JPS58191523A - Drift correcting device - Google Patents

Abstract

PURPOSE:To obtain a digital data with high accuracy where both of the drift and the offset are corrected, by correcting an error due to the offset of an AD converter. CONSTITUTION:A control section 9 performs the operation subtracting only the drift from an AD converting data of an analog input signal 1, by setting on or off a control switch 22. Then, the input signal is taken to 0V accurately and the control section 9 subtracts the drift from the AD-converted data and gives the result to a data bus 12. The data given to the data bus 12 is a data representing the offset value. The data of the offset value is set to an offset correcting switch 18. The control switch 22 is changed over so as to form the logic by which the control section 9 corrects both of the drift and offset. Thus, the digital data with high accuracy correcting both of the drift and the offset is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an analog signal drift correction device for an AD converter in a measuring instrument or an electronic computer.

Figure 1 is a block diagram showing a conventional AD conversion device.
In the figure, (1ν is the analog input signal, 12) is the analog input signal ground, (3: and (41 is the 70-ting ground, (51 is the analog data multiplexer,
(61 is a digital analog data multiplexer (5 is an amplifier that amplifies the selected analog signal, (7 is an amplifier that amplifies the selected analog signal.
) is an AD converter that AD converts the output of the amplifier (6), (
81 is a data bus that transmits the digital signal output from the ADf converter; (9) is a control unit that processes AD-converted digital data and controls the AD conversion device;
1 and ttnh analog data multiplexer (
Control signal line (2) for control section (5) is a data bus that transmits the output of the control section (9) to the next stage.

Note that several analog input signals are connected to the analog data multiplexer (5), and one of them is selected and AD converted. ) is shown.

Next, the drift of the AD converter will be explained. Drift occurs in the amplifier (6) and AD converter (7) over time and due to changes in temperature. Fig. 2 is a diagram showing the aspect of drift in the AD conversion device. In the figure, the horizontal axis represents the input signal (1), the vertical axis represents the output signal 131, and αQ and αQ have no drift. (171 is the amount of drift at input 0. If there is such a drift, the human input signal (drift is added to 11 and amplified). AD'& is replaced so AD
The digital output of the converter (7) contains the drift amount as is.
It will be a mistake. Therefore, there is a need to correct this drift in some way.

Conventionally, this drift was corrected as follows. That is, assuming that the characteristics of the amplifier 16) and the AD converter (71) are linear, in other words, the characteristic curve (g) and α→ in FIG. If the characteristic curve α → is shifted in parallel, the amount of drift is always constant regardless of the magnitude of the analog input signal, and the amount of drift when the analog input signal is 0 (equal to 171) Therefore, by calculating Doria) lft (lη when the input is 0) and subtracting this value from the value of the AD-converted output, the output after AD conversion with the drift corrected is obtained.Therefore, the drift when the input is 0 To obtain , short-circuit the input of the analog data multiplexer (5), set the analog input to 0, and then set the amplifier (6) and AD converter (
7) is obtained and subtracted from this value t-AD& converted data to obtain digital data after drift correction. Such drift correction calculations are performed by the control section (9), and the digital data resulting from the drift correction is output to the data bus Mio.

Drift correction of analog signals in conventional AD converters has been performed as described above, but there have been drawbacks as described below. In other words, if the input of the analog data e multiplexer (51) is short-circuited in order to perform drift correction, the analog input signal fi+ is thought to be 0, but in reality, the analog data multiplexer (5) has an L leakage current. Also, since the impedance of an analog switch is not 0, even if the input is shorted, the input will not strictly be 0 but will have a certain value.Furthermore, between ground (2) and floating ground 121 and +31. Therefore, even if the input of the analog data multiplexer is shorted, it will not be exactly equivalent to the input signal 0, but will be equivalent to the value difference between the input signal 0 and the input signal 0. This difference is called an offset, but the offset value is constant as long as the conditions of the analog input section are constant.With conventional AD converters, even if drift correction is performed, this offset cannot be corrected, so the offset value is There is a drawback that high-precision AD conversion cannot be performed because an offset is added.

This invention was made to eliminate the drawbacks of the conventional drift correction method as described above, and an object of the present invention is to correct errors caused by offset in an AD conversion device and provide a highly accurate analog drift correction device. It is something.

FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, (11 to (6) are the same or equivalent to the same reference numerals in FIG. 1. QgJ is an offset correction data setting switch, II is a floating ground, ■ is a data bus that transmits the output of the offset correction data setting switch US+ to the control unit (9), (2 is a data bus (20)
) Pull-up resistor for t pull-up, (22)
is an external control switch for switching the drift calculation method of the control section (9), (23) tj: ground for the external control switch (22), (24) is for input to the control section (2) This is a pull-up resistor.

Next, the operation of this invention will be explained. First, the control switch (22) is set to fully on or off, and the logic of the control section (9) is operated to subtract only the drift amount from the ADK conversion data of the analog input signal (1), similar to the conventional drift correction operation. Make sure to do the following.

Next, the analog input signal (1) is completely set as Ov, and the controller (51) subtracts the drift amount from the AD-converted data and sends it to the data bus (6). The data sent to the data bus 02 at this time is data indicating the offset value. This offset value data is set to an offset correction data switch (1 second).Next, the control switch (22) is switched to enable the control section (9) to correct both drift and offset.

The controller (9) then has a connection that corrects both drift and offset. In this state, if the input of the analog data multiplexer (5) is opened and the analog signal to be AD converted is input to the analog input signal (1), the output of the control section (9) will be free of both drift and offset. It becomes corrected digital data.

In the above embodiment, the offset correction data switch (181) is used, but if a memory circuit for storing the offset value is provided inside the control unit +91, the offset correction data switch (181) is not necessary.

FIG. 4 is a block diagram showing another embodiment of the present invention, and in the figure (11-(2), 081-(21)
#'i Indicates the same reference numeral or equivalent as in FIG. 3. (2
5) is a DA converter for DA converting the digital data for offset correction transmitted through the data bus (2) and sending it to the differential amplifier (26)K. (26) is a differential amplifier for offset correction. Next, to explain its operation, the offset value is calculated in the same way as in the case of Fig. 3, but the digital data of the offset value is sent to the AD converter (2
5), the analog data is input to the negative side of the differential amplifier (26), and offset correction is performed at the analog data stage. In FIG. 4, a differential amplifier (26) is used to correct the offset value, but any circuit that can subtract the offset value may be used.

As explained above, in the present invention, the AI) conversion device can correct the offset value e[, which cannot be corrected by the conventional drift correction device, so that it has the advantage of being able to perform AD conversion with high accuracy.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional AD conversion device including drift correction, Fig. 2 is an explanatory diagram showing aspects of drift, and Fig. 3
The figure is a block diagram showing one embodiment of the invention, and FIG. 4 is a block diagram showing another embodiment of the invention. In the figure, (6) and (26) are amplifiers, and (7) is A
A D converter, (91 is a control unit, A-level is an offset correction data switch, and (25) is an i) A converter. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Shin Kuzuno - -11:

Claims (1)

[Claims] An amplifier that amplifies an analog signal, an AD converter that converts the amplified analog signal into digital data, a control unit that performs predetermined data processing on the output of this AD converter, and the input of the amplifier are short-circuited. means for performing drift correction in the control section by using the output value of the AD converter as a drift value;
Output of the converter it - Means for setting so that this offset value can be given to the control section as an offset value, and drift correction in the control section. and means for controlling said switching.