JPH01321728A - Control method for analog/digital converter - Google Patents

Abstract

PURPOSE:To quickly subject a momently varying input voltage to analog/ digital(A/D) conversion without a sampling and holding circuit by charging a capacitor once in the period of A/D conversion. CONSTITUTION:When the A/D converting operation is started, a semiconductor switch 2 is turned on after a semiconductor switch 3. A capacitor 5 is charged by the potential difference between an input voltage VIN of a voltage input terminal 6 and a potential V0. Thereafter, the semiconductor switch 3 is turned off after the semiconductor switch 2, and a semiconductor switch 1 is turned on. A chopper comparator is kept in this state, and the output of a successive comparison register 8 is set to 816, and a reference voltage 1/2VREF of a switch group 7 is selected to obtain the difference between the input voltage VIN and the reference voltage 1/2VREF. Thus, A/D conversion is quickly performed to cope with the varying input voltage, and a sampling and holding circuit is not required.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for controlling an analog/digital converter;
In particular, we propose an R-2R resistance ladder analog/digital converter using a chopper comparator constructed on a semiconductor substrate and built into a semiconductor integrated circuit.

[Conventional technology]

FIG. 2 is a circuit diagram of an R-2R resistance ladder type ^/D converter, which is already known as an analog/digital converter (hereinafter referred to as ^/D converter) using, for example, a chopper type comparator. At each end of the resistor array 9, for example, a positive reference power input terminal 10 of a reference voltage %V and a reference voltage OV are connected.
The negative side reference power input terminals 11 of each are connected to each other. The voltage at each connection point connecting the resistors in the resistor array 9 and the value of a 4-bit successive approximation register 8 are manually input to the switch group 7. The reference voltage V IIEF, which is the output of the switch group 7, is applied to one end of the capacitor 5 through the first semiconductor switch 1, and the input terminal VIN of the voltage input terminal 6 is applied through the second semiconductor switch 2;
-It is given to one end of Yapasita 5. The other end of the capacitor 5 is connected to the input end of an inverter 4, and a third semiconductor switch 3 is connected in parallel to the inverter 4.

The difference between the input voltage V 1 H of the voltage input terminal 6 and the reference voltage V REF of the switch group 7 is obtained by using the capacitor 5 to turn on and off the semiconductor switches 1 and 2.3 at timings to be described later. The output of the impark 4 is given to the control circuit 12. The control circuit 12 is the inverter 4
The successive approximation register 8 and the semiconductor switches 1, 2.3 are controlled by the output of and the internal timing of the control circuit 12. In addition, the above-mentioned No. 1. Second. third semiconductor switch 1,
2, 3, capacitor 5, and inverter 4 constitute a chopper comparator.

Output of successive approximation register 8 8-0.8-1.8-2.8
-3 is bit O, bit 1. Bit 2. This is bit 3, and below, the output status is summarized as 4 bits in hexadecimal numbers 016~
It is expressed as F+6.

Next, the operation of this A/D converter will be explained with reference to FIGS. 2 and 3. FIG. 3 is a timing chart when analog/digital conversion tM <hereinafter referred to as ^/D conversion) is performed, and the horizontal axis is time.

First, the semiconductor switch 3 is turned on, and the input terminal and output side of the inverter 4 are brought to the same potential. This potential V.

is determined by the input/output characteristics of the inverter 4. Next, the semiconductor switch 2 is turned on, and the capacitor 5 is connected to the input voltage VIN of the voltage input terminal 6 and the potential (2). Charge the battery by applying a potential difference between the battery and the battery.

Thereafter, the semiconductor switch 2 is turned off, and then the semiconductor switch 3 is turned off, and then the semiconductor switch 1 is turned on, and the reference voltage V B E outputted by the switch group 7 to the capacitor 5 is
Give y. At this time, the value of the successive approximation register 8 is r
816J, and the reference voltage V R of switch group 7
For EF, a voltage of %V of the resistor array 7 is selected and output. At this time, the input voltage VIN of the inverter 4 is V
If l, l>'A VREF (7), inverter 4
The potential on the input side of is the potential ■. lower, so its output will be at rlJ, while VIN is at potential ■ if VREF. Higher the output will be "0". Now, VI
N>'A VREF T: Next, set the value of successive approximation register 8 to rc,,J, and set switch group 7 to 3/
4 Make sure to select V REF.

Furthermore, after turning on the semiconductor switches 3 and 2 again and recharging the capacitor 5, turning on the semiconductor switch 1, the input voltage at the voltage input terminal 6 and the reference voltage 3/4 V REF at the switch group 7 are set. compare. This kind of action is 4
The 4-bit A/D conversion operation is repeated several times, and the A/D conversion value is set in the 4-bit successive approximation register.

By turning on the semiconductor switch 2.3 in this manner, discharge of the capacitor 5 due to leakage current is prevented.

[Problem to be solved by the invention]

The control method of the R-2+1 resistor ladder type A/rl converter described above performs A/D conversion of the input voltage that changes instantaneously in order to recharge the capacitor each time the reference voltage output by the switch group is changed. In order to do this, it is necessary to provide a sample and hold circuit for sampling the input voltage at a stage preceding the input voltage terminal 6.

Further, there is a problem that the A/D conversion operation is slow because the semiconductor switch requires operation time for turning on and off for recharging.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a method for controlling an A/D converter that can quickly A/D convert an input voltage that fluctuates instantaneously without using a sample-and-hold circuit.

[Means to solve the problem]

The method for controlling an analog/digital converter according to the present invention includes:
The capacitor is charged once during the A/D conversion period.

[Effect]

Second. The third switch is turned on together, the first switch is turned off, and the capacitor is charged with the input voltage to be converted from analog to digital.

When the second switch is held off and the third switch is turned off and the first switch is turned on, a reference voltage is applied to the capacitor. The reference voltage is sequentially changed in relation to the difference between the input voltage and the reference voltage.

As a result, the output voltage of the analog/digital converter becomes the input voltage when charging the capacitor.

〔Example〕

The present invention will be described in detail below with reference to drawings showing embodiments thereof.

FIG. 1 is a timing chart of the operation of an analog/digital converter according to the method of controlling the analog/digital converter according to the present invention.
The A/D converter shown in FIG. 2 is used as the D converter.

To start the A/D conversion operation, first the semiconductor switch 3 is turned on, followed by the semiconductor switch 2. At this time, as with conventional A/D converters, the output voltage is the same as that of inverter 4.

Potential determined by output characteristics■. The capacitor 5 is charged by the potential difference between the input terminal VIN of the voltage input terminal 6 and the potential v0. After that, semiconductor switch 2 is turned off, semiconductor switch 3 is turned off, and semiconductor switch 1 is turned on. And keep the chopper comparator in this state,
First, the output of the successive approximation register 8 is set to 816, the reference voltage % VREF of the switch group 7 is selected, and the difference between the input voltage v1 and the reference voltage % VREF is obtained.

At this time, since vlN>〃vREF, inverter 4
The output of is "0". And then similarly 3/4V R
Get the difference with EF. At this time as well, semiconductor switches 1.2.
Since capacitor 5 is held at the initially charged input voltage VIN since neither of the capacitors 3 and 3 are turned on or off, the input voltage VI immediately before the semiconductor switch 2 is turned off is maintained at the input voltage VIN that was initially charged.
You will get the difference from N.

From then on, the comparison with the reference voltage 5/8 VIEF of the switch group 7 and the comparison with 11/16 V REF are all performed with respect to the input voltage VIN immediately before the semiconductor switch 2 is turned off, and finally when the semiconductor switch 2 is turned off. The A/D conversion value of the input voltage VIN just before the input voltage VIN is obtained from the successive approximation register 8. ``During this period of ^/D conversion, the semiconductor switches 1, 2, and 3 are not switched as in the conventional case, so the A/D conversion operation becomes extremely fast.

〔Effect of the invention〕

As described in detail above, the present invention turns on the second semiconductor switch that supplies the input voltage at the start of the A/D conversion operation, charges the capacitor with the input voltage to be converted from analog to digital, and then turns it off. This state is maintained, and after that, the difference between the reference voltage from the switch group selected by the value of the successive approximation register and the charging voltage of the capacitor is obtained, and the reference voltage is successively changed to change the output voltage of the A/D converter. Since it is used as the input voltage when charging the capacitor, ^/D conversion can be performed quickly.
This provides an excellent effect of providing an A/D converter that can respond to varying input voltages and does not require a sample bold circuit.

[Brief explanation of the drawing]

FIG. 1 is a timing chart of an analog/digital conversion operation according to the analog/digital converter control method according to the present invention, and FIG. 2 is a timing chart of an analog/digital conversion operation using an R-2R resistance ladder method.
The circuit diagram of the digital converter, FIG. 3, is a timing chart of analog/digital conversion operation using a conventional control method. 1.2.3...Semiconductor switch 4...Inverter 5...Capacitor 6...Voltage input terminal 7...
Switch group 8...Successive approximation register 9...Resistor array 12...Control circuit In the drawings, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. The output of the digital/analog converter that converts digital data output by the control circuit into analog data and the input voltage to be converted from analog to digital are applied to the capacitor via the first and second switches, respectively, and the third In the method for controlling an analog/digital converter of an R-2R resistance ladder type, the second switch enables charging of a capacitor, and determines digital data of the control circuit in relation to the charging voltage of the capacitor. Both the third switch is turned on, the first switch is turned off to charge the capacitor with the input voltage, and after charging, both the second and third switches are turned off, and the first switch is turned on to charge the capacitor with the input voltage. A method for controlling an analog/digital converter, characterized in that the output voltage of the analog/digital converter is made equal to the input voltage at the time of charging the capacitor by sequentially changing the reference voltage of the digital/analog converter. .