JPH0983363A - A/d converting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an A/D converter which accelerates speed and improves accuracy without switching any input. SOLUTION: This circuit has an operational amplifier 1 for outputting a differential signal Vd of an analog input signal Vi and an output signal Va of a D/A converter 5, A/D converter 3, comparator 2 parallelly connected to the output of the operational amplifier, and up/down counter 4 for counting clock pulses while switching up and down operations by the comparator 2 to perform an output Vc corresponding to the polarity of output from the operational amplifier 1, and is composed of the D/A converter 5 for converting an output Vo of the up/down counter 4 to an analog signal and outputting it to the operational amplifier 1. Then, a digital output is extracted from the A/D converter 3 and the up/clown counter 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D conversion circuit for converting an analog signal into a digital signal, and more particularly to improvement of an inexpensive, high speed and highly accurate A / D conversion circuit.

[0002]

2. Description of the Related Art FIG. 2 shows the structure of a conventional high-speed and highly accurate A / D converter. In the figure, reference numerals 21 and 22 are both operational amplifiers having different gains.
23 and 24 select either the operational amplifier 21 or 22 according to the size of the analog input signal and select the A / D converter 25.
A switch 25 connected to the input terminal 25 is an A / D converter that digitally converts the analog output of the connected operational amplifier. Now, if there is an analog input signal, its magnitude is detected by a level detecting means (not shown), and an operational amplifier 21 or 22 having a different gain according to the magnitude of the input is switched to an A / D converter by a switch 23 or 24. 25 was switched and connected, and A / D conversion was performed.

[0003]

However, in the prior art, there is a problem that it takes time for conversion because it is necessary to judge the size of the input and select another input, and the place where the input is switched is not linear. . It is an object of the present invention to provide a high speed and highly accurate A / D converter without switching the input.

[0004]

In order to solve the above-mentioned problems, the present invention relates to an operational amplifier for outputting a difference signal between an analog input signal and an output signal of a D / A converter, and an operational amplifier connected in parallel to the output of the operational amplifier. And an A / D converter and a comparator, and an up / down counter that counts clock pulses by switching up / down operations by the comparator that outputs according to the polarity of the output of the operational amplifier, and an output of the up / down counter Is converted into an analog signal and output to the operational amplifier, and a digital output is obtained from the A / D converter and the up / down counter. This is a combination of a high-speed and inexpensive D / A converter and an A / D converter, the upper data is composed of a D / A converter and a counter, the analog amount of which is compared by a comparator, and the lower data is A Quantize with the / D converter.

With the above means, a high-speed and accurate A / D conversion circuit can be constructed without switching the input as in the prior art.

[0006]

According to the structure of the present invention, the closed loop composed of the operational amplifier 1, the comparator 2, the up / down counter 4 and the D / A converter 5 A / D-converts the analog input signal and outputs the higher-order data. Since the / D converter 3 A / D converts the analog input signal and outputs the lower data,
A digital conversion output of an analog input signal can be obtained by synthesizing both conversion outputs.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 1 is an analog input signal V _i and D / A
An operational amplifier 2 that outputs a difference signal V _d from the output signal V _a of the converter 5 is a comparator that is connected in parallel with the A / D converter 3 on the output side of the operational amplifier 1, and the polarity of the signal output V _d of the operational amplifier 1 To judge. 3 is the lower digit A / which digitally converts the signal output V _d of the operational amplifier 1 and outputs it.
It is a D converter. Reference numeral 4 indicates up / down operation switched by different output levels of the comparator 2 that outputs V _c according to the polarity of the signal output V _d of the operational amplifier 1, counts clock pulses, and outputs the output V _o.
Down counter 5 is D / A converter for feeding back the output to the operational amplifier 1 converts the output V _o of the up-down counter 4 to an analog signal V _a.

The operation of the circuit configured as described above will be described. The operational amplifier 1 outputs the difference between the input analog signal V _i and the output V _a of the D / A converter 5 as it is to output V
_d . When there is a difference, the comparator 2 inverts and outputs, so that it is input as the up / down signal of the counter 4. When the counter is incremented, the data is incremented by 1, the output of the D / A converter is also increased, and the differential output V _d of the operational amplifier 1 is reduced. In this way, the loop from the operational amplifier 1 to the D / A converter 5 is in a balanced state, and the output V _{a of the} counter 4 is used as upper data.
A resolution finer than the least significant digit of the counter 4 is obtained by the A / D converter 3 and used as lower data. Then, the digital value may be obtained by combining the upper data and the lower data.

If the D / A converter is 8 bits and the A / D converter is 12 bits, an A / D converter corresponding to 20 bits can be obtained and a high precision A / D converter can be obtained. Further, the conversion error of the A / D converter 3 and the D / A converter 5 can be corrected by applying a known appropriate input signal to further improve the accuracy.

[0010]

As described above, according to the present invention, since the input is not switched, it is possible to construct an A / D converter with high accuracy at a low cost with a simple circuit having a short conversion time.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 operational amplifier 2 comparator 3 A / D converter 4 up / down counter 5 D / A converter 21, 22 operational amplifier 23, 24 switch 25 A / D converter

Claims (1)

[Claims] 1. An operational amplifier for outputting a difference signal between an analog input signal and an output signal of a D / A converter, an A / D converter and a comparator connected in parallel to the output of the operational amplifier, and an output of the operational amplifier. An up / down counter that counts clock pulses by switching up / down operations by the comparator that outputs according to polarity, and a D / A that converts the output of the up / down counter into an analog signal and outputs the analog signal to the operational amplifier. An A / D conversion circuit comprising a converter and obtaining a digital output from the A / D converter and an up / down counter.