JPS5931058A - Variable resistor - Google Patents

Abstract

PURPOSE:To obtain a variable resistor with small patterns by a method wherein diffusion resistance is formed in a semiconductor of the first conductivity type by means of diffused wiring layers of the second conductivity type, and these wiring layers are designated as the source and drain of a FET for resistance control purpose. CONSTITUTION:The variable resistor is composed of a ladder resistor consisting of diffused resistors 13, 14, and 15, a P-channel FET16, and a P-channel FET18. The FET16 has the source and drain formed by means of the resistors 13 and 14. The FET18 has the source and drain formed by means of the resistors 14 and 15. The resistance value of the variable resistor, i.e., the resistance value between terminals 11 and 12 is made variable by the potentials of gate terminals 18 and 19.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable resistance element in a semiconductor integrated circuit.

In recent years, a wide variety of electronic devices using AD conversion circuits and DA conversion circuits have been developed in large numbers, and it is expected that this trend will continue and the number of electronic devices will increase in the future.

And that AD conversion circuit.

Most of the DA conversion circuits are constructed of semiconductor integrated circuits, and a variable resistance element is always used in the AD conversion circuits and DA conversion circuits implemented as semiconductor integrated circuits. In other words, the variable resistance element in the semiconductor integrated circuit is
In particular, the demand for 1c AD conversion circuits and DA conversion circuits is increasing. In addition, demand for other circuits continues to increase, and it is desired to improve various drawbacks of conventional variable resistance elements.

As an example of a variable resistance element in a conventional semiconductor integrated circuit, one shown in FIG. 1 is generally used. In the figure, 1 and 2 are terminals of a variable resistance element, and the resistance value between these terminals 1 and 2 changes. 3, 4.5 are ladder resistors formed of diffusion or polysilicon, and 6, 7 are Ps that control the resistance value of the variable resistance element, respectively.
This is a channel field effect transistor (hereinafter simply referred to as a transistor). If the resistance value of the transistor 6.7 when it is in the ON state is α, then normally α is a value extremely smaller than the resistance values 1'L, , R2°R3 of the ladder resistors 3, 4.5, α<R. 8.9 is the gate terminal of the transistor 6.7.

Next, the operation of the variable resistance element shown in FIG. 1 will be explained. First, when the gate potentials of transistors 6 and 7 are both @H'' level, both transistors 6 and 7 are in the OFF state, and the resistance value between terminals 1 and 2 is It
1+几, +R3. Second, when the gate potential of transistor 6 is at "H" level, the gate potential of transistor 7 is "H" level.
At L'' level, transistor 6 is OFF, transistor I is ON, and the resistance value between terminals 1 and 2 is R,
Ten R.

becomes. Thirdly, when the gate potential of the transistor 6 is at the "L" level, the transistor 6 is in the ON state, so the resistance value between the terminals 1 and 2 is R8 regardless of whether the transistor T is ON or OFF. In this way, the variable resistance element shown in FIG. 1 has resistance values of R and +R.

Three resistance values can be provided: +R, R, and R. If it is desired to increase the number of resistance values to be supplied, this can be done by increasing the number of ladder resistors and resistance value control transistors.

However, when designing a pattern for this variable resistance element as a semiconductor integrated circuit, as shown in FIG. It is necessary to provide Therefore, since a considerable area is required for the pattern, there is a drawback that the chip cost increases.

The present invention has been made in view of the above-mentioned points, and provides a variable resistance element whose pattern area can be made extremely small compared to conventional ones. Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 3 is a diagram showing an embodiment of the variable resistance element according to the present invention. In the same figure, 11.12 is a terminal of a variable resistance element, which is made of aluminum or the like, and this terminal 11.1
The resistance value between the two changes as described below. 13,
14 and 15 are ladder resistors formed of diffused resistors. Reference numeral 16 denotes a P-channel field effect transistor (hereinafter simply referred to as a transistor) formed in a distributed pattern for controlling the resistance value of a variable resistance element with the ladder resistors 13 and 14 as sources and drains. Similar to the transistor 16, 17 is a P-channel field effect transistor (hereinafter simply referred to as a transistor) formed in a distributed manner that controls a variable resistance value and uses ladder resistors 14 and 15 as sources and drains. 18.19 is the gate terminal of the transistor 16.17.

Next, the operation of the variable resistance element shown in FIG. 3 above will be explained. First of all, when the gate potentials of transistors 16 and 17 are both at H'' level, both transistors 16 and 17 are in the OFF' state, and the resistance value of the variable resistance element, that is, the resistance value between terminals 11 and 12 is R+ +
J + Ra (where R,, IiL,, R,
are the resistance values of the ladder resistor 13°14.15, respectively).

2nd K) When the gate potential of the transistor 16 is at the "11" level and the gate potential of the transistor 11 is at the L" level, the transistor 16 is in the OFF state and the transistor IT is in the OFF state.
The state is N, and the resistance value between terminals 11 and 12 is R1+
(However, β is the combined resistance value obtained by connecting in parallel the series combined resistance of the ladder resistors 14 and 15 and the resistance between its drain and source when the transistor 17 is turned on.) The gate potential of the third IC transistor 16 is “L”
When the gate potential of the level transistor 11 is at "H" level, the transistor 16 is in the ON state and the transistor 17 is in the OFF state.
It becomes FF state, and the resistance value between terminals 11 and 12 is R1+γ
(However, γ is the series combined resistance of ladder resistors 13 and 14 and the drain of transistor 16 in the ON state.

(combined resistance value obtained by connecting the resistance between sources in parallel).

4th IC) When the gate potentials of transistors 16 and 17 are both at the K"L" level, both transistors 16 and 1T are in the KOH state, and the resistance value between terminals 11 and 12 is δ (however, δ is the ladder value). Resistor 13, 14.15
and the combined resistance of transistors 16 and 17, which is the combined resistance value obtained by connecting in series the resistances between the drain and source when transistors 16 and 17 are on.

As mentioned in 5 above, the resistance value of the variable resistance element shown in FIG. 3 is Rs + Rt + Rs - J + β, R5 + γ.
.

Four resistance values of δ can be provided. Now, α,
When designed so that β, γ, δ< R1e Rt p Rs, the resistance value that can be supplied by the variable resistance element is R1 + R2 + R,, R,, l circle 3. There are four resistance values of δ.

FIG. 4 shows an example in which the variable resistance element shown in FIG. 3 is converted into a pattern diagram of a semiconductor integrated circuit. As shown in the figure, since the ladder resistors 13, 14.15 and the source and drain of the transistor 16.17 that controls the resistance value of the variable resistance element can be shared, the pattern area is smaller than that of the conventional variable resistance element shown in Fig. 3. It can be designed to be extremely small compared to the previous pattern.

Further, FIG. 5 is a diagram showing another example of the pattern of the variable resistance element shown in FIG. 3. Similarly to the pattern diagram in Fig. 4, the pigeon coop shown in the same figure can share the source and drain of the ladder resistor 13°14.15 and the transistors 16 and 17 for controlling the resistance value of the variable resistor, so the pattern area is the same as that of the second pattern. It can be designed to be extremely small compared to the conventional variable resistance element pattern shown in the figure.

As described above in detail, the variable resistance element according to the present invention includes a diffused resistor formed by a second conductivity type diffusion wiring layer formed with an internal pressure of a first conductivity type semiconductor region, and the second conductivity type diffusion wiring layer itself. Compared to variable resistance elements in semiconductor integrated circuits such as sources and drains, a variable resistance element can be formed with an extremely small pattern area, and a semiconductor chip including a variable resistance element can be provided at a lower cost.

[Brief explanation of drawings]

FIG. 1 is a diagram of a variable resistance circuit in a conventional semiconductor integrated circuit, FIG. 2 is a diagram converted to a pattern thereof, FIG. 3 is a diagram of a variable resistance circuit in a semiconductor integrated circuit according to the present invention, and FIG.
The figure shows an example of conversion into the pattern, and FIG. 5 is a diagram showing another example of conversion into the same pattern. In the figure, 11.12 is a terminal, 13, 14.15 is a ladder resistor, and 16.17 is a transistor. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Makoto Kuzuno - (1 other person) Figure 1 Figure 3 1 Procedural amendment (voluntary) Figure 4 617 1 Figure 5 9 5. Subject of amendment 11 Summons 5 Dark "January 26th 1, Incident Display of patent application No. 57-141409 2
, Title of the invention Variable resistance element 3, Relationship to the case of the person making the amendment Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Corporation Representative Hitachi Katayama 4; Agent address: 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Detailed explanation column of the invention in the specification, Drawing 6, Contents of amendment (1) "Resistance value control transistor" on page 14, line 3 of specification ff. , corrected as "transistor for controlling resistance value". (2) Similarly, "Figure 3" on page 7, line 9 is corrected to "Figure 2." (3) Correct the figures 2, 4, and 5 of the drawings as shown in the attached sheet. Figure 4, Figure 5 299

Claims (1)

[Claims] A variable resistance element in a semiconductor integrated circuit includes a plurality of diffused resistors formed by a second conductivity type diffusion wiring layer formed in a first conductivity type semiconductor region, and the second conductivity type diffusion wiring layer itself serving as a source and a drain. A variable resistance element comprising a resistance value control field effect transistor formed in a distributed pattern.