JPS5826673B2 - variable capacity device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable capacitance device, and particularly to a variable capacitance device in which a plurality of variable capacitance diodes are formed within a single semiconductor substrate.

Variable capacitance elements are essential for the electronic tuner part of radios and televisions. For example, in the case of a superheterodyne radio, variable capacitance elements are required in three places: the antenna circuit, the high frequency amplification circuit, and the local oscillator circuit. It is.

From this point of view, a so-called integrated circuit in which three elements for each circuit are formed within a single semiconductor substrate has been developed.

FIG. 1 shows its sectional view, and FIG. 2 shows its equivalent circuit diagram.

1 is an N-type silicon substrate, 2, 2, 2 is a P-type head region, 3 is a surface protective film, 4, 4.4 is an anode electrode provided in each P-type head region 2, 2, 2, and 5 is an anode electrode provided in each P-type head region 2, 2, 2. A common cathode electrode 6 provided on the substrate 1 is a variable capacitance element.

A device having such a configuration has the great feature that it is possible to reduce the size of the device, and at the same time, it is possible to obtain devices with uniform characteristics because they are formed under the same conditions.

However, in such a configuration, since the cathode side of each diode 6 is common, it is not possible to apply a bias to the diode 6 unless the connection method shown in Fig. 3 is used to connect the tuning coil and form a tank circuit. do not have.

An equivalent circuit with the connection state shown in FIG. 3 is shown in FIG. 4, and as is clear from this figure, a bias resistor R is inserted in parallel with the tank circuit to reduce [Q].

In addition, in FIGS. 3 and 4, C is the capacitance value of the variable capacitance element 6, and C1 is a capacitor for DC blocking [・C>C1
).

Now, if we consider (Q), Q is Q=WC
/g=1/gWL g=1/R Note that W is the tuning frequency, and it is understood that in order to increase [Q], it is sufficient to increase [R], but the leakage of diode 6 Considering the current, the value of (R) cannot be increased arbitrarily, and in the usual case, a value of about 100Ω is used.

The present invention has been made to improve these problems, and proposes a variable capacitance device that can ignore the influence of the bias resistor [R] and also has a built-in capacitor for DC blocking.

FIG. 5 is a cross-sectional view showing the configuration of the device of the present invention, with 10
is an N-type silicon substrate, 11.11.11 is the substrate 10
P-shaped head area with a relatively large area formed within, 12, 12
, 12 are N-type regions provided within each P-type head region 11°11.11, and the area of each region 12, 12, 12 is much larger than that of the P-type head region 11.11.11. are selected to be small.

13. 13, 13 are the cathode electrodes provided in the N-type regions 12, 12, 12, and 14, 14, 14 are the P-type head regions 11.
An anode electrode provided at 11 and 11, a common electrode provided at 15 and a surface protective film 16, and an equivalent circuit of a device having such a configuration is shown in FIG.

That is, N type region 12.1212 and P type head region 11, 11, 1
The PN junction located between the variable capacitance diode 17 and
, 17, 17, and P-type head area 11.11.11
The PN junction between the capacitor and the N-type substrate 10 corresponds to the DC blocking capacitors 1B, 18, and 1B.

With the circuit configuration shown in any of these circuits, it is possible to adopt the circuit shown in FIG. 6 in which the bias resistor (R) does not reduce the (Q) of the tank circuit when configuring the tuning coil and tank circuit.

According to the circuit shown in FIG. 6, the bias resistor (R
Although the value of
Good results can be obtained in terms of SN ratio, F interference ratio, image interference ratio, etc.

As is clear from the above description, the present invention provides a plurality of regions of opposite conductivity type in a semiconductor substrate of one conductivity type, and a plurality of regions of one conductivity type within each region, and has a conductivity opposite to that of the one conductivity type region. The PN junction between the type region and the substrate is used as a variable capacitance element, and the PN junction between the opposite conductivity type region and the substrate is used as a DC blocking capacitor.

Therefore, since the anode and cathode electrodes of each variable capacitance element can be taken out independently, it is possible to create a high (Q, l) resonant circuit that is not affected by the bias resistance, and also has a built-in DC blocking capacitor. As a result, the number of external parts is reduced, labor during manufacturing can be omitted, and total cost can be reduced.Furthermore, since all elements are formed on the same substrate, characteristics are uniform. A variable capacitance device can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a conventional variable capacitance device, Fig. 2 is its equivalent circuit diagram, Fig. 3 is a tank circuit diagram, Fig. 4 is its equivalent circuit diagram, and Fig. 5 is a cross-section of the variable capacitance element of the present invention. 6 is an equivalent circuit diagram thereof, and FIG. 7 is a tank circuit diagram using the device of the present invention, in which 10 is a substrate, 11 is an opposite conductivity type region, and 12 is a tank circuit diagram using the device of the present invention.
13 indicates a one-conductivity type region, 13 a cathode electrode, 14 an anode electrode, 17 a variable capacitance element, and 18 a DC blocking capacitor, respectively.

Claims (1)

[Claims] 1 Consists of a semiconductor substrate of one conductivity type, a plurality of regions of opposite conductivity type formed on the substrate, and regions of one conductivity type provided in each of the regions of opposite conductivity type, each region of conductivity type, each region of opposite conductivity type. External terminals are provided on the mold region and the substrate, respectively, and the PN junction between each negative conductivity type region and each opposite conductivity type region is used as a variable capacitance element, and the PN junction between each opposite conductivity type region and the substrate is used as a variable capacitance element. A variable capacitance device characterized by its use as a DC blocking capacitor.