JPH0472820A - Current source circuit - Google Patents

Abstract

PURPOSE:To decrease a linearity error caused due to the dispersion in the manufacture and a temperature change by switching a current source in the order numbers obtained through the replacement of high-order bits and low-order bits of the number in reverse order in binary number notation when numbers 0, 1, 2...N-1 are designated to N-sets of the current sources in the order of the arrangement. CONSTITUTION:When numbers 0, 1, 2...N-1 are designated to N-sets of the current source 5 in the order of the arrangement, the current sources are switched in the order of numbers obtained through the replacement of high-order bits and low-order bits in binary number expression of the numbers in reverse order. That is, a decoder circuit 2 increments number of switches to be energized among switches in a switch array 4 by one as an input signal is being increased and the number of a valid sources among the current sources 5 is incremented by one. In such a case, when the number of the current sources is increased in the said order, even when some current sources are valid, the current sources are almost uniformly distributed among all the current sources. Thus, the linearity error of the current source circuit is decreased without addition of any circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a current source circuit that outputs a current having a current value determined by a human input signal.

BACKGROUND OF THE INVENTION An example of the configuration of a conventional current source circuit used as a main part of a DA converter is shown in FIG.

The human power signal 1 is a digital signal. Decoder circuit 2 (
飄 According to the input signal 1, some of the switches in the switch array 4 are rendered conductive, and some of the current sources in the current source array 5 are enabled. Since each current source in the current source array 5 is constructed identically, a current proportional to the number of conducting switches in the switch array 4 is obtained at the output 3. A first example of the relationship between the input signal 1 and the effective current sources in the current source array 5 at this time is shown in FIG. However, input signal 1
is expressed in decimal notation.

(In such a current source circuit, the current source array 5
For example, the linearity error increases when the current values of each current source are monotonically distributed.
In the figure, the current value of the current source in the current source array 5
As shown in Figure A, the current source 5-0.5-1.5-2. ...,
Assuming that it increases in the order of 5-15, the human power signal l
The relationship between and the current value obtained at output 3 is as shown in Figure 9, which has the drawback of increasing linearity error. This often happens because the characteristics of resistors and transistors are distributed according to their position on the substrate.

A second example of a conventional current source circuit devised to solve this drawback is shown in Figure 1.The configuration is the same as the first example above, but the content of the power decoder circuit 2 is different. . An example of the relationship between the human power signal 1 in the second example and the effective current sources in the current source array 5 is shown in FIG. and a current source 5-0.5-1.5-2. ..., 5-15, current source 5-8 is located almost in the center, so its current value is close to the average value of the current values of all current sources, and current source 5-8 The average of two current sources (for example, 5-6 and 5-10) with The linearity error of the relationship becomes smaller.

For this second example Lt, T, Mi k i
“An 80-MHz 8
- bit CMO3D/A Convert
er”, Journal of 5solid-sta
te C1rcuits), Vol, 5C-21
,pp, 983988, December 1
986.

However, in such a current source circuit, when the current values of each current source in the current source array 5 are distributed symmetrically as shown in Figure 8B, the effect of reducing linearity error is This kind of current value distribution, which had the disadvantage of generating a linearity error equivalent to the first example, is difficult to obtain when forming a resistor or transistor on a semiconductor substrate and using it to configure a current source. For example, this occurs due to temperature distribution such that the temperature at the center of the substrate is higher than at the periphery.

A third example of a conventional current source circuit devised to solve this drawback is shown in Figure 1.The configuration is similar to the first enemy described above.
The power\decoder circuit 2 is similar to the second example, but the contents of the decoder circuit 2 are different. An example of the relationship between the human input signal 1 and the effective current sources in the current source array 5 in the third example is shown in FIG.

This 41 The current source array 5 is divided into two groups, current sources 5-0 to 57 and current sources 5-8 to 5-15, and within each group, switching is performed in rows ( ＼ Switching is performed in the following order: two switches in one group are made conductive, and then two switches in the other group are made conductive.This third example About (to Yasuyuki Nakamura and others) ``10 bit 70MS/sCMO3D/
A converter" 1990 Spring National Conference of the Institute of Electronics, Information and Communication Engineers, Collected Papers, p. 5-237.

Problems to be Solved by the Invention (In the conventional current source circuit of the third example, the current values of each current source in the current source array 5 are distributed asymmetrically as shown in FIG. 8C. When the current value distribution is like this (for example, when a resistor or transistor is formed on a semiconductor substrate, This occurs due to temperature distribution, etc. when configuring a current source by .Temperature distribution 41 It is a special case that the current reaches its maximum at the center of the current source array as shown in Figure 8B.
Generally, the distribution is such that it has a peak at a point other than the center, as shown in FIG. 8C.

Figure 4 shows the calculation results of the linearity error.However, the number of current sources in the current source array 5 is assumed to be 32, and the current sources 50 to 5-31
Among them, 5-0 and 5-31 are the minimum and 90% of the average value, and 5-X (X is any one from 1 to 30) is the maximum and the average value is 110OA between 5-0 and 5-X. plate and 5
-X and 5-31 are assumed to change linearly.As is clear from this figure, the first
When switching is performed as shown in Figure 1, if the current value is distributed such that the current value of the 4th or 26th current source from the end is the maximum, the error will be maximum,
A linearity error of approximately 0.4 times the average value of the current value of the current source occurs.

The present invention was made as a result of devising and researching the above-mentioned drawbacks of conventional current source circuits, and aims to provide a current source circuit with small linearity errors caused by manufacturing variations and temperature. There is.

Means for Solving the Problems This invention solves the above problems.In order to solve the above problems, in a current source array consisting of &N current sources, the current sources are arranged in order of 0.1, 2, . . . When numbering N-1, the current source circuit switches the current sources in the order of the numbers obtained by exchanging the upper bits and lower bits of the binary representation of the number in reverse order.

According to the above-described configuration, as the input signal increases, the decoder circuit increases the number of switches in the switch array that are made conductive one by one, thereby reducing the number of effective current sources to one. At this time, if you increase the current sources in the order like the above configuration, no matter how many current sources are enabled, those current sources will be included in all the current sources. Almost uniformly distributed.

Therefore, even if there is a distribution of current values within the current source array and the maximum value exists at any position within the current source array, the current source that is enabled will have a Since they are almost evenly distributed and cancel each other out, the linearity error does not become large.

Embodiment FIG. 1 shows an example of the configuration of a current source circuit according to the present invention. This current source circuit is used as the main part of a DA converter.

The configuration is similar to the conventional current source circuit example mentioned earlier,
Sumo wrestlers that operate in the same way The contents of the decoder circuit 2 are different. An example of the relationship between the input signal l and the effective current sources in the current source array 5 is shown in FIG.

The human signal is 0.1, 2, 3. ..., 15, the current sources in the current source array 5 (0, 8, 4.1
2..., 15 are valid in this order.

A method for generating this order will be explained using FIG. 3.

(1) Number the current sources in the current source array 5 sequentially starting from 0 (Figure 3A).

(2) Next, express it in binary numbers (Figure 3B).

(3) Next, rearrange them in reverse order (Figure 3C).

(4) Finally, convert it into a decimal number (Figure 3 D).

Then, you can enable the current sources in the order of the numbers that appear there.

By the way, since the input signal l to the current source circuit is normally given as a binary digital signal, in order to make the current source effective as in the present invention (mainly) All you have to do is swap the upper and lower bits of , in reverse order, and there is no need to add any circuitry.

Figure 4 shows the calculation results of the linearity error. However, the conditions are the same as in other conventional examples. As it is clear from this figure
When switching is performed as in the present invention, no matter where the current value of the current source is distributed to be maximum, there is a linearity error (approximately 0% of the average value of the current value of the current source).
The average value of the linearity error is twice as low as that of the third conventional example. In addition, in the case of Figure 4, when there are six current sources from 13 to 18 with the maximum current value, the conventional third example has a smaller linearity error (such as The rate at which this occurs (decreases as the number of current sources increases) is shown in FIG. 5. Therefore, the present invention is more effective as the number of current sources increases.

In the example given here, it is assumed that the distribution of the current value of the current source is maximum at one point as shown in Figure 8C, and changes linearly at other points. However, this invention is effective.

This point will be explained below.

There are two ways of distributing the current value of the current source: one is due to random factors, and the other is due to factors related to the position of the current source. Even if the current source is enabled, the linearity will not be improved, so it is not considered here.

An example in which 16 current sources are arranged in a circle as shown in FIG. 6 will be explained.

Assuming that the current value of a current source is determined by a factor related to position, the current values of current sources that are close to each other are close to each other. For example, if the current value of one current source is larger than the average value, there is a strong possibility that the current value of the adjacent current source is also larger than the average value.

The farther the position is, the weaker the relationship between the current values of the two current sources becomes. Therefore, when you enable the current sources one after another, select the current source that is farthest from the current sources that have been enabled so far and enable it next. The average value of the current value of the source is close to the average value of the current value of all current sources.Also, when there are multiple current sources that are farthest from the current source that has been activated up to that point (L Select the current source that is farthest from the enabled current source When there are multiple current sources that are farthest from the last enabled current source (friend) Select the current source at the S% position, select the third from the last if there are multiple sources, and repeat this process.
Next, it is sufficient to determine the current source to be effective.

In Fig. 6, if the current source 5-0 is enabled first, then the farthest current source 58 is enabled second, and the third one is enabled from both 5-0 and 5-8. far 5-4
For example, let's choose 5-4. Then, the fourth score becomes 5-12. The 5th force is either 5-2.5-6 or 510.5-14 (the one farthest from the 4th choice 5-12 is 5)
-2.56, and the distance from the third choice 5-4 is also equal (5-2 is far from the second choice 5-8, so 5- 2 is enabled next.

When selected in this way, the order is the same as that explained in FIG. Therefore, the method of the present invention is effective regardless of the distribution of the current values of the current sources. The present invention is effective even when the elements are arranged in a polygonal manner or in a polygonal line.

Furthermore, this invention is effective even when the number of current sources is not a power of 2.

As described in detail, according to the present invention, the linearity error of the current source circuit can be reduced without adding any circuit. Therefore, it is extremely useful.

[Brief explanation of drawings]

Figure 1 shows the configuration of an example of the current source circuit of the present invention and a conventional current source circuit. Figures 2 and 3 show the order of the current sources that are effective in the current source circuit of the present invention. Figure 4 shows the calculated linearity. Error characteristics: Figure 5 shows the rate at which the linearity error is smaller in the conventional third example than in the present invention. Fig. 7 shows the order of effective current sources in the first conventional current source circuit. Fig. 8 shows the distribution of current values of the current sources. Fig. 9 shows the relationship between the human input signal and the output current. Figure 10 shows the sequence of effective current sources in the second example of the conventional current source circuit.
FIG. 1 is a sequential explanatory diagram of effective current sources in a third conventional current source circuit. 1...Human signal, 2...Decode same area 3...
Output, 4...Switcher IJ, 5...Current source IJ) Name of agent: Patent attorney Shigetaka Awano and one other person ℃I
＞COC＞9 No. η Length 1 ○ , -7゜○ ○ -q ○5-3

Claims (1)

[Claims] In a current source array consisting of N current sources, the current sources are 0, 1, 2,...N- according to the order of arrangement.
When assigning a number 1, the current source circuit switches the current sources in the order of the numbers obtained by exchanging the upper bits and lower bits of the binary representation of the number in reverse order.