JPS5830225A - Analog-to-digital converter - Google Patents

Abstract

PURPOSE:To easily realize a monolithic integrated circuit, by constituting so that an input terminal is connected in common, and input threshold voltage executes A/D conversion by plural invertor groups different each other. CONSTITUTION:Thie A/D converter is constituted of an MOS transistor, and is constituted by connecting in common plural invertor groups INV1-INVn having each different input threshold voltage, to an input terminal IN of an analog signal, and additionally providing output terminals O1-On, respectively. Subsequently, the analog signal is supplied to the input terminal IN, and a digital signal which becomes an L level or an H level in accordance with a different threshold level of each invertor is obtained from the output terminals O1-On.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for converting an analog input signal into a digital output signal, which eliminates the need for particularly high-precision comparators and digital-to-analog conversion devices, and allows monolithic integration, particularly MO8 type integration. The purpose of the present invention is to provide an analog-to-digital conversion device that is easy to apply to circuits.

Analog-to-digital converters (hereinafter referred to as A-D converters), which convert analog input signals to digital output signals, have evolved with the development of digital signals and signal processing devices such as digital computers that process information in digital amounts.
The need for this is rapidly increasing. Currently, high-precision A
Regarding the -D conversion method, in consideration of the required conversion speed and accuracy, a double integral type is mainly used in a low speed region, and a successive approximation type is mainly used in a medium speed region. These are comprised of an operational amplifier, a comparator, a reference voltage generation source, a DA converter, and the like. Therefore, ■ Simplify the complicated circuit configuration. ■Make each device operate at high speed.

■It is required to ensure high operational accuracy.

A variable threshold flash type A-D converter is a relatively simple device, but this A-D converter is relatively simple.
The D converter also requires the same number of high-precision A-A converters and comparators as the number of output digital bits. As a result, there are technical problems that make it difficult to realize monolithic integrated circuits in which it is difficult to fine-tune the internal characteristics of each circuit functional device.

On the other hand, accuracy and operating speed are not required at the above-mentioned level.
-The market needs for D conversion devices are also high.

In view of the drawbacks of the conventional art, the present invention provides an A-D converter with a new configuration particularly aimed at achieving monolithic integration at a low cost. Illustrated in the diagram.

The A-D converter shown in FIG. 1 has input terminals to which analog signals are input connected to the same node IN, and a group of n inverters (n is an integer of 2 or more) having different input threshold voltages. 1Nv1 to INVn, and output terminals o1 to On are attached to each inverter, respectively. FIG. 2 shows the output voltage V with respect to the input voltage VIN of each of the inverter groups I NV1 to I NV n of the A/D converter shown in FIG. 1. ut is a diagram illustrating the characteristics of the inverter NVi, where the input voltage (input voltage) - output voltage (input voltage).

The ut characteristic is denoted by Ti, and its input threshold voltage is vS
Indicated by Wi. Note that the input threshold voltage vSWi is defined as the input voltage value vINi at which the output voltage vOu□ becomes equal to the input voltage vINi.

FIG. 3 shows the basic operation of the A/D converter of the present invention. Now, consider a case where input signal 1 is applied to the input terminal IN of the A/D converter of the present invention.

When the input voltage of input signal 1 increases from 0 potential and exceeds vswl, the output terminal o1 of inverter Nv1 becomes ``H''.
A digital signal output that changes from the level to the L'' level is obtained.Similarly, at the point when the input voltage vIN of the inverter NVi (i is an integer from 1 to n) passes the input threshold voltage vswi, the inverter NVi A digital output signal that changes from "H" level to "L" level is obtained at output terminal 0 corresponding to .

That is, 01 to O for the analog input voltage Vswi,
= "L" level O1+1~on = @H" level is converted into an n-bit digital signal and output. In other words, analog input voltage vSWi - vSWi -1 vSWi + < vswt < vSVV
i”, the output terminal Oi of the inverter NVi is “H”
It is quantized into a digital signal that changes from "level" to "L level" and is output.

The operation of the A-D converter of the present invention has been explained above using as an example the case where the input voltage increases from 0 potential and exceeds vSWi, but it can also be applied when the input voltage decreases from vSWi potential to 0 potential. It is clear that it can be done. At this time,
At the time when the input voltage vIN passes through each input threshold voltage VSWi, the output terminal 0. In this case, a digital output signal that changes from "L" level to "H" level is obtained.

FIG. 4 shows an example in which the inverter is a complementary MO8 (hereinafter abbreviated as CMO8) inverter. Input terminal 2 is A-
It is connected to the input terminal IN of the D conversion device, and the output terminal 3 is connected to the A
This becomes the output terminal O1 of the -D conversion device. The input threshold voltage vsw of this CMOS inverter is the output voltage V. ut
When is defined as an input voltage value that is equal to the input voltage vin, it is expressed as follows. Here, IVTPl: P channel MO8) transistor 4
threshold voltage.

VTN: Threshold voltage of N-channel MOS transistor 5.

Vpp: Power supply voltage of CMOS inverter.

Wo' wn: Effective channel width of N-channel MOS transistor 6.

Ln': N-channel Mo8) Effective channel length of Langistaro.

Wp': P-channel MO8) Effective channel width of transistor 4.

Lp': Effective channel length of P-channel MOS transistor 4.

That is, the threshold voltages vTN and I of the MoS transistor determined by the power supply voltage vDD used and the Mo8 manufacturing process are
By changing only βR without changing vTPl, the input threshold voltage of the inverter can be designed to a desired value.

In this way, the input threshold voltage is determined by the geometric dimensions of the Mo8 transistor. M built into the same semiconductor substrate
o8) Variations in the channel width and length of the Rangistaro from the design dimensions are expected to be the same. Even including variations in the threshold voltages vTN, IVTP, and l determined in the MOS process, the variation in the input threshold voltage of the inverter is ±5 to 10%.
% can be easily achieved. Therefore, A-D conversion with excellent monotonicity can be obtained.

Although the embodiment has been described using a CMOS inverter as an example, it is an N-channel MOS inverter.

It is clear that the same implementation is possible with a P-channel MOS inverter or the like.

As described above, the A-D converter of the present invention not only has a simple structure, but is also composed of circuit elements that can be easily integrated into a monolithic circuit, and is not limited to the conventional operational amplifier, comparator, Since there is no need for a D-A converter, etc., there is an advantage that it is easy to put into practical use. Also,
Although the A/D converter of the present invention is particularly effective when formed into a monolithic integrated circuit, it can also be constructed using individual components.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of an A-D converter according to an embodiment of the present invention, FIG. 2 is a diagram showing input voltage-output voltage characteristics of an inverter group, and FIG. A diagram for explaining the basic operation of the D conversion device, and FIG. 4 is a diagram showing the configuration of a CMOS inverter. INV1~INVn...Inverter group, 01
~on... Output terminal of inverter group, IN...
...Input terminal of A-D converter, T-T...
...Input voltage-output voltage characteristics of invert group, vsV, 1 to positive...
...Input threshold voltage of inverter group, 1...
・Input signal, 2... Input terminal of CMOS inverter, 3... Output terminal of CMOS inverter, 4
...P-channel MoS transistor, 6...
...N-channel MoS transistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Fig. 82 Fig. Veal Fig. 3 Fig. 4 “Smoke ψ 4 →3 f 1 no-

Claims (4)

[Claims] (1) An inverter group consisting of n inverters (where n is an integer of 2 or more), each having a different input threshold voltage and whose input terminals to which analog signals are input are connected in common, and whose analog signals are input to the input terminals. n in the inverter group
An analog-to-digital conversion device that converts bits into digital signals. (2) The analog-to-digital converter according to claim 1, wherein the inverter is composed of transistors. (3) The analog-to-digital converter according to claim 1, wherein the inverter element is composed of an MO8 type transistor. (4) Claim 1, characterized in that all circuit elements are integrated into a single semiconductor substrate.
The analog-to-digital converter described in Section 1.