JPH04352466A - R-2r ladder-type resistor circuit - Google Patents

Abstract

PURPOSE:To obtain an R-2R ladder-type resistor circuit of a high accuracy easily, as the one to be used in an n-bit digital analog converter, etc. CONSTITUTION:A semiconductor diffusion layer 5 formed on the central part of a resistor island 4 is the one having no range of the width of a resistor, among respective semiconductor diffusion layers 5 formed in parallel with each other on the resistor island 4. This semiconductor diffusion layer 5 is made to be an MSB resistor, to which the highest accuracy of a resistance ratio is required. Therefore, in an n-bit digital analog converter, the accuracy of the analog output when a data is changed over from 2<m-2> to 2<n-1> can be prevented from lowering. Thereby, an R-2R ladder-type resistor circuit 2 of a high accuracy can be obtained easily, without necessity of changing the width and the shape of the resistor in particular.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an R-2R ladder resistance circuit constituted by a plurality of resistors each consisting of a semiconductor diffusion layer of a second conductivity type formed on a semiconductor region of a first conductivity type.

0002

2. Description of the Related Art FIG. 5 is a wiring diagram of a conventional n-bit digital-to-analog converter, and FIG. 6 is a plan view of an R-2R ladder resistance circuit used in this digital-to-analog converter.

As shown in FIG. 5, there are n changeover switches S, one of which is connected to the input terminal 1 to which a reference voltage Vref is applied, and the other of which is connected to the ground (GND).
1, S2,..., Sn, and an R-2R ladder resistance circuit 2 consisting of a plurality of resistors each having a resistance value of R.
is provided to constitute an n-bit digital-to-analog converter, and the configuration of the R-2R ladder resistance circuit 2 is as follows.

That is, as shown in FIG.
02 are connected in series, a resistor R02 is connected to the input terminal 1, and (n-1) resistors R02,..., R2n-4, R2n-2 are connected between the resistor R01 and the output terminal 3,
Resistors R11 and R12 are connected in series between the connection point of resistor R01 and resistor R02 and the common terminal of changeover switch S1, forming a resistor pair with a resistance value of 2R for the least significant bit (hereinafter referred to as LSB), and the same applies hereafter. and the resistance value of each bit is 2
A resistor pair of R is configured, resistors R2n-4 and R2n-2
Resistors R(2n-3)1 and R(2n-3)2 are connected in series between the connection point of and the common terminal of the changeover switch S1, and the resistance value of the most significant bit is 2R. A pair is formed, and resistors R(2n-1)1 and R(2n-1)2 are connected between the output terminal 3 and the common terminal of the changeover switch Sn.
are connected in series to form a resistor pair with a resistance value of 2R for the most significant bit (hereinafter referred to as MSB), and an R-2R ladder resistance circuit 2 is formed by each of these resistors.

Each of the changeover switches S1 to Sn of the n-bit digital-to-analog converter having the configuration shown in FIG. 1 side or the ground side, and an analog signal having a voltage value corresponding to the digital data is output from the output terminal 3.

At this time, each of the changeover switches S1 to Sn has a weight of 2m-1 (m=1, 2..., n), the weight of the changeover switch S1 is 1, and the weight of the changeover switch S2 is 2. , the weight of the changeover switch Sn is 2n-
1, and each resistor pair such as resistors R11 and R12 connected to these changeover switches S1 to Sn has the same weight as each changeover switch S1 to Sn, so the accuracy of the digital-to-analog converter is M
SB side resistance R(2n-1)1, R(2n-1)2
, depends largely on the changeover switch Sn.

By the way, the above-mentioned R-2R ladder resistance circuit 2 is constructed as shown in FIG. Then, a plurality of semiconductor diffusion layers 5 of the second conductivity type are formed to constitute each resistor, and these resistors are connected as shown in FIG. 5. In this case, each semiconductor diffusion layer of the resistor island 4 5 is used as a resistor pair for each bit in order from the left side to the right side, so the pair of LSB resistors R11 and R12 is located near the left end of the resistor island 4, and the MSB resistor R (2n -1)1 ,R(2
The pair n-1)2 is located at the right end of the resistive island 4.

[0008] In general, in a digital-to-analog converter, when the number of bits is large, low current and high resistance ratio accuracy are required, so each resistor, that is, each semiconductor diffusion layer 5
The width of the resistor tends to become narrower and longer, and as the number of bits increases, the width difference and diffusion difference of each resistor, which had been negligible until then, gradually begins to affect the accuracy of the digital-to-analog converter. become.

Furthermore, as shown in FIG. 6, the semiconductor diffusion layers 5 as each resistor are formed adjacently on the resistor island 4, so that the semiconductor diffusion layer 5 in the center of the resistor island 4 and the edge When comparing the semiconductor diffusion layer 5 located at the edge and the semiconductor diffusion layer 5 near the edge, the width conditions are different, and the difference in resistance value becomes large. Required MSB resistance R(2n-1)1
, R(2n-1)2 is located at the right end of resistive island 4, the data becomes 2n due to the influence of the resistance width difference mentioned above.
The accuracy when switching from -2 to 2n-1 becomes extremely poor.

On the other hand, the pair of resistors R11 and R12 located near the left end of the resistive island 4 is also affected by the difference in resistance width;
Since these resistor pairs have a weight of 1, they do not significantly affect the accuracy of the digital-to-analog converter.

[0011]

[Problems to be Solved by the Invention] As mentioned above, in the conventional R-2R ladder resistance circuit 2, the MSB resistors R(2n-1)1 and R(2n
-1) The pair of 2 is located at the end of the resistor island 4, and the difference in resistance width greatly affects the accuracy of the digital-to-analog converter, so it is impossible to make the resistance width narrower, and on the contrary, it is impossible to make the resistance width wider. It is better to make the length commensurate with the width,
R used for digital/analog converters with a large number of bits, etc.
There is a problem in that it is difficult to easily obtain a highly accurate -2R ladder resistance circuit.

The present invention was made to solve the above-mentioned problems, and it is possible to easily obtain a high-precision R-2R ladder resistor circuit for use in an n-bit digital-to-analog converter, etc. The purpose is to make it possible to

[0013]

[Means for solving the problem] R-2R according to the present invention
The ladder resistance circuit is composed of a plurality of resistors made of semiconductor diffusion layers of a second conductivity type formed in the same direction, in the same shape, and in the same size on a semiconductor region of the first conductivity type. In the ladder resistance circuit, the semiconductor diffusion layer located in the center of each of the semiconductor diffusion layers is used as a resistor that requires the highest resistance ratio accuracy for operation.

[0014]

[Operation] In this invention, among the semiconductor diffusion layers formed on the semiconductor region, the central semiconductor diffusion layer is made the resistor that requires the most resistance ratio accuracy for operation. A semiconductor diffusion layer in the center with no difference in resistance width is used, and there is no need to change the width or shape of the resistance, making it easy to obtain a high-precision R-2R ladder resistance circuit, which can be used for digital/analog circuits with a large number of bits. When applied to a converter, deterioration in accuracy of analog output is prevented.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view of an embodiment of the R-2R ladder resistor circuit of the present invention, and FIG. 2 is a wiring diagram, showing the case where the circuit is applied to an n-bit digital-to-analog converter.

1 is different from FIG. 6 in that the resistances R(2n-1)1, R( 2n-1
)2, R2n-2, and the semiconductor diffusion layer 5 at the right end of the resistive island 4 is set to the almost middle bit resistance R2m-2, R(2m
-1)1 ,R(2m-1)2 (1<m<n)
and the resistance R(2n-1)1 on the MBS side in FIG.
, R(2n-1)2 , R2n-2 and the intermediate bit resistance R2m-2, R(2m-1)1 , R(2m-1)2
This means that the .

By the way, FIG. 2 is a wiring diagram of an n-bit digital-to-analog converter using the R-2R ladder resistance circuit 2 of FIG. 1, and has the same configuration as that shown in FIG. Resistance R of the omitted middle bit (2m
-1)1 ,R(2m-1)2 ,R2m-2,R2m
-1 and the changeover switch Sm connected to the resistor R(2m-1)2.

At this time, as mentioned above, since the weight of the changeover switch Sm is 2m-1, the resistance R(2m-1
)1, R(2m-1)2 also has a weight of 2m-1, but the MSB changeover switch Sn and resistor R(2n
-1)1, R(2n-1)2 weight 2n-1 (n
> m), and the weight of the pair of middle bit resistances R(2m-1)1, R(2m-1)2 is much smaller than that of the MSB resistances R(2n-1)1, R(2m-1). 1)2
Since the weight of the pair is 1/2n-m, even if the intermediate bit resistances R(2m-1)1 and R(2m-1)2 are at the right end of the resistor island 4, the difference in resistance width The impact on the accuracy of the digital-to-analog converter is negligible.

Furthermore, since the resistances R01 and R02 of the LSB are also located at the left end of the resistance island 4, the difference in resistance width is large as described above, but the weight is 1, and the resistance R (2n
-1)1 , 1/ compared to the weight of R(2n-2)2
2n-1, and the influence of the difference in resistance width on the accuracy of the digital-to-analog converter is even less than in the case of intermediate bit resistances.

Therefore, among the semiconductor diffusion layers 5 formed in parallel to the resistor island 4, the central semiconductor diffusion layer 5 with no difference in resistance width is made the MSB resistor where resistance ratio accuracy is most required. , it is possible to prevent a decrease in the accuracy of analog output when the data switches from 2n-2 to 2n-1 in an n-bit digital-to-analog converter, and there is no need to particularly change the width or shape of the resistor. -2R ladder resistance circuit 2 can be easily obtained.

Next, FIG. 3 is a plan view of another embodiment of the present invention.

3, the difference from FIG. 1 is that the semiconductor diffusion layer 5 below the dashed line in FIG.
is the resistance R(2n-1)1 of one side of the MSB, the semiconductor diffusion layer 5 on the left side of the semiconductor diffusion layer 5 having this resistance R(2n-1) is the resistance R(2n-1)2, and the semiconductor diffusion layer 5 on the right side is the resistance R(2n-1)2. The diffusion layer 5 is designated as a resistor R2n-2, and the semiconductor diffusion layers 5 on the left and right sides are assigned in the same manner as the resistance of the lower bits, and the leftmost semiconductor diffusion layer 5 is assigned as a resistor R02, and the rightmost semiconductor diffusion layer 5 is assigned as a resistor R02. The semiconductor diffusion layer 5 is a resistor R01,
The resistors are distributed symmetrically to the left and right in order of weight with respect to the center line of the resistor island 4, and the resistors are connected in the prescribed manner. In this case as well, the same effect as in the case of Fig. 1 can be obtained. Obtainable.

By the way, FIG. 4 is a wiring diagram of an n-bit digital-to-analog converter using the R-2R ladder resistance circuit 2 of FIG. 3, and has the same configuration as that shown in FIG. This figure shows resistors R31 and R32 of the second bit from the lower order side, which have been omitted, and a changeover switch S2 connected to resistor R32.

In the above embodiment, the case where the R-2R ladder resistance circuit is applied to an n-bit digital-to-analog converter was explained, but it is not limited to digital-to-analog converters. Of course, this method can also be applied to detection.

[0025]

As described above, according to the R-2R ladder resistance circuit of the present invention, the central semiconductor diffusion layer among the semiconductor diffusion layers formed in the semiconductor region has the highest resistance ratio accuracy in operation. Since the required resistance is used, there is no need to particularly change the width or shape of the resistor, and a high-precision R-2R ladder resistance circuit can be easily obtained, making it suitable for applications such as digital-to-analog converters with a large number of bits. It becomes possible to provide highly accurate digital-to-analog converters and the like.

[Brief explanation of drawings]

FIG. 1 is a plan view of an embodiment of the R-2R ladder resistance circuit of the present invention.

FIG. 2 is a wiring diagram of FIG. 1;

FIG. 3 is a plan view of another embodiment of the invention.

FIG. 4 is a wiring diagram of FIG. 3;

FIG. 5 is a wiring diagram of a general n-bit digital-to-analog converter.

6 is a plan view of the R-2R ladder resistance circuit in FIG. 5. FIG.

[Explanation of symbols]

2 R-2R ladder resistance circuit 4 Semiconductor region (resistance island) 5 Semiconductor diffusion layer

Claims (1)

[Claims] Claim 1: R constituted by a plurality of resistors made of semiconductor diffusion layers of a second conductivity type formed in the same direction, in the same shape, and in the same size on a semiconductor region of the first conductivity type.
-2R ladder resistance circuit, wherein the semiconductor diffusion layer located in the center of each of the semiconductor diffusion layers is used as a resistor that requires the highest resistance ratio accuracy for operation.