JPH09232866A - Local oscillation circuit and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a local oscillation circuit which is capable of coping with the oscillation frequency bands of a wide range by applying soldering on a microstrip line to be a central conductor to change the oscillation frequency band. SOLUTION: In a local oscillation circuit having the central conductor part formed by a microstrip line L on a printed board 1, solder 4 is applied on the microstrip line L to be the central conductor part to change an oscillation frequency band. In the method, the solder application is performed at the same time when the solder application on the patterns for other chip mount parts on the same board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite broadcast receiver D.
The present invention relates to a local oscillator circuit used in a BS tuner or the like, and more particularly to a local oscillator circuit using a microstrip line formed on a printed circuit board as its central conductor and a manufacturing method thereof.

[0002]

2. Description of the Related Art A local oscillator circuit of a DBS tuner used in a satellite broadcast receiver will be described with reference to FIG. FIG. 6 is a circuit diagram of a conventional local oscillator circuit. The local oscillation circuit of FIG. 6 has a λ / 2 resonance circuit composed of a center conductor L and varicap diodes D1 and D2. TR1 is an oscillating transistor, and C1 and C2.
Is a feedback capacitance, R1, R2 and R3 are bias resistors, C3
Is a coupling capacitor, C4 and C5 are bypass capacitors, and R4 and R5 are resistors. Vin is a terminal for applying a voltage to this local oscillation circuit, and Vcc is a constant voltage input terminal.

Since this local oscillator oscillates a relatively high frequency, a microstrip line formed on a printed board is used as the center conductor L.

[0004]

By the way, the oscillation frequency (1429.5 MHz to 2) required for the conventional local oscillation circuit is used.
The bandwidth of 529.5 MHz was about 1100 MHz, but the input frequency band of the DBS tuner was expanded with the recent increase in the number of channels (oscillation frequency is 13
(79.5 MHz to 2629.5 MHz), and the oscillation frequency bandwidth needs to be expanded to about 1250 MHz. To deal with this, the following methods have been conventionally used.

First, the circuit of FIG. 6 is a circuit having a λ / 2 resonance circuit 10, but for simplification, this is considered as a circuit having a λ / 4 resonance circuit as shown in FIG. 7 in a pseudo manner. Figure 7
In, the λ / 4 resonance circuit 11 is composed of a center conductor L and a varicap capacitor C _B. The same functional parts as those in FIG. 6 are denoted by the same symbols.

Here, assuming that the capacitance surrounded by the dotted line is C ₀ , the resonance frequency of the circuit of FIG. 7 is 1 / (ω × (C _B + C ₀ )) = Z ₀ × tan according to a well-known formula. (2.times..pi..times.l / .lamda.) ... expressed by equation (1).

Here, ω: angular frequency (ω = 2 × π × f, f: resonance frequency) C (= C _B + C ₀ ): resonant capacitance Z ₀ : characteristic impedance l: length of center conductor λ: wavelength Is.

The formula (1) is cited from page 224 of the document "Transistor Circuit Design Manual" by Gentaro Miyazaki, Haruo Kusaka, Ohmsha.

Therefore, it is understood that the resonance frequency can be changed by changing the resonance capacitance C, for example.

In FIG. 7, the oscillation frequency can be changed by using a varicap diode whose capacitance value changes with the reverse bias voltage as C _B.
However, C- of this varicap diode C _B
The V characteristic shows a characteristic that the capacitance change is small in a region where the reverse bias voltage is large, and therefore the oscillation frequency hardly changes. Therefore, in order to expand the bandwidth of the oscillation frequency, a varicap diode C _B having a large capacitance change ratio may be used. Generally, a varicap diode having a large capacitance change ratio is rs (series equivalent resistance). )
Is large and oscillation stop easily occurs.

There is also a method of using a transistor having a high f _T (transition frequency), but the cost is high and the cost of the product is increased.

Therefore, an object of the present invention is to provide a local oscillation circuit capable of supporting a wide range of oscillation frequency bands without using a varicap diode having a large capacitance change ratio or a transistor having a high f _T as described above. It is in.

[0013]

In order to achieve the above object, the first aspect of the present invention is to change the oscillation frequency band in a local oscillation circuit having a center conductor formed of a microstrip line on a printed circuit board. Further, it is characterized in that solder is applied on the microstrip line serving as the central conductor.

A local oscillator circuit according to a second aspect is a local oscillator circuit in a DBS tuner of a satellite broadcast receiver.

According to a third aspect of the present invention, in a method of manufacturing a local oscillation circuit having a chip mount component and a central conductor formed of a microstrip line on a printed circuit board, solder coating is applied to a pattern portion of a printed circuit board on which the chip mount component is mounted. At the same time, the solder is applied onto the microstrip line.

According to a fourth aspect of the present invention, in the method of manufacturing a local oscillator circuit according to the third aspect, a screen having a pattern portion of a printed board on which the chip mount component is mounted and an opening portion provided corresponding to the microstrip line. A mask is provided, and solder is applied to the pattern portion and the microstrip line through the screen mask.

According to a fifth aspect of the present invention, in the method of manufacturing a local oscillator circuit according to the fourth aspect, the solder coating amount is adjusted by changing the size of the opening of the screen mask corresponding to the microstrip line. It is characterized by doing.

The operation of each claim will be described below.

According to the first aspect, since the solder is applied to the microstrip line serving as the central conductor, the copper foil thickness of the microstrip line can be increased.

As described above, increasing the copper foil thickness reduces the characteristic impedance of the microstrip line. Then, as the characteristic impedance decreases, the resonance frequency bandwidth increases. That is, the resonance frequency bandwidth can be increased by increasing the thickness of the copper foil.

With this, it is possible to easily and inexpensively provide a local oscillation circuit capable of supporting a wide range of oscillation frequency bands without using a varicap diode having a large capacitance change ratio or a transistor having a high f _T. Also,
Since the thickness of the microstrip line can be freely changed by changing the application amount of solder, the frequency band can be easily adjusted.

The ability to expand the frequency bandwidth in this way is particularly useful for a DBS tuner in which the number of channels has been increased in recent years and the input frequency band has been expanded, as shown in claim 2. For example, in the conventional case, the frequency bandwidth is about 1100 MHz (1429.5 MHz to 2
However, since the input frequency band of the DBS tuner has been expanded with the recent increase in the number of channels, the oscillation frequency bandwidth of the local oscillator circuit has been increased to 1250 MHz.
MHz (1379.5 MHz to 2629.5 MHz) is required. On the other hand, it is difficult to oscillate the upper limit of 2629.5 MHz in the local oscillation circuit having the conventional structure, but according to the present invention, this oscillation can be easily achieved with a simple structure.

According to the third aspect, the solder is applied to the microstrip line serving as the central conductor portion at the same time as the solder is applied to the pattern portion of the other chip mount component.
It can be easily realized without significant changes compared to conventional processes.

Specifically, as described in claim 4, an opening corresponding to a microstrip line is formed in the screen mask similarly to the opening to the pattern portion of another chip mounting component, and the opening is formed from above. This can be achieved by simply changing the solder coating.

According to the fifth aspect, the thickness of the solder can be freely changed only by changing the area of the opening corresponding to the microstrip line. That is, the frequency bandwidth can be easily adjusted.

Even when the opening has an area smaller than that of the microstrip line, the solder is promptly placed on the microstrip line in the substrate heating step when the chip mount component is mounted on the substrate and the reflow heating is performed. Spreads and becomes a uniform solder layer.

On the contrary, even if the area of the opening is slightly larger than that of the microstrip line, the solder around the microstrip line is absorbed on the microstrip line during reflow heating, and the layer thickness can be further increased. .

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The feature of the present invention is that the oscillation frequency bandwidth of a local oscillator circuit is used in a circuit configuration in which a microstrip line is used as a central conductor in a local oscillator circuit used in a DBS tuner for satellite broadcast reception. In order to widen the impedance, the impedance of the microstrip line is lowered. Specifically, solder is applied on the microstrip line.

A detailed description will be given below.

The oscillation frequency of the local oscillator circuit is also changed by changing the characteristic impedance Z ₀ as shown in the equation (1). The inventor paid attention to this point.

First, the structure of the microstrip line portion related to the characteristic impedance is as shown in FIG. FIG.
Is the final structure of the present embodiment in which solder is applied on the microstrip line L. First, let us consider the state without this solder application.

As shown in FIG. 1, conductors 3 are formed on the front and back of a base material 2 (dielectric: relative permittivity ε) of a printed circuit board 1. Here, the base material 2 of the printed circuit board 1 serving as a dielectric
Is h, the copper foil thickness of the microstrip line L is t, and the width is w.

In such a structure, the printed circuit board 1
The characteristic impedance Z ₀ of the upper microstrip line L is Z ₀ = 42.4 / (ε + 1) ^1/2 × ln (1+ (4h / W ′) × (b + (b ² + a × π ² ) according to a well-known formula. ) ^1/2 )) ... Represented by formula (2).

Here, W ′ = W + a × ΔW ΔW = t / π (1 + ln (4 / (t / h) ² + 1 / (π
(W / t + 1.1)) ² ) ^1/2 )) a = (1 + 1 / ε) / 2 b = (14 + 8 / ε) / 11 × 4 × h / W ′ ε: relative permittivity of the substrate.

This equation (2) is given on page 26 of the document “Design and Implementation of High-Frequency Circuits” written by Yukihiko Miyamoto, Japan Broadcasting Corporation.
More quoted.

As can be seen from the equation (2), the characteristic impedance Z ₀ also changes depending on the thickness t of the copper foil of the microstrip line L. FIG. 2 is a characteristic diagram showing the relationship between the copper foil thickness t and the characteristic impedance Z ₀ based on the equation (2). As is clear from FIG. 2, the copper foil thickness t
It can be seen that the characteristic impedance Z ₀ can be reduced by increasing the value.

On the other hand, the characteristic impedance Z ₀ and the resonance frequency bandwidth have the following relationship.

Here, description will be made with reference to FIG. FIG. 3 shows the relationship between the resonance frequency f and the resonance capacitance C (= C _B + C ₀ ) when the characteristic impedance Z ₀ of the equation (1) is used as a parameter. For example, the resonance capacitance C is C
If a (pF) changes to Cb (pF), the resonance frequency changes from f ₁ to f ₂ when Z ₀ = 100 (Ω),
When Z ₀ = 75 (Ω), it changes from f ₃ to f ₄ . here,
Each resonance frequency bandwidth is Δf ₂₁ = f ₂ −f ₁ = 11
50 MHz and Δf ₄₃ = f ₄ −f ₃ = 1300 MHz.

That is, as the characteristic impedance Z ₀ decreases, the resonance frequency bandwidth increases (150 in this example).
MHz expansion).

To summarize the above, it was found that the characteristic impedance Z ₀ can be reduced by increasing the copper foil thickness t of the microstrip line L serving as the central conductor as described above. Then, as described above, the resonance frequency bandwidth increases as the characteristic impedance Z ₀ decreases. That is, it can be seen that the resonance frequency bandwidth can be increased by increasing the copper foil thickness t of the microstrip line L.

In the present invention, as shown in FIG. 1, the thickening of the copper foil thickness t is realized by applying the solder 4 on the microstrip line L.

Although the oscillation frequency bandwidth can be expanded by simply making the microstrip line L thicker than before, the microstrip line L is usually used.
On the printed circuit board 1 on which are formed, chip mount parts and the like which form other local oscillation circuits are also mounted. Therefore, it is not desirable to increase the cost by increasing the film thickness of only the microstrip line L while leaving the pattern or the like for mounting these chip mount components as it is.

Further, if the thickness of the microstrip line L is determined at the stage of the printed circuit board, the design change cannot be made according to various local oscillation circuits, whereas according to the method of the present invention, each circuit can be changed. Accordingly, there is an advantage that the thickness of the microstrip line L can be freely adjusted.

FIG. 4 is a characteristic diagram showing the relationship between the tuning voltage and the oscillation frequency of the local oscillation circuit when the solder 4 is applied to the microstrip line L shown in FIG. 1 by about 500 μm. In the figure, a dotted line P indicates a conventional structure in which solder is not applied,
The solid line Q is the structure of the present invention in which solder is applied.

In FIG. 4, horizontal lines A and B respectively indicate
The upper and lower limits of the oscillation frequency required recently (26
29.5 MHz and 1379.5 MHz). As is clear from the drawing, with the conventional characteristic P in which solder is not applied, even if the tuning voltage is raised to about 30V, A
It can be seen that the oscillation frequency cannot be increased to the line. That is, the predetermined oscillation frequency cannot be generated. On the other hand, according to the characteristics of the present invention in which solder is applied, it can be seen that the line A is reached when the tuning voltage is set to about 23V. As described above, according to the present invention, it is possible to obtain an oscillation frequency which has not been achieved conventionally by a very simple change.

Further, the tuning voltage for obtaining the same oscillation frequency can be set lower than in the prior art, which can contribute to power saving. For example, the frequency of the line of C (oscillation frequency: 2.
The tuning voltage for obtaining (5 MHz) is about 21 V in the case of the conventional characteristic, whereas it is about 1 V in the case of the characteristic of the present invention.
8.5V may be sufficient.

Further, as is clear from FIG. 4, the slope of the characteristic of the present invention is larger than that of the conventional characteristic. That is, since the change in the oscillation frequency with respect to the tuning voltage in the same range (resonance capacitance in FIG. 3) is large, a wide oscillation frequency bandwidth can be covered with a small change in the tuning voltage.

By the way, in the above embodiment, about 500 μ of solder is used.
In the case of m coating, the characteristics naturally slightly change depending on the solder thickness. However, as can be seen from FIG. 2, the solder thickness is set to a certain thickness or more, for example, about 1000
Even if it is set to μm, the change (reduction) of the impedance Z ₀ hardly occurs. That is, a large increase in the oscillation frequency bandwidth cannot be expected.

The results of the experiment confirm that it is possible to reliably secure the oscillation frequency band between the lines A and B by applying solder of about 500 μm or more.

The above-mentioned solder application is performed as follows, for example.

First, other chip mount components constituting a local oscillation circuit are usually mounted and fixed on the same substrate as the printed circuit board 1 on which the microstrip line L is formed. In order to fix these chip mount parts, there is a step of applying cream solder to the board pattern for the chip mount parts as a pre-process of fixing the solder. Then, after the cream solder is applied, the entire substrate is heated by reflowing to complete the solder fixing. The solder application to the microstrip line L according to the present invention is performed at the same time as the cream solder application.

That is, an opening is provided at a portion corresponding to the microstrip line L of the screen solder for cream soldering with respect to other chip mounting parts, and at the same time when the cream soldering for chip mounting parts is applied, this microstrip line is also formed. Apply cream solder. here,
To adjust the magnitude of the characteristic impedance Z _0, the amount of solder applied may be controlled, but this can be done by changing the area of the opening of the screen mask.

That is, as shown in FIG. 5, the screen mask 5 is provided with an opening 6 smaller than the area of the microstrip line L, and solder application is performed in this state. The solder 4 is applied only to the inner side of the microstrip line L. However, in the reflow process performed after mounting the chip mount component on the substrate, the printed circuit board 1 is heated, so that the solder 4 is quickly applied to the microstrip line L. And spreads over the entire conductor surface to form a uniform solder layer.

Here, the microstrip line L shows the case of using a U-shape. In this structure, a bridge 7 is provided in the opening 6 so that the R portion is not peeled off in the state of the screen mask.

Contrary to the above, even if the area of the opening 6 is made slightly larger than the microstrip line L, the solder 4 around the microstrip line L is also absorbed on the microstrip line L during reflow heating. Further, the layer thickness can be increased.

According to the method described above, it is not necessary to provide a new process for applying solder to the microstrip line L, and the conventional manufacturing process can be used as it is, so that there is no significant increase in cost.

[0057]

As described above, according to the present invention, it is possible to realize a local oscillation circuit capable of generating a wide range of oscillation frequencies which cannot be dealt with by the conventional structure, by simply changing the structure. Further, the applied voltage for generating the oscillation frequency can be lowered for the same oscillation frequency bandwidth as the conventional one.

Moreover, since this structure hardly changes the conventional manufacturing process, it can be realized without a large increase in cost.

[Brief description of drawings]

FIG. 1 is a sectional view of a microstrip line portion of a local oscillator circuit according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the copper foil thickness of the microstrip line and the characteristic impedance of the local oscillation circuit.

FIG. 3 is a characteristic diagram showing a relationship between a resonance frequency and a resonance capacitance of a local oscillation circuit.

FIG. 4 is a characteristic diagram showing the relationship between the tuning voltage and the oscillation frequency of the local oscillation circuit for showing the effect of the structure of FIG.

FIG. 5 is a top view for explaining the method for manufacturing the local oscillator circuit according to the embodiment of the present invention.

FIG. 6 is a circuit diagram of a local oscillator circuit according to a conventional example.

FIG. 7 is a circuit diagram in which the circuit of FIG. 6 is simplified.

[Explanation of symbols]

 1 Printed Circuit Board 4 Solder 5 Screen Mask 6 Opening L Micro Strip Line

Claims (5)

[Claims] 1. A local oscillation circuit having a central conductor formed of a microstrip line on a printed circuit board, wherein solder is applied on the microstrip line serving as the central conductor in order to change the oscillation frequency band. Characteristic local oscillator circuit. 2. The local oscillator circuit according to claim 1, wherein the local oscillator circuit is a local oscillator circuit in a DBS tuner of a satellite broadcast receiver. 3. A method of manufacturing a local oscillation circuit having a chip mount component and a center conductor formed of a microstrip line on a printed circuit board, wherein the solder is applied to a pattern portion of a printed circuit board on which the chip mount component is mounted, and at the same time. A method for manufacturing a local oscillation circuit, comprising applying solder onto a microstrip line. 4. The method for manufacturing a local oscillator circuit according to claim 3, further comprising a screen mask having an opening provided corresponding to the pattern portion of the printed board on which the chip mount component is mounted and the microstrip line. A method for manufacturing a local oscillator circuit, characterized in that solder is applied to the pattern portion and the microstrip line through the screen mask. 5. The method of manufacturing a local oscillator circuit according to claim 4, wherein the solder coating amount is adjusted by changing the size of the opening corresponding to the microstrip line of the screen mask. A method of manufacturing a local oscillation circuit having a feature.