Oscillators – Frequency stabilization – Temperature or current responsive means in circuit
Reexamination Certificate
2002-02-27
2004-01-13
Nuton, My-Trang (Department: 2816)
Oscillators
Frequency stabilization
Temperature or current responsive means in circuit
Reexamination Certificate
active
06677827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to temperature compensated crystal oscillators for easily adjusting output frequencies, and more particularly to a temperature compensated crystal oscillator and method for adjusting an output frequency thereof, which can adjust the output frequency of the crystal oscillator by inserting a thin film resistor between layers comprising a layered structure and trimming the thin film resistor through a bottom layer a laser beam.
2. Description of the Prior Art
Crystal oscillators using crystal vibrating chip are essential parts to generate oscillation frequencies for controlling transmission and reception of signals between mobile communication terminals. The crystal oscillators have excellent frequency stability compared with other oscillators. A generally used crystal oscillator is a temperature compensated crystal oscillator (TCXO) for solving the problem of the variation of an oscillation frequency due to ambient temperature,
FIG. 1
is an equivalent circuit diagram of a conventional temperature compensated crystal oscillator. As shown in
FIG. 1
, the temperature compensated crystal oscillator comprises a frequency adjusting circuit
10
, a temperature compensation circuit
20
, a crystal oscillator
30
and an oscillation circuit
40
realized as an IC chip. The temperature compensation circuit
20
controls the crystal oscillator
30
to resonate at a predetermined frequency to correspond to capacitance and inductance varied according to ambient temperature using a thermistor. Then, the crystal oscillator
30
oscillates at the compensated resonance frequency through the oscillation circuit
40
.
The temperature compensation crystal oscillator additionally has the frequency adjusting circuit
10
so as to provide a correct output frequency at room temperature. In the temperature compensated crystal oscillator, it is impossible to adjust inductance as in a voltage controlled oscillator (VCO). Therefore, the temperature compensated crystal oscillator generally uses a method for adjusting a trimmer capacitor or a trimmable chip resistor. Especially, the trimmable chip resistor
9
, which is favorable in terms of an arrangement area and easiness of trimming operation, is generally used as shown in FIG.
1
.
FIGS. 2
a
and
2
b
are respectively a side sectional view and a schematic perspective view of a conventional temperature compensated crystal oscillator
50
. The temperature compensated crystal oscillator
50
is an embodiment of the temperature compensated crystal oscillator of
FIG. 1
, and shows the structure for adjusting a frequency using a trimmable chip resistor. As show in
FIG. 2
a,
the temperature compensated crystal oscillator
50
has a structure in which a crystal oscillating unit
53
, parts
55
for temperature compensation and oscillation circuits, and a trimmable chip resistor
59
are mounted on the top layer
51
of layered structure comprised of two layers. Further, a metal case
57
is covered on the upper surface of top layer
51
, such that a mounting area on the upper surface of top layer
51
is shielded from external electrical and mechanical influences. Because the case
57
is made of a metal, a hole
57
a
is formed at the metal case
57
so as to trim the chip resistor
59
with a laser beam, as shown in
FIG. 2
b,
and then the chip resistor
59
is trimmed through the hole
57
a.
However, the trimmable chip resistor employed in the conventional temperature crystal oscillator of
FIG. 2
has a size of several mm
2
. As a result, it requires a considerable mounting area compared with the crystal oscillator having a size of only approximately 5.0×3.2 mm
2
or 4.7×2.9 mm
2
. Consequently, the size of trimmable chip resistor increases the size of a final product, and makes the miniaturization suitable for mobile communication terminals difficult.
Accordingly, in this technical field, it is strongly required to develop a temperature compensated crystal oscillator having a new structure and a method of adjusting the output frequency using the new structure, wherein a trimmable chip resistor can be mounted without greatly increasing the product size and can be trimmed in the state of final product, that is, at the last step of the process.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a temperature compensated crystal oscillator, in which a planar thin film resistor is formed on the upper surface of a bottom layer of a layered structure, thus minimizing an installation area occupied by the thin film resistor for adjusting an output frequency.
Another object of the present invention is to provide an output frequency adjusting method, by which an output frequency can be adjusted in the state of a final product by trimming a planar thin film resistor with a laser beam through the lower surface of a bottom layer having an upper surface on which the planar thin film resistor is arranged.
In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a temperature compensated crystal oscillator including a crystal oscillating unit and at least one part for temperature compensation and oscillation circuits, comprising a plurality of layers having an upper layer on which the crystal oscillating unit and the part are mounted, and at least one layer on which conduction patterns are formed; and a planar thin film resistor arranged on an upper surface of a bottom layer of the layered structure for adjusting an output frequency of the temperature compensated crystal oscillator.
The present invention can be provided in two types, according to a mounting structure formed on the upper layer.
In a preferred embodiment of this invention, a layered structure is comprised of a first layer on which conduction patterns for mounting the crystal oscillator and the part are formed, a second layer arranged under the first layer and provided with an upper surface on which other conduction patterns connected to the conduction patterns of the first layer are formed, and a third layer arranged under the second layer, wherein the first layer is the upper layer on which the crystal oscillating unit and the part are mounted, and the third layer is the bottom layer on which the planar thin film resistor is formed.
Further, in another embodiment of this invention, a layered structure is comprised of a first layer having an upper surface on which the crystal oscillating unit is arranged and having a cavity formed therein, a second layer on which conduction patterns for mounting the part for temperature compensation and oscillation circuits are formed at a region exposed to the cavity of the first layer, and a third layer arranged under the second layer, wherein the first and second layers compose an upper layer on which the crystal oscillating unit and the part are respectively formed on upper surfaces of the first and second layers, and the third layer is the bottom layer on which the planar thin film resistor is formed on its upper surface.
Moreover, in the preferred embodiment of this invention, at least one fourth layer is additionally arranged between the second and third layers so as to sufficiently realize signal lines of the temperature compensated crystal oscillator, wherein other conduction patterns connected to conduction patterns of other layers can be formed on the upper surface of the fourth layer. In this case, the second to fourth layers can be preferably manufactured as a single printed circuit layer so as to form signal lines, such as the temperature compensation circuit, the oscillation circuit and the frequency adjusting circuit, in one process.
More preferably, the conduction patterns formed on the upper surface of the fourth layer are formed at a remaining region except a region vertically overlapped with a region, at which the planar thin film resistor i
Lowe Hauptman & Gilman & Berner LLP
Nuton My-Trang
Samsung Electro-Mechanice Co., Ltd.
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