JPS61261928A - A/d converting circuit - Google Patents

Abstract

PURPOSE:To improve the resolution without using an A/D converter of a high resolution by switching a reference use power source in accordance with an analog voltage level. CONSTITUTION:A holding signal is inputted to a sample and hold circuit 1, and an analoy input is held and inputted to a level detecting circuit 4. By this input, its voltage level is decided, one of switches 5a-5c is turned on, and subsequently, a switch 6 is turned on. As a result, a prescribed reference voltage is supplied to an A/D converter 2, and also, a voltage VS is inputted to an analog input terminal. In this case, by applying a conversion start signal to the A/D converter 2, a conversion to a digital code from an analog code is executed, and the digital code to (VS/V1)X2<n> is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an A/D conversion circuit with improved resolution.

[Conventional technology]

FIG. 3 is a block diagram of a conventional A/D conversion circuit that converts an analog quantity into a digital code. In the figure, 1 is a sample hold circuit into which analog input voltage V and sample/hold signals are input, 2 is an A/D converter that has n-pit resolution and receives a conversion start signal, and 3 is an A/O converter. This is a reference voltage circuit that provides an analog voltage vRzr corresponding to the full scale of .

Next, the operation will be explained. By inputting a hold signal to the sample and hold circuit 1, the analog input voltage V at that point in time is held within the sample and hold circuit 1 and input to the A/D converter 2. Here, by giving a conversion start signal to this A/D converter 2,
/n converter 2 is J.

The conversion is started and a digital vaip' code corresponding to V x 2n is output. After this conversion is completed, the sample and hold circuit 1 releases the hold signal and remains in a sampling state in preparation for the next conversion. FIG. 4 is a state diagram showing the relationship between analog human power V (horizontal axis) and digital output vertical axis when the resolution n of the A/D converter 2 is, for example, 3 bits and compolar operation is performed.

[Problem that the invention seeks to solve]

Since the conventional A/D conversion circuit is configured as described above, the resolution for analog input is the resolution V of the A/D converter.
It is determined by aEr/2n, and in order to improve this resolution, it is necessary to use an A/D converter with high resolution, which poses a problem in that it results in a large increase in cost.

This invention was made to solve the above-mentioned problems, and its purpose is to obtain an inexpensive A/D conversion circuit that can improve resolution using a low-resolution A/D converter. shall be.

[Means for solving problems]

The A/D conversion circuit according to the present invention includes a plurality of reference power supplies, a level detection circuit that detects the level of an analog input, and an A/D converter, and has a reference voltage applied to the A/D converter. It is configured to switch between.

[Effect]

In this invention, the plurality of reference power supplies correspond to the level of the analog input and are selected and applied as the reference voltage of the A/D converter, thereby shifting the analog voltage corresponding to the full scale of the digital code. High resolution digital output can be obtained.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In the figure, 1 and 2 are exactly the same as the same reference numerals in FIG. The voltage values of 3a, 3b, and 3c are Vo and V, respectively.
l, V2 reference power supply, 4 is a level detection circuit, 5
A, 5b, 5c and 6 are switches for switching signals.

Next, the operation of the above embodiment will be explained with reference to FIG. Figure 2 is A to make the explanation easier to understand in Figure 1.
/ Resolution n of D converter 2 is 3 bits, reference power supply 3a
, 3b, 3c are v2=7Vo, v1=-zv.

This shows the relationship between digital output and analog human power V. Here V. is usually chosen equal to the maximum value of the analog human power V. Further, the level detection circuit 4 detects in which range of θ to vo the output signal VB of the sample and hold circuit 1 is, and determines that 1) V 1 < VS ≦
If vo, switch 5a (ll) v2 ku v8≦v
If 1, then switch 5b (if 1010≦VB≦v2, switch 5C is turned on, and then switch 6 is also turned on. (1), (1)
, (till) A level detection signal representing which state is output is output.The operation when the analog human power V is in the region of V2 < v≦vl will be explained step by step as an example. By being input, the analog input V is held and input to the level detection circuit 4. The voltage level is determined by this input, the switch 5b is turned on, and then the switch 6 is turned on.
is turned on. As a result, Vl is supplied to the A/D converter 2 as the reference power supply vagr, and Vl is supplied to the analog input terminal.

is input. By applying a conversion start signal to the A/D converter 2, conversion from analog to digital code is executed, and a digital code corresponding to lX 2 n is output.

Here, the analog value for one unit of digital code, that is, the resolution is vl/2n, which is 70,771 times higher than the resolution V6/2n of the conventional circuit shown in FIG. 4, which is not based on the present invention. Similarly, 0≦V≦v2
In the case of , the resolution is 70,772 times higher, and the lower the analog human power V is, the higher the resolution is.

The output code for the analog human power V changes as shown by the thick line in FIG. The digital code obtained in this way corresponds to the input vVc, but the digital code obtained by A/D conversion is often digitally processed by a microprocessor or the like, and in such cases, Digital data K obtained by the above embodiment, after performing necessary arithmetic processing, the level detection signal from the level detection circuit 4 is interpreted and doubled or doubled.
v.

True calculation results for force V can be obtained with high accuracy.

Like v2. It is better to select vl.

In the above embodiment, the case where three reference power supplies are provided has been described, but it goes without saying that increasing or decreasing this number depending on the desired accuracy will have the same effect as in the above embodiment.

〔Effect of the invention〕

As described above, according to the present invention, a plurality of reference power supplies and a means for detecting the analog voltage level are provided, and the reference power supply is switched in accordance with the analog voltage level, so that high resolution is achieved. This has the effect of providing an inexpensive A/O conversion circuit that can improve resolution without using an A/D converter.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an A/D conversion circuit showing an embodiment of the present invention, Fig. 2 is a state diagram showing the input/output relationship of Fig. 1, and Fig. 3 is a diagram showing a conventional A/D conversion circuit. FIG. 4 is a state diagram showing the input/output relationship of FIG. 3. In the figure, 2 is an A/D converter, 38 to 3C are reference power supplies, and 4 is a level detection circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts. Patent Applicant Mitsubishi Electric Co., Ltd. Agent Patent Attorney 1) Hiroshi Sawa (2 others) Figure 2 7 Naroku Input ■ Figure 3 Figure 4 Ana 09 λ force V Procedural amendment (voluntary)

Claims (1)

[Claims] an A/D converter that converts an analog voltage into a digital code; a plurality of reference power supplies that are switchably connected to the A/D converter; A/D including a level detection circuit for switching the plurality of reference power sources for the A/D converter.
conversion circuit.