JP2000147071A - Characteristics inspection device for analogue circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a characteristics inspection device for an analogue circuit, wherein the characteristics at a specified part of an analogue circuit generated inside an IC is measured easily and accurately. SOLUTION: An IC1 comprises a digital circuit part 2 and an analogue circuit part 3, and characteristics inspection points 4a-4n for inspecting characteristics of the analogue circuit part 3 are connected, corresponding to inspection circuits 5a-5n provided outside the analogue circuit part 3. Furthermore, a register 6, where the inspection result of the inspection circuits 5a-5n is stored, a reference current generating circuit 7 for supplying a reference current for setting the threshold value of the inspection circuits 5a-5n, a threshold control circuit 8 for controlling the level of the threshold are provided with a CPU 9 for controlling the device as a whole. The inspection results recorded in the register 6 are read out sequentially for an output terminal 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog circuit characteristic inspection apparatus for examining the characteristics of an analog circuit in a semiconductor integrated circuit including the analog circuit.

[0002]

2. Description of the Related Art Conventionally, semiconductor integrated circuits (hereinafter referred to as "IC")
), The digital circuit and the analog circuit have been created as separate ICs. However, in recent years, the degree of integration has increased with technological development, and the digital circuit and the analog circuit have been integrated into one IC. Is being done. However, as the digital circuit and the analog circuit are mixedly mounted, and the scale of the mixed analog circuit is increased, it is difficult to know the characteristics of a predetermined portion of the analog circuit.

[0005] Circuit characteristics have been inspected by a method in which a test pin is pulled out from a portion where the characteristics inside the IC are to be known. However, in this method, the number of pins increases as the number of inspection sites increases, and the characteristic deterioration due to pulling out becomes a problem.

In order to suppress an increase in the number of pins, there is also provided a switching circuit for switching the signal from each part to extract an analog signal from one pin, that is, a multiplexer. There has been an error due to the influence or insufficient performance of the multiplexer.

Further, at the IC design stage, a method of directly setting a needle on an IC chip and confirming the characteristics of a target portion has been adopted. However, the parasitic capacitance due to the needle affects the characteristics, and the production is difficult. In a wafer, it is necessary to provide a pad for setting a needle for each part to be inspected, which increases the chip size and increases the cost.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an analog circuit characteristic inspection apparatus capable of easily and accurately measuring the characteristics of a predetermined portion of an analog circuit formed inside an IC. Aim.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a first threshold having a first threshold value for testing a voltage of a predetermined portion in an analog circuit in a semiconductor integrated circuit. A second comparator having a second threshold value;
A comparator using a window comparator whose first threshold is higher than a second threshold; and a reference voltage for generating the first threshold and the second threshold. And a threshold voltage control means for controlling a second threshold value of the second comparator.

In addition, a first comparator having a first threshold value and a second comparator having a second threshold value for testing voltages at a plurality of portions in an analog circuit in a semiconductor integrated circuit. A plurality of inspection means using a window comparator wherein the first threshold is higher than the second threshold;
A reference voltage generator for generating a reference voltage for generating the first threshold and the second threshold, and a second threshold of a second comparator of the plurality of checkers. A threshold value control means; and a test result storage means for storing test results by the plurality of test means, wherein a characteristic test apparatus for an analog circuit for sequentially reading test results from the plurality of test means from the test result storage means. Constitute.

Further, the above-mentioned problem is solved by adding a configuration in which the set level of the reference voltage by the reference voltage generating means is sequentially changed in accordance with the test signal of the analog circuit.

In the analog circuit characteristic inspection apparatus having the above-described configuration, the level of the inspection part of the analog circuit is determined by each of the comparison reference levels of the two comparators, and the inspection results of the plurality of inspection parts are integrated into the IC. Can be sequentially read out from the storage means formed in the storage device. Further, the comparison reference level of the comparator can be adjusted from the outside, and various inspections can be performed.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an I / O circuit including an analog circuit.
C means for inspecting the electrical characteristics of an analog circuit, wherein two comparators having different thresholds are provided, and the threshold is changed by an external signal to detect the operation of the analog circuit. In addition, it is possible to measure the frequency of the analog circuit, and furthermore, a means for storing the detection results is provided in the IC, and the detection results are sequentially read out from the storage means, thereby increasing the number of output pins. It is characterized in that electrical characteristics of a large number of points can be measured.

Next, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a circuit block of an IC having an analog circuit characteristic inspection apparatus according to the present invention. 2 is a diagram showing an example of the reference current generation circuit shown in FIG. 1 and an example of a test circuit. FIG. 3 is a configuration example of a test output stage. FIG. 4 is another example of the reference current generation circuit. It is. FIG. 5 is a diagram for explaining the inspection operation. FIG. 6 is an example of an inspection circuit having a threshold switching circuit of the analog circuit characteristic inspection apparatus according to the present invention.

First, the configuration of an analog circuit characteristic inspection apparatus according to the present invention will be described. A semiconductor integrated circuit including an analog circuit according to the present invention as shown in FIG. 1,
That is, the IC 1 has a digital circuit section 2 and an analog circuit section 3. The analog circuit section 3 has a plurality of characteristic test points 4 a to 4 n for which characteristics are to be tested. The inspection circuits 5a to 5n are provided, and the characteristic inspection points 4a to 4n
To 5n.

A register 6 for storing test results of the test circuits 5a to 5n; a reference current generating circuit 7 for supplying a reference current for setting a comparison reference level of the test circuits 5a to 5n, ie, a threshold value; A threshold control circuit 8 for controlling a threshold level is provided. Further, control of the entire apparatus is performed by the CPU 9, and the recorded inspection results are sequentially read from the output terminal 10 from the register 6.

Next, the configuration of the inspection circuits 5a to 5n will be described using the inspection circuit 5a as an example. Inspection circuit 5b ~
The same applies to 5n. As shown in FIG. 2, the inspection circuit 5a has two comparators 11 and 12 in a two-stage configuration, and the voltage of the characteristic inspection point 4a is input to each + terminal. The negative terminal of the comparator 11 is connected to the current source 13 from the power supply Vcc, the negative terminal of the comparator 12 is connected to the resistor R1 from the negative terminal of the comparator 11, and the negative terminal of the comparator 12 is connected to the negative terminal. A resistor R2 is inserted between GND.

Here, assuming that the current value of the current source 13 is I0, the potential of the minus terminal of the comparator 11 is (R1 + R2) × I0 (that is, the first threshold value), and the potential of the minus terminal of the comparator 12 is Is R2.times.I0 (that is, the second threshold value). The threshold value used as the reference for the two comparators has a potential difference of R1.times.I0, forming a so-called window comparator. The potential of the characteristic inspection point 4a is determined by the combination of the output levels of the comparators 11 and 12 based on these thresholds.

As a circuit for generating the current I0 of the current source 13, there is a reference current generating circuit 7. The reference voltage V is input to the + terminal of the arithmetic unit 14 via the control input terminal 15, and the transistor T connected to the output terminal of the arithmetic unit 14
A current I0 flows through the resistor R3 via r1, and this current is turned back by the current mirror, so that the current value of the current source 13 becomes I0.
Therefore, when the reference voltage V is changed, the threshold values of the comparators 11 and 12 change accordingly, and it is possible to cope with various analog voltage tests. Note that the resistor R4
Is for canceling the offset caused by the resistor R5.

In the example of the reference current generating circuit 7 shown in FIG. 2, an internal reference voltage Vref and an external voltage V are switched by a switch 16. Further, the voltage V is configured to be changed. Here, when the switch 16 is turned off and the reference voltage Vref is connected, the threshold value VTH1 of the comparator 11 and the threshold value VTH2 of the comparator 12 are expressed by the following (1).
Expression (2) and Expression (2). VTH1 = (Vref / R3) .times. (R1 + R2) (1) VTH2 = (Vref / R3) .times.R2 (2)

Further, as can be seen from the equations (1) and (2), the thresholds are set above and below the reference voltage Vref by setting the respective resistors in a relationship of R2 <R3 <R1 + R2. The threshold width VTH1−VTH2 =
(Vref / R3) × R1 can be set arbitrarily. Since the resistances R1, R2 and R3 determine the threshold value, I
It is desirable to configure the semiconductor device in C with a length that can ensure accuracy as a semiconductor.

Therefore, in order to check whether the analog voltage to be inspected is the target voltage, the reference voltage Vref may be set to the target voltage. That is, the switch 16 is switched to connect the external voltage V, and the voltage is adjusted to a predetermined voltage for inspection. At this time, two comparators 1
If both outputs of logics 1 and 12 are logic "H", the analog voltage is higher than the target voltage, and if both are logic "L", the analog voltage is lower than the target voltage. If the logic "L" and the output of the comparator 12 are logic "H", it is understood that the output is within the two set thresholds.

The outputs from the comparators 11 and 12 appear at the terminals 17 and 18. However, if there are many points to be inspected, providing output pins for all of them requires an enormous number of pins. It is as described in the prior art that there is a possibility of making it possible. As a countermeasure against this, the present invention employs a configuration in which the register 6 is provided as shown in FIG. 1, the inspection result is recorded at a predetermined position of the register 6, and then read out sequentially. As a result, the output terminal is 1
All you need is a book. The correspondence between the sequentially read test results and the test points of the analog circuit can be determined based on, for example, a clock by the CPU 9.

Instead of directly taking out the output from each comparator, it is determined whether the voltage to be inspected is within a predetermined range, higher than the predetermined range, or lower than the predetermined range, and the result is determined. You may make it output.

For example, as shown in FIG.
And an AND gate 22. By connecting the output of the comparator 11 (terminal 17) to the terminal 23 and connecting the output of the comparator 12 (terminal 18) to the terminal 24,
Is higher than the predetermined range if the output of the terminal 25 is logic "L" and the output of the terminal 26 is logic "H" if the output of the terminal 25 is logic "H". Is lower than the predetermined range if the output of the terminal 26 is logic "L" and the output of the terminal 26 is also logic "L". Of course, these forms of signals may be recorded in the register 6 and taken out.

Further, a digital circuit and a D / A converter may be used as the reference voltage. For example, as shown in FIG. 4, a D / A converter 31 and a digital reference voltage generation circuit 32 are provided, and the reference voltage V can be set by digital data from the digital reference voltage generation circuit 32. In this case, it is easy to make the voltage value fluctuate according to a predetermined program. That is, after the reference voltage value is scanned and data within a predetermined range is obtained, the input frequency to the analog circuit is changed, and the CPU 9 sequentially performs inspection to measure the frequency characteristics of the analog circuit. You can also. In this case, the operation of the digital reference voltage generating circuit 32 may be executed by a program of the CPU 9.

The measurement result of the frequency characteristic can be determined as follows. First, as an initial setting of the measurement, FIG.
As shown in FIG.
The reference voltage V is set so that the output of No. 8 becomes logic “L”. That is, the threshold value VTH1 of the comparator 11 and the threshold value VTH2 of the comparator 12 are both set to be higher than the input voltage.

Next, the reference voltage V is lowered, and FIG.
As shown in (b), the output of terminal 17 is always set to logic "L", while the output of terminal 18 is set so that logic "H" is generated in a pulsed manner. In this state, the magnitude of the output at the input frequency can be determined. If this state is maintained even when the frequency is changed, it is understood that the frequency characteristic is flat in the frequency range.

In this state, as shown in FIG. 5C, the output of the terminal 17 is that when the logic "H" is generated in a pulse shape, the gain is increased. As shown, if the outputs of the terminals 17 and 18 are always at the logic "L", it can be understood that the gain has decreased.

In addition, FIG.
An accurate frequency characteristic can be obtained by searching for the reference voltage V as shown in FIG. That is, the inspection output of the output terminal 10 is monitored by the CPU 9, the digital reference voltage is scanned in accordance with the output state, converted into an analog voltage by the D / A converter 31, and input from the control input terminal 15,
When the state shown in FIG. 5B is detected, the scanning is stopped, the reference voltage at that time is stored, and inspection is performed by sequentially changing the frequency in the same manner.

FIG. 6 shows a threshold control circuit for adjusting the threshold difference VTH1 -VTH2 between the comparator 11 and the comparator 12 when the difference is too small to be suitable for another measurement. It is an example of a test circuit having. A resistor R6 is connected to a connection point between the resistors R1 and R2, and the resistor R6 is connected to GND via a transistor Tr2.

In particular, it goes without saying that the characteristic inspection apparatus having the above-described configuration can inspect a direct current (DC) level in addition to an alternating current (AC) analog signal. In this case, however, the threshold between the comparator 11 and the comparator 12 is used. It is also possible to set the value difference VTH1−VTH2 to be small to perform a highly accurate DC level detection. However, the difference between the threshold values set here is too narrow for the purpose of testing an AC analog signal,
The test signal may not be stable, making the measurement difficult. Therefore, the threshold value control circuit can be used to change the threshold value according to the purpose of testing the DC level and the AC analog signal.

Next, the operation of the threshold control circuit shown in FIG. 6 will be described. When a switching signal is input to the base of the transistor Tr2, the transistor Tr2 turns on,
The current I2 flows through the resistor R6 and the transistor Tr2 to GND.
And the current I1 flowing through the resistor R2 is I1 = I0-I2
Therefore, the potential of the negative terminal of the comparator 12 is R2 × I
It becomes 1 and its potential drops. Comparator 1
The potential of the negative terminal of the terminal 1 also decreases and does not change to the difference between the threshold values. However, if the reference voltage V is adjusted to a predetermined level, the current I0 increases, and eventually the threshold difference R
1 × I0 will be enlarged.

It is needless to say that the level of the two thresholds and the difference between the thresholds can be arbitrarily set by adjusting the magnitude of the current I2 and the reference voltage V.

It is to be noted that the present invention is not limited to the above-described embodiment, but may take any circuit configuration embodying the technical idea of the present invention.

[0034]

As described above, according to the analog circuit characteristic inspection apparatus of the present invention, it is possible to omit the routing of an analog signal for inspecting the analog circuit characteristics inside the IC, thereby deteriorating the circuit characteristics. The characteristics of the analog circuit can be inspected without the need, and the circuit scale can be reduced.

Further, since the number of pins of the IC is not increased, the size of the IC is reduced, which contributes to a reduction in cost.

Further, in an IC equipped with the analog circuit characteristic inspection apparatus of the present invention, the system for inspection can be simplified.

Further, since the DC level can be accurately measured by limiting the threshold width to be narrow, and no external signal is required, it is possible to perform a self-test of the system constituted by using this IC.

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit block of an IC having an analog circuit characteristic inspection apparatus according to the present invention.

FIG. 2 is a diagram illustrating an example of a reference current generation circuit illustrated in FIG. 1 and an example of an inspection circuit.

FIG. 3 is a configuration example of a test output stage of the analog circuit characteristic test device shown in FIG. 1;

FIG. 4 is another example of the reference current generation circuit shown in FIG.

FIG. 5 is a diagram for explaining an inspection operation.

FIG. 6 is an example of a test circuit having a threshold control circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... IC, 2 ... Digital circuit part, 3 ... Analog circuit part,
4a to 4n: characteristic inspection points, 5a to 5n: inspection circuits, 6:
Register 7, reference current generating circuit 8, threshold control circuit 9, CPU 10, output terminal 11, 12, comparator 13, current source 14, arithmetic unit 15, control input terminal 16, ... Switches 17, 18, 23, 24, 25,
26 terminal, 21 INV gate, 22 AND gate, 31 D / A converter, 32 digital reference voltage generation circuit

Claims (4)

[Claims] A first comparator having a first threshold value and a second comparator having a second threshold value for testing a voltage at a predetermined portion in an analog circuit in the semiconductor integrated circuit; An inspection means using a window comparator whose first threshold value is higher than a second threshold value; and a reference for generating a reference voltage for generating the first threshold value and the second threshold value. A characteristic inspection apparatus for an analog circuit, comprising: a voltage generator; and a threshold controller for controlling a second threshold of the second comparator. 2. A semiconductor device comprising: a first comparator having a first threshold value and a second comparator having a second threshold value for testing voltages at a plurality of portions in an analog circuit in a semiconductor integrated circuit. A plurality of inspection means using a window comparator whose first threshold value is higher than a second threshold value; and a reference voltage for generating the first threshold value and the second threshold value. Reference voltage generating means, threshold value control means for controlling a second threshold value of the second comparator of the plurality of test means, and test result storage means for storing test results of the plurality of test means. A characteristic inspection apparatus for an analog circuit, comprising: sequentially reading inspection results from the plurality of inspection units from the inspection result storage unit. 3. The apparatus according to claim 1, wherein the reference voltage generated by said reference voltage generating means is configured to sequentially change a set level in accordance with a test signal of an analog circuit.
4. The characteristic inspection apparatus for an analog circuit according to claim 1. 4. The configuration according to claim 2, wherein the reference voltage generated by the reference voltage generation means changes a set level sequentially in accordance with an inspection signal of an analog circuit.
4. The characteristic inspection apparatus for an analog circuit according to claim 1.