JPS6278868A - Semiconductor condenser - Google Patents

Abstract

PURPOSE:To reduce the variation of capacitance due to direct current voltage impressed to a capacitor, by connecting two junction capacitor elements in series for impressing DC bias voltage and in parallel with regard to AC. CONSTITUTION:The P-electrode of the first capacitor element 4 and the N- electrode of the second capacitor elements 5 are connected to make the first terminal 6. A DC bias voltage is impressed between the N-electrode of the element 4 and the P-electrode of the element 5, and these two electrodes are short-circuited with regard to AC to form the second terminal 8. Then the capacitance for the terminal 8 becomes a resultant capacitance C1+C2. The capacitance change of C1 and C2 are inverse relation with each other in respect to the ground potential of the terminal 8, so that the change of the resultant capacitance C1+C2 is offset. Thus, the change of capacitance due to the fluctuation of DC voltage impressed to the terminal 6 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor capacitor incorporated into a semiconductor integrated circuit (hereinafter referred to as an IC) or the like.

[Prior Art] When forming a CR type filter in an IC chip, a junction type capacitor having a relatively large capacitance value formed by a PN junction to which a bias voltage is applied is often used as the capacitor. Figure 3 is a diagram showing the connections and characteristics of this conventional semiconductor junction capacitor, where (1) is the junction capacitor, (2) and (3) are its terminals, and the horizontal axis is the terminal (2).
(3) The bias voltage applied between the two, and the vertical axis is the capacitance value of the capacitor (1).

As is clear from the figure, the capacitance value of the junction capacitor (1) has a characteristic that it decreases as the bias voltage value increases.

[Problems to be solved by the invention] Conventional semiconductor capacitors are constructed as described above, and the capacitance value changes depending on the voltage applied to both ends of the capacitor, so when using it for a filter etc., the cut frequency changes depending on the voltage. The problem was that it changed.

The present invention was made to solve this problem, and an object of the present invention is to obtain a semiconductor capacitor whose capacitance value changes little with respect to changes in the DC voltage applied between the terminals.

[Means for Solving the Problems] A semiconductor capacitor according to the present invention includes a first capacitor element and a second capacitor element formed by a PN junction, and a P electrode of the first capacitor element and a second capacitor element are connected to each other. The N electrode of the second capacitor element is connected as the first terminal, and a DC bias voltage is applied between the N electrode of the first capacitor element and the P electrode of the second capacitor element, and these electrodes are connected in an alternating current. It is short-circuited and used as a second terminal.

[Function] In this invention, the DC bias voltage is applied in series to the first capacitor element and the second capacitor element, and the input/output voltage between both terminals is applied in parallel. Therefore, when one of the changes in the DC voltage between the terminals increases, the other decreases, and the resulting change in the parallel capacitance value is canceled out and becomes smaller.

[Example code] An embodiment of the present invention will be described below with reference to the drawings.

Figure 1 is a connection diagram showing an embodiment of the present invention, and Figure 2 is its characteristic diagram. In Figure 0, (4) is the first junction capacitor element, and (5) is the second junction capacitor element. element,
(6) is the P electrode of the first capacitor element (4) and the second
The first terminal is connected to the N electrode of the capacitor element (5), (7) is the DC bias power supply positive terminal, and (8) is the ground terminal. Although the bias power supply is not shown, it is a so-called Vcc power supply used in general IC circuits, has a large capacitance value, and is short-circuited between the positive terminal (7) and the ground terminal (8). This ground terminal (8) is used as the second terminal of the capacitor. Changes in the capacitance values C8 and C2 of the first and second capacitor elements (4) and (5) with respect to the ground potential of the first terminal (6) are as shown in FIG. Now, the terminal (
7) Since (8) is AC grounded, the capacitance of the first terminal (6) to the ground, that is, to the second terminal (8) is C
,,+C,. Since CI and C2 exhibit capacitance changes in opposite directions with respect to the ground potential of the first terminal (8), the changes in the combined capacitance values c and +C are canceled, and the
Changes in capacitance due to fluctuations in DC voltage are reduced.

In one or more embodiments, the DC power supply positive terminal (7) is connected to the N electrode of the first capacitor element (4), and the P electrode of the second capacitor element (5) is connected to the ground terminal (8). However, it is clear that the same effect can be achieved even if the N electrode of the first capacitor element (4) is grounded and the P electrode of the second capacitor element (5) is connected to the negative terminal of the DC power supply.

[Effects of the Invention] As described above, the present invention connects two junction capacitor elements in series and applies a DC bias voltage.

Since the capacitors are connected in parallel in terms of alternating current, it is possible to reduce changes in capacitance value due to direct current voltage applied to the capacitor.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram thereof, and FIG. 3 is a diagram showing connections and characteristics of a conventional semiconductor junction capacitor. In the figure, (4) is the first capacitor element, (5) is the second capacitor element, (6) is the first terminal, (7) is the DC bias power supply terminal, and (8) is the second terminal. .

Claims (1)

[Claims] It consists of a first capacitor element and a second capacitor element formed by a PN junction, and the P electrode of the first capacitor element and the N electrode of the second capacitor element are connected to form the first capacitor element.
and the N electrode of the first capacitor element and the second
A semiconductor capacitor characterized in that a DC bias voltage is applied between the P electrode of the capacitor element and the two electrodes are short-circuited in an AC manner to form a second terminal.