JPS59196616A - print filter - Google Patents

Abstract

PURPOSE:To obtain a BPF having a pass band of 60-72MHz on a dielectric board by decreasing an inductance of a coil through the impedance conversion, converting the circuit into a circuit having lots of capacitors and using the plane circuit. CONSTITUTION:The impedance conversion is attained by providing a tap B' to a coil L1, and the circuit including capacitors and an ideal transformer required for the conversion is converted B into a pi circuit comprising capacitors Ca-Cc by means of the Norton conversion. Then, this conversion B is attained by the plane circuit. That is, the coil is made spiral so as to have an inductance and the capacitor is formed by a plane electrode and a distributed capacitance of coil pattern. Coils 11, 13 are formed by the pattern of L1 and coils 10, 12 have a pattern of L4. Then, the capacitor Cb is formed by the distributed capacitance of plane electrodes 26a, 26b. A capacitor C4 is formed between patterns 28a and 28b. A capacitor C1 is formed equivalently between patterns 27a and 27b, between patterns 31a and 31b, or the like. The short amount of coils is formed by patterns 8, 9 on the board 6.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a bandpass filter inserted into a high frequency signal transmission path, such as a bandpass filter used in an RF converter for a VTR.

Conventional configuration and its problems The frequency bands used in VTR RF converters, etc. are Japan 1,2 ch (90-102λ1ll), America 8,4ch (60-72 λ1ll), and Western Europe 8.
,'4ch (54-6814k) are used.

By the way, printed circuits can easily create spiral coil patterns (spiral coils), parallel electrode capacitor patterns, etc., so filter elements for these frequency bands, that is, coil elements, and especially capacitor elements can be used in planar circuits (
By providing a filter (printed circuit) on both sides of a dielectric substrate, a filter that occupies almost no space and can be mass-produced can be realized. Therefore, the circuit configuration example shown in FIG. 1 is suitable for this printed circuit filter.

However, the low frequency bands 54~68111h, 60~
There are obstacles to downsizing models such as 72 meters. For example 60~
To illustrate the circuit constants of 72 meters in Fig. 1, L1
=62nH, C1=98pE, L2=191n
H, C2 = 12 pF, C5 = 18 pF. Also,
Considering the shape to be approximately 8 gff x 11111 m, the problems are the thickness of the dielectric substrate, the dielectric constant, the spacing between the patterns, and the shape of the coil pattern.

If, for example, an inexpensive magnetic capacitor board is used as the F1 body board, the thickness needs to be about 0.8 to 0.6 mm in consideration of the bending strength. In addition, the dielectric constant is electrode area 5=5×8d,
Substrate thickness d=Q, 4ffjf, capacitance C-98pF
If so, the dielectric constant ε=about 280. That is, a high dielectric constant is desirable for miniaturization.

Furthermore, reducing the inter-pattern spacing reduces the required occupied area. However, on the other hand, stray capacitance increases, coupling occurs, and high frequency signals pass through. Even with miniaturization, the minimum spacing is at least as thick as the substrate, and shielding is required to reduce capacitive coupling.

Next is the size of the helical inductance configured in a spiral shape. The formula for calculating the approximate value is from the Radio Engineering Pocket Book: L=f (rz/r+) ・r2 ・N2X 1O−
3 (μH) where rl: inner diameter of helical (1), r
2: Outer diameter of helical ('') + N: Number of turns of helical, :F (r2/r1): Function of r2/r1. For example, r2-5mm l rl''2. EJIM
If rr2 / rl-2e N ''' 2, then L=
It is 85-45.

In order to increase the helical inductance, it is necessary to increase the helical outer diameter or increase the number of turns. The former increases stray capacitance and causes coupling, which poses an obstacle to miniaturization. The latter has the disadvantage that the winding resistance increases and the Q of the coil decreases.

As explained above, by providing (adhering) spiral coil patterns on both sides of a dielectric substrate and connecting both sides of the coil with through holes, etc., distributed capacitance can be created in the portions of the coil patterns that substantially face each other. arise. By utilizing this distributed capacitance, a parallel resonant circuit can be easily realized. Therefore, it can be seen that the circuit shown in FIG. 1 is suitable for being constructed as a planar circuit using a dielectric substrate. Therefore, if a ceramic capacitor board with a relatively high dielectric constant is used in order to reduce the cost and size, the inductance L+ = 62 nH and C1 = 98 pF can be easily achieved with a thickness of about 0.4 cm. That is, C,=989F can be realized by combining the coil pattern of (1) and the plane electrode. However, in a parallel circuit with inductance L2 = 191nH and capacitance C2 = 12 pF, the coil pattern of 191nH is larger than Ll, so C2 = 1
The value of 2 pF is small as a value formed by the distributed capacitance of the pattern of the coil L2, and therefore it is difficult to form it by the coil pattern, and the value of C2 formed by the distributed capacitance is larger than 12 pF.

Further, even when the mutual spacing between the patterns is at the minimum substrate thickness (for example, 0.8 to 0.5 mm), stray capacitance occurs and electrostatic coupling occurs. When the dielectric constant is 100 to 400, electrostatic coupling cannot be ignored. Stray capacitance C811 as shown in Figure 2
CO2 is produced and Cot becomes electrostatically coupled, allowing high frequency signals to pass through, resulting in poor characteristics. Generally, due to the structure of the pattern, Co1>Co2, and for Co2, several p
Since it is less than F, it does not impair the characteristics of the pass band and has the effect of shutting off high frequency signals in the high range.

As described above, there are many problems in miniaturizing devices whose passband is less than the 60-72 rule.

OBJECTS OF THE INVENTION The object of the present invention is to improve the problems of the prior art and to provide an iflint filter that is small and easy to mass produce.

Structure of the Invention The present invention provides an input terminal, a ground terminal, and an output terminal on a dielectric substrate, and connects a first coil L1 and a first coil in parallel with the input terminal.
A first parallel resonant circuit consisting of a capacitor c1 is deposited and formed, a tap B is provided on the first coil L1, and impedance conversion is performed so as to lower the impedance of a series branch connected to this tap B, and The series branch circuit is made into a series circuit of a parallel resonant circuit consisting of the second coil L4 and the second capacitor C4, and the eighth capacitor C5, so that the impedance value of the second coil L4 can be reduced by this impedance conversion. , further, to transform the circuit back to its original impedance, consider a circuit containing an eighth capacitor C5 and an ideal transformer T, and convert this circuit into a Norton
Perform the equivalent transformation of 4. Consisting of a π-type circuit consisting of fifth and sixth capacitors C-1#Cb*Cc,
Here, since the metamorphic ratio φ2 is White〉1, the equivalent converter Cc
is a negative value, but this negative value Cc is compensated as a near zero or positive stray capacitance fitco2, including the apparent stray capacitance C02' generated at the output terminal, and the capacitor Ca is connected to the coil pattern and ground pattern. It is formed of stray capacitance or distributed capacitance, and the ground pattern is used in combination as a shield pattern and a capacitor pattern.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Third
The figure shows the impedance conversion process of the circuit of Fig. 1, and Fig. 4 shows a further conversion of No. 8 UA, which is the circuit used in the gate of this invention.

In FIG. 8, a tap B is provided in the coil L1 to perform impedance conversion. Assuming that the transformation ratio is φl=i on the input terminal (1) side and 1 on the 2+tap B side, L in Fig. 1
2- The values of C2 and C3 are L4 = 188 nH,
C4=171)F.

C3=261]F.

Next, an ideal transformer T is provided after the capacitor C5 to perform impedance conversion again. For example, if the input and output have the same impedance, the transformation ratio of the ideal transformer T is φ2-1. ．． 2 + capacitor C
It is sufficient to set it to 1 on the b side.

By the way, when the circuit (4) including the series capacitor C5 and the ideal transformer T is subjected to Norton transformation, it is composed of a π-type circuit consisting of the capacitors Ca and (-b+Lc) shown in (5) in Fig. 4(a). However, since φ2 is φ2>1, the value of Cc becomes a negative value and cannot be realized.Can C
An example of the value of b+Cc is Ca=4.8pF, C
b = 21.7 pF, Cc = -8.6 pF.

Since the circuit is constructed by attaching a circuit element pattern to a dielectric substrate, the output terminal (2) and the ground terminal (3)'
A small amount of stray capacitance (several pF or less) of CO2 exists between the two. Therefore, this negative Cc is converted into a positive floating capacitance flt
c. By compensating in the form included in 2, circuit (5)' can be realized. Cc is corrected by the apparent stray capacitance CO2' and becomes CO2
It is realized as. As will be described later, Ca is formed as a stray capacitance between patterns (27c) and (27b) in FIG. 5(a). The pattern (27b) is a ground pattern, and since it is located between the output terminal pattern and the coil pattern, it has a shielding effect.

Next, a method of constructing the circuit shown in FIG. 4(b) on a dielectric substrate will be explained. The circuit shown in FIG. 4(b) reduces the inductance of the coil by impedance conversion and is converted into a circuit with a large number of capacitors, so it is more suitable for construction on a dielectric substrate using a planar circuit.

FIG. 5 is a diagram of a pattern formed on a dielectric substrate.

FIG. 5 will be explained in correspondence with the circuit diagram of FIG. 4(b).

First, in FIG. 5(a), (7) is a dielectric substrate with a relatively high dielectric constant (temporarily dielectric constant ε=250 to 850),
For example, it is made of magnetic capacitor material. (1) is the board (
The input terminal is on the 7a) side, (2) is the output terminal on the (7a) side of the board, (3) and (3)' are the ('N)) of the board.
This is the ground terminal on the side. The coil is formed into a spiral shape to provide inductance. Capacitors utilize the distributed capacitance of planar electrodes and coil patterns.

01) on surface (7a) is a part of the pattern of coil L1, (
Q3 on the 71)) side is a part of the pattern of the coil L1 facing (II) and is connected to the ground terminal (3).

B in surface (7a) is the pull-out portion of the tap.

(10 is a part of the pattern of coil L4, (
The plane (6) of the plane 71)) is a part of the pattern of the coil L4 facing θQ, and is connected to the plane (26b) of the plane electrode (71) forming the capacitor CI. (7a)
The surface (26a) is a planar electrode opposite to (26b), which forms a capacitor C5 and is connected to the output terminal (2). In addition, (26a) forms a 7￥ play capacity 1C62 with (29b) and (81b) on the surface (7b) of the ground pattern.

The stray capacitance between (27b) and (27c) on the (7b) plane forms a capacitor Ca. (28a) of (7a) side
A capacitor C4 is formed between the (2sb) and (7b) planes. Next, (27a) of surface (7a) and (27b) of surface (7b), (81a) and (7b) of surface (7a)
surface (gtb), (7a) surface (80a) and (7
b) Planar electrode (80b) and (7a) plane electrode (29a)
) and the plane electrode (29b) on the plane (7b) to form a capacitor C1 isometrically. Also, (7b) surface (7)
(27b), (31b), and (80b) are also shield patterns.

FIG. 5(b) shows the pattern of the missing portions of the coils L, L4, and (6) is a dielectric substrate with a low dielectric constant (temporarily having a dielectric constant of 10 or less), such as a ceramic capacitor substrate.

Consists of an alumina porcelain board and a glass epoxy board for printed wiring. (9) is the pattern of the missing part of coil L1,
(9) The outermost peripheries of (I+) (to) are substantially opposed to each other.

(e) The slope is a hole for electrical connection, and may be a through hole. (8) is the pattern of the insufficient portion of the coil L4, and (8) the outermost peripheral portions of QOU are substantially opposed to each other.

04 QQ is a hole for electrical connection, and may be a through hole.

The substrate (6) is polymerized onto the substrate (7) resulting in a structure as shown in FIG. FIG. 6 is a view of FIG. 5 viewed from the A side. The hole (G) coincides with the land (goods), and the land (c) is connected to 03 on the (7b) surface by the through hole (a). On the other hand, the hole matches the pattern (Boa). Then, if ) and Ql, (80a) and Qυ are electrically connected (using conductive paste or soldering, etc.),
A coil L1 with a multilayer structure is produced. Further, the hole α coincides with the land (A), and the land (A) is connected to (6) on the (7b) surface by a through hole (E). On the other hand, the hole 0Q coincides with the pattern (27a). Therefore,
(a) and QG.

If (27a) and (b) are electrically connected, a multilayered coil L4 can be obtained.

Finally, the substrates (6) and (7) may be bonded or sandwiched together in a polymerized state.

Since this embodiment has the circuit configuration and structure as described above,
It has the following effects.

(1) By reducing the inductance and increasing the number of capacitors to a value that is easy to achieve with a printed circuit, this capacitor pattern can be used in conjunction with a shield pattern (used to remove stray capacitance Cot). .

(2) In order to compensate for the negative equivalent capacitance generated by Norton transformation by including it in the stray capacitance generated in the dielectric substrate, it can be realized as a positive element using the stray capacitance.

(3) Using substrates with different dielectric constants, the coil has a multilayer structure, and the substrate with a high dielectric constant forms an equivalent parallel capacitor with a capacitor or a part of the coil of the parallel resonant circuit, and the substrate with a low dielectric constant forms the coil. Since the inductance deficit part of the inductance of
4= 1aanH) and a small value capacitor (C4=
The second parallel resonant circuit consisting of 17 pF can be made smaller even if the number of turns of the coil L4 is increased, and the distributed capacitance that can be formed by this coil pattern, that is, c4, can be realized as small as about 17 pF. Suppose that the dielectric constant is large ((ε=
250 to 350), if a similar L4 is constructed using the same board, the coil diameter will be even larger, and the value of c4 will also be several 1°p.
F becomes large, and the predetermined constant cannot be realized by a distributed constant.

Since the coil has a multilayer structure, the mutual induction inductance is large, and a large inductance can be achieved with a small size. Moreover, since a substrate with a low dielectric constant is used, stray capacitance between patterns is small and high frequency signals do not pass through, resulting in improved characteristics.

Note that it is more desirable that the substrate (6) having a low dielectric constant be thinner than the thickness of the substrate (7) (for example, about 0.1 fflff or less).

Characteristics showing the effects of this example are shown in FIGS. 7 and 8. FIG. 7 shows the characteristics excluding the pattern (27b) on the plane (7b), in which the f2 power is shifted to the low frequency side, and high frequency signals are allowed to pass through, resulting in poor high frequency characteristics. That is, the pattern (27b) is located between the coil pattern and the output terminal pattern, forms a capacitor pattern, and also serves as a shield pattern.

This shows that (27b) uses both the effect of the capacitor Ca and the effect of the shield.

By the way, if f3 in FIG. 8 is to be shifted further to the higher frequency side according to the required characteristics, C on plane (7b) in FIG.
When the part is cut off and (81b) is connected to (aob) instead, the Leege inductance created by the pattern 81b-C-80b becomes smaller, and f3 shifts to the higher frequency side.

In addition to the effects of the invention, according to the present invention, it is possible to realize a filter that is compact and can be easily mass-produced because it uses a printed circuit. Furthermore, there is an advantage that the pattern for forming a capacitor can also be used as a shielding pattern.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of a bandpass filter, Figure 2 is a circuit diagram showing an example of a bandpass filter.
The figure is an equivalent circuit diagram that takes stray capacitance into consideration, Figure 8 is a circuit diagram showing the impedance conversion process in Figure 1, and Figure 4 (a).
The circuit containing the third open series capacitor and the ideal transformer is No.
Perform rton conversion and convert negative Cc to apparent stray capacitance C62
Figure 4(b) is a circuit diagram showing the process of including and compensating for C62 and realizing it as C62.
The final equivalent circuit diagram includes a circuit in which c is realized as a stray capacitance of CO2. Figures 5(a) and 5(b) are diagrams of the pattern shown in Figure 4(b) formed on a dielectric substrate. 5 as viewed from side A, FIG. 7 is a characteristic diagram when the pattern (27b) is excluded, and FIG. 8 is a characteristic diagram based on one embodiment of the present invention. (υ...input terminal, (2)...output terminal, (3)
(3)'...Earth terminal, (LIXL2)...1st
and second coils, (CI) (C2) (C3) --- first. second and eighth capacitors, (Ca) (Cb) (C
c)...4th. Fifth and sixth capacitors, (T)
...Ideal transformer, (Cot)...Capacitive coupling capacitance, (C
O2)... Stray capacitance agent between terminals (2) (3)'

Claims (1)

[Claims] 1. Provide an input terminal, a ground terminal, and an output terminal on a dielectric substrate, and form a first parallel resonant circuit consisting of a first coil and a first capacitor in parallel with the input terminal; A tap is provided on the coil, and a second coil is provided in series with the tap.
a second parallel resonant circuit consisting of a coil and a second capacitor, a fourth capacitor, and a third capacitor connected to the output terminal through an ideal transformer; The circuit containing the capacitor and the ideal transformer is subjected to Norton's equivalent transformation, and the fourth. It is composed of a π-type circuit consisting of a fifth and a sixth capacitor, and the negative elements of the fourth and fifth capacitors become zero or positive values without impairing the pass band characteristics. like,
Compensates for stray capacitance generated in the dielectric substrate, including negative elements,
At least the fourth. A printed filter characterized in that two of the fifth and sixth capacitors are formed by stray capacitance or distributed capacitance of a coil pattern and a ground pattern, and the ground pattern is used in combination as a shield pattern and a capacitor pattern.