JPH0955625A - Oscillator - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] In a Colpitts oscillator in which a load capacitance is connected in series to an oscillator and the oscillation frequency is determined by the load capacitance characteristic of the oscillator, part of the load capacitance is at the bottom layer of the laminated ceramic plate. It is characterized in that it is formed, and the frequency is finely adjusted by adjusting the variable capacitance section while the metal case is fixed to the oscillator. Means for Solving the Problems In the lowermost layer portion of a laminated substrate, upper and lower electrodes are formed by using the substrate as a dielectric, the upper electrode is a flat surface, and the rear electrode pattern is a plurality of small electrodes connected in series. An oscillator having a variable capacitance having a structure in which a plurality of the connecting electrodes are connected in parallel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillator requiring fine frequency adjustment means, and more particularly to a frequency adjustment means in a small oscillator used as a reference frequency source of a synthesizer in a mobile radio telephone or the like.

[0002]

2. Description of the Related Art Generally, a reference oscillator used in a mobile radio is required to have high frequency stability, high accuracy and miniaturization. As conventional oscillators, there are a pierce type, a Colpitts type, a Clapp type, and the like, among which the Colpitts type is often used. In this oscillator, a load capacitance is connected in series to an oscillator (for example, a crystal oscillator), and the frequency of the oscillation circuit is determined by the load capacitance characteristic of the oscillator. In manufacturing a small oscillator, various chip electronic components are mounted on the substrate.
It is fixed by using a method such as R reflow and at the same time electrically connected, a terminal and a case are attached to the substrate, the frequency is adjusted by a trimmer capacitor, and then various electrical and mechanical tests are performed to complete the process. For downsizing and automation,
A method in which the conventional trimmer capacitor is replaced with another capacitance varying means is disclosed in Japanese Utility Model Laid-Open No. 60-79727 and Japanese Patent Laid-Open No. 2062-2.
03 and JP-A-6-204081.

The configuration and adjusting method of the electrostatic capacitance, which is an important element for frequency adjustment, is summarized from the above publication,
A brief description will be given with reference to FIGS. 7 (a), (b), and (c).
In FIG. 7A, comb-shaped electrodes are combined and formed on a silicon plate so as to face each other, and Al and N are used as electrode materials.
iCr-Ar or the like is used, and the teeth of the comb-teeth-shaped electrode each have a plurality of elongated electrode fingers, and a capacitance is formed between adjacent electrode fingers. FIG. 7B shows a laminated component in which a spiral or U-shaped trimming electrode having an open end is provided to face the internal electrode to form a capacitor. In addition, FIG. 7C is composed of a surface electrode having electrode portions having different areas on the surface of the dielectric and an internal electrode facing the surface electrode, and each surface electrode has an area of 2n (n) with respect to the minimum electrode area. = 1, 2, 3, ...) times the electrode structure is formed, and these capacitors are connected in parallel. Figure 7
In each of (a), (b) and (c), the formed variable capacitance electrode is cut by a means such as a laser to remove the capacitance and adjust the frequency of the circuit.

In the conventional trimming method, the variable capacitance on the substrate is adjusted by using a laser or sandblast to adjust the frequency, and then a metal case is attached to the oscillator and mounted on a printed board or the like. At this time, it is general to shield with a metal case in order to avoid electromagnetic and electrostatic influences from electric parts in the peripheral portion. However,
In such a conventional method, by sealing the metal case,
The stray capacitance between each component, wiring, and ground changed slightly, and as a result, a trimmer capacitor was necessary to adjust the oscillation frequency to a specified value after the case was sealed. Further, it is possible to devise a method such as shifting the frequency in anticipation of the frequency shift due to the case sealing, but it is difficult to adjust it to a desired frequency due to variations in the oscillator and electric parts. Also, in the method of trimming the variable capacitance using a laser, the intense heat generated by the laser diffuses to the peripheral portion through the ceramic substrate with good thermal conductivity, and affects the electrical components in the peripheral portion thermally. It has been a factor to shift the oscillation frequency. In addition, after the case is sealed, the method of adjusting the variable capacity using sandblasting makes it difficult to remove sand, grinding dust, etc., inside.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in a Colpitts type oscillator in which the frequency of a circuit is determined by the load capacitance characteristic of an oscillator, it is compact and mechanical without using a trimmer capacitor as in the conventional case. It is an object of the present invention to provide a high-precision oscillator that is resistant to vibration and is inexpensive.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is a Colpitts oscillator in which a circuit frequency is determined depending on a load capacitance value. At least a part of the load capacitance is formed by laminating a plurality of substrates. The structure is such that a part of the load capacitance is formed on the lowermost substrate of the laminated substrate, electrodes are formed on the upper and lower surfaces of the substrates, and an electrode pattern on the rear surface of the electrodes is formed by connecting a plurality of small electrodes in series with lead electrodes. Finely adjust the oscillation frequency of the circuit by cutting the lead electrode of the small electrode on the bottom surface of the bottom layer in an assembled oscillator with a structure in which connecting electrodes are connected in parallel and terminals and a case are attached. Is characterized by.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the embodiments shown in the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a metal case, which covers an upper portion of a ceramic substrate 2 on which required components are mounted, and a dielectric substrate 3 is arranged on the bottom surface. The ceramic substrate 2 has a crystal unit 4 and a resistor 5 (R ₁ ~
R ₄ ), chip capacitor 6 (C ₃ ), mini-mold transistor 7, chip capacitors 8 and 9 (C ₁ , C ₂ ) are mounted, and a circuit is formed on the back surface of the substrate by a wiring pattern. The symbols in parentheses () following each symbol indicate the circuit diagram symbols of FIG. 4 described later. The dielectric plate 3 is, for example, a ceramic substrate, the planar electrode 10 is formed on the upper surface of the substrate by silver palladium (Ag-Pd), and the lower surface thereof is shown in FIG.
As shown in (1), a plurality of small area electrodes 11 and 12 are connected in series, and the connected small electrodes are connected in parallel.
According to this configuration, the whole surface electrode is connected to one surface across the dielectric 3 and a large number of small area electrodes as shown in FIG. Function. Therefore, the lead electrodes 13 are provided as shown in FIG.
The capacitance value can be changed by cutting and 16. If this variable capacitance is used as C4 of the Colpitts oscillator of FIG. 4, the frequency can be adjusted without using a trimmer capacitor. When selecting the ceramic dielectric, it is necessary to consider the temperature characteristic as the capacitance.

In this example, the small electrodes 12 all have the same area, and the capacitance is designed to be 1 pF based on the thickness and the area of the dielectric to facilitate the selection of the capacitance when adjusting the frequency. By making the area half, it is set to 0.5 pF, which is convenient for fine adjustment. As is well known, the capacitance when parallel electrodes are provided above and below a dielectric material is expressed by the following equation. C = ε ₀ εS / d (1) where ε ₀ and ε are the vacuum and the dielectric constant of the dielectric, respectively, and S
Is the area of the electrode, and d is the thickness of the dielectric plate. When the dielectric material is selected, ε becomes a constant, and the electrostatic capacitance is inversely proportional to the thickness d of the dielectric flat plate and proportional to the electrode area S.

In the present embodiment, in order to make the explanation easy to understand, the ceramic substrate 2 on which the circuit components are mounted and the dielectric plate 3 forming the capacitor are separately fired, and the electronic components are mounted on each of them. Alternatively, the case of forming variable capacitors and stacking them has been illustrated, but in practice, in a laminated substrate, each substrate layer is formed to be extremely thin, and a printed wiring board and a variable capacitor substrate are sandwiched between reinforcing substrates. A substrate obtained by firing and stacking a large number of layers is used. Electronic components are mounted on the laminated substrate as shown in FIG. 1, and the components are fixed and electrically connected by IR reflow or the like. As a matter of course, the electrical connection between the layers is conducted by a method such as a through hole. Measure IR
After the reflow, the metal case is fixed and the assembly of the oscillator is completed, and the frequency adjustment process is started. Since it is fixed by the metal case, it is not affected by external electromagnetic and electrostatic effects, and the stray capacitance that affects the oscillation frequency is kept at a constant value, so that the frequency is sufficiently stabilized.

Before explaining the frequency adjusting method for the oscillator of the present invention, the relationship between the load capacitance and the oscillation frequency of the oscillator will be briefly described in order to facilitate understanding of the present invention. The resonance frequency of the oscillator is f _S , the electrostatic capacitance is C _0, and the motional capacitance is C _m . When the resonance frequency when the load capacitance C _L is connected in series to the oscillator is f, f is expressed by the following equation. (F-fs) / fs = Cm / {2 (C 0 + C L)} (2) the load capacity of the oscillator becomes the volume in the oscillation loop when viewed from the oscillator in the circuit diagram shown in FIG. 4, C _{1 to} C ₄ , more accurately, includes the capacitance of the transistor circuit during operation. This total capacity is represented by C _{L0 to} C _L2 , and the change in frequency due to the load capacity is shown in FIG. 6 when the vertical axis represents frequency and the horizontal axis represents total load capacity. Infinite load capacity,
That is, when the load capacitance is short-circuited, the resonance frequency of the oscillator itself becomes f _S , and the frequency rises away from f _S as the load capacitance becomes smaller.

The parameters of the oscillator and the constants of the oscillation circuit can be calculated at the design stage based on the load capacitance characteristic curve of FIG. 6, and the difference df between the desired frequency f ₀ and the oscillation frequency f is determined based on this figure. Then, the load capacity value can be obtained. That is, a df vs. standard load capacity matrix table can be created. However, this is not enough to exactly match the oscillation frequency with the desired value, and in an actual product, variations in each component must also be taken into consideration. It is assumed that when the desired frequency is f ₀ , the load capacitance at that frequency is C _L0 . Now, when the frequency of the oscillator at the time of completion of assembly is f ₁ , the load capacitance is C _L1 , and the default capacitance value is deleted and the load capacitance is C _L2 , the frequency is f 1.
_Suppose it becomes ₂ . The difference d C _L12 between C _L2 and C _L1 is known as described above, and from this and the measured frequency, the variation from the design value of the motional capacitance C _m is predicted, and df vs. the standard load capacitance matrix table Can be corrected.

The frequency adjustment in the oscillator according to the present invention is based on the above-mentioned df vs. standard load capacitance matrix table obtained by cutting the lead electrodes connected to the small electrodes 11, 12 shown in FIG. It may be adjusted to a desired value so that the obtained load capacity is obtained. In the example of the pattern of FIG. 2, the capacitance is designed to be 1 pF except the electrode 11, and the electrode 11 is designed to be 0.5 pF, so that the work is easy. The frequency adjustment of the oscillator is performed by, for example, the device shown in the block diagram of FIG. That is, the frequency of the output of the oscillator is measured by the frequency counter, and at the same time, the output is mixed with the reference oscillator of the desired frequency, and the difference df from the reference frequency is detected. The difference df is d prepared for the computer.
The load capacitance value is converted from the f vs. standard load capacitance matrix table or calculation, the deleted capacitance for matching the oscillation frequency with the desired frequency is calculated, and the number of small electrodes to be cut is obtained. The lead electrode cutting position of the variable capacitance is determined from this, and the load capacitance value is adjusted to a desired value by irradiating the corresponding lead electrode with a laser to cut the lead. As a result, the load capacitance of the oscillator changes, and the frequency of the oscillator can be adjusted to the desired frequency.

In order to further improve the frequency adjustment accuracy, it is possible to carry out the adjustment in consideration of the variation of the oscillator and the circuit including the transistor, the resistor and the capacitor as described above. That is, the frequency change amount df when a plurality of small electrodes having a capacitance value of 1 pF are cut off and the deleted capacitance is expressed as d above.
The frequency adjustment accuracy can be improved by a method in which the deviation from the standard is used as a correction value specific to the oscillator in comparison with the f vs. standard load capacitance matrix table. When the capacitance to be deleted is small, the 0.5 pF electrode 11 is cut off. If you need to adjust a smaller volume,
Fine tune the 0.5 pF or 1 pF electrode with a laser,
The frequency is adjusted to the desired value by adjusting the capacitance of 0.5 pF or less.

FIG. 4 is a structural view showing another embodiment of the present invention, which is an example in which a variable capacitor is constituted by a laminated portion in which a plurality of dielectrics 30 are laminated. Reference numerals 17 to 19 in FIG.
Reference numeral 20 represents a lead electrode, and an electrode facing the capacitance forming electrodes 17 to 19 is also formed on the back surface of the dielectric plate. There is also a method of cutting the lead connected to the planar electrode for adjusting the variable capacitance portion of the laminated body, but by cutting the lead electrode led to the side surface portion of the laminated plate, for example, the required portion of 21, 22, 23 in FIG. There is also a way to adjust. The variable capacitance by such a laminated substrate is effective when a large capacitance is required.

In the example shown in FIG. 2, the capacitance value of the small electrode is set to 1 pF or 0.5 pF, but it does not necessarily have to be this value and it is not necessary to arrange the electrodes regularly in a grid pattern. . In short, the purpose can be achieved if the capacitance value is regular and a large number of small electrodes are connected in series. Further, if such connected electrodes are connected in parallel, the capacitance can be easily selected, the adjustment accuracy can be improved, and the time required for the adjustment can be shortened.

[0016]

As described above, according to the present invention, the frequency can be adjusted by laser trimming after sealing with the metal case, so that the frequency can be finely adjusted without being affected by the stray capacitance. be able to. In addition, since the adjusting variable capacitance section and the oscillation circuit can be spatially and physically separated by the laminated plate, the influence of heat during laser trimming on the frequency can be significantly suppressed. Further, since a plurality of small electrode patterns are further arranged in series and in parallel, when the shift amount df from the standard frequency is measured, the capacitance value to be deleted is immediately obtained from the df vs. standard load capacitance matrix table and deleted. The electrode pattern to be determined is determined in a short time, and moreover, it can be adjusted accurately and is suitable for automation.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a pattern on a dielectric plate for forming a capacitor used in the present invention.

FIG. 3 is a frequency adjustment block diagram of an oscillator.

FIG. 4 is a view showing another embodiment of the present invention and is a perspective view in which only the laminated variable capacitance substrate portions are enlarged and displayed.

FIG. 5 is a diagram showing an example of a Colpitts oscillator circuit to which the present invention is applied.

FIG. 6 is a load capacitance characteristic diagram of the oscillator.

FIG. 7 is a diagram showing an example of a conventional variable capacitance section, in which (a) is a plan view of a comb-shaped electrode structure. (B) is a plan view of the spiral electrode. FIG. 7C is a plan view of a structure in which the size of the capacitance electrode is doubled.

[Explanation of symbols]

 1 Metal Case 2 Substrate 3 Dielectric Substrate 4 Oscillator 5 Chip Resistor 6, 8, 9, Chip Capacitor 7 Transistor 10, 11, 12, 17, 18, 19 Capacitance Electrode 13, 20 Lead Electrode 14, 15, 16, 21 , 22, 23 Cut location 30 Dielectric substrate 1

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H03B 1/00 7922-5E H01G 4/34

Claims (1)

[Claims] 1. In a Colpitts type circuit in which a load capacitance is connected in series to an oscillator and the oscillation frequency depends on the load capacitance value, at least a part of the load capacitance is formed of a laminated substrate in which substrates are laminated, and The variable capacitance substrate is the lowermost layer, and a part of the load capacitance is formed on the substrate by forming electrodes on the upper and lower surfaces, and the electrode pattern on the back surface of the electrode is formed by connecting a plurality of small electrodes in series with lead electrodes. An oscillator having a structure in which a plurality of connecting electrodes are connected in parallel, and the oscillation frequency can be adjusted by cutting the lead electrode portion of the small electrode in the lowermost layer with an oscillator having a terminal and a case attached.