JPS5875323A - Analog-digital converter - Google Patents

Abstract

PURPOSE:To perform a conversion with the accuracy higher than the resolution, by varying the period of a sawtooth wave signal with the program signal fed from a microcomputer system. CONSTITUTION:The synchronizing signal fed from a microcomputer system MSC is applied to a sawtooth wave oscillator STW, and the oscillating output of the sawtooth wave signal synchronizing with the synchronizing signal is led into an adder ADD to be added with the analog input signal fed from a terminal TA. As a result, the period of the sawtooth wave signal can coincide with the time required for the conversion of an analog-digital converter ADC. Thus a conversion is possible with the accuracy higher than the resolution of the converter ADC, and furthermore, the converting accuracy higher than the resolution and the time required for the conversion can be changed optionally.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides analog digital f:#l! It is related to the device.

For example, in a measuring instrument using a microcomputer, the detection output of a sensor is generally an analog signal, so this detection signal must be converted into a digital signal by an analog-to-digital converter and then introduced into the micro combi coater.

An analog-to-digital converter has a resolution that corresponds to its configuration, and it is impossible to perform fine digital conversion beyond this resolution. Therefore, when a high degree of conversion accuracy is required, a high-resolution analog-to-digital converter is used. It is necessary to use a container. However, an analog-to-digital converter with high resolution requires a long conversion time and a complicated structure, which makes it more expensive.

The present invention provides an analog-to-digital converter that can perform conversion more finely than the resolution of an analog-to-digital converter by adding a simple device, and can arbitrarily change the conversion accuracy higher than this resolution and the time required for conversion. The purpose is to realize this.

FIG. 1 is a block diagram showing one embodiment of the present invention.
A is an analog signal input terminal, ADD is an adder, STW is a sawtooth wave oscillator, ADc is an analog-to-digital converter, and MC8 is a microcomputer system. Below, as an analog-to-digital converter ADO, the input voltage dynamic range is 0 to IOV and the digital output is 1.
A case will be explained in which a digital output with a resolution of 16 bits is obtained using a zero and one point analog-to-digital converter.

In the analog-to-digital converter ADc, when the analog input changes by 10V + 2'' = i9.77mV, the lowest digit of the digital output changes by 1, and the range of change in the analog input is within 9.77mV. In Figure 2 (the horizontal axis is time t5 and the vertical axis is voltage RIV), the upper and lower dotted lines indicate the changing points of the digital output, and the voltage difference between the upper and lower changing points is 9.77 mV. If the digital output is a when the magnitude of the analog input signal is between these upper and lower change points, then the analog input is within the range of 9.77 mV above the change point indicated by the upper dotted line. a+ if it is within
1 (this 1 is the 1 in the least significant digit of the digital output)
And the same applies hereafter. ), and when the analog input is within a range of 9.77 mV below the change point indicated by the lower dotted line, the digital output is a-1.

To convert such a 10-pit digital output to a 16-bit digital output, the maximum value of 16 bits is 64 times the maximum value of 10 pits (2''-" = 64).
Therefore, if the analog input changes by 9.77 mV ÷ 64 0.153 mV, the least significant digit of the 16-bit digital value will change by 1. Microcomputer system MS in the figure
A synchronizing signal as shown in FIG. 3 (horizontal and vertical axes are the same as in FIG. 2) is added to the sawtooth wave oscillator STW from C to oscillation output synchronized with this synchronizing signal, that is, as shown in FIG. 4 (horizontal and vertical axes are the same as in FIG. The peak value is 9.77 m as shown in (the vertical axis is the same as in Figure 2)
When a sawtooth wave signal of V is oscillated and this oscillation output is introduced into the adder ADD and added to the analog input signal axis → + from the terminal TA, the Kerr output is The waveform is shown in (same as the figure). Note that the period of the sawtooth Q wave signal shown in FIG.
DCt is made to match the time required to perform 2''+210=64 (times) conversions. Addition 5AD
When the addition output of D is introduced into an analog-to-digital converter ADO and sequentially converted 64 times, its digital outputs become a and a+1. In other words, the addition output shown in Fig. 5 is 9.77 m below the change point indicated by the dotted line in the center.
While it is within the width range of V, the digital output is a, and when the addition output is within the range of 9.77rnV above the center change point, the digital output becomes a+1, and the number of outputs of a is, for example, 26 times, the number of outputs of a+1 is 38
It will be times.

When these 64 digital values are taken into the microcomputer system MO8 and added, the result is 26a + 38 (
a+I)=64a+38.

Next, the analog input signal changes from the magnitude shown in the fifth diagram to 0, I5
Assuming that it increases (or decreases) by 3 mV, the number of times that the digital output of the analog-to-digital converter ADO becomes a is 25 (or 27), and the number of times that it becomes a +1 is 39 (or 37), and the microcomputer system MOB The calculation result at I is 25a +3
9 (a+1) ==64a +39 or 27a +37 (a+1) =64a +37.

Furthermore, each time the analog input signal increases by 0.153 mV, the calculation result is 64a + 40.64a + 41,
... = 64a +63.64a +64, and each time the analog input signal decreases by 0.153mV, the calculation result is 64a +36.64a +35, ...
...64a+1.64a10.

That is, the microcomputer system MO8 responds to changes in the analog input signal by 0.153+nV. The result of the arithmetic processing is a value that changes by 1 between um and a+I in 64 equal divisions, which means that the 10-bit digital output of the analog-to-digital converter ADC has been converted into a 16-bit digital value. .

The above explanation deals with the case where the period of the sawtooth signal is held constant, but for example, an analog input signal ゛゛ that does not require high conversion accuracy but requires a high conversion speed, and a slow conversion speed is acceptable. When an analog input signal that requires high conversion accuracy is applied to the alternating adder ADD, the oscillation period of the sawtooth oscillator STW can be changed by changing the oscillation period of the sawtooth oscillator STW to the microcomputer system M.
The program signal 1 from Cs causes the change, and when conversion accuracy is required, the period of the sawtooth signal is lengthened.
When high conversion speed is required, analog-to-digital conversion can be achieved by shortening the period of the sawtooth wave signal, interrupting the oscillation of the sawtooth wave oscillator STW, or cutting off the introduction of the sawtooth wave signal to the adder ADD. By controlling the conversion characteristics of the converter ADO, a digital output corresponding to an analog input signal can be obtained.

Separate methane and non-methane hydrocarbons in the atmosphere, e.g. by chromatography or by using a flame ionization detector
Therefore, when each concentration of methane and non-methane hydrocarbons is detected alternately, the time width of the methane concentration signal is generally 1Z40 seconds and is relatively short when converting each detected concentration signal into a digital value. short, non-methane hydrocarbon, tj
The time width of the h-degree signal is approximately 4 minutes, which is relatively long, and conversion accuracy is required. Therefore, when using the device of the present invention as a conversion device, it is necessary to shorten the period of the sawtooth signal when converting methane and seismic intensity signals. , the introduction of the sawtooth wave signal to the adder ADD is stopped to increase the conversion speed, and when converting the non-methane hydrocarbon temperature signal, the period of the sawtooth wave signal is lengthened to increase the conversion accuracy, making it more efficient. Digital conversion can be performed.

Although the above example illustrates the case where a sawtooth wave signal is added to an analog input signal, the present invention can also be implemented even when a triangular wave signal is added, and an analog-to-digital converter with a different dynamic range from that described above can be used. Of course, the present invention can also be practiced when the digital output signal has a code structure other than a binary code, such as a binary coded decimal code.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
Figures 5 through 5 are waveform diagrams for explaining the operation.
A: Analog signal input terminal, ADDn〃O device, STW
: saw 9-wave oscillator, ADO: analog-to-digital converter, M(W: microcomputer system).

Claims (1)

[Claims] an adder introduced for the analog input signal to be converted and the oscillation output signal of the sawtooth wave or triangular wave oscillator; an analog-to-digital converter to which the output of the adder is added; An analog-to-digital converter comprising: a microcomputer system that classifies and adds the digital values converted and identified in the analog-to-digital converter, and sends a control signal for the oscillation cycle of the sawtooth wave or triangular wave oscillator.