JP2959174B2 - Integrated circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is used for integrated circuits,
In particular, a central processing unit (hereinafter referred to as C) of a microcomputer
It is called PU. ), An analog-to-digital converter and an operational amplifier on an integrated circuit.

[0002]

2. Description of the Related Art Conventionally, when testing a microcomputer, a digital integrated circuit incorporating a pattern generator, a logic analyzer, and the like for generating a signal for accurately and quickly evaluating and testing the function of an internal sequential circuit. (Hereinafter referred to as a digital tester).

In the case of testing an integrated circuit consisting of only an analog circuit such as an operational amplifier, an analog-to-digital converter and a frequency measurement circuit for accurately and quickly evaluating and testing the frequency characteristics and gain thereof are also used. (Hereinafter referred to as an analog tester, and digital testers and analog testers are collectively referred to simply as testers).

However, in recent years, with the advent of integrated circuits in which analog circuits and digital circuits are mixed, the test method has begun to become a problem. If the test to be performed is a test for technical evaluation, as long as the required data can be collected, even if it takes some time, multiple testers that can measure efficiently for each peripheral circuit whose characteristics are to be evaluated are required. The purpose can be achieved by selectively using one of the above testers.

[0005]

However, in the case of a test for judging a non-defective product or a defective product in a mass-production production process, such a method of selectively using such a tester to evaluate the test time. However, there is a disadvantage that profitability is extremely deteriorated in terms of manufacturing cost.

Conventionally, testers are generally designed to efficiently test either digital integrated circuits or analog integrated circuits. With the advent of integrated circuits that incorporate both such digital and analog sections, I can not cope. Even if the tester manufacturer provided a tester that quickly and efficiently tests both the digital and analog sections, the integrated circuit manufacturer could easily make capital investments and produce expensive testers for mass production. The reality is that you can't afford to get many.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned drawbacks so that the test of an operational amplifier of an integrated circuit including an operational amplifier can be easily performed only by a digital tester without using an analog tester. It is to provide a circuit.

[0008]

An integrated circuit according to the present invention is an integrated circuit including an operational amplifier and an analog-to-digital converter, wherein external terminals for inverting, non-inverting input and output of the operational amplifier are taken out. A plurality of external output terminals for extracting the output of the analog-to-digital converter to the outside, an external signal input terminal of the analog-to-digital converter, and one end connected to the output of the operational amplifier. , "On" when testing
A first switch set to a state, and an output when a test signal having 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 rectifying circuit for rectifying a signal, a smoothing circuit for smoothing an output signal of the rectifying circuit, and a switch for switching an input of the analog-to-digital converter to the external signal input terminal in a normal state and to an output of the smoothing circuit in a test. And a container.

The integrated circuit according to the present invention further comprises a test signal generating circuit for generating a test signal having a constant voltage and a variable frequency, and one end connected to the inverting input of the operational amplifier and the other end connected to the test signal generating circuit. A second switch connected to the output of the circuit and set to an "off" state during normal use and an "on" state during testing.

[0010]

When testing the operational amplifier, the output of the operational amplifier is set by the first switch and the switch so as to be input to the analog-to-digital converter via the rectifier circuit and the smoothing circuit. And to the inverting input of the operational amplifier,
An AC test signal having a constant voltage and a variable frequency is input from an external or internal test signal generation circuit. An output signal amplified at a predetermined amplification degree is output from the operational amplifier, an analog signal rectified by the rectifier circuit and smoothed by the smoothing circuit is input to the analog-to-digital converter, digital-converted, and output to an external output terminal. Is 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, it is possible to easily test the operational amplifier by measuring the output characteristics of the analog / digital converter, for example, by observing the output value at a fixed frequency.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a main part 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. You. The other end of the switch 15 is connected to the anode side of a diode 17 through a resistor 16 and further connected to a diode
The cathode side of 17 is connected to one end of a parallel circuit of a resistor 22 and a capacitor 23 and to the a1 side of the switch 24. Resistance 22 and capacitance
The other end of the parallel circuit with 23 is connected to the non-inverting input of the operational amplifier 11. The b side of the switching unit 24 is connected to an analog-to-digital converter (A / D) 25, and the output of the analog-to-digital converter 25 is forcibly controlled by software of a CPU (central processing unit) or in an external output terminal in a test mode. Connected to 26. The reason why the switch 24 is necessary is that
This is because it is assumed that the analog-to-digital converter 25 is also provided to the user when the operational amplifier 11 is normally provided to the user. This is for switching. Therefore, a signal source for converting when the user uses the signal, generally a signal input terminal 27 for analog input, is connected to the a2 side of the switch 24. The non-inverting input external terminal 13 is externally supplied with a reference voltage from 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 and a non-inverting input external terminal 13 of the operational amplifier 11 are provided.
And output external terminal 14 and analog / digital converter 25
Are connected to the output of the operational amplifier 11, and are turned off during normal use, and turned on during testing. The first switch 15 set to the state, and connected to the other end of the first switch 15, a test signal having a constant voltage and a variable frequency input to the inverting input terminal of the operational amplifier 11 was input. A resistor 16 and a diode 17 as a rectifier circuit for rectifying an output signal at the time, and a resistor 22 as a smoothing circuit for smoothing an output signal of the rectifier circuit.
And a switch 23 for switching the input of the analog-to-digital converter 25 to the external signal input terminal 27 at normal times and to the output of the smoothing circuit at the time of testing.

Next, the test method of the first embodiment will be described with reference to the flowchart shown in FIG. During normal use, the operational amplifier 11 has the switch 15 in the “OFF” state, and is disconnected from the circuit for testing such as the resistor 16. Therefore, the inverting input external terminal 12 and the non-inverting input external terminal
The three terminals 13 and the output external terminal 14 are provided to the user. However, this does not apply to a structure in which the characteristics of the operational amplifier do not deteriorate from the viewpoint of the user even if the circuit for the test is not cut off.

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 between the inverting input external terminal 12 and the external output terminal 14 of the operational amplifier 11, and the inverting input external terminal
A capacitor 20 and an input resistor 21 are connected in series between 12 and the signal input terminal 19, respectively. These are configured outside the integrated circuit 40. Up to this point is the initial setting in the flowchart of FIG. 2 (step S1).

Next, an AC signal having a variable frequency is supplied from the external signal input terminal 19 while the voltage is kept constant.
(Step S2). Then, when the frequency is relatively low, the output external terminal 14 of the operational amplifier 11 is connected to the signal input terminal.
The amplified voltage is amplified to a voltage obtained by multiplying the voltage given to 19 by the value obtained by dividing the resistance value of the feedback resistor 18 by the resistance value of the input resistor 21 (step S3). Specific means for providing an AC signal having a variable frequency while the voltage has a constant amplitude will be described later.

The voltage obtained here is an AC voltage similar to the signal supplied to the signal input terminal 19, and its amplitude value cannot be measured unless an AC voltmeter or an oscilloscope is used. Therefore, this voltage is switched on
Rectification is performed by a rectifier circuit composed of a resistor 16 and a diode 17 connected through the line 15 (step S4).
Convert to DC voltage by smoothing circuit composed of 22 and capacitor 23
(Step S5). Then, the converted DC voltage is represented by a1
Is sequentially converted to a digital value by an analog-to-digital converter 25 connected through a switch 24 set on the side (step S6) and output to an external output terminal 26.
(Step S7). When the output analog-to-digital conversion values can be collected, the frequency of the signal applied to the signal input terminal 19 is changed, and the processing from step S2 is performed again (steps S8 and S9).

A series of operations is as described above. Next, specific means for supplying an AC signal having a variable frequency to the signal input terminal 19 while keeping the voltage at a constant amplitude, and the analog-digital converter 25 Data processing of a digital value obtained as an output will be described.

Although the clock generator of a digital tester is generally a rectangular wave, the amplitude and frequency of the generated clock can be programmed relatively easily with high accuracy. Therefore, it is easy to program so as to give a clock with a fixed amplitude and a variable frequency. When a signal generated by the program is given to the signal input terminal 19, the operational amplifier 11
If the frequency is low, the voltage applied to the signal input terminal 19 is applied to the feedback
The voltage appears as a voltage obtained by multiplying the resistance value of 18 by the resistance value of the input resistor 21. However, as the frequency is varied, the characteristics shown in FIG. 4 are obtained. 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-digital converter 25 naturally has a small value. That is, by monitoring the output of the analog-to-digital converter 25 with respect to the signal supplied to the signal input terminal 19, the frequency characteristic of the operational amplifier operating in analog mode can be measured only by digital processing.

In this manner, while gradually changing the frequency of the test signal applied to the signal input terminal 19, the output of the analog-to-digital converter 25 at each frequency is collected as data.
A characteristic diagram as shown in FIG. 4 is created. In FIG. 4, the horizontal axis indicates the frequency of the test signal, and the vertical axis indicates the gain ratio when the converted value of the analog-to-digital converter 25 when the frequency is low is 100%. Then, by performing this for a plurality of samples, statistical characteristics such as variation are obtained. At the time of screening in the mass production process, pay attention to the characteristics of non-defective products, where the characteristics obtained by the previous evaluation are the lower limit to the required characteristics, and convert the analog-to-digital conversion value at a specific frequency of the sample to the screening standard. Set. Then, a signal of that specific frequency is given to each product, and if an analog-to-digital conversion value of a value equal to or greater than the standard value is obtained, it means that there is a gain equal to or higher than the good product with the lower limit of the characteristic. It is insufficient, and is determined to be defective.

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

The second embodiment differs from the first embodiment shown in FIG. 1 in that the inverting input of the operational amplifier 11 is connected to one end of a switch 29, and the other end of the switch 29 is connected to a clock signal generated by a timer 30. Is input to the output of a signal generation circuit 31 that generates a signal of a small amplitude voltage, and a signal input terminal 19,
The capacitor 20 and the input resistor 21 are omitted.

A feature of the present invention is that, in FIG.
40a is a timer 30 and a signal generation circuit 31 as a test signal generation circuit for generating a test signal having a constant voltage and a variable frequency in addition to the first embodiment of FIG. Test signal generation circuit connected to input and the other end
It is connected to the output of 31.
A second switch 29 which is set to an “ON” state during a test is included.

The processing flow of the second embodiment during the test is the same as that of the first embodiment, and will be described with reference to the flowchart of FIG.

First, initial settings are made in the same manner as in the first embodiment (step S1). That is, when testing the operational amplifier 11, first, the integrated circuit 40a is set to the test mode by some means, the switches 15 and 29 are turned on,
The switch 24 is set to the a1 side. In this state, the operational amplifier
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 11, and a reference voltage source 28 is connected to the non-inverting input external terminal 13.

Next, the frequency is set by the timer 30 and the amplitude is set by the signal generation circuit 31, respectively, 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). Timer 30
Is a peripheral circuit mounted for the purpose of being provided to the user during normal use, similarly to the analog-to-digital converter, not prepared exclusively for the test. Signal generation circuit 31
Is a voltage adjusting circuit for generating a small amplitude voltage having a frequency set by the timer 30. That is, in the first embodiment, the input signal of the operational amplifier 11 is given from the outside of the integrated circuit. However, in the second embodiment, the signal is also generated in the same integrated circuit as the operational amplifier. is there. The signal given to the inverting input external terminal 12 in this way is
The signal 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.

The second embodiment is different from the first embodiment in that
Although the number of signal generation circuits and the means for connecting them are increased, the number of components connected to the outside of the integrated circuit can be reduced.
Another advantage is that a program for setting the frequency of the signal supplied from the digital tester can be eliminated.

[0030]

As described above, the present invention is performed using an analog-to-digital converter on the same chip.
The frequency characteristic test of an operational amplifier operating in analog mode can be performed using only a digital tester or by generating a test signal internally, like a digital test. Therefore, it is possible to use a digital tester to perform a single test using a digital tester, which is a two-time test that requires a lot of time and money. , Leading to significant cost reduction. If the test of the operational amplifier with the analog tester was simplified and only the test with the digital tester was performed, the analog test items could be added, and at the same cost, more rigorous tests could be performed. A high quality integrated circuit can be provided.

Therefore, according to the present invention, it is not necessary to newly introduce a combined analog and digital tester by capital investment, and furthermore, a small number of components such as a peripheral circuit and a diode which are conventionally mounted on an integrated circuit. Can be realized, and the effect is great.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing a processing flow at the time of the test.

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

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03M 1/00-1/88 H03F 1/00-3/72 G01R 31/28-31/30

Claims (2)

(57) [Claims] 1. An integrated circuit including an operational amplifier and an analog-to-digital converter, an external terminal for taking out an inverting input, a non-inverting input, and an output of the operational amplifier, respectively, and an output of the analog-to-digital converter. A plurality of external output terminals, an external signal input terminal of the analog-to-digital converter, and one end connected to the output of the operational amplifier, which are set to an "off" state during normal use and an "on" state during a test. A first switch, connected to the other end of the first switch, and a rectifier for rectifying an output signal when a test signal having a constant voltage and a variable frequency is input to the inverting input terminal of the operational amplifier; A circuit, a smoothing circuit for smoothing an output signal of the rectifier circuit, and an input of the analog-to-digital converter which is normally connected to the external signal input terminal. An integrated circuit, which sometimes includes a switch for switching to an output of the smoothing circuit. 2. The integrated circuit according to claim 1, wherein a test signal generating circuit for generating a test signal having a constant voltage and a variable frequency, and one end connected to an inverting input of the operational amplifier and the other end connected to the test circuit. An integrated circuit, comprising: a second switch connected to an output of the signal generation circuit and set to an “OFF” state during normal use and an “ON” state during a test.