is a view showing the structure of a conventional ceramic resonator of this type. In FIG. 13, 1 is a piezoelectric ceramic substrate,
Reference numerals 2 and 3 denote a pair of divided electrodes formed on one surface side of the piezoelectric ceramic substrate 1 in the thickness direction, and 4 denotes a pair formed on the other surface of the piezoelectric ceramic substrate 1 so as to face the divided electrodes 2 and 3. Common electrode. FIG. 14 shows a ceramic filter circuit obtained by combining two ceramic resonators shown in FIG. 13 with a capacitor C. <Problems to be Solved by the Invention> By the way, the filter used for the IF stage of the FM tuner or the like has a group delay time-frequency characteristic (hereinafter GD
T characteristics) are required. On the other hand, in Japan, we are heading for an era of FM multi-station,
In addition, due to the development of car audio and the like, a filter having a high rejection capability of an adjacent station and a high selectivity has been required. However, in the conventional ceramic filter shown in FIGS. 13 and 14, when the selectivity is increased, the distortion of the GDT characteristic is increased, and when the GDT characteristic is flattened to secure a low distortion rate, There is a drawback that the selectivity is deteriorated, and it has not been possible to satisfy the demand for a high selectivity at the same time as reducing the distortion rate by flattening the GDT characteristics. 15 to 17 show the GDT of the ceramic filter described above.
FIG. A1 to A3 in Fig. 15 to Fig. 17 are GDT
Characteristics, B1 to B3 are attenuation characteristics, and GDT (μS) is plotted on the right vertical axis.
, The attenuation (dB) is plotted on the left vertical axis, and the frequency (MHz) is plotted on the horizontal axis. Figure 15 shows the Qm of the ceramic resonator.
When Qm = 300 is selected as high as Fig. 16, Fig. 16 shows Qm = 200
The characteristics when the general-purpose ceramic resonator is used, and FIG. 17 shows the characteristics when Qm is reduced to Qm = 100. In the case of FIG. 15, by selecting a high value of Qm = 300, the rise and fall of the attenuation characteristic B1 are sharp, and a good selectivity can be obtained. However, the GDT characteristic A1 has a bimodal characteristic that is concave downward at around 10.7 MHz, causing significant distortion. On the other hand, in FIG. 17, although the GDT characteristic A3 is made flatter than in the case of FIG. 15, the rise and fall of the attenuation characteristic B3 become gentle, and the selectivity is deteriorated. Moreover, the insertion loss is about
It is very large at 9dB. For this reason, when the filters having the characteristics shown in FIG. 17 are connected in multiple stages to increase the selectivity, the insertion loss increases extremely in proportion to the number of stages, and becomes impractical. An object of the present invention is to provide a filter or a phase shift element suitable for obtaining a group delay equalizer capable of simultaneously satisfying high selectivity and low distortion. <Means for Solving the Problems> In order to solve the above problems, the phase shift element according to the present invention is cascaded with a filter or a filter circuit having a group delay time-frequency characteristic depressed at an intermediate portion. The phase shift element according to the present invention is a first phase shift element that is in series with the transmission path.
And at least one pair of a second resonator and a second resonator that is parallel to the transmission line. The first resonator has a resonance frequency of the second resonator.
It has an anti-resonance frequency Fa1 higher than Fr2, and has a maximum group delay time at a first frequency lower than the anti-resonance frequency Fa1, and a group delay time in a direction from the first frequency to a higher frequency. It shows a GDT characteristic in which the group delay time is sharply reduced and the group delay time is minimized near the anti-resonance frequency. In the second resonator, the group delay time is minimized at the resonance frequency Fr2, and the group delay time sharply increases in the direction in which the frequency increases from the resonance frequency Fr2, and is higher than the resonance frequency Fr2. The GDT characteristic at which the group delay time becomes maximum at the second frequency is shown. The first frequency and the second frequency are selected to be close to each other. And the GDT characteristic of the first resonator and the second
By superimposing the GDT characteristics of the resonator described above, a GDT characteristic that is convex upward at an intermediate portion between the resonance frequency Fr2 and the anti-resonance frequency Fa1 is obtained. <Operation> In the phase shift element according to the present invention, the GDT characteristic
A sharp delay occurs at the anti-resonance frequency of the resonator and the resonance frequency of the second resonator, and the characteristic has an upward convexity between the anti-resonance frequency and the resonance frequency. This GDT characteristic is opposite to the GDT characteristic of the conventional ceramic filter which is depressed in the middle part.
It can be used as a GDT equalizer with flattened T characteristics and no distortion. In addition, the attenuation characteristics are such that the amplitude rapidly attenuates at the anti-resonance frequency of the first resonator and the resonance frequency of the second resonator, and the amplitude sharply changes between the anti-resonance frequency and the resonance frequency. The characteristics will increase. Therefore, excellent selectivity can be ensured. <Embodiment> FIG. 1 is a symbol diagram of a phase shift element according to the present invention.
In the figure, reference numeral 5 denotes a first resonator which is connected in series to a transmission line formed of a four-terminal network, and reference numeral 6 denotes a second resonator which is connected in parallel to the transmission line. In this embodiment, only one combination of the first resonator 5 and the second resonator 6 is provided, but a multistage connection may be used. The anti-resonance frequency Fa1 of the first resonator 5 and the second resonator 6
Are different from each other. That is, F
a1 ≠ Fr2. More specifically, Fa1> Fr2. In the first resonator 5, electrodes 52 and 53 are formed on both surfaces of a piezoelectric ceramic substrate 51, and the electrode 52 is connected to the input terminal 7 and the electrode 53 is connected to the output terminal 9. In the second resonator 6, electrodes 62 and 63 are formed on both surfaces of a piezoelectric ceramic substrate 61, and the electrodes 62 and 63 are connected between input terminals 7-8. FIG. 2 is a drive circuit diagram of the phase shift element according to the present invention.
In the figure, reference numeral 11 denotes a portion of the phase shift element according to the present invention, 12 denotes a signal line, Rin denotes an input resistance, and Rout denotes an output resistance. The input resistance Rin and the output resistance Rout are set to 300Ω. In the circuit of FIG. 2, the GDT characteristic is the characteristic A of FIG.
As shown in FIG. 4, the frequency rapidly advances at the anti-resonance frequency Fa1 of the first resonator 5 and the resonance frequency Fr2 of the second resonator, and projects upward between the anti-resonance frequency Fa1 and the resonance frequency Fr2. Characteristic. This GDT characteristic A4 is opposite to the GDT characteristic (FIG. 15 or 16) of the conventional ceramic filter,
Therefore, by combining with a conventional ceramic filter, it can be used as a GDT equalizer that can flatten the GDT characteristics. Moreover, the attenuation characteristic is, as shown by the characteristic B4 in FIG.
Anti-resonance frequency Fa1 of first resonator 5 and second resonator 6
At the resonance frequency Fr2, the amplitude sharply attenuates, and the amplitude sharply increases between the anti-resonance frequency Fa1 and the resonance frequency Fr2. Therefore, excellent selectivity can be ensured. Next, the reason why the characteristics shown in FIG. 3 are obtained will be described. As shown in FIG. 4A, a ceramic resonator in which electrodes 2 and 3 are formed on both surfaces of a piezoelectric ceramic substrate 1 is a fourth type.
It shows impedance and phase characteristics as shown in FIG. Z1 is an impedance characteristic, PH1 is a phase characteristic, Fr is a resonance frequency, and Fa is an anti-resonance frequency. As shown in FIG. 5 (a), input resistance Rin = 300Ω, Rout
= 300Ω, when the ceramic resonator 6 is connected in parallel to the transmission line and driven by the signal source 12, the GDT drops sharply at the resonance frequency Fr2 as shown in FIG. 5 (b).
The characteristic A5 and the attenuation characteristic B5 are obtained. Ceramic resonator 6
Is that the group delay time (μs) is minimized at the resonance frequency Fr2, the group delay time (μs) is rapidly increased from the resonance frequency Fr2 toward the higher frequency, and the second delay time is higher than the resonance frequency Fr2. The GDT characteristic A5 at which the group delay time (μs) becomes maximum (about 0) at the frequency f2 is shown. The second frequency f2 is about 10.72 MHz. On the other hand, when the ceramic resonator 5 is driven by being connected in series to the transmission line as shown in FIG. 6 (a), the GDT rapidly drops at the anti-resonance frequency Fa1 as shown in FIG. 6 (b).
The characteristic A6 and the attenuation characteristic B6 are obtained. As shown in FIG. 6B, the ceramic resonator 5 has an anti-resonance frequency F2 higher than the resonance frequency Fr2 of the ceramic resonator 6 (about 10.56 MHz).
a1 (about 10.89 MHz), the group delay time (μS) becomes maximum (about 0) at the first frequency f1 lower than the anti-resonance frequency Fa1, and the frequency increases from the first frequency f1. As a result, the group delay time (μs) rapidly decreases, and the GDT characteristic A6 in which the group delay time (μs) is minimized near the anti-resonance frequency Fa1 is shown. The first frequency f1 is about 10.73 MHz
z, which is a value close to the second frequency f2 (about 10.72 MHz). The circuit shown in FIG. 2 is substantially the same as the circuit shown in FIG. 5A and the circuit shown in FIG. Therefore, the characteristic shown in FIG.
The characteristic shown in FIG. 3 in which the characteristic shown in FIG. That is, the superposition of the GDT characteristic A5 in FIG. 5B and the GDT characteristic A6 in FIG.
GDT characteristics that are convex upward in the middle part of the anti-resonance frequency Fa1
A4 (see FIG. 3) is obtained. FIG. 7 shows another embodiment of the phase shift element according to the present invention. In this embodiment, the second resonator 6 is connected to the output terminal 9
Connected between -10. Also in the case of this embodiment, the same operation and effects as those of the embodiment of FIG. FIG. 8 shows an example in which the phase shift element 11 according to the present invention is used as a GDT equalizer in combination with a conventional ceramic filter 13. The GDT characteristic of the ceramic filter 13 is
Although the bimodal characteristic is concave downward as shown by the characteristic A7 in FIG. 9, the GDT characteristic of the phase shift element 11 according to the present invention is upward as shown by the characteristic A4 in FIG. The characteristic becomes convex. Therefore, by combining the characteristic A7 and the third characteristic A4 in FIG. 9,
As shown by the characteristic A8 in FIG. 10, a flat GDT characteristic is obtained. Regarding the attenuation characteristic, a characteristic as shown by a characteristic B8 in FIG. 10 is obtained by combining the characteristic B7 in FIG. 9 and the characteristic B4 in FIG. In the attenuation characteristic B8, the attenuation from the frequency region where a flat GDT characteristic is obtained to the frequency regions on both sides thereof is large, and a characteristic with high selectivity is obtained. FIG. 11 is a plan view showing a specific structure of the phase shift element shown in FIGS. 1 and 7, and FIG. 12 is a bottom view of the same. In this embodiment, an electrode 53 constituting the ceramic resonator 5 and an electrode 63 constituting the ceramic resonator 6 are arranged at an interval on one surface side of the piezoelectric ceramic substrate 1 formed in a plate shape. On the other surface side of the ceramic substrate 1, the electrodes 5
2, 62 are formed. The electrode 52 and the electrode 62 are the lead electrode 5
Connected in common by 6. The lead terminals 14 and 15 are connected and fixed to the lead electrode 531 extended from the electrode 53 and the lead electrode 631 extended from the electrode 63, respectively, and the lead terminal 16 is connected to the lead electrode 56. In the case of configuring the phase shift element of FIG.
Is connected to the input terminal 7, the lead terminal 14 is connected to the output terminal 9, and the lead terminal 15 is connected to the input terminal 8 and the power collecting terminal 10. 7, the lead terminal 14 is connected to the input terminal 7, the lead terminal 16 is connected to the output terminal 9, and the lead terminal 15 is connected to the input terminal 8 and the output terminal 10. Connecting. <Effects of the Invention> As described above, according to the present invention, a phase shift element suitable as a filter or a GDT equalizer capable of simultaneously satisfying a low distortion factor and a high selectivity due to equalization of GDT characteristics is provided. can do.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a symbol diagram of a phase shift element according to the present invention, FIG. 2 is a drive circuit diagram of the phase shift element shown in FIG. 1, and FIG. 3 is a drive circuit of FIG. FIG. 4A is a diagram showing a GDT characteristic and a damping characteristic obtained by the method shown in FIG.
FIG. 4 (b) is a diagram of the impedance and phase shift characteristics, FIG. 5 (a) is a drive circuit diagram in which a ceramic resonator is connected in parallel to a transmission line, and FIG. 5 (b) is FIG. 5 (a). A diagram showing GDT characteristics and attenuation characteristics obtained by the drive circuit of
FIG. 6A is a drive circuit diagram in which ceramic resonators are connected in series to a transmission line, and FIG. 6B is a diagram showing GDT characteristics and attenuation characteristics obtained by the drive circuit in FIG. 6A. Seventh
FIG. 8 is a symbol diagram of another embodiment of the phase shift element according to the present invention, FIG. 8 is a diagram showing an example in which the phase shift element according to the present invention is combined with a ceramic filter and used as a GDT equalizer, and FIG. GDT of ceramic filter in Fig. 8
FIG. 10 is a diagram showing characteristics and attenuation characteristics, FIG. 10 is a diagram showing GDT characteristics and attenuation characteristics obtained by the circuit of FIG. 8, and FIG. 11 is a diagram of the phase shift element shown in FIGS. 1 and 7. FIG. 12 is a plan view showing the same structure, FIG. 12 is a bottom view thereof, FIG. 13 is a view schematically showing a configuration of a conventional ceramic resonator, and FIG.
A conventional ceramic filter circuit using the ceramic resonator shown in FIG. 13, and FIGS. 15 to 17 are diagrams showing the GDT characteristics and the attenuation characteristics thereof. 5, 6 ... resonators 7 to 10 ... terminals

Claims (1)

(57) [Claims] A phase shift element cascaded with a filter or a filter circuit having a group delay time-frequency characteristic depressed at an intermediate portion, wherein the first resonator is in series with a transmission line, and is in parallel with the transmission line. At least one pair with a second resonator is provided, and the first resonator has a resonance frequency Fr of the second resonator.
2 having an anti-resonant frequency Fa1 higher than 2,
The group delay time becomes maximum at the first frequency lower than Fa1, and the group delay time decreases rapidly from the first frequency toward the higher frequency, and the group delay time near the anti-resonance frequency The second resonator has a minimum group delay time at the resonance frequency Fr2, and has a minimum group delay time-frequency characteristic. Rapidly increases, and shows a group delay time-frequency characteristic in which the group delay time is maximized at a second frequency higher than the resonance frequency Fr2. The first frequency and the second frequency are values approximate to each other. And the group delay time-frequency characteristic of the first resonator and the group delay time-frequency characteristic of the second resonator are superimposed on each other. Wavenumber Fr2 and the anti-resonance frequency convex become group delay time on the middle portion of Fa1 - phase shifting elements to obtain the frequency characteristics. 2. The phase shift element according to claim 1, wherein the second resonator is connected between input terminals. 3. The phase shift element according to claim 1, wherein the second resonator is connected between output terminals. 4. 2. The method according to claim 1, wherein the first resonator and the second resonator are ceramic resonators.
Item 4. The phase shift element according to item 2 or 3. 5. The phase shift element according to claim 4, wherein the first resonator and the second resonator are formed on a common piezoelectric ceramic substrate.