JP2634798B2 - Phase shift element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission circuit used as a filter circuit or a group delay equalizer, and more particularly to a filter circuit or a group delay equalizer capable of simultaneously satisfying high selectivity and low distortion. Is obtained.

2. Description of the Related Art For example, in an IF stage or the like of an FM tuner, a ceramic filter circuit 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, 2 and 3 are a pair of divided electrodes formed on one surface side of the piezoelectric ceramic substrate 1 in the thickness direction, and 4 is divided on the other surface side of the piezoelectric ceramic substrate 1. This is a common electrode formed to face the electrodes 2 and 3.

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 Meanwhile, a filter circuit used in an IF stage of an FM tuner is required to have a flat group delay time-frequency characteristic (hereinafter referred to as a GDT characteristic) due to a requirement for a low distortion factor. I have.
On the other hand, in Japan as well, the era of FM multi-station and the development of car audio, etc., require a filter with high rejection capability of adjacent stations and high selectivity.

However, in the conventional ceramic filter circuit shown in FIG. 13 and FIG.
Distortion of characteristics increases, and conversely, when trying to flatten the GDT characteristics and secure a low distortion, there is a disadvantage that the selectivity is deteriorated. The request could not be met at the same time.

15 to 17 show the above-described ceramic filter circuit.
It is a GDT and attenuation characteristic figure. A1 to A3 in FIGS. 15 to 17 are G
DT characteristics, B1 to B3 are attenuation characteristics, and GDT (μ
S), the amount of attenuation (dB) is plotted on the left vertical axis, and the frequency (MHz) is plotted on the horizontal axis. Figure 15 shows the Q of the ceramic resonator.
Characteristics when m is selected as high as Qm = 300, Fig. 16 shows Qm = 20
FIG. 17 shows the characteristics when a general-purpose type ceramic resonator of 0 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, the GDT characteristic A3 is flatter than in the case of FIG. 15, but 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 filter elements 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, making it impractical.

An object of the present invention is to provide a transmission circuit such as a filter circuit or a group delay equalizer that can simultaneously satisfy high selectivity and low distortion.

Means for Solving the Problems To solve the above-described problems, a transmission circuit according to the present invention includes a phase shift element and a filter element. The phase shift element is configured by connecting at least a pair of resonators having different anti-resonance frequencies or resonance frequencies in parallel, and is upwardly convex.
Has GDT characteristics. The filter element has a U-shaped GDT characteristic depressed at an intermediate portion, and is cascaded with the phase shift element.

In the phase shift element included in the transmission circuit according to the present invention,
When a pair of resonators having different anti-resonance frequencies are connected in parallel, the GDT characteristics rapidly change at different anti-resonance frequencies or resonance frequencies of the respective resonators, and become upwardly convex between the anti-resonance frequencies. This GDT characteristic is opposite to the GDT characteristic of the conventional ceramic filter element having the U-shaped GDT characteristic recessed in the middle part, and therefore, in combination with the conventional ceramic filter element, the GDT characteristic is flattened and the distortion is eliminated. It can be used as a GDT equalizer or filter circuit.

In addition, the attenuation characteristic is such that the amplitude changes rapidly at each anti-resonance frequency of the resonator, and the amplitude sharply increases between the anti-resonance frequencies. Therefore, excellent selectivity can be ensured.

In the case of a phase shift element in which a pair of resonators having different resonance frequencies are connected in parallel, they are used by being connected in parallel to a four-terminal transmission circuit. In this case, the same characteristics as described above can be obtained at each resonance frequency with respect to the GDT characteristics and the attenuation characteristics.

Embodiment FIG. 1 is a symbol diagram of a phase shifter constituting a transmission circuit according to the present invention. In the figure, 5 and 6 are resonators connected in parallel. The resonators 5, 6 have a structure in which electrodes (52, 53), (62, 63) are formed on both surfaces of the piezoelectric ceramic substrates 51, 61, and the electrodes 52-62 and 53-63 are commonly connected. . 7 and 8 are terminals. The resonators 5 and 6 have different anti-resonance frequencies or resonance frequencies. That is, the anti-resonance frequency of the resonator 5 is Fal, the anti-resonance frequency of the resonator 6 is Fa2, and Fal ≠ Fa2, or the resonance frequency of the resonator 5 is Fr1, and the resonance frequency of the resonator 6 is Fr2. And Fr1 ≠ Fr2. In this embodiment, the resonators 5 and 6
Are connected in parallel, but a larger number of resonators may be connected in parallel.

FIG. 2 shows the phase shifter shown in FIG.
FIG. 4 is a drive circuit diagram when the anti-resonance frequency Fa1 is different from the anti-resonance frequency Fa2 of the resonator 6, that is, when Fa1 ≠ Fa2. In this embodiment, Fa1
The case of> Fa2 will be described. In the figure, 9 is a phase shift element portion, 10 is a signal source, Rin is an input resistance, and Rout is an output resistance. Input resistance Rin and output resistance Rout are 300Ω
Is set to

In the circuit of FIG. 2, the GDT characteristic is the characteristic A of FIG.
As shown in FIG. 4, the characteristics change sharply at the anti-resonance frequency Fa1 of the resonator 5 and the anti-resonance frequency Fa2 of the resonator 6, and have an upwardly convex characteristic between the anti-resonance frequency Fa1 and the anti-resonance frequency Fa2. Becomes This GDT characteristic A4 is opposite to the GDT characteristic (FIG. 15 or 16) of the conventional ceramic filter element,
Therefore, by combining with a conventional ceramic filter element, it can be used as a GDT equalizer that can flatten GDT characteristics.

Moreover, the attenuation characteristic is, as shown by the characteristic B4 in FIG.
At the anti-resonance frequency Fa1 of the resonator 5 and the anti-resonance frequency Fa2 of the resonator 6, the amplitude sharply attenuates, and the amplitude sharply increases between the anti-resonance frequency Fa1 and the anti-resonance frequency Fa2. Become. 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. 4 (a), the input resistance Rin = 300Ω, Rout
= 300Ω in the circuit, the resonator 5
Is connected and driven by the signal source 10, as shown in FIG. 4 (b), a GDT characteristic A5 and an attenuation characteristic B5 which drop sharply at the anti-resonance frequency Fa1 are obtained.

Next, as shown in FIG. 5 (a), when the resonator 6 is connected in series to the transmission line and driven, as shown in FIG. 5 (b), the GDT characteristic drops sharply at the anti-resonance frequency Fa2. A6 and the attenuation characteristic B6 are obtained.

The circuit of FIG. 2 is substantially the same as the circuit obtained by superposing the circuit shown in FIG. 4A 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.

FIG. 6 shows another embodiment in which the resonance frequencies Fr1 and Fr2 of the resonators 5 and 6 are different from each other. A parallel circuit of the resonators 5 and 6 is connected in parallel to a four-terminal transmission circuit. It is. Also in the case of this embodiment, with respect to the GDT characteristics and the attenuation characteristics, the same characteristics as described above can be obtained at the respective resonance frequencies Fr1 and Fr2. 11 and 12 are input terminals, and 13 and 14 are output terminals.

FIG. 7 shows a transmission circuit according to the present invention in which the above-described phase shift element 15 is combined with a conventional ceramic filter element 16. This transmission circuit shows an example of a GDT equalizer. The GDT characteristic of the ceramic filter element 16 is a bimodal characteristic that is concave downward as shown by characteristic A7 in FIG.
The GDT characteristic of the phase shift element 15 is a characteristic that becomes convex upward as shown by the characteristic A4 in FIG. Therefore, the characteristic A7 in FIG.
A flat GDT characteristic is obtained as shown by a characteristic A8 in FIG. 9 by combining the characteristic with the characteristic A4 in FIG. Regarding the attenuation characteristic, the characteristic B7 in FIG. 8 and the characteristic B4 in FIG.
The characteristic as shown by the characteristic B8 in FIG. 9 is obtained. Attenuation characteristics
B8 has a large attenuation from the frequency domain where a flat GDT characteristic is obtained to the frequency domain on both sides of it.
High selectivity characteristics are obtained.

FIG. 10 is a plan view showing a specific structure of a phase shift element constituting a transmission circuit according to the present invention, and FIG. 11 is a bottom view of the same. In this embodiment, an electrode 52 forming the ceramic resonator 5 and an electrode 62 forming the ceramic resonator 6 are formed on one side of the piezoelectric ceramic substrate 1 formed in a flat shape at an interval. , These electrodes 52-62
Are conducted by the lead electrode 17, and the terminal 7 is connected and fixed to the lead electrode 521 extended from the electrode 52. On the other hand, electrodes 53 and 63 are formed on the other surface of the piezoelectric ceramic substrate 1 so as to face the electrodes 52 and 62, respectively.
53-63 are conductively connected by the lead electrode 18, and the terminal 8 is connected and fixed to the lead electrode 631 extending from the electrode 63.

The anti-resonance frequency Fal and the resonance frequency Fr1 of the resonator 5 and the anti-resonance frequency Fa2 and the resonance frequency Fr2 of the resonator 6 are set so that Fa1 ≠ Fa2 or Fr1 ≠ Fr2 as shown in FIGS. In the example, the areas of the electrodes 52 and 53 of the resonator 5 and the areas of the electrodes 62 and 63 of the resonator 6 are different.

As another means for making the anti-resonance frequencies Fa1 and Fa2 and the resonance frequencies Fr1 and Fr2 different, as shown in FIG. 12, the electrodes 52 and 53 of the resonator 5 and the electrodes 62 and 63 of the resonator 6 are used. Means for applying the solder resist 20 to the surfaces of the electrodes 62 and 63 of the resonator 6 (or the resonator 5) so that the solder resist 20 has an appropriate thickness and area is also effective. .

Effects of the Invention As described above, according to the present invention, it is possible to provide a transmission circuit such as a filter circuit or a GDT equalizer that can simultaneously satisfy a low distortion rate due to flattening of GDT characteristics and high selectivity. .

[Brief description of the drawings]

FIG. 1 is a symbol diagram of the phase shift element constituting the transmission circuit 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 obtained by the drive circuit of FIG. FIG. 4 (a) is a drive circuit diagram in which the resonator 5 is connected in parallel to the transmission line, and FIG. 4 (b) is obtained by the drive circuit of FIG. 4 (a). FIG. 5 (a) is a diagram showing the GDT characteristics and attenuation characteristics obtained, FIG. 5 (a) is a diagram of a drive circuit in which a resonator 6 is connected in series to a transmission line, and FIG. 5 (b) is obtained by the drive circuit of FIG. 5 (a). A diagram showing the obtained GDT characteristics and attenuation characteristics,
FIG. 6 is a symbol diagram of another embodiment of the phase shift element constituting the transmission circuit according to the present invention, FIG. 7 is a view showing a GDT equalizer according to the present invention combined with a phase shift element and a ceramic filter, FIG. 9 is a diagram showing the GDT characteristics and attenuation characteristics of the ceramic filter in FIG. 7, FIG. 9 is a diagram showing the GDT characteristics and attenuation characteristics obtained by the circuit of FIG.
FIG. 0 is a plan view showing a specific structure of a phase shift element constituting the transmission circuit according to the present invention, FIG. 11 is a bottom view thereof, and FIG.
FIG. 12 is a plan view of another embodiment, FIG. 13 is a diagram schematically showing the configuration of a conventional ceramic resonator, and FIG. 14 is a conventional ceramic filter circuit using the ceramic resonator shown in FIG. 15 to 17 are diagrams showing the GDT characteristics and the attenuation characteristics thereof. 5, 6 ... resonator

Claims (6)

(57) [Claims] 1. A transmission circuit including a phase shift element and a filter element, wherein the phase shift element is configured by connecting at least a pair of resonators having different anti-resonance frequencies or resonance frequencies in parallel, A transmission circuit that has a group delay-frequency characteristic that is convex upward, and the filter element has a U-type group delay time-frequency characteristic that is concave at an intermediate portion, and is cascaded with the phase shift element. . 2. The transmission circuit according to claim 1, wherein the phase shift element is configured by connecting at least a pair of resonators having different anti-resonance frequencies in parallel. 3. The transmission circuit according to claim 1, wherein the phase shift element is formed by connecting at least a pair of resonators having different resonance frequencies in parallel. 4. The transmission circuit according to claim 1, wherein said resonator of said phase shift element is a ceramic resonator. 5. The transmission circuit according to claim 4, wherein said resonator is formed on a common piezoelectric ceramic substrate. 6. The transmission circuit according to claim 1, wherein the transmission circuit is used as a filter circuit or a group delay equalizer.