JPH0286310A - Integration circuit - Google Patents

Abstract

PURPOSE:To control the integration speed of an analog signal digitally with high accuracy by providing an operational amplifier in which a feedback capacitor is connected between an integration output terminal and an inverting input terminal so as to input a current output to the inverting input terminal. CONSTITUTION:An analog signal Vin and a digital signal DATAin are multiplied in the inside of a D/A converter 5 and a current output Iout is outputted. The said current output Iout is integrated by an operational amplifier 2 and a feedback capacitor 4 and an integration output is outputted from an integration output terminal 3. Then the integration speed of the analog signal Vin depends on the time constant depending on a value of the digital signal DATAin with respect to a D/A converter 5 and the capacitance C of the feedback capacitor 4. Thus, the integration time constant is revised and controlled digitally simply in this way. Then the circuit is controlled with high accuracy depending on the high resolution of the D/A converter 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an integrating circuit used in an analog signal system such as an analog computer.

2. Description of the Related Art Generally, when constructing an analog computer, an integrating circuit (including an adding/integrating circuit) is one of its circuit elements.

Figure 5 shows the configuration of the simplest integration circuit (integrator),
An operational amplifier 1 is provided, an input resistor R is connected to its inverting input terminal (-), and a feedback capacitor C is connected between the output terminal of the operational amplifier 1 and the inverting input terminal (-).

Problems to be Solved by the Invention When attempting to change the time constant that regulates the integration speed in such an integrating circuit, the only option is to change the value of the input resistor R or replace the feedback capacitor C. It's inconvenient.

In this regard, as shown in Fig. 6, human resistors R, , R1, and R3 with different resistance values are prepared in parallel, and
There is also a system in which feedback capacitors Cl1c2+C3 with different capacities are prepared in parallel, and when changing the time constant, the resistance value and capacitance are selected by switching the switches SW, -SW connected to each feedback capacitor. Even in this case, it is inconvenient to change the time constant by changing the switch.

Means for solving the hearing point An operational amplifier with a feedback capacitor connected between the integral output terminal and the inverting input terminal is provided, an analog signal is input to the reference voltage input terminal, and a digital signal for time constant setting is input to the digital signal input terminal. A digital-to-analog converter is provided which receives a signal and inputs a current output to an inverting input terminal of the operational amplifier.

The working analog signal and the digital signal for time constant setting are calculated inside the digital-to-analog converter, and a current output is output as a result. This current output is integrated by an operational amplifier having a feedback capacitor, and an integrated output is output from an integrated output terminal. In other words, the integration speed of the analog signal is
Integration can be performed at a time constant speed determined by the value of the time constant setting digital signal for the digital-to-analog converter and the capacitance of the feedback capacitor 4, and the integration time constant can be easily changed and controlled digitally.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. First, an operational amplifier 2 is provided, and a feedback capacitor 4 having a capacitance of C [μF] is connected between its integral output terminal 3 and its inverting input terminal (-). The non-inverting input terminal (10) is grounded. However,
A digital-to-analog converter (D/A converter) 5 is provided on the input side of the operational amplifier 2. This D/
The A converter 5 is of a multiplication type, and the analog signal Vin is input to the reference voltage input terminal Vref, and the digital signal DA T becomes the digital signal input for setting the time constant.
A in is input to the digital signal input terminal via the digital bus 6, and the current output Iout from the /A converter 5 is input to the inverting input terminal (
-) is connected so that it is input. Therefore, it is also connected to one end of the feedback capacitor 4.

In such a configuration, the analog signal Vin and the digital signal 1) ATAin are multiplied inside the D/A converter 5, and the resultant current output Iout is output. This current output Iout is integrated by an operational amplifier 2 and a feedback capacitor 4, and an integrated output is sent out from an integral output terminal 3.

That is, the integration speed of the analog signal Vin can be integrated at a speed of a time constant determined by the value of the digital signal DATAin for the D/A converter 5 and the capacitance C of the feedback capacitor 4. In this case, the digital signal DATAin for time constant setting can be easily changed and input using data sent from a digital computer or the like. In this way, the integral time constant can be easily changed and controlled digitally. Moreover, the control can be performed with high precision and high resolution due to the resolution of the D/A converter 5.

Incidentally, the integrating circuit of this embodiment is implemented in an analog computer together with a control system, for example, as shown in FIG. First, a first analog switch ASW is interposed between the output of the D/A converter 5 and the feedback capacitor 4. Also, the inverting input terminal (−
), a second analog switch ASW is interposed on the input side of the switch. Further, for the operational amplifier 2, an input resistance Rs and a feedback resistance R are connected to the initial setting input terminal 7.
f is connected. the second analog switch AS
One switching terminal of W is connected to the connection midpoint of these resistors Rs and Rf. Also, a third analog switch A switches the grounding of the feedback capacitor 4 and the feedback resistor Rf.
SW is provided. Furthermore, input terminal 7 for initial setting
An analog switch ASW is provided between the input resistor Rs and the input resistor Rs.

In such a configuration, the modes include a set mode, a hold mode, and a start mode, and in each mode, the analog switches ASW1 to ASW are switched and controlled as shown in the table below.

However, the switch state shown in FIG. 2 is set to H.

First, in the set mode, the equivalent figure 3 (a)
The circuit is in the state shown in FIG. 1, and the D/A converter 5 is disconnected, and the initial voltage V 1ntiaα is input from the initial setting input terminal 7 to charge the feedback capacitor 4 and perform initial setting.

Next, in the hold mode, the D/A converter 5 remains disconnected, and the analog switch ASW
is opened to disconnect the initial setting input terminal 7 as well, resulting in the equivalent state shown in FIG. 3(b), and the feedback capacitor 4 is maintained at a charged voltage state.

Then, in the start mode, which is the integration start mode, by closing the analog switch ASW, the operational amplifier 2 is
The A converter 5 is brought into a connected state. As a result, the current output Iout after the analog signal Vin and the digital signal DATAin are multiplied by the D/A converter 5 is output to the addition point (one end of the feedback capacitor 4), and the above-described integration operation is started.

Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment is configured as an addition/integration circuit. First, two D/A converters 5a and 5b are provided to receive an analog signal V in, .

V in is a digital signal DATA that is input to the reference voltage input terminals Vref, Vref, of each D/A converter 5a, 5b and serves as a digital signal for setting a time constant.
in, , DATAin are each digital buses 6a.

The signal is input to the digital signal input terminal via 6b.

The current outputs I out, , I out from these D/A converters 5a and 5b are both connected to the connection point (summing point) between one end of the feedback capacitor 4 and the inverting input terminal (-) of the operational amplifier 2. has been done.

In such a configuration, digital signals DATAin, , DATAin input to the D/A converters 5a and 5b via the data buses 6a and 6b
, gives weights to the analog signals V in, , V in, adds them, and integrates them.

By increasing the number of D/A converters, etc., the addition/integration circuit can be similarly configured with not only two but three or more.

Also, when implementing it on an analog computer, the second
This can be done in the same way as in the case shown in the figure. That is, a pair of D/A converters 5a and 5b may be connected instead of D/A converter 5 in FIG. 2.

Effects of the Invention The present invention provides an operational amplifier in which a feedback capacitor is connected between an integral output terminal and an inverting input terminal as described above, and an analog signal is input to a reference voltage input terminal, and a digital signal input terminal is used for setting a time constant. Since a digital-to-analog converter is provided that inputs a digital signal and inputs a current output to the inverting input terminal of the operational amplifier, the integration time constant is determined by the value of the digital signal for time constant setting and the capacitance of the feedback capacitor. Therefore, the integration speed of the analog signal can be digitally controlled easily and accurately.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a first embodiment of the present invention, Fig. 2 is a circuit diagram showing an example of implementation in an analog computer, Fig. 3 is an equivalent circuit diagram in each mode, and Fig. 4 is a circuit diagram showing an example of implementation in an analog computer. A circuit diagram showing the second embodiment, and FIGS. 5 and 6 are circuit diagrams showing a conventional example. 2... operational amplifier, 3... integral output terminal, 4...
Feedback capacitor, 5...Digital-to-analog converter

Claims (1)

[Claims] An operational amplifier with a feedback capacitor connected between an integral output terminal and an inverting input terminal is provided, and an analog signal is input to the reference voltage input terminal, and a digital signal for time constant setting is input to the digital signal input terminal, so that the operational amplifier An integrating circuit characterized by being provided with a digital-to-analog converter that inputs a current output to an inverting input terminal.