JPH0457518A - A/d converter - Google Patents

Abstract

PURPOSE:To expand the degree of freedom of the layout by arranging odd number comparators and even number comparators in axial symmetry with a reference resistor of a resistor string inbetween. CONSTITUTION:The A/D converter consists of odd number comparators 1, even number comparators 2, a resistor string 3, reference resistors 4, a low level side reference input terminal 5 and a high level side reference input terminal 6. Since the odd number comparators 1 and the even number comparators 2 are arranged with the resistor string 3 comprising the reference resistors 4 inbetween, the height of one comparator is selected to be twice. Thus, the large degree of freedom of the layout is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an A/D converter, and more particularly to an A/D converter in which the arrangement of a reference resistor and a comparator is improved.

[Conventional technology]

A conventional parallel type A/D converter has a resistor string in which a reference resistor is connected in series, and a comparator that compares the divided voltage of the resistor string with the reference voltage.

FIG. 3 is a configuration diagram of an A/D converter showing an example of such a conventional A/D converter.

As shown in FIG. 3, the conventional parallel type A/D converter has a reference resistor 4 connected in series and a low potential side reference input terminal 5 at both ends.
and a high potential side reference input terminal 6 are connected to each other, and 64 comparators 7 are connected to the voltage dividing points thereof. Furthermore, a resistor string 3 consisting of 2'' (n is the number of bits) reference resistors 4 constituting a parallel A/D converter and 2n comparators 7 are arranged in series. In a type A/D converter, the reference resistor 4 and comparator 7 are not normally 2" arranged in a straight line due to chip size issues.
It is placed by folding back from an appropriate location depending on the chip size.

FIG. 4 is a block diagram of another example of such a conventional A/D converter.

As shown in FIG. 4, in this A/D converter, the first half comparator 7A is placed on the right side of the resistor strings 3, and the second half comparator 7B is placed on the left side of the resistor strings 3. Therefore, the resistor strings 3 constituting the A/D converter are arranged such that the wiring of the reference resistor 4 at one turning point is lengthened.

[Problem to be solved by the invention]

The conventional A/D converter shown in FIG. 3 described above requires 2f1 comparators to be arranged in series. Therefore, considering the chip size, the height of each comparator must be reduced, which has the drawback of making the layout quite difficult.

Further, in the A/D converter shown in FIG. 4 described above, the wiring connecting the reference resistors in the folded portion is longer than the reference resistors in other portions. Therefore, only the resistance of the folded portion becomes larger in resistance value than the other partial resistances by the wiring resistance. In such an A/D converter, the accuracy is affected by the relative ratio of the reference resistances formed by the resistor strings, so if the resistance value of the folded portion is larger than the other resistance values, the accuracy of the A/D converter will be affected. It has the disadvantage of making things worse. Also, it is conceivable to consider the wiring resistance of the folded part in advance and make only the resistance of the folded part smaller than the other resistances. It is difficult to adjust.

An object of the present invention is to provide an A/D converter that can expand the degree of freedom in layout and improve conversion accuracy.

[Means to solve the problem]

The A/D converter of the present invention has a resistor string in which 2" (n is the number of bits) reference resistors are connected in series and a reference voltage is applied to both ends of the resistor string. A reference voltage divided into 2n resistors is sequentially and alternately applied. The device has an odd numbered comparator and an even numbered comparator, and is configured such that the odd numbered comparator and the even numbered comparator are arranged separately with the resistor strings in between.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an A/D converter showing a first embodiment of the present invention.

As shown in FIG. 1, this embodiment has 211 reference resistors 4
resistor strings 3 connected in series and having both ends connected to the low potential side reference input terminal 5 and the high potential side reference input terminal 6.
Odd numbered comparators 1 and even numbered comparators 2 are sequentially and alternately connected to the voltage dividing point of the resistor strings 3.
It has Furthermore, among these 2'' comparator groups, the odd numbered comparators 1 and the even numbered comparators 2 are arranged line-symmetrically with the resistor strings 3 in between. 3, and an odd-numbered comparator 1 and an even-numbered comparator 2 are connected to both ends of each reference resistor 4.

The A/D converter having such a configuration differs from the conventional example in Section 3 mentioned above in the arrangement of the comparator. In other words, in order to arrange the odd-numbered comparators 1 and even-numbered comparators 2 across the resistor string 3 consisting of the reference resistor 4, one comparator block is made twice as high as the A/D converter shown in FIG. This allows a great deal of freedom in layout.

FIG. 2 is a block diagram of an A/D converter showing a second embodiment of the present invention.

As shown in FIG. 2, in this embodiment, as compared with the first embodiment described above, the reference resistors 4 constituting the resistor strings 3 are arranged laterally, and each is formed in a pair.

Therefore, in this embodiment, unlike the conventional example shown in FIG. 4 described above, only the resistance value of the retarded resistor does not become larger than that of the other resistors. That is, the relative accuracy of resistance including wiring resistance is improved, so the accuracy of the A/D converter is improved.

〔Effect of the invention〕

As explained above, the A/D converter of the present invention has double the height of the conventional comparator block by arranging the odd-numbered comparators and the even-numbered comparators line-symmetrically across the reference resistance of the resistor string. This has the effect of increasing the degree of freedom in layout. Further, the present invention provides a reference resistor string consisting of reference resistors having the same shape and pitch between the comparator groups, and wiring both ends of each reference resistor to the odd-numbered comparators and the even-numbered comparators. The relative accuracy of the resistor can be improved, so
This has the effect of improving conversion accuracy.

1... Odd number comparator, 2... Even number comparator, 3... Resistor strings, 4... Reference resistor,
5...Low potential side reference input terminal, 6...High potential side reference input terminal.

Claims (1)

[Claims] 2^n of resistor strings in which 2^n (n is the number of bits) reference resistors are connected in series and a reference voltage is applied to both ends of the resistor strings.
an odd-numbered comparator and an even-numbered comparator to which reference voltages divided into individual voltages are sequentially and alternately input, and the odd-numbered comparator and the even-numbered comparator are arranged separately with the resistor strings in between. Characteristic A/D converter.