JPS6376523A - Analog-to-digital converter - Google Patents

Abstract

PURPOSE:To minimize the number of required voltage comparators and make an output encoder unnecessary, by controlling the reference voltage of a voltage comparator which outputs low-order bits by using the output signal of another voltage comparator which becomes the high-order bit of digital signals and, at the same time, directly converting the output signal of the voltage comparator into digital signals. CONSTITUTION:When the input of a buffer 20 is connected with the output of a voltage comparator 11, the input reference voltage of another voltage comparator 10 becomes 1/4VREF, since the output transistor of the buffer 20 becomes L if the output of the voltage comparator 11 is L. When the input voltage Vin is <=1/4VREF, the output of the voltage comparator 10 becomes L and, when >=1/4REF the output becomes H. Moreover, when the output of the voltage comparator 11 is H, the input reference voltage of the voltage comparator 10 becomes 3/4VREF, since the output transistor of the buffer 20 is cut off and the output is set in an opened state and, when the input voltage Vin is <=3/4VREF, the output of the voltage comparator 10 becomes L. When the input voltage Vin is >=3/4VREF, the output of the voltage comparator 10 becomes H.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to analog signal/digital signal conversion technology, and in particular to a converter with a simple configuration, low cost, and high speed.

[Conventional technology]

A conventionally used analog-to-digital signal converter will be explained with reference to FIGS. 3 and 4. In FIG. 3, 1 indicates the reference voltage (VRIIF). The reference voltage is the same as the maximum voltage of the analog signal serving as the input signal. In FIG. 3, the input signal voltage is 0V-VR.

■The range is as follows. 2 is an analog signal input terminal, 5 to 6
10 to 12 are voltage comparators, 17 is an encoder for converting the output signal of the voltage comparator to a 2-bit digital signal, 13.14 is an inverter, and 15.16 is a NAND. Shows the circuit. In FIG. 3, the voltages applied to the comparator reference voltage terminals 7 to 9 are obtained by dividing the reference voltage 1 by resistors 3 to 6, and each voltage is -V□2. Σ
vRMI + τvR. Here, voltage comparator 10~
12 are respectively shown in FIG.

As shown in FIG. 6, the input terminal voltage v2 is the reference voltage V.

If the input terminal voltage v2 is very high, the output becomes High level, and the input terminal voltage v2 is the reference voltage V, and if it is very low, the output becomes Low level.

Note that FIG. 5 is a circuit diagram in which the circuit configuration of the voltage comparator is redrawn), and FIG. 6 is an explanatory diagram showing the input/output signal relationship in the comparator of FIG. 5.

Based on the above, the analog-to-digital converter shown in FIG.
in (a When VH is active, the outputs of voltage comparators 10 to 12 are all Low % 'bxr < Vin T Vu
When y, only the output of the voltage comparator 10 is Hlgh, and the rest are Low s2'/RIF < Vin < 4
When Viny, only the output of the voltage comparator 12 is Low, and the rest is Hlgh, τV*xv <Vin≦”RI
When F, the outputs of the voltage comparators 10 to 12 all become Hlgh. The output of this voltage comparator is converted into a shifted-bit digital signal by an inverter 3.14 and a NAND circuit 15.15, and the analog input signal is converted into a digital signal by applying it to the output terminal 1 [3, 19]. ing. These circuits are described in "Integrated Circuit Technical Data CMO8 A/D Converter" published by Toshiba, September 1985 edition.

[Problem that the invention seeks to solve]

The above conventional technology uses three voltage comparators and requires an encoder to convert the output signal of the voltage comparator into a 2-bit digital signal, which not only increases the cost but also increases the circuit size. However, there was a problem in that it was difficult to downsize.

An object of the present invention is to provide a low-cost and compact analog-to-digital converter.

[Means for solving problems]

In order to achieve the above object, the circuit is designed to reduce the number of components used in the voltage comparator and encoder sections, which are expensive and large components.

[Effect]

In order to solve the above problem, the present invention uses the output signal of the voltage comparator which is the upper bit D1 of the digital signal and controls the reference voltage of the voltage comparator which outputs the lower bit. By reducing the number of voltage comparators and making the output signals of the voltage comparators directly become digital signals, it was possible to eliminate the need for an encoder.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In FIG. 1, reference numeral 20 denotes a buffer whose output terminal is connected only to the collector of an internal output transistor, and whose ONL output is grounded only when the input is at a low level. is H1gh
level, the output transistor is cutoff L
Bubbles 7a and 21 to 25 that do not affect the output circuit are resistors that divide the reference voltages v and 11 to generate reference voltages for the voltage comparators 10 and 11. In FIG. 1, the resistor 24 and the resistor 25 have the same resistance value, and 2VjllF is applied to the comparator reference voltage input terminal 8. Further, the resistance values of the resistors 21 to 23 have the following relationship.

R21:p, 22:a2s=sH1:8 Therefore, the comparator reference voltage input terminal 7 is set depending on the output state of the buffer 20)
The following voltages are applied:

Buffer output Comparator reference voltage Low 7 vRIFHLgh
7vRU (that is, by connecting the input of the buffer 20 to the output of the voltage comparator 11), the output of the voltage comparator 11 is Low.
level, the output transistor of the buffer 20 is Low.
Therefore, the input reference voltage of the voltage comparator 10 is -VUt
If the input voltage Vin is less than 2-v8, the output of the voltage comparator 10 will be low level.
4 If the voltage is higher than Ruff, the output of the voltage comparator 10 is H.
1gh level. Also, the output of the voltage comparator 11 is H!
When the output transistor of the buffer 2o is at the Lgh level, the output transistor of the buffer 2o is cutoff, and the L output is in an open state, so the input reference voltage of the voltage comparator 10 is HvR□r,3.If the input voltage is vin or less than VRIF, the voltage comparator The output of voltage comparator 10 is low level, and when the input voltage is 3 Vin or more than τVRD, the output of voltage comparator 10 is high.
gh level.

Since the single voltage of 110 voltage comparators is -2vuI, if the input voltage Vin is TVR□ or less, the output will be Lo.
When the input voltage Vin is 2 vRIiF or higher, the output becomes a High level.

The above operations are summarized in FIG. 2.

As described above, according to the present invention, it is possible to realize a low-cost, small-sized analog-to-digital converter that uses a minimum number of voltage comparators and eliminates the need for an output encoder section.

〔Effect of the invention〕

According to the present invention, it is possible to realize a low-cost and compact digital-to-analog converter by minimizing the number of voltage comparators used and eliminating the need for an output encoder.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram illustrating the level relationship of each part signal to explain its operation, and Fig. 3 is a conventional analog-to-digital conversion diagram. 4 is an explanatory diagram that organizes and shows the level relationships of the signals of each part to explain its operation, and FIG. 5 is a circuit diagram that redraws the comparator in FIG. 6. FIG. 6 is an explanatory diagram that organizes and shows the level relationship of signals of each part in the comparator shown in FIG. 3. 1...Basis voltage source, 10-12...Voltage comparator 3
~6,21~25・γ・Base voltage generation resistor 17...
Encoder, 2... Input terminal 18... Output terminal (lower bit DO) 1121 21 yen 1 3rd Figure 1"1 ?! 14121 5 (2) 6th port

Claims (1)

[Claims] 1. An analog-to-digital converter that converts an input analog signal into a digital signal and outputs the digital signal, comprising: a reference voltage source; and a first voltage converter that divides the reference voltage source to generate a first comparison voltage. a first comparator that receives and compares the first comparison voltage and the input analog signal (input voltage) and outputs a logic 1 or 0 depending on the magnitude relationship; and the reference voltage. a second resistor that divides the voltage of the source to generate a second comparison voltage; and a second resistor that receives and compares the second comparison voltage and the input voltage, and outputs a logic 1 or 0 depending on the magnitude relationship. It comprises a second comparator and a comparison voltage value variable means for varying the value of the second comparison voltage generated at the second resistor depending on the logical value of the output of the first comparator. An analog-to-digital converter, characterized in that the outputs of the first and second comparators are used as an output digital signal. 2. In the analog-to-digital converter according to claim 1, the first comparison voltage generated by the first resistor is half the voltage of the reference voltage source, and the second
The second comparison voltage generated by the resistor 3 of the reference voltage source
/4 voltage, and the comparison voltage value variable means
An analog-to-digital converter characterized in that the value of the second comparison voltage generated at the resistor is made to vary between 1/4 and 3/4 of the reference voltage source.