JPH04312019A - Integrated circuit - Google Patents

Abstract

PURPOSE:To easily test an operational amplifier without using an analog tester for an integrated circuit containing the operational amplifier and a digital/analog converter on the same chip. CONSTITUTION:At the time of test, a constant-voltage variable-frequency test signal is impressed to the inverted input external terminal 12 of the operational amplifier 11, and its output signal is inputted to an analog/digital converter 25 through a rectifier circuit consisting of a switch 15, a resistor 16, and a diode 17, a smoothing circuit consisting of the resistor 22 and a capacitor. 23, and the switch 24. Then, the digitally converted output signal is taken out of an external terminal 26, and the operational amplifier is tested by a digitally converted value characteristic to the frequency of the test signal.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applied to integrated circuits,
In particular, the central processing unit of a microcomputer (hereinafter referred to as C
It is called PU. ), an analog-to-digital converter, and an operational amplifier are mounted on the same chip, and the present invention relates to an integrated circuit in which the operational amplifier can be easily tested.

0002

[Prior Art] Conventionally, when testing a microcomputer, a digital integrated circuit has a built-in pattern generator, logic analyzer, etc. that generates signals to accurately and quickly evaluate and test the functions of its internal sequential circuits. A test device (hereinafter referred to as a digital tester) is used.

[0003] Furthermore, when testing integrated circuits such as operational amplifiers that are composed only of analog circuits, analog-to-digital converters and frequency measurement circuits are also needed to accurately and quickly evaluate and test their frequency characteristics and gains. A testing device for analog integrated circuits (hereinafter referred to as an analog tester; digital testers and analog testers are collectively referred to simply as the tester) is used.

However, in recent years, with the advent of integrated circuits that include both analog and digital circuits, testing methods have begun to become a problem. If the test to be performed is for technical evaluation, as long as the required data can be collected, multiple testers can be used to efficiently measure each peripheral circuit whose characteristics are to be evaluated, even if it takes some time. It is possible to achieve this objective by selectively using one of these testers.

[0005]

[Problem to be Solved by the Invention] However, in the case of a test to determine whether the product is good or defective in the production process of mass production, the method of selectively using such a tester for evaluation reduces the test time. However, the disadvantage is that profitability is extremely poor in terms of manufacturing costs.

Conventionally, testers have generally been designed with specifications for efficiently testing either digital or analog integrated circuits, and with the advent of such integrated circuits that incorporate both digital and analog parts, I can not cope. Even if a tester manufacturer could quickly provide a tester that efficiently tests both the digital and analog parts, it would be easy for an integrated circuit manufacturer to make the capital investment and buy an expensive tester for mass production. The reality is that it is not possible to purchase multiple units at once.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide an integrated circuit that can easily test operational amplifiers of integrated circuits including operational amplifiers using only a digital tester without using an analog tester. The purpose is to provide circuits.

[0008]

[Means for Solving the Problems] The integrated circuit of the present invention includes an operational amplifier and an analog-to-digital converter, and includes an external terminal for taking out an inverting input, a non-inverting input, and an output of the operational amplifier to the outside. , a plurality of external output terminals for taking out the output of the analog-to-digital converter to the outside, an external signal input terminal for the analog-to-digital converter, one end of which is connected to the output of the operational amplifier, and is in an "off" state during normal use. , "on" during testing
A first switch that is set to the state, and an output when a test signal with a constant voltage and a variable frequency is input to the inverting input terminal of the operational amplifier, which is connected to the other end of the first switch. A rectifier circuit that rectifies a signal, a smoothing circuit that smoothes the output signal of this rectifier circuit, and a switch that switches the input of the analog-to-digital converter to the external signal input terminal during normal times and to the output of the smoothing circuit during testing. It is characterized by including a container.

The integrated circuit of the present invention further includes a test signal generation circuit that generates a test signal with a constant voltage and a variable frequency, one end of which is connected to the inverting input of the operational amplifier and the other end of which is connected to the test signal generation circuit. and a second switch connected to the output of the circuit and set to the "off" state during normal use and the "on" state during testing.

0010

[Operation] When testing an operational amplifier, the first switch and switch are used to set the output of the operational amplifier to be input to the analog-to-digital converter via the rectifier circuit and the smoothing circuit. Then, to the inverting input of the operational amplifier,
An alternating current test signal with a constant voltage and variable frequency is input from the outside or from an internal test signal generation circuit. The operational amplifier outputs an output signal that has been amplified at a predetermined amplification degree, and the analog signal that has been rectified by the rectifier circuit and smoothed by the smoothing circuit is input to the analog-to-digital converter, where it is digitally converted and sent to the external output terminal. Output. In this case, since the gain of the operational amplifier decreases as the frequency of the test signal increases, the output of the analog-to-digital converter also has a predetermined characteristic that decreases depending on the frequency of the test signal.

Therefore, by measuring the output characteristics of this analog-to-digital converter, for example, by fixing the frequency and observing the output value at that time, it becomes possible to easily test the operational amplifier.

0012

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the main parts of a first embodiment of an integrated circuit according to the present invention.

In FIG. 1, an operational amplifier (OP) 11 is provided with an inverting input external terminal 12, a non-inverting input external terminal 13, and an output external terminal 14, and the output is also connected to one end of a switch 15. Ru. The other end of the switch 15 is connected to the anode side of the diode 17 through a resistor 16.
Further, the cathode side of the diode 17 is connected to one end of a parallel circuit of a resistor 22 and a capacitor 23 and to the a1 side of a switch 24. The other end of the parallel circuit of the resistor 22 and capacitor 23 is connected to the non-inverting input of the operational amplifier 11. The b side of the switch 24 is an analog/digital converter (A/D) 25
The output of the analog-to-digital converter 25 is connected to C.
It is forcibly connected to the external output terminal 26 under software control of the PU (central processing unit) or in test mode. The reason why the switch 24 is necessary is that when the operational amplifier 11 is normally provided to the user, it is assumed that the analog-to-digital converter 25 is also provided to the user. This is because the input signal is switched depending on either the test time or the test time. Therefore, the a2 side of the switch 24 is connected to a signal source to be converted when used by the user, generally a signal input terminal 27 for analog input. A reference voltage is externally applied to the non-inverting input external terminal 13 by a reference voltage source 28 .

A feature of the present invention is that in an integrated circuit 40 including an operational amplifier 11 and an analog-to-digital converter 25, an inverting input external terminal 12, a non-inverting input external terminal 13, and an output external terminal 14 of the operational amplifier 11 are connected to an analog A plurality of external output terminals 26 for taking out the output of the digital converter 25 to the outside, an external signal input terminal 27 of the analog-to-digital converter 25, and one end of which are connected to the output of the operational amplifier 11, and are in an "off" state during normal use. A first switch 15 is set to the "on" state during testing, and a test signal with a constant voltage and variable frequency is connected to the other end of the first switch 15 and is applied to the inverting input terminal of the operational amplifier 11. Resistor 1 as a rectifier circuit that rectifies the output signal when input
6 and a diode 17, and a resistor 22 and a capacitor 23 as a smoothing circuit for smoothing the output signal of this rectifier circuit.
and a switch 24 that switches the input of the analog-to-digital converter 25 to the external signal input terminal 27 during normal times and to the output of the smoothing circuit during testing.

Next, the test method of the first embodiment will be explained with reference to the flowchart shown in FIG. When the operational amplifier 11 is normally used, the switch 15 is in the "off" state, and the operational amplifier 11 is disconnected from the circuit for testing the resistor 16 and the like. Therefore, all three terminals, the inverting input external terminal 12, the non-inverting input external terminal 13, and the output external terminal 14, are provided to the user. However, this does not apply if the structure is such that the characteristics of the operational amplifier seen by the user do not deteriorate even if the circuit for testing is not disconnected.

When testing the operational amplifier 11, first, the integrated circuit 40 is set to a test mode by some means, the switch 15 is turned on, and the switch 24 is set to the a1 side. In this state, a feedback resistor 18 is connected in series between the inverting input external terminal 12 and the external output terminal 14 of the operational amplifier 11, and a capacitor 20 and an input resistor 21 are connected in series between the inverting input external terminal 12 and the signal input terminal 19. Connecting. These are configured outside the integrated circuit 40. The steps up to this point are the initial settings in the flowchart of FIG. 2 (step S1).

Next, an AC signal with a variable frequency is applied from the external signal input terminal 19 while keeping the voltage at a constant amplitude (step S2). Then, if the frequency is relatively low, the output external terminal 14 of the operational amplifier 11 is multiplied by the voltage applied to the signal input terminal 19 divided by the resistance value of the feedback resistor 18 by the resistance value of the input resistor 21. (Step S3). Specific means for providing an alternating current signal with a variable frequency while maintaining a constant voltage amplitude will be described later.

The voltage obtained here is an alternating current voltage similar to the signal applied to the signal input terminal 19, and its amplitude value cannot be measured without using an alternating current voltmeter, oscilloscope, or the like. Therefore, this voltage is rectified by a rectifier circuit composed of a resistor 16 and a diode 17 connected through the switch 15 in the "on" state (step S4),
Further, it is converted into a DC voltage by a smoothing circuit composed of a resistor 22 and a capacitor 23 (step S5). Then, the converted DC voltage is sequentially converted into a digital value by the analog-digital converter 25 connected through the switch 24 set on the a1 side (step S6), and output to the external output terminal 26 (step S7). . Once the output analog-digital conversion values have been collected, the frequency of the signal applied to the signal input terminal 19 is changed and the process returns to step S.
Processing from step 2 is performed (steps S8 and S9).

Now, the series of operations is as described above.Next, a concrete means for supplying an AC signal with a variable frequency while keeping the voltage at a constant amplitude to the signal input terminal 19, and an analog-to-digital converter 25. The data processing of the digital values obtained as output will be described.

Although the clock generator included in a digital tester generally has a rectangular wave, the amplitude and frequency of the clock it generates can be programmed relatively easily and with high precision. Therefore, it is easy to program to provide a clock with a fixed amplitude and a variable frequency. When a signal generated by the program is applied to the signal input terminal 19, the output external terminal 14 of the operational amplifier 11 receives a voltage corresponding to the voltage applied to the signal input terminal 19 if the frequency is low. ,
A voltage appears as a product of the resistance value of the feedback resistor 18 divided by the resistance value of the input resistor 21. However, as the frequency is varied, the characteristics become as shown in FIG. 4, and as the frequency increases, the gain of the operational amplifier 11 decreases, and the voltage appearing at the output external terminal 14 decreases. Then, the conversion result of the analog-to-digital converter 25 naturally becomes a small value. That is, by monitoring the output of the analog-to-digital converter 25 with respect to the signal applied to the signal input terminal 19, the frequency characteristics of the analog-operated operational amplifier can be measured only by digital processing.

In this method, while gradually changing the frequency of the test signal applied to the signal input terminal 19, data is collected from the output of the analog-to-digital converter 25 at each frequency, and a characteristic diagram as shown in FIG. 4 is created. In FIG. 4, the horizontal axis shows the frequency of the test signal, and the vertical axis shows the gain ratio when the converted value of the analog-to-digital converter 25 is 100% when the frequency is low. Then, by performing this on a plurality of samples, statistical characteristics such as dispersion are obtained. Also, during selection in the mass production process, we focus on the characteristics of good products whose characteristics obtained in the previous evaluation are the lower limit of the required characteristics, and use the analog-to-digital conversion value at a specific frequency of the sample as the selection standard. Set. Then, if a signal with a specific frequency is applied to each product, and an analog-to-digital conversion value that is greater than the standard value is obtained, it means that the gain is greater than the lower limit of the characteristic of a good product, and if it is less than a good product, the gain is This indicates that the product is insufficient and is determined to be defective.

FIG. 3 is a block diagram showing the main parts of a second embodiment of the integrated circuit of the present invention.

In the second embodiment, in the first embodiment shown in FIG. In this configuration, the signal input terminal 19, capacitor 20, and input resistor 21 are omitted.

The feature of the present invention is that in FIG. 3, an integrated circuit 40a includes, in addition to the first embodiment shown in FIG. and a signal generation circuit 31, one end of which is connected to the inverting input of the operational amplifier 11 and the other end connected to the output of the test signal generation circuit 31, which is set to the "off" state during normal use and the "on" state during testing. and a second switch 29.

The processing flow during testing in the second embodiment is similar to that in the first embodiment, and will be explained using the flowchart in FIG.

First, initial settings are performed in the same manner as in the first embodiment (step S1). That is, when testing the operational amplifier 11, first test the integrated circuit 40 by some means.
Set a to test mode and switch switches 15 and 29 to
"ON" state, set the switch 24 to the a1 side. In this state, a feedback resistor 18 is connected to the outside of the integrated circuit 40a between the inverting input external terminal 12 and the output external terminal 14 of the operational amplifier 11, and the reference voltage source 28 is connected to the non-inverting input external terminal 13.
Connect.

Next, the timer 30 sets the frequency and the signal generating circuit 31 sets the amplitude to generate a signal. Then, the signal output from the signal generation circuit 31 is input to the inverting input terminal of the operational amplifier 11 inside the integrated circuit 40a through the switch 29 in the "on" state (step S2
). The timer 30 is not prepared exclusively for testing, but is a peripheral circuit that is provided to the user during normal use, similar to an analog-to-digital converter. The signal generation circuit 31 is a voltage adjustment circuit, and the timer 3
Generates a small amplitude voltage with a frequency set to 0. That is, in the first embodiment, the input signal to the operational amplifier 11 was given from outside the integrated circuit, but in the second embodiment, the signal is also generated within the same integrated circuit as the operational amplifier. be. The signal thus applied to the inverting input external terminal 12 is amplified by the operational amplifier 11 and appears at the output external terminal 14 (step S3). The subsequent processing is the same as in the first embodiment.

[0029] Compared to the first embodiment, the second embodiment has the following points:
Although the number of signal generation circuits and means for their connections increases, the number of components connected external to the integrated circuit can be reduced. Further, there is an advantage that a program for setting the frequency of the signal supplied from the digital tester can be eliminated.

[0030]

[Effects of the Invention] As explained above, since the present invention uses analog-to-digital converters on the same chip,
Frequency characteristic tests of analog-operated operational amplifiers can be performed like digital tests using only a digital tester or by generating test signals internally. Therefore, instead of spending money and time to test the digital part using a digital tester and testing the operational amplifier using an analog tester, it is now possible to do it in one test using a digital tester. , leading to significant cost reductions. If you are simplifying the test using an analog tester for operational amplifiers and are only testing using a digital tester, you can add analog test items, which will allow you to perform more rigorous testing at about the same cost and at a higher cost. We can provide quality integrated circuits.

Therefore, according to the present invention, there is no need to newly introduce a dual-purpose analog and digital tester through investment in equipment, and moreover, it can be implemented using just a few components such as peripheral circuits and diodes that are conventionally mounted on integrated circuits. This can be achieved by adding , and the effect is great.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing main parts of a first embodiment of the present invention.

FIG. 2 is a flowchart showing the processing flow during the test.

FIG. 3 is a block configuration diagram showing main parts of a second embodiment of the present invention.

FIG. 4 is a characteristic diagram of the output value of the analog-to-digital converter with respect to the frequency of the test signal input to the operational amplifier.

[Explanation of symbols]

11 Operational amplifier (OP) 12 Inverting input external terminal (of operational amplifier) 13
Non-inverting input external terminal 14 (of operational amplifier)
Output external terminals 15, 29 (of operational amplifier)
Switch 16, 22 Resistor 17 Diode 18 Feedback resistor 19 Signal input terminal 20, 23 Capacitor 21 Input resistor 24 Switch 25 Analog-digital converter (A/D) 26
External output terminal 27 External signal input terminal 28 Reference voltage source 30 Timer 31 Signal generation circuits 40, 40a Integrated circuits S1 to S9 Steps

Claims (2)

[Claims] 1. An integrated circuit including an operational amplifier and an analog-to-digital converter, comprising an external terminal for taking out an inverting input, a non-inverting input, and an output of the operational amplifier, respectively, and an external terminal for taking out the output of the analog-to-digital converter to the outside. a plurality of external output terminals to be taken out to the analog-to-digital converter, an external signal input terminal of the analog-to-digital converter, and one end connected to the output of the operational amplifier, which is in an "off" state during normal use;
a first switch that is set to an "on" state during testing;
A rectifier circuit is connected to the other end of the first switch and rectifies the output signal when a test signal with a constant voltage and variable frequency is input to the inverting input terminal of the operational amplifier; An integrated circuit comprising: a smoothing circuit that smoothes an output signal; and a switch that switches the input of the analog-to-digital converter to the external signal input terminal during normal times and to the output of the smoothing circuit during testing. 2. The integrated circuit according to claim 1,
a test signal generation circuit that generates a test signal with a constant voltage and a variable frequency; one end connected to the inverting input of the operational amplifier and the other end connected to the output of the test signal generation circuit, which is "off" during normal use; and a second switch that is set to the "on" state during testing.