JPS62178018A - Integration type analog-digital converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an integral type A/D converter, particularly an integrator.

[Conventional technology]

Conventionally, integral type A/D converters have been widely used as relatively low-speed A/D conversion means because they have a simpler configuration than successive approximation types and can easily perform high-precision measurements. It has also been applied to control systems using microprocessors.

By the way, in this fractional A/D conversion method, switching of the measurement range or measurement resolution is performed using the integration start voltage and 4
It is necessary to change the i1 minute time constant, and as shown in FIG.
An integrating capacitor 3 is provided in parallel between the inverting terminals 2 and 2. b is led to the reference potential Vcc via a switch 5 that switches integrating resistors 4' and 4'' arranged in parallel, and furthermore, a changeover switch 6 is connected from the non-inverting terminal 2C.
By configuring the integrator 1 by grounding the integrator 1 through the voltage dividing resistor 7' or 7'', the range or resolution can be changed.

As an integral type A/D converter, for example, there is one having the configuration shown in FIG. On the other hand, the output signal E of the integrator 1 is input manually to the other input terminal. Now, the reset switch 11, which is provided with a minute discharge resistor 10 on the short circuit line between the output terminal 2a and the inversion terminal 2b, is turned on.
When , the output terminal 2a and the inverting terminal 2b are short-circuited, the integrating capacitor 3 is in a discharged state, and the output E is connected between the non-inverting terminal 2c and the reference potential Vcc. The integration start voltage is determined by the voltage dividing resistor 12' connected to the voltage dividing resistor 12' and the voltage dividing resistor 12'' which is connected to the ground (time period to -tl shown in FIG. 3).

Then, when the reset switch 11 is turned OFF by the signal C, integration is started by the integrating resistor 13 and the integrating capacitor 3 provided between the inverting terminal 2b and the Vcc, and at time t1 as shown in FIG. , signal E
becomes a ramp waveform (between times t+ and t2), and is compared with the signal 1 in the comparator 9. After time t2, when the magnitude relationship of both E and D is reversed, the output signal B of the comparator 9 is inverted. Then, when the reset switch 11 returns to ON (time t3), the integrating capacitor 3 is reset and the signal E is output.

returns to the integration start voltage.

By the way, the time T from when the reset switch 11 is turned off until the output signal B of the comparator 9 is inverted depends on the voltage of the output signal A. The input signal A is A/D converted by counting the pulses of the signal.

The resolution of A/D conversion can be changed by changing the integration time constant, so the constant of the integration resistor 13 can be changed by providing a switch or the like.

[Problem that the invention aims to solve]

However, in the above case, the slope of the ramp waveform of the signal E becomes steep, as shown by the dashed line in FIG.
The time To of data for v is shortened to the time T'o, and as a result, A/D converted data with an offset added may be obtained, which may be inconvenient. Therefore, in order to solve this problem, see (L) in the same figure.
As shown by the dashed line, the integration start voltage is increased to increase the time To.
Therefore, if the configuration shown in FIG. 5 is adopted, there is a problem in that the changeover switches 5 and 6 must be operated at the same time.

[Means for solving problems]

In view of the circumstances, the present invention provides an inverting input terminal of an integrating operational amplifier and an inverting input terminal of an integrating operational amplifier in an integrator. The purpose of the present invention is to solve this problem by connecting each of the non-inverting input terminals and connecting the connecting point of the two resistors to a certain reference voltage using a switch.

[Effect]

Therefore, the resolution of A/D conversion and the measurement range can be changed using the single switch.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

First, I will explain the configuration.

In the integrator 21 in this embodiment, both ends of the time constant changing integrating resistor 22 and the integration start voltage changing resistor 23 connected in series are connected to the inverting terminal 2b and the non-inverting terminal 2c of the integrating operational amplifier 2, respectively. and the two resistors 2
A connection point 24 of 2.23 and a certain reference potential Vcc are connected via a switch 25.

Next, the effect will be described.

First, when the switch 25 is OFF, the inverting terminal 2b, which is the re-input terminal of the integrating operational amplifier 2, and the non-inverting terminal 2b
Since c is at the same potential, the time constant changing integrating resistor 22 and the integration start voltage changing resistor 23 have no relation to the integrating operation.

Next, when the switch 25 is turned on, the integral resistor 13 and the time constant changing integral resistor 22 are placed in parallel, so the time constant becomes smaller, the resolution of A/D conversion is lowered, and the measurement range is expanded. However, if things continue as they are, the above-mentioned figure 4(b)
Since the state shown in Fig. 4(a) is reached, the voltage dividing resistor 12' and the integration start voltage changing resistor 23 are connected in parallel to change the voltage dividing resistance ratio and increase the integration start voltage. The state shown can be achieved.

Note that the time constant can be changed in various ways by connecting the switch 25 not only to the reference potential Vcc but also to another constant reference potential.

〔Effect of the invention〕

As explained above, the present invention has the advantage that it is possible to realize the measurement range of A/D conversion without causing an offset by using a simple structure such as on an eave and by operating a switch once.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of a conventional integral type A/D converter, and FIG. 3 is a block diagram of an integral type A/D converter.
The waveform diagram of each signal of the D converter, Figure 4, is a comparison diagram of the integral waveform according to the measurement range switching method, and Figure 4 (a) is:
FIG. 4(b) is a diagram showing the case where no offset occurs, FIG. 4(b) is a diagram showing the case where an offset occurs, and FIG. 5 is a configuration diagram showing an example of a conventional integrator. 2... Integrating operational amplifier 2b... Inverting terminal 2C... Non-inverting terminal 22... Integrating resistor for time constant change 23...
・Resistance 24 for changing the integration start voltage...Connection point 25...Switch

Claims (1)

[Claims] In an integral type A/D converter, both ends of an integrating resistor for changing a time constant and a resistor for changing an integration start voltage connected in series are connected to each other.
An integrating type A/D, which is connected to the inverting and non-inverting terminals of an integrating operational amplifier, and further connected between the connection point of both of the resistors and a constant reference potential via a switch.
converter.