JPH0338779B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is used in various measurement fields,
The present invention relates to an A/D conversion circuit used in a maximum/minimum detection circuit for quickly detecting minute fluctuations in the maximum or minimum value of a monotonically changing analog signal input.

[Technical Background of the Invention] This type of conventional maximum/minimum detection circuit was constructed as shown in FIG. In other words, 11 is an analog signal input A/D (analog/digital)
It is an A/D converter that performs conversion, and its digital data output is guided to the register 12 and becomes one input A of the comparator 13. The other input B of this comparator 13 is the register 1
2 data is led, and comparator 13 inputs A
>When it is determined that the input is B, a comparison output pulse is generated and used as one input of the AND gate 14. As the other input of this AND gate 14, the A/D
An EDC pulse is led from the converter 11 every time an A/D conversion operation is completed, and the AND gate 14 generates a pulse output CP when both inputs have pulse inputs. The register 12 stores the digital data from the A/D converter 11 as update data when the pulse output CP from the AND gate 14 is input, and the alarm device 15 issues an alarm every time the data in the register 12 is updated. is starting to occur.

Therefore, in the maximum/minimum detection circuit described above, when the analog signal input level becomes larger than the past maximum value, the comparator 13 detects the input A>
The input B is determined, and the data stored in the register 12 (the maximum value in the past) is stored in the A/D converter 1 at this time.
The alarm device 1 is updated to the digital data from 1.
An alarm is generated from 5. Note that the comparator 13
If the judgment condition is input A < input B, then the digital data of the minimum value of the analog signal input is in register 1.
It will be stored in 2.

That is, according to the maximum/minimum detection circuit described above,
An alarm can be generated by quickly detecting minute fluctuations in the maximum or minimum value of an analog signal that monotonically increases or decreases.

[Problems with Background Art] Incidentally, since the digital data output of the A/D converter 11 includes errors, it is not possible to accurately detect the maximum value or minimum value of the analog signal input. Here, the error of the A/D converter 11 will be considered. The error included in the A/D conversion output can be considered to be due to the error in the analog reference value A _REF , which is a reference for measuring the analog input amount in the A/D converter 11. That is,
If the digital value of the A/D conversion output includes a nonlinear error of ±1/2 LSB (least weight bit) in addition to the quantization error, the A/D conversion characteristics shown in Figure 2 on the analog axis The analog input _Aio , which should be a fixed value (absolute value), appears to vary between points A←→B. This is because the analog reference voltage includes an error, and the true value is measured using the reference voltage A _REF including this error as a reference. For example, in the case of an error in the analog reference voltage with respect to the digital output value, if the error of the A/D converter 11 excluding the quantization error is zero, then the value of the analog reference voltage is A _{REF1 (V).} A _REF1 = A _io + b...(1). On the other hand, the analog reference voltage of the A/D converter 11 containing an error in the analog reference voltage is
If A _REF2(V) , then A _REF2 = A _io + a (2). Therefore, the error ΔA _io becomes ΔA _io =|A _REF1 −A _REF2 |=|b−a| (3) from equations (1) and (2).

To illustrate the relationship between equations (1), (2), and (3) above, the third
As shown in the figure, it can be seen that the digital conversion value for the same analog input amount A _io differs depending on the value of the analog reference voltage. In other words, when the error in the reference voltage is zero, the digital value for the analog input _Aio is N-2 (N is an integer).
When there is an error ΔA _io in the reference voltage, the digital value becomes N-1 with respect to the analog input A _io .

[Object of the invention] The present invention has been made in view of the above circumstances, and
The present invention provides an A/D conversion circuit that is suitable for accurately detecting the maximum value or minimum value of an analog signal input and is capable of obtaining a highly accurate A/D conversion output.

[Summary of the invention] That is, the A/D conversion circuit of the present invention
The first input to the converter is an analog signal input, and the second input is the output of the differential amplifier. Then, the A/D conversion output data N at the first input of the A/D converter is stored, and this data N is input to the upper digit side of a D/A converter having a higher resolution than the A/D converter. The output of this D/A converter and the analog signal input at this time are guided to the differential amplifier. The digital value of the analog signal input is determined by a predetermined calculation of the A/D conversion output data M at the second input of the A/D converter and the stored data N.

Therefore, by finding the difference between the highly accurate feedback signal from the D/A converter and the analog signal input, it is possible to make the error in the analog reference voltage in the A/D converter as close to zero as possible, and the analog signal input A digital value close to the true value of is found.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 4, 20 is an input terminal to which an analog signal input is guided, and 21 is an input terminal for guiding the analog signal input to the input terminal of the A/D converter 22 or one input terminal (+) of the differential amplifier 23. 1 switching circuit, 24 is a second switching circuit for guiding the output of the D/A converter 25 to the other input terminal (-) of the differential amplifier 23, and the output of the differential amplifier 23 is connected to the It is led to the input end of the A/D converter 22. Reference numeral 26 denotes a control calculation circuit to which the output of the A/D converter 22 is input, which supplies a predetermined switching control signal to the first and second switching circuits 21 and 24, and stores and calculates input values. , perform comparison judgment, hold maximum or minimum value,
It provides a high-resolution digital input to the D/A converter 25 and provides an alarm signal to the alarm device 27.

Note that the A/D converter 22 has an n-bit, for example, 8-bit output, and has an analog reference voltage A _REF
is, for example, 5.12V, and the nonlinear error (absolute error) is, for example, ±LSB. Therefore, the maximum value max of the analog reference voltage error ΔA _io is calculated from the previous equation (3) as ΔA _{io nax} = |b− a| = 5120mV/2 ⁸ × {1LSB (quantization noise) + 1LSB (absolute error)} = 5120mV/256 × 2LSB = 40mV (4). Further, the D/A converter 25 has a higher resolution than the A/D converter 22, for example, 16
It has a bit resolution and has an error of ±1/2 LSB.

Next, the operation of FIG. 4 with the above configuration will be explained. Initially, the control calculation circuit 25 inputs the analog signal input directly to the A/D converter 22, and the D/A
The operating states of the first and second switching circuits 21 and 24 are controlled so that the output of the converter 25 is not input to the differential amplifier 23, and the output of the A/D converter 22 at this time (its digital value is ) is memorized. In this case, the analog reference voltage ΔA _io in the A/D converter 22 is 40 mv as shown in the previous equation (4).
Next, the control calculation circuit 26 inputs the analog signal input to the differential amplifier 23 and also inputs the analog signal input to the D/A converter 2.
The operating states of the first and second switching circuits 21 and 24 are controlled so that the output signal of No. 5 is not input to the differential amplifier 23, and the data (digital value N) stored as described above is set as the upper 8 bits. 16-bit digital data is generated by adding "0" to the lower 8 bits and output to the D/A converter 25. At this time, the differential amplifier 23 calculates the difference (1 LSB of the A/D converter 22) between the high precision analog signal output of the D/A converter 25 and the analog signal input of the signal input terminal 20.
) and amplify this difference by a factor of ²⁸ . Therefore, the output of the A/D converter 22 obtained at this time (the digital value thereof is assumed to be M)
is the error ΔA _{io nax} of the reference voltage of the A/D converter 22 determined with 16-bit resolution.
Then, the control calculation circuit 26 reads the input data at this time and performs the calculation of N×2 ⁸ +M . . . (5) using the above-mentioned stored data. The digital value that is the result of this calculation is the error ΔA _{io nax} of the analog reference voltage in (4) above.
It corresponds to the A/D conversion output obtained when approaching ΔA _{io nax} = 40 mV → 40 mV / 2 ⁸ = 156 μV (6), in other words, A with 16-bit resolution and nonlinear error of ±1/2LSB. It corresponds to the output of a /D converter and is highly accurate.

Further, the control calculation circuit 26 controls the A/D conversion operation to be repeated twice as described above, and receives the calculation result data every time the calculation (N×2 ⁸ +M) of the above equation (5) is completed. is larger than, for example, past maximum value data (already detected and held), and if it is, the maximum value data is updated and held with the calculation result data obtained this time, and an alarm signal is sent. is output to the alarm device 27.
As a result, an alarm is generated every time the maximum value is updated.

According to the A/D conversion circuit as described above, the D/D
Since the A converter 25 performs high-precision feedback and calculates the difference with the analog signal input,
The error in the analog reference voltage in the A/D converter 22 can be made as close to zero as possible, and a digital value corresponding to the analog signal input close to the true value can be obtained. Therefore, even if an inexpensive A/D converter 22 with low resolution is used, the maximum value or minimum value can be detected accurately.

Note that the alarm device 27 is omitted when there is no need to generate an alarm.

[Effects of the Invention] As described above, the A/D conversion circuit of the present invention can accurately detect the maximum value or minimum value of an analog signal input, and is suitable for use in various measurement fields.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional maximum/minimum detection circuit, Figs. 2 and 3 are characteristic diagrams shown to explain the operation of the A/D converter shown in Fig. 1, and Fig. 4 is a block diagram showing a conventional maximum/minimum detection circuit. FIG. 2 is a block diagram showing one embodiment of such an A/D conversion circuit. 21, 24...Switching circuit, 22...A/D converter,
23...Differential amplifier, 25...D/A converter, 26...
Control calculation circuit.

Claims (1)

[Claims] 1 n-bit A/D converter and m-bit (m>n) D/D converter with higher resolution than this A/D converter.
an A converter, a switching control means for controlling switching of an input signal to the A/D converter, and an A converter when an analog signal input is led to the A/D converter as a first input by the means; /D conversion output data N
storage means for storing the above data N, means for similarly providing the data N as an input on the upper digit side of the D/A converter, and means for providing data of a predetermined value on the input on the lower digit side thereof; and an analogue of the D/A converter. a differential amplifier that takes the difference between a signal output and an analog signal input and amplifies it by a predetermined time; and an output signal of this differential amplifier is guided as a second input to the A/D converter by the switching control means. an A/D conversion circuit comprising: arithmetic means for performing an arithmetic operation of (N×2 ⁿ +M) using A/D conversion output data M at the time and data N stored in the storage means.