JPH0733033U - A / D converter - Google Patents

Abstract

(57) [Summary] [Structure] One channel of the channel selection unit 2 is grounded as a discharge channel, and the discharge channel is selected and A / D conversion is performed on another channel before A / D conversion. The capacitor 4 is discharged. [Effect] The disconnection on the input side of the A / D converter can be easily determined. Therefore, it is possible to easily avoid an erroneous conversion in which the voltage of the channel before switching is A / D converted and output as it is, despite the disconnection on the input side. Moreover, since the discharge circuit of the sample and hold unit is configured using the existing channel selection unit, the configuration is simple and the cost is low.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an A / D converter incorporated in a microcomputer that is widely used for converting an analog signal into a digital signal in various control circuits and diagnostic circuits, and more specifically, a disconnection on the input side thereof. The present invention relates to an A / D converter that is improved by preventing erroneous conversion due to the above and making an abnormality judgment.

[0002]

[Prior art]

 Generally, in this type of A / D converter, a channel selection unit and a sample and hold unit are connected to the input side of the conversion unit to enable selective connection of the input system and hold the input value for a certain period of time. By doing so, conversion time is earned. FIG. 2 is a block conceptual diagram showing a main part of this conventional A / D converter. In the figure, 101 is an A / D conversion unit, and a channel selection unit 102 and a sample hold unit 103 are connected to this input side. As a concrete circuit of each of these parts, a known circuit is appropriately used, and an A / D converter is constituted by them. The sample / hold unit 103 is basically composed of a capacitor 104 and a switching element 105.

[0003]

[Problems to be solved by the device]

 By the way, since the conventional A / D converter built in the microcomputer does not have a switch for discharging, if a disconnection occurs at the input section, the voltage of the channel before switching that was connected up to that point Remains charged in the capacitor 104 of the sample and hold unit 103. Therefore, the residual voltage of the capacitor 104 is A / D converted and output as an incorrect conversion value, which is extremely dangerous depending on the application. As a countermeasure, it may be possible to add a switch circuit for discharging to the outside, but this also increases the cost. The present invention has been made in view of the above circumstances. The purpose of the present invention is to eliminate the drawbacks of the prior art, avoid the erroneous conversion caused by the disconnection on the input side, and An object of the present invention is to provide an A / D converter having a solution that can be determined by a simple structure and is inexpensive.

[0004]

[Means for Solving the Problems]

 The present invention comprises an A / D conversion unit, a channel selection unit connected to the A / D conversion unit, and a sample and hold unit. In the A / D converter incorporated in the microcomputer, one of the channel selection units is provided. One of the channels is grounded as a discharge channel, and the discharge channel is selected to discharge the sample / hold unit before A / D conversion in another channel.

[0005]

[Action]

 According to the present invention, the conversion in each channel is performed immediately after the conversion, by selecting the discharge channel and discharging the sample and hold unit once. If judged, the disconnection on the input side can be easily found.

[0006]

【Example】

 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block conceptual diagram showing a main part of an A / D converter of the present invention. In the figure, 1 is an A / D conversion unit, 2 is a channel selection unit, 3 is a sample and hold unit, and this A / D converter is constituted by these as in the conventional case. Similarly, the sample and hold unit 3 is basically composed of the capacitor 4 and the switching element 5. One feature of the present invention is that one channel of the channel selection unit 2 is grounded as a discharge channel, and this A / D conversion channel is selected before the A / D conversion in the other channel to select the sample / hold unit 3. The point is to discharge the capacitor 4. In this embodiment, the Nch of the channel selection unit 2 is selected as a discharge channel and is grounded.

However, in a normal conversion operation, an analog signal is input through the channel selected by the channel selection unit 2, sampled by the sample and hold unit 3, and then converted by the A / D conversion unit 1. Is converted into a digital signal by. In this case, each time channel switching is performed in the channel selection unit 2, the channel is connected to the Nch once selected as the discharge channel. Therefore, this causes the capacitor 4 of the sample and hold unit 3 to be discharged.

When the input voltage after the channel switching operation is performed and the discharge is performed in this way is less than or equal to a preset set value, it is determined that a disconnection occurs on the input side, and if necessary, it is determined. An alarm is issued and the operation is stopped. As a result, it is possible to avoid the erroneous conversion in which the voltage of the channel before switching is A / D converted and output as it is, even though the input side is disconnected as in the conventional case.

[0009]

[Effect of device]

 As described above, the present invention can obtain the following effects based on the configuration. (1) A disconnection on the input side of the A / D converter can be easily determined. (2) Therefore, it is possible to easily avoid the erroneous conversion in which the voltage of the channel before switching is A / D converted and output as it is, despite the disconnection on the input side as in the conventional case. (3) Moreover, since the discharge circuit of the sample and hold unit is configured by using the existing channel selection unit, the configuration is simple and the cost is low.

[Brief description of drawings]

FIG. 1 is a block conceptual diagram showing a main part of an A / D converter of the present invention.

FIG. 2 is a block conceptual diagram showing a main part of a conventional A / D converter.

[Explanation of symbols]

 1 ... A / D converter 2 ... Channel selection unit 3 ... Sample and hold unit 4 ... Capacitor 5 ... Switching element

Claims (1)

[Scope of utility model registration request] 1. An A / D converter built in a microcomputer, comprising an A / D conversion unit, a channel selection unit connected to the A / D conversion unit, and a sample and hold unit. An A / D converter characterized in that one channel is grounded as a discharge channel and the sample / hold unit is discharged by selecting the discharge channel before A / D conversion in another channel.