JPH03220462A - Reference voltage setting circuit - Google Patents

Abstract

PURPOSE:To enable the setting of a reference voltage handily and safely by connecting a variable resistance and an internal power source within an LSI between a reference voltage applying terminal and the ground. CONSTITUTION:When resistance elements 14-1, 14-2... are made the same in resistance value, a level of a reference voltage to be applied to comparators 3-1, 3-2... is set for a microprocessor 17 beforehand. At first, an internal power source 8 is connected to a terminal 9 without driving relay contacts 15-1, 15-2.... A voltage of the terminal 9 is measured by a voltage measuring means 16 to be informed to the microprocessor 17 to judge. Then, when some of the relay contacts 15-1, 15-2... are driven, the voltage of the terminal 9 can be set to a specified value easily. Then, when resistance values of the elements 14-1, 14-2... are set so that they become binary therebetween beforehand, the resistance value is given by R1=R2/2=R3/4=... = Rn/2<n-1>. In this case, a change in voltage of the terminal 9 can be made easy to be linear thereby facilitating the changing of a reference voltage to a set value.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a reference voltage setting circuit that sets a reference voltage to be applied to an LSI that includes a logic circuit and the like and is subjected to an operation test. The purpose of this circuit is to provide a reference voltage setting circuit that can set a reference voltage, and includes a comparator connected to a voltage under test terminal and a reference voltage application terminal to compare the magnitude of the voltage at both terminals, and the output of the comparator In an LSI reference voltage setting circuit that has the function of checking the voltage appearing at the voltage terminal under test of an LSI including a logic circuit by taking it out from the scan-out signal terminal, the It is constructed by comprising a variable resistor and an internal power supply within the LSI.

[Industrial Application Field] This invention relates to a reference voltage setting circuit that sets a reference voltage to be applied to an LSI including a logic circuit and the like, which is subjected to an operation test.

When testing LSIs on a printed circuit board, which are comprised of logic circuits and the like, sequentially through a scanning process, it is necessary to externally apply a DC reference voltage to measure the operation of the LSIs.

Since the reference voltage used an external DC power supply, in the event of an erroneous operation or failure, a high voltage would be applied to the LSI, potentially destroying all the LSIs on the board. Therefore, it has been desired to develop a power supply device for applying a safe reference voltage that will not destroy the LSI.

[Prior Art] Operation tests are performed on LSIs that are mounted on printed circuit boards and are configured to include logic circuits and the like, and are sequentially checked by scanning processing. At this time, a functional test and a network test are usually performed. Perform a functional test on each LSI by applying a predetermined input signal to the connector terminals between boards equipped with multiple LSIs and checking whether the expected value corresponding to the input signal is obtained from the output terminals of each LSI. . In other words, depending on whether the terminal voltage applied to the LSI is above or below the reference value, the output value of the LSI will be "1" or "0".
Make a judgment. Determine whether the logic matches the expected value.

In addition, the net test tests the wiring that connects the output terminal of the preceding stage LSI and the input terminal of the succeeding stage LSI arranged on the board. The voltage at both ends of the wiring is compared with a reference voltage using a comparator, and the accuracy of the wiring is determined eight times based on the magnitude of the voltage drop that occurs between the two ends of the wiring.

FIG. 3 shows a reference voltage setting circuit. A converter is used for comparison with the reference voltage for the above test, and in order to apply the reference voltage to one terminal of the comparator, 8-
Reference numeral 1 indicates, for example, a -1,3■ DC power supply, and reference numeral 8-2 indicates a resistor element, which is an internal power supply. Further, numeral 10 indicates an external DC power source whose voltage can be varied. If the reference voltage application terminal 9 is left open, the reference voltage Vr will be a fixed value of -1.3. When the reference voltage application terminal 9 is connected to the power supply 10, the voltage of the terminal 9 becomes equal to the voltage of the power supply 10. Therefore, the reference voltage can be adjusted to any value by the value of the external DC type SIO.

[Problems to be Solved by the Invention] The circuit shown in FIG. 3 applies a reference voltage Vr to the reference voltage side terminal of each comparator. A large number of LSI chips are arranged side by side on a printed board, and a common reference voltage application terminal 9 is used.
is used to provide the necessary reference voltage to a large number of LSIs. Therefore, if the DC type a10 shown in FIG. At that time, there is a risk that the entire LSI will be destroyed in an instant.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reference voltage setting circuit which can overcome the above-mentioned drawbacks and easily and safely set a reference voltage when sequentially testing LSIs through scan processing.

[Means for Solving the Problems] FIG. 1 is a diagram showing a rear-stage LSI when conducting a net test of an LSI as the principle configuration of the present invention. In Figure 1, 1 is an LSI, 2 is a logic circuit, 3-1.3-2--
- is a comparator, 4 is a scan control circuit, 5 is a control signal terminal for the scan control circuit, 6 is a scan out signal terminal, 9 is a reference voltage application terminal, 8 is an internal power supply (internal resistance Ri), 12 is a variable resistor ( For example, Re), 13 indicates grounding.

A comparator 3-L3-2- is connected to the voltage terminal under test 11-1. Reference voltage setting for an LSI having a function of checking the voltage appearing at the voltage terminal under test 11-1.11-2- of the LSI including the logic circuit 2 by taking out the output of 3-2- from the scan-out signal terminal 6 The circuit of the present invention has the following configuration. That is, it includes a variable resistor 12 connected between the reference voltage application terminal 9 and the ground 13, and an internal power supply 8 within the SI.

[Function] When the output voltage of the preceding stage LSI (not shown in FIG. 1) appears at the voltage under test terminal 1l-Lll-2-, that voltage is connected to the voltage of the reference voltage application terminal 9 by the corresponding comparator 3-.
Compare 1.3-2-. When the voltage at the terminal 11 is smaller than the reference voltage, the output of each comparator 3 is "0", and when it is larger, the output is "1".

A signal applied to the control signal terminal 5 of the scan control circuit is applied in order to output the output of the comparator 3 to the scan out signal terminal in relation to the voltage terminal under test 11. Therefore, from scan out signal terminal 6, “1” or “
0'', it is possible to judge whether the wiring between the circuit and the previous stage LSI is good or bad.Furthermore, by changing the connection with the comparator 3 and performing a functional test, it is possible to judge whether the logic circuit 2 is good or bad.

At this time, the voltage of the reference voltage application terminal 9 is obtained by dividing the voltage of the internal power supply 8 by resistance. That is, it is determined by the ratio between the internal resistance Ri of the internal power source and the external resistance Re.

By changing Re to O-■, the voltage at the reference voltage application terminal 9 changes from OV to the voltage from the power supply 8, for example 1.3.
It can be varied up to v. Since the external resistor 12 is not equipped with a high-voltage power source, there is no risk of the LSI being destroyed.

[Embodiment] FIG. 2 shows an example of the present invention in which the variable resistor 12 of FIG.
FIG.

In Fig. 2, 14-1.14-2- is a resistance element;
Reference numerals 15-1 and 15-2 indicate relay contacts, 16 a voltage measuring means, and 17 a control means such as a microprocessor.

Note that it is effective to use the control means 17 also as the central processing unit of an LSI tester for testing LSI. When the resistance element 14-Li2-2- is set to the same resistance value, the magnitude of the reference voltage to be applied to the comparator 3-L3-2- is set in advance in the microprocessor 17, and initially the relay contact The internal power supply 8 is connected to the terminal 9 without driving the terminals 15-1 and 15-2-.

The voltage at the terminal 9 is measured by the voltage measuring means 16 and notified to the microprocessor 17, which then makes a determination. By driving some of the relay contacts 15-Li2-2-, the voltage at the terminal 9 can be easily set to a predetermined value.

Next, if the resistance values of the resistance elements 14-1, 14-2, etc. are set to be binary, the resistance values are R1=R2/2=R3/4---=Rn
/2I'I-direct, and in this case, the voltage change at the terminal 9 can be easily made linear. Therefore, the set value of the reference voltage can be easily changed.

[Effects of the Invention] In this way, according to the present invention, the reference voltage applied to the comparator can be set using only passive elements such as resistors. This has the effect of not destroying the LSI.

1-・LSI 2-・Logic circuit 3-L3-2--Comparator 6-・Scan out signal terminal 8...Internal power supply 9--Reference voltage application terminal 11-1. IL2-・Voltage under test terminal 12-variable resistor 13-Grounding

Claims (1)

[Claims] I, voltage terminal under test (11-1) (11-2)...
... and a reference voltage application terminal (9), and a comparator (3-1) (3-
2)..., the comparator (3-1) (
3-2) Connect the output of... to the scan out signal terminal (
6), L containing the logic circuit (2)
Test voltage terminals (11-1) (11-2) of SI (1)
L that has the function of checking the voltage appearing on...
In the SI reference voltage setting circuit, the variable resistor (12) connected between the reference voltage application terminal (9) and the ground (13) and the internal power supply (8) in the LSI (1)
) A reference voltage setting circuit comprising: II. As the variable resistor according to claim 1, a plurality of series circuits of resistors and relays are connected in parallel, and a measured value of a voltage measuring device connected to both ends of the series circuit is applied to a microprocessor. The reference voltage setting circuit is characterized in that the make position of the contact of the relay is controlled so that the voltage at both ends of the series circuit becomes a desired value.