Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Passive components in ics
Reexamination Certificate
1998-12-16
2001-07-10
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Passive components in ics
C257S533000, C257S538000
Reexamination Certificate
active
06259150
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a voltage dividing resistor and a voltage dividing circuit. In particular, it relates to a voltage dividing resistor and a voltage dividing circuit which may be used in a reference voltage divider of an A/D converter.
2. Description of the Related Art
In an A/D converter, a voltage dividing circuit
30
as shown in the left side of
FIG. 8
has heretofore been used to generate a group of voltages as comparative references.
In the voltage dividing circuit
30
, a reference voltage
32
is divided by a voltage dividing resistor
33
provided with taps to generate comparative reference voltages at a group of necessary output terminals
37
. The generated comparative reference voltages are supplied to comparators
31
and compared with an input signal from a comparison input terminal
34
, and the input signal is converted into digital data.
Each of impedances of the output terminals
37
arranged as described above has a combined impedance of the resistance between the output terminal
37
and an input terminal
35
and the resistance between the output terminal
37
and an earth terminal
36
in parallel (It is noted that the voltage
32
in
FIG. 8
may be regarded as a short, because the discussion is given here on high frequencies.). Accordingly, the impedance at the output terminal
37
at the ½ position of the resistance element is highest as shown in FIG.
5
. When the A/D converter is in action, various noise currents flow into the output terminals
37
from the comparison input terminal
34
of the subsequent comparators
31
through a parasitic capacity of the comparators
31
or the like to cause fluctuations in voltage. Magnitude of the fluctuations is proportional to the impedance of the output terminal
37
and frequency of the signal. Accordingly, the fluctuation is largest at the output terminal
37
at the ½ position of the resistance element. Further, voltages per se, which are to serve as references in A/D conversion become more unstable as the frequency becomes higher. This creates a factor which adversely affects the effective dividing capacity of the A/D converter and creates distortion at a high frequency.
Japanese Unexamined Patent Publication No. 22137/1993 discloses an A/D converter which has wire connections improved in such a manner that a wiring for an input signal is led to a plurality of comparators so as to improve high frequency characteristics of the A/D converter. In contrast thereto, the present invention is directed to improvement of high frequency characteristics by stabilizing comparative reference voltages.
To solve the above problem, it has heretofore been practiced that a capacitive element
38
is connected to the output terminal
37
at the ½ position of the resistance element whose impedance is highest, thereby lowering the impedance in a high frequency range. In other words, the capacitive element
38
is connected to the output terminal
37
at the middle of the resistance element with a view to lowering the impedance in a high frequency range.
FIG. 9
is a sectional view showing one form of the structure of the voltage dividing resistor
33
used in the circuit in
FIG. 8. A
silicon oxide layer
41
as insulator is provided on resistor
42
prepared by doping a p-type silicon substrate with n-type impurities. The silicon oxide layer
41
is formed with holes, and aluminum electrodes
43
are disposed therein to provide output electrodes.
Since the influx of noise currents occurs mainly through the parasitic capacity, magnitude of the noise currents is large in a high frequency range, i.e., the noise expends to a high frequency range. Accordingly, the connection of the capacitive element is an effective means to suppress fluctuations of the voltage.
However, the above-described means has a problem, in that it is necessary to allocate a large space in a chip to the capacitive element for eliminating influence of the noises, thereby leading to an increased cost of a chip. Further, the capacitive element is connected to the resistance element in a localized manner, i.e., at the one point in the middle of the resistance element. Accordingly, as shown in
FIG. 6
, the impedances in a high frequency range show such undesirable undulatory characteristics that the impedance at the output terminal
37
at the ½ position of the resistance element is locally minimum and those at the output terminals
37
at the ¼ and ¾ positions of the resistance element are locally maximum.
SUMMARY OF THE INVENTION
It is an object of the present invention to lower impedances of output terminals in a high frequency range while avoiding an increase in a surface area of a chip and undulation of the impedances of the output terminals in a high frequency range.
To solve the above problems, the present invention provides a voltage dividing resistor comprising:
an input terminal,
a resistance element for dividing a voltage inputted from the input terminal, and
a plurality of output terminals for outputting the divided voltages;
the voltage dividing resistor being provided with at least one capacity electrode, the at least one capacity electrode substantially constituting at least one capacitive element together with said resistance element.
It is preferred that the resistance element have its surface partially coated with insulator, and the output terminals be connected to output electrodes disposed in holes formed in the insulator coating and connected to the resistance element, and the capacity electrodes being so disposed in holes formed in the insulator coating as to hold, together with the resistance element, dielectric therebetween.
The resistance element may be a doped portion in the semiconductor substrate and thus it can be prepared by a semiconductor manufacturing technique.
It is preferred that the resistance element be provided on a semiconductor substrate via dielectric interposed therebetween, and the resistance element be substantially coated with insulator, and the output terminals be connected to output electrodes disposed in holes formed in the insulator coating and to the resistance element, with the semiconductor under the resistance element serving as the capacity electrode.
The semiconductor substrate under the resistance element may be provided therein with a doped island, which serves as the capacity electrode, and thus it can be prepared utilizing semiconductor manufacturing technique.
It is preferred that the dielectric be provided in a thickness smaller than that of the insulator coating, thereby obtaining a large capacity of the capacitive element.
It is preferred that the dielectric have a specific inductive capacity higher than that of the insulator, thereby obtaining a further increased capacity of the capacitive element.
According to the present invention, there is also provided a voltage dividing circuit comprising the above-mentioned voltage dividing resistor, each of the at least one capacity electrode of the voltage dividing resistor being connected to earth voltage or a low impedance quasi-earth voltage.
By the use of the resistance element as described above, which is compositely provided with the at least one capacitive element in the reference voltage dividing circuit in view of high frequencies, an area overlapping the space in which the resistance element is located can be used as a space for providing, each capacitive element. Accordingly, it is not necessary to separately make a large space for disposing each capacitive element in a chip. Consequently, increase in a chip cost is suppressed as compared with conventional means. Further, the capacitive element extends, on the capacitive elements are distributed, through the resistance element. By virtue of this, as shown in
FIG. 7
, no substantial undulation of impedance in a high frequency range such as that found in conventional means occurs thus, and a flat-top characteristic of impedance is attained.
In a doped resistor, resistance of the res
Crane Sara
Sharp Kabushiki Kaisha
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