Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
1999-12-20
2001-08-21
Trost, William (Department: 2746)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S315000, C455S333000, C257S295000, C257S347000, C257S327000
Reexamination Certificate
active
06278871
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an integrated circuit comprising a series of layers formed by low-resistance materials called conducting layers, separated in pairs by layers of insulating material called insulating layers, which integrated circuit includes a first capacitive element offering between a first and a second terminal a capacitance of fixed value, said capacitive element being formed by a stack of conducting plates cut out of the conducting layers and electrically insulated from said layers.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,685,197 describes an integrated circuit that includes a capacitive element formed by two conducting layers separated by an insulating layer and mentions, without describing an embodiment thereof, the possibility of using more than two conducting layers to increase the value of the capacitance of such a capacitive element.
SUMMARY OF THE INVENTION
The present invention is linked with the following considerations: The realization of such a capacitive element in integrated form requires a series of manufacturing steps of which the number is a function of the number of conducting layers included in the capacitive element. Each manufacturing step introduces imperfections in the integrated circuit, which cause a difference of the real value of the capacitance of the capacitive element relative to its nominal value.
During mass production, it may happen that the same manufacturing step causes offsets to occur whose values are different from one integrated circuit to another. The extent of these differences is called dispersion. Such differences introduce an uncertainty in the real values of the capacitances of the capacitive elements included in the integrated circuits thus produced, which values may vary considerably from one integrated circuit to another. This uncertainty turns out to be very bad when these integrated circuits are intended for applications where the real value of the capacitance they contain is to be precisely known.
A systematic measurement of the real value of the capacitance included in each integrated circuit at the end of production is unrealistic, for it is difficult and expensive to achieve repetitively. Moreover, the detection of a too large offset relative to the nominal value will only lead to the rejection of the thus identified integrated circuit, which will lower the production efficiency. It is thus preferable to reduce the dispersion in a preventive manner by means of an appropriate design of the integrated circuit.
It is an object of the present invention to remedy these drawbacks described above by proposing an integrated circuit that includes a capacitive element whose real value can be predicted more easily and is less vulnerable to isolated influences of each of the manufacturing steps of the circuit.
Indeed, an integrated circuit in accordance with the opening paragraph is characterized according to the invention in that the first capacitive element comprises as many conducting plates as the integrated circuit comprises conducting layers, the first and the second terminal of the first capacitive element being connected to the conducting plates that form the ends of the stack.
The construction of the first capacitive element included in the integrated circuit according to the invention requires the largest possible number of manufacturing steps, since all the conducting layers are present therein. This implies that the relative influence of each of these manufacturing steps on the real value of the capacitance thus produced is reduced to the highest degree. Thus, the extent of the differences from one circuit to another between the offset of the real value of the capacitance and its nominal value, that is to say, the dispersion, is also reduced considerably. The real values of the capacitances of the capacitive elements included in a set of integrated circuits in conformity with the invention will thus be comprised in a shorter interval and may thus be more easily predicted.
In a particular embodiment of the invention, an integrated circuit as described above, comprising a substrate that is used as a support for an alternating series of N insulating layers and N conducting layers numbered in rising order from the substrate, is characterized in that the i
th
conducting plate of the first capacitive element (for i=3 to N) is connected to the (i−2)
th
conducting plate of said capacitive element, the first and the second terminal of the first capacitive element being connected to its first and its N
th
conducting plate, respectively.
The capacitive element thus obtained consequently includes N−1 capacitors arranged in a parallel combination, each formed by two conducting layers separated by an insulating layer that acts as a dielectric.
A particular embodiment of the invention is characterized in that a first bulk, which has a given type of conductivity, is installed inside the substrate, so that the stack that forms the first capacitive element is superposed on said bulk, which bulk is connected to the surface of the substrate covered by said stack via an area that has the same type of conductivity as the bulk.
In this embodiment, an additional capacitor appears between the first conducting layer and the area connecting the surface of the substrate to the first bulk, which thus forms an additional conducting layer and introduces another manufacturing step in the manufacturing process of the integrated circuit, which further reduces the influences relating to each of the manufacturing steps on the real value of the capacitance of the first capacitive element. The dispersion is thus further reduced.
In an advantageous embodiment of the invention, the first bulk is connected to a reference terminal forming the ground of the integrated circuit.
Such an embodiment enables to get the capacitance under control that exists between the first conducting layer and the substrate. The first capacitive element will thus present a better quality factor.
A variant of the invention offers an integrated circuit as described above, characterized in that it further includes a second capacitive element, intended to develop between a first and second terminal a capacitance whose value depends on a tuning voltage applied to the first terminal, the second terminal of the second capacitive element being connected to one of the terminals of the first capacitive element.
This variant enables to have a variable capacitor, while the number of manufacturing steps necessary for manufacturing the integrated circuit is further increased. Indeed, the second capacitive element will most often be an active element that calls for specific diffusions.
In a preferred embodiment of the invention, an integrated circuit as described above is characterized in that the second capacitive element is a varicap diode, built on top of a second bulk that has a given conductivity type installed inside the substrate, of which a cathode and an anode form the first and the second terminal, respectively.
In another variant of the invention, an integrated circuit as described above further includes an inductive element of which a first terminal is connected to a supply terminal and of which a second terminal is connected to the second terminal of the first capacitive element, thus forming an output terminal of an oscillator intended to deliver an output signal whose frequency depends on the value of the tuning voltage.
Such an integrated circuit forms a voltage-controlled oscillator of which the evolution of the oscillation frequency as a function of the value of the tuning voltage is easily predictable because of the reduction of the dispersion, made possible by the invention.
If the present invention can be used in all types of applications involving capacitive elements of which the value must precisely be known, its use is particularly advantageous in receiving loops for receiving radio signals. The invention thus likewise relates to a radio signal receiving device comprising:
an antenna and filter system enablin
Butaye Benoît
Jovenin Fabrice
Milord Marlean
Trost William
U.S. Philips Corporation
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