JPS60220867A - Voltage setting circuit - Google Patents

Abstract

PURPOSE:To supply a high-precision testing voltage by attenuating a control input to a value equivalent to the voltage variation, and synthesizing the result with an output reference voltage and outputting the synthesized voltage. CONSTITUTION:A control input code from a microcomputer, etc., is supplied to a D/A converter 1, whose conversion output is compressed by a resistance attenuator 2 and supplied to the minus terminal of an operational amplifier 3, which is synthesized with the output reference voltage supplied to its plus terminal and outputs the synthesized voltage. An attenuator 2 compresses the output full- scale voltage of the converter 1 to the value corresponding to voltage variation required for final output. Consequently, the center value of the output reference voltage of the amplifier 3 is set with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION +al Technical Field of the Invention The present invention relates to a circuit for setting a power supply voltage and a test voltage in an automatic tester or the like.

(b) Background of the Technology Testing equipment used for testing for shipping and evaluation of electronic components has been automated for digital circuits, but automation for analog circuits has lagged behind. For example, the development of automatic testers for linear ICs has lagged behind that for digital ICs, and is currently often performed manually. One of the reasons is
The power supply voltage and input signal voltage required for automatic testing are
This is because it has been difficult to obtain a circuit that can be set and supplied with high precision at a relatively low cost.

(0) Prior art and problems Conventionally, a digital/analog converter (hereinafter referred to as DAC) has been used as a method for setting and supplying power supply voltage and input signal voltage with high precision in order to automatically test linear ICs, etc. The method used was to directly control the power supply of the load using

With this conventional method, the accuracy of the DAC immediately becomes the setting accuracy of the voltage to be supplied, so an extremely accurate DAC can be used.
AC was required. For example, if an accuracy of 5 mV is required for the fluctuation step of the voltage setting value for the required test, and the full-scale voltage of the DAC is IOV, then 10V15+sV = 'l', so a high precision of 11 bits is required. A DAC is required and is very expensive.

(d) Purpose of the Invention The object of the present invention is to eliminate the problems of the prior art and provide a power supply voltage setting circuit that supplies a test voltage with high accuracy.

(al Structure of the invention) The above object is to attenuate the output full-scale voltage of the digital/analog converter to a value corresponding to the voltage fluctuation required in the final output, and to combine it with the output reference voltage and output it. This is achieved by the configured present invention.

In other words, by attenuating the output full-scale voltage of the DAC to correspond to the voltage fluctuation required in the final output, the step width of the voltage fluctuation can be compressed and made smaller while satisfying the required voltage fluctuation range. In addition to obtaining high accuracy, the necessary reference voltage center value is provided by combining with the output reference voltage.

(f) Example of the Invention An example of the present invention will be described below. FIG. 1 shows a block diagram of a voltage setting circuit according to the present invention. 1 is 0
^C, 2 is a resistive attenuator, 3 is an operational amplifier, RA,
RB and R1 are resistors, Vin is the AC input code signal, VD is the DAC output voltage, Vref is the output reference voltage,
Vout indicates the final output voltage.

In order to automatically and accurately set the power supply voltage and input signal voltage required in the automatic tester, a control input code Vin is applied to the DAC 1 from a microcomputer or the like. The output analog voltage VD of the DAC 1 is applied to a resistive attenuator 2 to be attenuated (compressed), and its output is applied to one terminal of an operational amplifier 3. An output reference voltage is applied to the child terminal of the operational amplifier 3, and the output voltage Vo of the operational amplifier 3 is
ut becomes the desired final output voltage.

FIG. 2 shows an equivalent circuit of the resistive attenuator 2 shown in FIG. In the figure, 2 shows a resistance attenuator, and 2' shows an equivalent circuit of the resistance attenuator 2. The resistance R and voltage VD' in the equivalent circuit 2 can be expressed by the following equation.

R=RA-RB/ (RA + RB) ・・・・
−・−−1−−−・−・−・−(1) VD' = (R
B/ (RA + RB) ) VD =------
--(21R indicates the impedance of the resistive attenuator seen from the operational amplifier side, and vOo indicates the value attenuated by the attenuator of the DAC output voltage VD.

Returning to FIG. 1 again, by introducing the results of equations (11 and (21) and finding the relationship between the input and output of the operational amplifier 3, we get the following.

Vout= (1+R1/R) Vref −(R1/
R) VD'-1---------------------
・(3) The first term on the right side of equation (3) is the output voltage Vou
It shows the voltage value that is the reference for t, and the second term shows the variation in voltage. The first term (1+R1/R) is the voltage gain of the operational amplifier, and if this is k, the first term can be expressed as Vref ! ! It is determined by the voltage and K applied. The voltage variation in the second term is determined by the output voltage VO of 0^C and the resistances RA and RB of the resistance attenuator.

Figure 3 shows the output voltage Vou of the voltage setting circuit related to the present invention.
FIG. 3 is a diagram showing the relationship between t, a reference voltage, and a voltage fluctuation range. Apply Vref and adjust the attenuation ratio of the attenuator to satisfy the required reference voltage and voltage variation range. As a result, the input Vin of the DAC becomes the output voltage V
Only the variation ΔVout of out is controlled, and the variation step width when using a DAC with n input bits is ΔVout/2", allowing highly accurate control. For example, ΔVout=1 .OV+n
= 8 bits, the variation step width becomes a highly accurate value of 1.OV/2''=4 mV, regardless of the absolute value of Vout.

(gl As described in detail about the invention, in the voltage setting circuit according to the present invention, the DAC controls only the variation of the output voltage, so a relatively low precision DAC is used to achieve extremely high precision. The voltage can be set, and therefore it is very effective in realizing an automatic tester for linear ICs and the like at a relatively low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a voltage setting circuit according to the present invention;
FIG. 2 is an equivalent circuit diagram of the resistance attenuator, and FIG. 3 is a diagram showing the relationship between the output voltage Vout of the voltage setting circuit, the reference voltage, and the voltage fluctuation range. In the drawing, 1 is a D-^ converter, 2 is a resistance attenuator, 2
' is an equivalent circuit of a resistive attenuator, and 3 is an operational amplifier. ￥1 Incident 2 Gacho 3 Battle 7

Claims (1)

[Claims] A voltage setting circuit characterized in that the output full-scale voltage of a digital/analog converter is configured to attenuate the output full-scale voltage to a value corresponding to the voltage fluctuation required in the final output, synthesize it with an output reference voltage, and output the combined result.