JP2949940B2 - Self-diagnosis device for D / A converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved self-diagnosis device for a digital / analog (D / A) converter.

[0002]

2. Description of the Related Art A D / A converter is a circuit widely used in various electric appliances, and requires a device for diagnosing whether or not its function is operating normally.

Conventionally, a self-diagnosis device of a D / A converter for performing such a diagnosis is disclosed in Japanese Patent Application Laid-Open No. 58-154528.
There was a thing disclosed in the issue.

FIG. 11 shows a self-diagnosis device having a configuration similar to that disclosed in this document.
The D / A converter self-diagnosis apparatus shown in FIG. 1 provides a D / A converter (hereinafter abbreviated as DAC) 10 to be diagnosed with a command value via a data bus 12 to a CPU 14.
And a reference voltage circuit 16 for generating two kinds of reference voltages
A comparator 18 that compares the output of the DAC 10 when a command value is given from the CPU 14 to the DAC 10 with a reference voltage output from the reference voltage circuit 16, and a parallel input / output circuit that inputs the output of the comparator 18 to the CPU 14 ( Hereinafter, abbreviated as PIO) 20 and a memory 22 for storing programs, data, and the like necessary for the operation of the CPU 14.
And is composed of

In an apparatus having such a configuration, FIG.
The self-diagnosis of the DAC 10 is performed by the operation shown in FIG. First, the CPU 14
Is given a predetermined command value. This command value is such that the output voltage becomes v ₀ when the DAC 10 is functioning normally. On the other hand, the reference voltage supplied from the reference voltage circuit 16 to the comparator 18 is v ₁ and v _2. The reference voltage v ₁ is treated as an upper limit and v ₂ is treated as a lower limit. That is, the output voltage of the DAC 10
_When it is ₀ and smaller than the reference voltage v _{1 and} larger than v ₂ , the DAC 10 can be regarded as functioning normally. At this time, the comparator 18 outputs a voltage value indicating normality, for example, 5 in FIG.
Output V. Conversely, if the output voltage of the DAC _{10 is} higher than the reference voltage v ₁ or lower than v ₂ , D
AC10 can be considered abnormal and comparator 18 outputs 0V. The CPU 14 fetches the comparison result from the comparator 18 via the PIO 20, and determines whether the DAC 10 is functioning normally based on the fetched result.

As described above, conventionally, whether the operation of the DAC 10 is normal or not is determined by the reference voltages v ₁ and v
Diagnosis was possible by comparison with ₂ .

[0007]

However, in the conventional self-diagnosis apparatus having such a configuration, the number of diagnosis points is limited to one, and for example, linearity diagnosis when the DAC is operated in a full range is performed. Can not. For example, when the DAC has a non-linear output characteristic as shown in FIG. 14, it is diagnosed that the diagnosis point A is functioning perfectly, but the data values 000H and A deviation from linearity near FFFH cannot be detected. However, FIG.
Assumes a 12-bit DAC.

As described above, conventionally, there has been a problem that the diagnostic points of the DAC are limited and linearity diagnosis cannot be performed. When linearity diagnosis is to be performed by applying a conventional device, a large number of reference voltages to be compared with the DAC output must be generated, and the circuit configuration must be complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has a simple circuit configuration.
It is an object of the present invention to provide a DAC self-diagnosis device capable of performing C linearity diagnosis.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides command means for giving a step-like output command value simulating a straight line having a constant gradient to a DAC, and smoothing the output of the DAC. Output smoothing means.
The stepped output that is output when the above stepped output command value is given to AC and the DAC is operating normally.
And a differentiating means for differentiating the output of the smoothing means and outputting the signal. The stepping output command value is given from the command means to the DAC. And when the DAC is operating normally, a differentiating means for outputting a DC value is compared with the vertical variation appearing in the output of the differentiating means to determine whether the variation is within a predetermined range, and a determination result is output. It is characterized by comprising comparison means, and diagnosis means for diagnosing whether the operation of the DAC is normal based on the output of the comparison means.

[0011]

In the present invention, a step-like output command value is given to the DAC. Then, the output of the DAC becomes a step-like output corresponding to the step-like output command value. The DAC output in a stepped form is smoothed by the smoothing means and further differentiated by the differentiating means. Then, if the output characteristics of the DAC are high in linearity, the output of the differentiating means is substantially a DC value. Conversely, if the linearity is low, the output of the differentiating means includes a relatively large vertical fluctuation. The output of the differentiating means is used by the comparing means to determine whether or not it belongs to a predetermined range, and the diagnosis means diagnoses the operation of the DAC based on the output of the comparing means. Therefore, if the vertical fluctuation of the output of the differentiating means is not large and does not belong to the predetermined range, it can be considered that the linearity of the output characteristic of the DAC is low, whereby the self-diagnosis regarding the linearity of the DAC is realized. Become.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. Note that the same components as those of the conventional example shown in FIGS. 11 to 14 are denoted by the same reference numerals, and description thereof is omitted.

FIG. 1 shows a DAC according to an embodiment of the present invention.
1 shows the configuration of the self-diagnosis device. The device shown in this figure is different from the conventional example shown in FIG.
Is added. The linearity diagnostic unit 24 calculates D
It has a function of receiving an analog signal output from the AC 10, performing predetermined processing, and outputting the processed signal to the comparator 18. A switch 26 is provided at a stage preceding the linearity diagnostic unit 24. The switch 26 supplies the output of the DAC 10 to the linearity diagnostic unit 24 or the output of the comparator 18.
This is a switch to switch between supplying directly to the device.

The linearity diagnostic section 24 includes a filter 28 and a differentiating circuit 30. The filter 28 smoothes the analog signal supplied from the DAC 10 via the switch 26 and supplies the analog signal to the differentiating circuit 30. Differentiating circuit 30
Supplies the output of the filter 28 to the comparator 18 after differentiation. When the switch 26 is switched to the side of the linearity diagnostic unit 24, the comparator 18 outputs the output of the linearity diagnostic unit 24 to the reference voltage v from the reference voltage circuit 16.
₁ and v _2, and the comparison result is provided to the CPU 14 via the PIO 20.

Next, the operation of this embodiment will be described with reference to the drawings. First, when the DAC 10 operates normally, that is, when the linearity of the DAC 10 is well maintained, the operation as shown in FIGS. 2 to 5 is performed.

FIG. 2 shows a voltage output from the DAC 10 in accordance with a step-like command value supplied from the CPU 14 to the DAC 10 via the data bus 12. In this figure, t ₁ is the repetition period of the output command value from the CPU 14,
v ₃ is a full-scale output of DAC10. In the case of this embodiment, the output command value given from the CPU 14 to the DAC 10 changes stepwise with the minimum variable unit (1 LSB) as one step.

The output of the DAC 10 is supplied to a filter 28 when the switch 26 is switched to the linearity diagnostic section 24. The filter 28 smoothes the output of the DAC 10 as shown in FIG. 2 to form a sawtooth waveform as shown in FIG. The output of the filter 28 is differentiator 3
Since it is differentiated by 0, as shown in FIG. 4, the voltage applied from the differentiating circuit 30 to the comparator 18 becomes a DC value v ₄ except for falling in a pulse shape at time nt ₁ (n = integer). .

On the other hand, the comparator 18 is supplied with reference voltages v ₁ and v ₂ as shown in FIG. Comparator 18 determines whether falling within the scope which is defined an output voltage of the differentiation circuit 30 with a reference voltage v1 and v _2, the voltage by the upper limit value v ₁ and v _2. The comparator 18 supplies 5 V to the PIO 20 when it belongs, and 0 V when it does not. Therefore, when the output voltage of the differentiating circuit 30 as shown in FIG. 4 is obtained, the output voltage of the comparator 18 is substantially constant at 5 V as shown in FIG.

Therefore, the CPU 14 can diagnose that the DAC 10 is functioning with good linearity based on the information obtained through the PIO 20. That is, time nt
If the DC value is other than ₁ , it can be diagnosed that the linearity of the DAC 10 is well maintained within a predetermined accuracy.

Next, a case where an abnormality occurs in the linearity of the DAC 10 will be described.

As shown in FIG. 6, the CPU 14
Despite giving a stepped command value to C10, DA
When a part of the output waveform of C10 does not have a step shape (when a defect is generated), the output of the filter 28 that smoothes the output waveform from time t _{a to} t t as shown in FIG.
a waveform different 3 in _b. When this was further supplied to the differentiation circuit 30 performs a differential, at time t _a ~t _b, a higher or a reference voltage v voltage value lower than ₂ than the reference voltage v _1.

In this embodiment, the comparator 18 compares the output of the differentiating circuit 30 with the reference voltages v ₁ and v ₂ from the reference voltage circuit 16 to determine whether or not the output falls within the aforementioned range. As a result, the output of the comparator 18 at time _t a ~t _b becomes 0V, CPU 14 is P
The linearity abnormality of the DAC 10 is known via the IO 20.

Therefore, according to the present embodiment, even when the linearity of the DAC 10 is not good, the linear
By monitoring the output, the CPU 14 can be informed, and self-diagnosis relating to linearity can be performed.

In this embodiment, since the differentiation is performed, when an offset occurs in the output of the DAC 10 as shown in FIG. 10, that is, the output of the filter 28 should be like a broken line. However, in the state shown by the solid line, since the linearity exists, the output of the comparator 18 becomes 5 V and cannot be detected as abnormal. Therefore, in the present embodiment, it is possible to switch whether the output of the DAC 10 is supplied to the linearity diagnostic unit 24 or directly supplied to the comparator 18 by the switch 26. That is, when the switch 26 is tilted toward the comparator 18, the offset voltage can be detected as abnormal by the same operation as in the conventional example.

In this embodiment, the CPU 14 changes the output of the DAC 10 in the positive direction, but this may be changed in the negative direction. In this case, DAC1
The output of 0 may be inverted and then supplied to the filter 28.

[0026]

As described above, according to the present invention,
Linearity diagnosis can be performed for a predetermined range of the DAC output, for example, a full range, and such diagnosis can be realized only by adding a circuit having a simple configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a DAC self-diagnosis device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the operation of this embodiment, particularly the DAC output when the linearity of the DAC is good.

FIG. 3 is a diagram showing the operation of this embodiment, in particular, the filter output when the linearity of the DAC is good.

FIG. 4 is a diagram showing the operation of this embodiment, particularly the output of the differentiating circuit when the linearity of the DAC is good.

FIG. 5 is a diagram showing the operation of this embodiment, particularly the output of the comparator when the linearity of the DAC is good.

FIG. 6 is a diagram showing the operation of this embodiment, particularly the DAC output when the linearity of the DAC is not good.

FIG. 7 is a diagram showing the operation of this embodiment, in particular, the filter output when the linearity of the DAC is not good.

FIG. 8 is a diagram showing the operation of this embodiment, particularly the output of the differentiating circuit when the linearity of the DAC is not good.

FIG. 9 is a diagram showing the operation of this embodiment, particularly the output of the comparator when the linearity of the DAC is not good.

FIG. 10 is a diagram illustrating an offset voltage related to an output of a DAC.

FIG. 11 is a block diagram illustrating a configuration of a DAC self-diagnosis device according to a conventional example.

FIG. 12 is a diagram showing a DAC output in a conventional example.

FIG. 13 is a diagram showing a comparator output in a conventional example.

FIG. 14 is a diagram illustrating an example of output characteristics of a DAC.

[Explanation of symbols]

 Reference Signs List 10 DAC (D / A converter) 14 CPU 18 Comparator 24 Linearity diagnostic unit 28 Filter 30 Differentiator circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-19828 (JP, A) JP-A-63-258117 (JP, A) JP-A-1-240017 (JP, A) JP-A-58-1982 172560 (JP, A) JP-A-57-24121 (JP, A) JP-A-1-123530 (JP, A) JP-A-3-270414 (JP, A) JP-A-60-232721 (JP, A) JP-A-62-38618 (JP, A) JP-A-2-135923 (JP, A) JP-A-61-73069 (JP, A) Japanese Utility Model Application No. 64-44727 (JP, U) Japanese Utility Model Application No. 58-1554928 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H03M 1/00-1/88

Claims (1)

(57) [Claims] 1. Command means for giving a step-like output command value simulating a straight line having a constant gradient to a D / A converter, and smoothing means for smoothing and outputting the output of the D / A converter, , The step-like output command value is given to the D / A converter and the step-like change output when the D / A converter is operating normally is eliminated , and the change is made according to the above-mentioned straight line. A smoothing means for outputting a signal; and a differentiating means for differentiating and outputting the output of the smoothing means, wherein the step-like output command value is given from the command means to the D / A converter, and the D / A conversion is performed. When the detector is operating normally, a differentiating means that outputs a DC value is compared with a vertical-direction variation appearing in the output of the differentiating means to determine whether the variation is within a predetermined range, and a comparison result is output. Means and operation of the D / A converter based on the output of the comparing means Self-diagnosis system of the D / A converter, characterized in that it comprises a diagnostic means for diagnosing whether normal or not.