JPH10111342A - Programmable load circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce uncertain voltage width in a programmable load circuit. SOLUTION: When DUT output voltage of a terminal T is smaller than a threshold voltage Vth, transistors Q5, Q8 are turned on and transistors Q6, Q7 are turned off, and therefore transistors Q1, Q4 are turned on and transistors Q2, Q3 are turned off. Therefore, set electric current i1 flows into the DUT. When the threshold voltage is smaller than DUT output voltage, the transistors Q6, Q7 are turned on and the transistors Q5, Q8 are turned off, therefore the transistors Q2, Q3 are turned on and the transistors Q1, Q4 are turned off. Therefore, set electric current 12 is flown from the DUT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a programmable load circuit.

[0002]

2. Description of the Related Art FIG. 4 is a basic circuit diagram of a conventional programmable load circuit.

When the DUT outputs a voltage equal to or lower than V _th -0.7 (V), the current set by the constant current source I ₁ flows like i ₁ , and is equal to or higher than V _th +0.7 (V). when outputting the voltage, current set by the current source I ₂ flows as i _2. Here, 0.7 (V) is the forward voltage V _F of the diode constituting the diode bridge.

[0004]

SUMMARY OF THE INVENTION A current source I_Two Set in
Current i_Two Flows from DUT to programmable load circuit
The threshold voltage V_thThan the diode
V_f (= 0.7 (V)) higher voltage is output from the DUT.
It's time for That is, the programmable load circuit
The voltage required for operation is V_th+0.7 (V) or more
It is. Also, the programmable load circuit is compatible with the DUT.
And the current i₁ Can be explained in the same way when supplying
Voltage required to operate the programmable load circuit
Is V_th−0.7 (V) or less. Here, the output of the DUT
Force voltage to V_D Then, the output voltage V _D Is V_th−0.7 (V) <V_D <V_thIn the range of +0.7 (V), the programmable load circuit
Set current i₁Or i_TwoCan not supply.
Hereinafter, this voltage range is referred to as a voltage uncertainty width.

As a method of reducing the influence of _Vf , it is conceivable to increase the current size of the diode with respect to the current value set by the programmable load circuit.
However, in this case, the junction capacitance of the diode increases.
As a result, the I / O capacity of the pin electronics increases, adversely affecting the performance of the IC test system.

When an attempt is made to make a programmable load circuit monolithic, a Schottky diode cannot be used depending on the process in some cases. In such a case, it can be realized as shown in FIG. However, when the output voltage V _{D of the} DUT is sufficiently higher (or lower) than the threshold voltage V _th ,
A large reverse voltage is applied between the base and the emitter of the transistor. Unlike a Schottky diode, the diode connection of a transistor has a small reverse breakdown voltage, and as a result, the reliability of the transistor is reduced. To compensate for the low reverse breakdown voltage, there is a method of connecting a plurality of diode connections of transistors as shown in FIG. 6, but this method causes an increase in the voltage uncertainty described above.

An object of the present invention is to provide a programmable load circuit in which the voltage uncertainty width is smaller than in the prior art.

[0008]

The programmable load circuit according to the present invention comprises a first constant current source having one end connected to a high voltage source, and a second constant current source having one end connected to a low voltage source. , One end is connected to the other end of the first constant current source, and the other end is
A first switching transistor connected to a terminal to which a DUT output voltage is input, a second switching transistor having one end connected to the other end of the second constant current source, and the other end connected to the terminal; Comparing a threshold voltage source, a DUT output voltage of the terminal with a threshold voltage of the threshold voltage source, and when the DUT output voltage is smaller than the threshold voltage, only the first switching transistor is turned on; A voltage comparison circuit that turns on only the second switching transistor when the voltage is larger than the threshold voltage;

Since the switching transistor is used instead of the diode, the influence of _{Vf on} the voltage uncertainty is eliminated, and the voltage uncertainty is reduced.

[0010] Another programmable load circuit according to the present invention comprises a first constant current source having one end connected to a high voltage source, a second constant current source having one end connected to a low voltage source, and a first constant current source having one end connected to a low voltage source. A first transistor connected to the other end of the first constant current source, the other end connected to a terminal to which the output voltage of the DUT is input, and one end connected to the other end of the first constant current source; A second transistor having the other end connected to the voltage source, a third transistor having one end connected to the other end of the second constant current source, and the other end connected to the terminal; A fourth transistor connected to the other end of the constant current source, the other end of which is connected to the voltage source; a threshold voltage source; and a fifth transistor, whose base is connected to the threshold voltage source and the terminal, respectively.
A sixth transistor, wherein when the DUT output voltage is lower than a threshold voltage of the threshold power supply, the first transistor and the second transistor are turned on and off, respectively;
A first differential switch that turns off and on a first transistor and a second transistor respectively when the output voltage is lower than the output voltage;
And a third transistor and a fourth transistor which are turned off and on when the DUT output voltage is smaller than the threshold voltage, respectively, wherein the threshold voltage is lower than the threshold voltage of the DUT. A second differential switch that turns on and off the third transistor and the fourth transistor when the output voltage is lower than the output voltage;

The programmable load circuit of the present invention uses a differential switch as a voltage comparison circuit.

Still another programmable load circuit according to the present invention comprises a first current source having one end connected to a high voltage source, the other end connected to a terminal to which a DUT output voltage is input, and one end connected to a low voltage source. A second current source having the other end connected to the terminal;
A threshold voltage source, a comparator that compares the DUT output voltage with a threshold voltage of the threshold voltage source, and outputs a voltage difference between the threshold voltage source and a first current source and a second current source. It has a function unit that is controlled by a preset function as a variable.

[0013] The programmable load circuit of the present invention varies the current of the current source in accordance with the voltage difference between the threshold voltage and the DUT output voltage.

[0014]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a programmable load circuit according to one embodiment of the present invention.

The programmable load circuit according to the present embodiment includes constant current sources I ₁ and I ₄ having one ends connected to the high voltage source V _1.
When the constant current source I _2, one end of which is connected to the low voltage source V _2,
And I _3, and the emitter is connected to the other end of the constant current source I ₁ connected, collector respectively DUT terminal T, the transistor Q _1, Q ₂ connected to ground and the emitter to the other end of the constant current source I ₂ The collectors are connected to the DUT terminal T, the transistors Q ₃ and Q ₄ connected to the ground, the threshold voltage source V _th , the resistors R ₁ , R ₂ ,..., R _6, and the emitter is connected to the constant current source I ₃ . Connected, and the collectors
₁ the transistor to Q ₁ base, connected to the base of the resistor R ₂ and the transistor Q _2, the base is the threshold voltage source V _th, respectively, the transistors Q _5, Q _6, which are connected to the DUT terminal T, the emitter constant current source I ₄ , the collectors are respectively connected to the resistor R ₃ and the base of the transistor Q ₃ , the resistor R ₄ and the base of the transistor Q ₄ , and the bases are respectively threshold voltage sources V _th , DU
It is composed of transistors Q ₇ and Q ₈ connected to the T terminal T.

Here, the transistors Q ₅ and Q ₆ , the constant current source I ₃ and the resistors R ₁ , R ₂ and R ₅ constitute a first differential switch, and the transistors Q ₇ and Q ₈ and the constant current source I ₄ and the resistors R ₃ , R ₄ and R ₆ constitute a second differential switch.

[0018] Incidentally, the collector of the transistor Q ₂ low voltage source V _2, may be connected to the collector of the transistor Q ₄ to a high voltage source V _1.

Next, the operation of the present embodiment will be described. 1) When the DUT output voltage V _{D at the} terminal T is lower than the threshold voltage V _th , the transistors Q ₅ and Q ₈ turn on, and the transistors Q ₆ and Q ₆ turn on.
Since the Q ₇ is turned off, the transistor Q _1, Q ₄ is turned on,
The transistors Q ₂ and Q ₃ are turned off. Therefore, the set current i ₁ flows to the DUT. 2) When the threshold voltage is lower than the DUT output voltage V _D , the transistors Q ₆ and Q ₇ turn on, and the transistors Q ₅ and Q ₅ turn on.
Since the Q ₈ is turned off, the transistor Q _2, Q ₃ is turned on,
The transistors Q ₁ and Q ₄ are turned off. Therefore, the set current i ₂ is pulled from the DUT.

FIG. 2 shows DUs of the present embodiment and a conventional example (FIG. 4).
9 is a graph showing the relationship between the T output voltage and the output current of the programmable load circuit (when V _th = 1.5 (v) and the set currents of the current sources I ₁ and I ₂ are set to 30 (mA)). As is clear from this graph, the voltage uncertainty width of the present embodiment is smaller than the voltage uncertainty width of the conventional example. This is because, in the present embodiment, there is no influence of the voltage _Vf of the diode.

FIG. 3 is a circuit diagram of a programmable load circuit according to a second embodiment of the present invention. In the present embodiment, the threshold voltage V _th and the output voltage V _{D of the} DUT are compared with the comparator C
P, and using the voltage difference as a variable, the function unit F uses a function F to set the currents i ₁ , i ₂ of the current sources I ₁ , I _2.
2 is set. Function, for example, i
_By setting ₁ = (V _th −V _D ) / R and i ₂ = (V _D −V _th ) / R, it becomes equivalent to a DUT having a resistance load of R (Ω). By enabling the value of R to be set arbitrarily, an effect equivalent to a resistance load can be obtained, and a programmable load circuit that can change the constant of the load resistance can be realized.

[0022]

As described above, the present invention has the following effects. (1) The inventions of claims 1 and 2 have a small voltage uncertainty width. (2) According to the third aspect of the invention, the voltage uncertainty width is small and the constant of the load resistance of the DUT can be changed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a programmable load circuit according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an output current and a DUT output voltage of the programmable load circuit of FIG. 1 and the programmable load circuit of FIG.

FIG. 3 is a circuit diagram of a programmable load circuit according to another embodiment of the present invention.

FIG. 4 is a basic circuit diagram of a conventional programmable load circuit.

FIG. 5 is a circuit diagram of a programmable load circuit in which transistors are diode-connected.

FIG. 6 is a circuit diagram of a programmable load circuit having two stages of diode connections of transistors.

[Explanation of symbols]

Q _{1 to} Q ₈ Transistors R _{1 to} R ₆ Resistance I _{1 to} I ₄ Constant current source V ₁ , V ₂ , V _th voltage source CP Comparator F function unit T DUT terminal

Claims (3)

[Claims] 1. A first constant current source having one end connected to a high voltage source, a second constant current source having one end connected to a low voltage source, and another end having one end connected to the first constant current source. And the other end is DU
A first switching transistor connected to a terminal to which the T output voltage is input, a second switching transistor having one end connected to the other end of the second constant current source, and the other end connected to the terminal; Comparing a threshold voltage source with a DUT output voltage of the terminal and a threshold voltage of the threshold voltage source, and when the DUT output voltage is smaller than the threshold voltage, only the first switching transistor is turned on, and the DUT output voltage is A programmable load circuit having a voltage comparison circuit that turns on only a second switching transistor when the voltage is higher than a threshold voltage. 2. A first constant current source having one end connected to a high voltage source, a second constant current source having one end connected to a low voltage source, and another end having one end connected to the first constant current source. And the other end is DU
A first transistor connected to a terminal to which the output voltage of T is input, a second transistor connected at one end to the other end of the first constant current source, and the other end connected to the voltage source; Is connected to the other end of the second constant current source, the other end is connected to the terminal, a third transistor, one end is connected to the other end of the second constant current source, and the other end is connected to the voltage source. A fourth transistor connected thereto, a threshold voltage source, and fifth and sixth transistors each having a base connected to the threshold voltage source and the terminal, respectively,
When the UT output voltage is lower than the threshold voltage of the threshold power supply, the first transistor and the second transistor are turned on and off, respectively. When the threshold voltage is lower than the DUT output voltage, the first transistor and the second transistor are turned off. A first differential switch for turning off and on a transistor, respectively; a seventh and an eighth transistor each having a base connected to the threshold voltage source and the terminal, respectively;
When the UT output voltage is smaller than the threshold voltage, the third transistor and the fourth transistor are turned off and on, respectively, and when the threshold voltage is smaller than the DUT output voltage, the third transistor and the fourth transistor are turned on. , A programmable load circuit having a second differential switch to be turned off. 3. A first current source having one end connected to a high voltage source, the other end connected to a terminal to which a DUT output voltage is input, one end connected to a low voltage source, and the other end connected to the terminal. A second current source, a threshold voltage source, a comparator that compares the DUT output voltage with a threshold voltage of the threshold voltage source, and outputs a voltage difference between the DUT output voltage and the first current source and the second current source. A programmable load circuit having a function unit that controls a current with a preset function using the voltage difference as a variable.