JPS63125021A - Analog-digital converter - Google Patents

Abstract

PURPOSE:To obtain a proper digital signal by converting a digital signal into an analog signal and converting the signal into a 2nd digital signal by the same device so as to obtain the difference between the both. CONSTITUTION:An analog signal is converted into a 1st digital signal by using a 1st A/D converter 4, a comparator 6 and a logic circuit 7, then converted into a 2nd analog signal by using a 2nd D/A converter 5 and converted again into the 2nd digital signal by using the same circuit. If the accuracy of the comparator is deteriorated and the level of the 1st digital signal is increased by S from an accurate value, after the 1st digital signal is converted into the 2nd analog signal and the quantity of the 2nd digital signal obtained through digital conversion by the same comparator again is increased by nearly 25 more than the accurate value. Thus, the error S is obtained by subtracting the 1st digital signal from the 2nd digital signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an A/D converter, and more specifically, to the configuration of an A/D converter that makes it possible to obtain accurate digital signals.

(b) Prior Art FIG. 2 is a block diagram of a conventional A/D converter. (
1) is a D/
The A converter (2) is a humperator that compares the levels of the analog signal a to be A/D converted and the analog signal output from the D/A converter (1). D/A based on the comparison result detection signal of 2)
This is a logic circuit that controls the switch group of the converter (1).

In the figure, V□ is a reference voltage, and the number of resistors R and the number of switches are both 256.

Next, the operation of the conventional A/D converter will be explained. The signal level of analog human power a is now 254.5/256XV
□.

First, the logic circuit (3) outputs the b signal of V□ from the D/A converter (1) by turning on only the central switch among the switch group. Huntsmeleta 2 is a
The signal is compared with the b signal, and the result (a>b) is stored in the logic circuit (3) with the most significant bit of the digital conversion data being 1''.

Next, the logic circuit (3) selects and turns on only a specific switch from the switch group, thereby setting the output of the b signal to 3/4 V*ty. Comparator 2 is this b
The signal is compared with the a signal, and since a>b, the bit next to the most significant bit also becomes "1".

Similarly, the level of the b signal is set to 7/8vRIF, 15/
16 V*! r, 31/32 V*tt, 63
/64 V**v, 127/12g■□, to obtain each digit bit of the digital data, but since these are all higher than the level of the a signal, each digit bit becomes "1". .

Next, when you turn on the bottom switch, D/A converter 1
255/256 V□ is output. At this time a
Since <b, this last digit bit becomes “On”.

In this way, the digital conversion data of this analog signal becomes (11111110).

In this way, the conventional A/D converter can successfully convert an analog signal into a digital signal.

(c) Problems to be Solved by the Invention Incidentally, the characteristics of a humperator change due to offset voltage, temperature drift, and fluctuations in power supply voltage, and measurement accuracy deteriorates. However, according to the configuration of a conventional A/D converter, There is a problem in that the conversion accuracy is deteriorated due to this influence.

The present invention was created in view of such conventional problems, and an object of the present invention is to provide an A/D converter that can maintain high conversion accuracy even if the characteristics of the comparator vary.

(d) Means for Solving the Problems The A/D converter of the present invention is characterized by having a first D/A converter, a second D/A converter, a comparator, and a logic circuit. .

(*) Operation First, the first analog signal to be measured is converted into a first digital signal using a first D/A converter, a comparator, and a logic circuit in the same manner as in the conventional example.

A second D/A converter then converts the first digital signal into a second analog signal.

This second analog signal is changed into a second digital signal using a first D/A converter, a comparator, and a logic circuit.

Suppose now that the accuracy of the frequency converter has deteriorated and the magnitude of the first digital signal obtained by converting the input analog signal has become larger by S than the original accurate value. After converting this first digital signal into a second analog signal, the magnitude of the second digital signal obtained by digitally converting the second analog signal through the same humperator is higher than the original accurate value. (It becomes larger by about 2S.

Therefore, for example, by subtracting the first digital signal from the second digital signal, the error S can be obtained.
Accurate digital signals can be easily obtained.

(F) Embodiments 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 built into a microcomputer according to an embodiment of the present invention.

In the figure, (4) is a first D/A converter, and its switch is controlled on/off by a logic circuit (7). (5) is a second D/A converter that shares a resistance ladder with the first D/A converter, and its switch on/off is controlled by a control signal output from a CPU (not shown). .

Further, (6) is a comparator that compares the levels of analog signals c and d, and (7) is a comparator that turns on the switch of the first D/A converter (4) based on the comparison result of the hum comparator (6).
This is a logic circuit that controls off.

(8) is a changeover switch which selects either the analog input to be measured or the analog output of the second D/A converter (5) and inputs it to the comparator (6).

Next, the operation of the embodiment of the present invention will be explained.

First, the analog input to be measured is input to the comparator (6) using the changeover switch (8). The A/D converter, which consists of a first D/AIe converter (4), a comparator (6>), and a logic circuit (7), operates in the same way as a conventional one.This converts the analog input into a digital signal. .

For convenience of explanation, it is assumed that the value of the digital signal should be R if it can be converted accurately, but the digital signal obtained due to the deterioration of the accuracy of the comparator (6>) is R + S1. In other words, Sl is an error. be.

Next, the CPU generates a second signal based on this digital signal R+S.
controls the switch of the D/A converter (5) of the second D/A converter (5).
/A converter (5) outputs an analog signal corresponding to R+S. The switch (8) then switches to input this analog signal to the comparator (6).

An A/D converter composed of a first D/A converter (4), a humparator (6), and a logic circuit (7) converts this analog signal into a digital signal. Incidentally, in this case as well, since digital conversion is performed using a comparator (6) with degraded accuracy, an error S2 occurs.

Therefore, the value of this digital signal is R+81+52.

Generally, the values of 51 and S2 are different, but since this value is originally small, even if it is assumed to be 81-32-8, it will have little effect on the actual measurement results. Now, assuming this, the difference between the first digital signal (R+S) and the second digital signal (R+S+S) is S, so it is easy to obtain the correct digital signal value R from this. be able to.

As described above, according to the embodiment of the present invention, the comparator (6
Even if the accuracy of ) is poor, it is possible to obtain correct digital signal data.

(G) As described in detail, according to the present invention, high-precision A/D conversion can be performed using a low-cost comparator that is not very accurate. Furthermore, even if the accuracy of the comparator deteriorates over time, this can be compensated for and appropriate digital conversion data can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an A/D converter according to an embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of a conventional A/D converter. (1)...D/A converter, (2), (6)...
Comparator, <3), (7)...logic circuit, (
4)...first D/A converter, (5)...second D/A converter, (8)...changeover switch. Applicant Sanyo Electric Co., Ltd. and one other agent Patent attorney Takuji Nishino and one other person Figure 1 e11'Lll? rll)%i

Claims (1)

[Claims] It is composed of a first D/A converter, a second D/A converter, a comparator, and a logic circuit. converting an analog signal into a first digital signal; and then converting the analog signal into a first digital signal by the second D/A converter.
After converting the digital signal into a second analog signal,
The second analog signal is again converted into a second digital signal by the first D/A converter, comparator and logic circuit, and a proper digital signal is further converted from the first digital signal and the second digital signal. An A/D converter characterized by obtaining.