JPH0518064B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is applicable to a laser trimming device that trims a part of a resistor of an electronic circuit such as a hybrid IC or a resistor module to adjust it to a predetermined value, and a laser trimming device that trims a part of a resistor of an electronic circuit such as a hybrid IC or a resistor module to adjust it to a predetermined value, and a resistor of a printed circuit board. The present invention relates to a high-precision resistance measuring instrument used for measuring and determining resistance, such as an in-circuit tester that checks the resistance value of a circuit.

BACKGROUND ART As a conventional example, FIG. 4 shows a principle diagram of a resistance measuring device used in a laser trimming device.

In the figure, 1 is an operational amplifier, 2 is an operational amplifier 1
an analog-to-digital converter (hereinafter abbreviated as an A-D converter) that converts the output voltage V _O of the output voltage V O into a digital value D _O ;
3 is the resistor R _x1 to be laser trimmed
A digital-to-analog converter (hereinafter abbreviated as DA converter) converts the setting input data D _I corresponding to the target resistance value of R _x3 into an analog voltage V _I , 4 is the above-mentioned V _O
Compares the voltages of V I and V _I , and when the condition of V _I > V _O is met, the laser trimming device stops emitting laser light and outputs a judgment signal D _C to finish trimming.
This is a voltage comparator that outputs . R _s1 ~ _{R s3} and
V _s1 to V _s3 are a precision resistor and a reference constant voltage source, respectively, which are very stable in the ambient environment such as temperature and humidity and have little change over time. P ₁ and P ₂ are terminals for measuring unknown resistance,
SV ₁ to _{SV 3} , SS ₁ to _{SS 3} are relay contacts for selecting the resistance range of this measuring instrument, and S _x1 to _{S x6} are relay contacts for determining which of the resistances to be measured is selected. , for example, when selecting R _x1 , select S _x1 and S _x4
Turn on.

Now, in the measuring device configured as above, if the output of operational amplifier 1 is V _O , the precision resistance selected by the relay is R _s , the reference voltage is V _s , and the value of the unknown resistance is R _x , then the formula is It is expressed by a relational expression like (1).

R _x = -V _s /V _O R _s ...(1) Therefore, the voltage V _O is
If the known values of V _s and R s are registered by converting them into digital values D _O and inputting them into a microcomputer (not shown), the value of the unknown resistance value R _x can _be calculated from equation (1). can. Also, simply set the resistance to be measured R _x to a predetermined value.
When determining whether R _a is greater than or less than R a, set the D-A converter so that the digital value D ₁ becomes the voltage V _I shown in equation (2), and the judgment output
You can get D _c .

V _I = −R _s /R _a V _s (2) Problems to be Solved by the Invention However, in the above configuration, it is difficult to determine whether laser trimming exceeds the target value and to eliminate errors in resistance value measurement. In order to achieve high accuracy of 0.1% or less, in addition to the stability of the reference power supply and precision resistor, there are also the zero point drift of the operational amplifier 1 and voltage comparator 4, and the AD converter 2 and DA converter 3. Since the conversion gain and drift of the zero point affect accuracy, the condition is that the change in the surrounding environment of each of the above circuit components is 0.01% or less. Therefore, it is necessary to carefully select the parts to be used, use only the best ones, and devise mounting techniques to reduce circuit drift, resulting in high costs and requiring periodic accuracy adjustments.

In view of the above-mentioned problems, the present invention provides a high-precision resistance measuring instrument that limits high-performance components to only precision resistors and that determines and measures resistance values at low cost and with high precision.

Means for Solving the Problems In order to solve the above problems, the present invention determines whether the resistance value of the unknown resistor exceeds the target resistance value.
In a high-precision resistance measuring instrument that outputs bit ON/OFF signals, two ultra-precision resistors R _r1 and R _r2 with known and stable resistance values are provided for each measurement range.
A reference power supply that generates a constant voltage or current, a measurement terminal for connecting an unknown resistance, a resistance value-to-voltage conversion circuit that amplifies the current or voltage between the measurement terminals and converts it into voltage, and a digital-to-analog converter. , the resistance value-voltage conversion circuit and the digital
Is it ON by comparing it with the output voltage of the analog converter?
A voltage comparator outputs an OFF signal, and a given target resistance value R ₁ is converted into the input data D _D of the digital-to-analog converter by D _P −B/R ₁ +Z _B (B and
Z _B is a constant); a switching relay circuit for selecting one of the ultra-precision resistor and the unknown resistor and connecting it to the measurement terminal; and the ultra-precision resistor R _r1 , R _r2 are connected, and the output of the voltage comparator is ON in each state.
detection means for finding the input data D _D1 , D _D2 of the digital-to-analog converter that is in the OFF boundary state, and the constant B=(D _D2 −D _D1 )・R _r1・
R _r2 / (R _r2 − R _r1 ), Z _B = (D _D1・R _r1 −D _D2・
R _r2 )/(R _r2 - _{R r1} ).

Effect As described above, in the present invention, the microcomputer calculates the zero point and conversion gain of the analog circuit every short period of several seconds to several tens of seconds, so drifts in the zero point and gain of the measuring instrument do not accumulate as measurement errors. . Additionally, the only component that requires high stability is the ultra-precision resistor.

Embodiment FIG. 1 shows an embodiment in which the resistance value measurement range is limited to a single range of 10KΩ to 100KΩ in order to explain the principle of the present invention in an easy-to-understand manner. As in the conventional example, 1 is an operational amplifier, 2 is an A-D converter, and 3 is a D
-A converter; 4 is a voltage comparator; and 5 is a microcomputer equipped with input/output interface, memory, calculation and judgment functions. _P1 ,
_P2 is the measurement terminal, R _x1 ~ _{R x3} are unknown resistances,
In this case, the range is 10KΩ to 100KΩ. R _r1 ,
R _r2 is an ultra-precision resistor whose resistance value hardly changes due to aging, temperature, or humidity (less than a few ppm), and is 10.000KΩ and 100.00KΩ, respectively. R _s is an ordinary (several tens to hundreds of ppm) precision resistance. S _x1 ～
S _x6 and SR ₁ ~ SR ₄ are relay contacts, and the above R _x1 ~
Either R _x3 or R _r1 or R _r2 is selected, and the microcomputer 5 controls SR ₁ to SR ₄ . S _x1 and S _x6 may be controlled by an external control device. V _s is a reference constant voltage source. now,
When V _s = -(V) and the relay contacts SR ₁ and SR ₂ are selected, V _O = 10 (V) according to the above equation (1), and the value is converted from A to D and sent to the microcomputer. 5
is input. However, as mentioned above, the operational amplifier 1 and the A-D converter 2 have a zero point drift, and the values of V _s and R _s change due to changes in the surrounding environment and change over time. In reality, the output data D _A of the A-D converter 2 equivalent to 10 (V) cannot be obtained stably for a long time. The output data of the A-D converter at this time is D _A1 , the total zero point drift of operational amplifier 1 and A-D converter 2 is Z _A , the conversion gain including the reference voltage V _s and precision resistor R _s is represented by A, the following equation holds between them.

D _A1 = A/R _r1 + Z _A (3) Similarly, when R _r2 is selected, it is expressed by the following formula.

D _A2 = A/R _r2 + Z _A (4) where D _A2 is the output data of the A-D converter.

A solution is found from equations (3) and (4) with A and Z _A as unknowns.

A=D _A2 −D _A1 ／R _r1 −R _r2・R _r1・R _r2 …(5) Z _A ＝D _A1 R _r1 −D _A2 R _r2 ／R _r1 −R _r2 …(6) Now, the unknown resistance When the value R _x , A-D converter 2
When the output of is D _Ax , the following equation holds true similarly to equation (3).

D _Ax = A/R _x + Z _A …(7) Therefore, R _x = A/D _Ax −Z _A …(8) Therefore, using the values of A and Z _A above,
R _x can be calculated. The microcomputer 5 is
The value of R _x above is output to the outside as measurement data R _O.

Similarly, it is thought that the zero point and conversion gain of the voltage comparator 4 and the DA converter 3 change as well. Now, convert the D-A converter 3 using the method described below.
When the input data D _D is D _D1 , the output of voltage comparator 4 is OFF, and when it is 1 greater than D _D1 ⁺¹ , it is ON.
Assuming that the input data D _D1 is set such that the condition is such that the output V ₀ of the operational amplifier 1 and the output V _I of the DA converter 3 are equal. Therefore, operational amplifier 1
Let Z _B be the total zero point drift of voltage comparator 4 and D-A converter 3, and B be the conversion gain including D-A converter 3, reference voltage V _s , and precision resistor R _s , then R _r1 If selected, it is expressed by the following formula D _D1 = B/R _r1 + Z _B (9).

When R _r2 is selected, it is expressed by equation (10).

D _D2 = B/R _r2 + Z _B …(10) However, D _D2 is D- at the ON-OFF boundary when the output of voltage comparator 4 is selected when R _r2 is selected.
This is input data of the A converter 3.

Similarly to equations (5) and (6), when finding the solution with B and Z _B as unknowns, B=D _D2 −D _D1 /R _r2 −R _r1・R _r1・R _r2 …(11) Z _D =D _D1 R _r1 −D _D2 R _r2 /R _r2 −R _r1 …(12).

Therefore, since B and Z _D are known values, when the target resistance value R _I is given as setting data,
The microcomputer 5 converts the input data D _D of the D-A converter 3 into the following equation (13) by replacing R _r1 in equation (9) with R _I.
Calculate with.

D _D =B/R _I +Z _B (13) In the manner described above, the zero points and gain coefficients of all analog circuits of the measurement circuit of the present invention can be calculated.

Next, the input data _D
The operation of the microcomputer 5 to set the value to D _D1 or D _D2 will be explained with reference to the flowchart shown in FIG. In this embodiment, the D-A converter 3 has 16
resolution in bits. First, select the ultra-precision resistor R _r1 (step 1), and then set D-A to the registers G _A , G _B , and G _C in the microcomputer 5, respectively.
Maximum value (FFFF in hexadecimal) and minimum value O of converter 3
and an intermediate value (8000 in hexadecimal) (step 2). The value of G _C is set in the D-A converter 3 (step 3), and after a certain period of time including the response time of the D-A converter 3, the judgment output of the voltage comparator 4 is output.
The microcomputer 4 inputs D _C (steps 4 and 5). When the judgment output is ON, that is, when the input data G _C of the D-A converter 3 is greater than the output of the operational amplifier 1, the value of the register G _C is written to G _A , and the D-
The input data value G _C of A converter is (G _C + G _B )/2
(Step 6). In the opposite case, the value of register G _C is written to G _B , and the input data of the DA converter is set to (G _C +G _A )/2 (step 7).
By repeating this operation up to 15 times, G _A , G _B ,
Since the values of G _C are equal with a difference of 1 digit or less (step 8), the obtained value of G _C is defined as the value of D _D1 . Also, the value of D _D2 is also relayed in the same way.
It can be determined by turning off SR ₁ and SR ₂ and turning on relays SR ₃ and SR ₄ .

In the above explanation, the resistance measurement range is 10KΩ~
The explanation has been limited to a single range of 100KΩ, but for a multi-range resistance measuring instrument, such as a measurement range of 1Ω to 100MΩ, the same method can be used to provide two ultra-precise resistors for each range. It is clear that the zero point drift and conversion gain of can be calculated.

A second embodiment of the invention is shown in FIG. In this example, the measurement circuit uses a constant current I _s instead of the reference constant voltage source V _s .
are using. 6 is a differential amplifier with a very large input impedance and a gain of 1. The theoretical formula for the output voltage V _p of the differential amplifier and the unknown resistance R _x is as shown in formula (14).

V _p = I _s R _x (14) However, the zero point drift Z _C that combines the differential amplifier 6 and the A-D converter 2, and the conversion gain C that includes the reference constant current source are as shown in Fig. 1. As with any case, there are changes due to the surrounding environment and changes over time. Therefore, the output of the A-D converter when selecting the ultra-precision resistor R _r1 is
When D _A1 is assumed, D _A1 = CR _r1 + Z _C (15), and the values of Z _C and C can be calculated by the microcomputer 5 in the same way as in the case of FIG.

Please note that relay contacts SR ₂ and SR ₄ are due to the circuit configuration.
Although it operates without it, two relay contacts are required for the circuit that selects the unknown resistances R _x1 to R _x3 , so they are provided to make the effects of thermoelectromotive force and contact potential difference the same.

As described above, the conversion gain and zero point of the measuring instrument are calculated for each range, but this operation, for example in a laser trimming device or an in-circuit tester, is performed when the board to be manufactured or inspected is loaded into the equipment. This is done by starting with a start signal S _C at a time when the resistance measuring device is not measuring the unknown resistance, and returning a completion signal S _E when the correction calculation is completed. Therefore, the stability of the components in the measuring instrument is only several seconds to several tens of seconds, which is the time required to measure or judge one board, and inexpensive components can be used.

Effects of the Invention As described above, according to the present invention, the measurement terminal of the resistance measurement circuit is configured to be able to perform measurement by switching to two ultra-precision resistances per range using a relay contact, and it is possible to measure the resistance value or to set the target value. By providing calculation means for calculating the total conversion gain and zero point drift for each range of the analog circuit that determines whether the signal is high or low, laser irradiation can be stopped promptly and the It is possible to reduce the cost of components and mounting, and make it easier to adjust the circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a high-precision resistance measuring device according to a first embodiment of the present invention, FIG. 2 is a flowchart for bringing input data of the digital-to-analog converter of the present invention into a boundary state, and FIG. 3 4 is a block diagram of a high-precision resistance measuring device according to a second embodiment of the present invention, and FIG. 4 is a block diagram of a conventional resistance measuring device. 1... operational amplifier, 2... analog-digital converter, 3... digital-analog converter, 4...
...Voltage comparator, 5...Microcomputer, 6...Differential amplifier, _Vs ...Reference constant voltage source, _Is
...Reference constant current source, R _r1 , R _r2 ... Ultra precision resistor,
SR ₁ to _{SR 4} ... Relay contacts, P ₁ , P ₂ ... Measurement terminals.

Claims (1)

[Claims] 1. In a high-precision resistance measuring instrument that outputs a 1-bit ON/OFF signal to indicate whether the resistance value of an unknown resistance exceeds the target resistance value, two resistance values are known and stable for each measurement range. Precision resistance R _r1 ,
A reference power supply that generates a constant voltage or current with R _r2 , a measurement terminal for connecting an unknown resistance, and a resistance value-voltage conversion circuit that amplifies the current or voltage between the measurement terminals and converts it into a voltage; a digital-analog converter, a voltage comparator that compares the output voltage of the resistance value-voltage conversion circuit and the digital-analog converter and outputs _an ON or OFF signal; Digital·
Input data D _D of analog converter D _P −B/R ₁ +
a first calculating means for calculating Z _B (B and Z _B are constants); a switching relay circuit for selecting one from the ultra-precision resistor and the unknown resistor and connecting it to the measurement terminal; Detection means for connecting ultra-precision resistors R _r1 and R _r2 and finding input data D _D1 and D _D2 of the digital-to-analog converter such that the output of the voltage comparator is in a boundary state between ON and OFF in each state; , the constant B=(D _D2 −
D _D1 )・R _r1・R _r2 / (R _r2 − R _r1 ), Z _B = (D _D1・R _r1 −
A high-precision resistance measuring instrument comprising: second calculation means for calculating as D _D2 ·R _r2 )/(R _r2 −R _r1 ).