JPH07212231A - Semiconductor integrated circuit device - Google Patents

Abstract

PURPOSE:To improve the accuracy of A/D conversion by converting a reference voltage corresponding to an analog voltage concerning an A/D converter built in the semiconductor integrated circuit device. CONSTITUTION:The analog voltage to be converted is inputted from a data input VAIN and inputted to the input parts of comparators 2-5. At such a time, a CPU 18 detects the analog voltage value inputted from the data input VAIN and based on that value, data showing which of switches 13-16 is changed over are outputted to a switching register 17. These data are decided by a program previously inputted by the CPU 18 based on the detected analog voltage value. The switching register 17 can flexibly switch an intermediate reference voltage by changing over the prescribed switch corresponding to those data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an A / D converter A
The present invention relates to a / D conversion technique, and particularly to a technique effectively applied to a semiconductor integrated circuit device having an A / D converter built therein.

[0002]

2. Description of the Related Art A semiconductor integrated circuit device having a built-in A / D converter of this type, for example, as shown in a certain type of data sheet, uses a reference voltage for determining the A / D conversion dynamic range by, for example, a resistor. The voltage is divided to input from a predetermined external input pin.

The input of this reference voltage is the maximum reference voltage V
_There are a type that inputs _REFT and the minimum reference voltage V _REFB, and a type that inputs only the reference voltage V _REF .

[0004]

However, in the conventional semiconductor integrated circuit device as described above, since the input reference voltage is as small as two types, if the input value range of the analog voltage to be converted is large, it becomes 1. The decomposition performance per bit becomes large, and the conversion accuracy deteriorates.

Further, since the reference voltage is generated by dividing the voltage outside the semiconductor integrated circuit device with a resistor or the like, the reference voltage cannot be easily changed in accordance with the change of the input analog voltage.

Further, in a semiconductor integrated circuit device having one type of reference voltage input, the conversion accuracy becomes worse.

An object of the present invention is to provide a semiconductor integrated circuit device which can flexibly and easily convert a reference voltage according to an input analog voltage.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0009]

Of the inventions disclosed in the present application, a representative one will be briefly described below.
It is as follows.

That is, according to the first aspect of the present invention, an A / D converter incorporated in the semiconductor integrated circuit device is provided with an input terminal to which a reference voltage of an intermediate potential is input, and a connecting means for making an electrical connection. , Switching means for switching the connection means in response to a predetermined control signal.

Further, according to a second aspect of the invention, the switching means is provided in the A / D converter.
It is less than or equal to the number of comparators that compare the analog voltage for conversion and the reference voltage.

Further, in the invention of claim 3, the switching means is controlled by a CPU incorporated in the semiconductor integrated circuit device.

[0013]

According to the semiconductor integrated circuit device with the built-in A / D converter having the above-described structure, the reference voltage can be changed flexibly, so that the conversion characteristic of the A / D converter can be made variable.

As a result, a wide range of analog voltages can be converted into digital data with high accuracy.

Further, it becomes possible to easily correct the temperature characteristic and offset of the analog voltage value.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a main part of an A / D converter incorporated in a semiconductor integrated circuit device according to one embodiment of the present invention, and FIG. 2 is a switch and a switching register according to one embodiment of the present invention. FIG.

In the first embodiment, the A / D converter 1 incorporated in the semiconductor integrated circuit device has comparators 2 to 2 for comparing the input analog voltage with the reference voltage.
5, an AND circuit 6 for detecting the data output from the comparators 2 to 5, an encoder 7 for converting the data compared by the comparators 2 to 5 into a bit code,
A conversion result register 8 for temporarily storing the data converted by the encoder 7, resistors 9 to 12a for setting a reference voltage, and a switch (connection means) for voltage switching.
It consists of 13-16.

Further, the converted analog voltage input from the data input V _AIN is input to one input portion of each of the comparators 2 to 5. Further, the other input section of the comparators 2 to 5 is connected to the switches 13 to 16, and the respective input sections are connected via the resistors 9 to 12a.

The other of the switches 13 to 16 is connected to the intermediate reference voltage input (input terminal) V _REFM, and the intermediate reference voltage is input.

Further, one side of the resistor 9 is connected to the highest reference voltage input V _REFT , the highest reference voltage is inputted thereto, and the input part of the comparator 5 connected to the switch 16 has the lowest reference voltage input V _REFB. Is connected to and the minimum reference voltage is input.

Further, the switches 13 to 16 are operated by the switching register 17. The control of the switching register (switching means) 17 is performed by the CPU 18 incorporated in the semiconductor integrated circuit, and the control data is output via the bus 19.

Next, the operation of this embodiment will be described.

The analog voltage converted from the data input V _AIN is input and input to the input sections of the comparators 2-5. At this time, the CPU 18 detects the analog voltage value input from the data input V _AIN .

Based on the voltage value, the CPU 18 outputs to the switching register 17 a control signal indicating which of the switches 13 to 16 should be operated. This control signal is generated by the CPU 18 based on the detected analog voltage value.
It is determined by the program entered in advance.

The operation of the switch by the switching register 17 is, for example, as shown in FIGS. 2 (a) and 2 (b), one bit corresponds to one switch,
Alternatively, a decoder 17a is provided to correspond to the switch with a small number of bits, and the data in the switching register 17 is decoded to correspond to the switch.

Next, the CPU 18 switches the switches 13-16.
Predetermined control data indicating which one of them is operated is output to the switching register 17. Then, the switching register 17
In accordance with the control data, the intermediate reference voltage can be changed flexibly by operating a predetermined switch among the switches 13 to 16 to make it conductive.

For example, when the CPU 18 determines that the detected analog voltage value makes the switch 15 conductive, C
The PU 18 outputs control data for operating the switch 15 to the switching register 17.

The switching register 17 operates the switch 15 according to the control data.

When the switch 15 is turned on, a potential difference between the voltage applied from the highest reference voltage input V _REFT and the voltage applied from the intermediate reference voltage input V _REFM is applied to the resistors 9 to 11. Therefore, the potential difference between the inputs of the comparators 2 to 4 is the resistances 9 to 11
A voltage divided by is applied.

The potential difference between the voltage applied from the intermediate reference voltage input V _REFM and the voltage applied from the lowest reference voltage input V _REFB is applied to the input of the comparator 5.
The voltage is divided by 2 and 12a and applied, and the voltage is input to the input side of the comparator 5.

These input voltages serve as reference voltages for the comparators 2 to 5 and convert the analog voltage input from the data input V _AIN into digital data,
A / D conversion is performed by being input to the encoder 7 via the AND circuit 6, converted into a bit code, the conversion result being input to the conversion result register 8 and being output to the CPU 18.

Further, by constantly detecting the analog voltage value, it is possible to constantly switch the switches 13 to 16 so that the A / D conversion most suitable for the voltage value can be performed.

As a result, in the first embodiment, the intermediate reference voltage can be changed flexibly by the program of the CPU 18 incorporated in the semiconductor integrated circuit device.
Even if the range of change in the input analog voltage value is large, A / D conversion can be performed using the optimum reference voltage.

Further, by inputting a program for correcting the temperature characteristic and the offset of the analog input voltage into the CPU 18 in advance, it is possible to obtain a highly accurate A without the error.
/ D conversion can be performed.

Although the invention made by the present inventor has been concretely described above based on the embodiments, the present invention is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, the switches 13 to 16 are not switched after the analog input voltage is detected, but
A predetermined switch of the switches 13 to 16 may be turned on in advance and programmed to switch to another switch when a predetermined condition is satisfied.

In the above embodiment, the number of switches and the number of comparators are the same, but the number of switches may be smaller than the number of comparators.

[0039]

The effects obtained by the typical ones of the inventions disclosed by the present application will be briefly described as follows.
It is as follows.

(1) According to the present invention, the intermediate reference voltage can be flexibly changed by the program of the built-in CPU according to the analog input to be converted.

(2) Further, in the present invention, according to the above (1), even an analog input voltage in a wide range can be converted into digital data with high accuracy.

(3) Further, in the present invention, the temperature characteristic and offset of the analog input voltage can be corrected.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an A / D converter of a semiconductor integrated circuit device according to an embodiment of the present invention.

2A and 2B are block diagrams showing the relationship between switches and switching registers according to an embodiment of the present invention.

[Explanation of symbols]

1 A / D converter 2-5 Comparator 6 AND circuit 7 Encoder 8 Conversion result register 9-12a Resistance 13-16 Switch 17 Switching register 17a Decoder 18 CPU 19 Bus V _AIN Data input V _REFT Maximum reference voltage input V _REFM Intermediate reference voltage Input V _REFB Minimum reference voltage input

Claims (3)

[Claims] 1. A semiconductor integrated circuit device having a built-in A / D converter, wherein the A / D converter has an input terminal to which a reference voltage is input, a connection means for electrically connecting, and a predetermined connection. A semiconductor integrated circuit device comprising: switching means for switching the connecting means according to a control signal. 2. The switching means is less than or equal to the number of comparators provided in the A / D converter for comparing an analog voltage for A / D conversion with a reference voltage. Semiconductor integrated circuit device. 3. The semiconductor integrated circuit device according to claim 1, wherein the switching means is controlled by a CPU incorporated in the semiconductor integrated circuit device.