JP4581172B2 - Input protection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a protection device against an overvoltage input of an electronic circuit.
[0002]
[Prior art]
An example of a conventional input protection device will be described with reference to FIG. The figure is an example of a signal input unit of an LSI test system.
[0003]
The LSI test system simultaneously handles input signals of several tens to several hundreds of pins according to the number of output pins of an LSI (DUT: Device Under Test) to be tested. Therefore, measurement circuits having the same circuit structure are prepared for the number of outputs of the DUT, and each performs measurement simultaneously. In the example of the figure, the measurement unit for each output pin has two signal paths A and B. When the signal path A is selected for each output pin, the switch circuits SWA1 to SWA3 are turned on from the on / off control unit 10. Is output to each switch circuit, and a control signal for turning off the switch circuits SWB1 to SWB3 is output from the on / off control unit 20 to each switch circuit. As a result, the output of each output pin is input to a measurement circuit (not shown) connected to the signal path A. Similarly, when the signal path B is selected for each output pin, a control signal for turning off the switch circuits SWA1 to SWA3 is output from the on / off control unit 10 to each switch circuit, and the switch circuit SWB1 from the on / off control unit 20 A control signal for turning on SWB3 is output to each switch circuit. As a result, the output of each output pin is input to the measurement circuit connected to the signal path B.
[0004]
All the measurement circuits are provided with a diode clamp circuit as shown in FIG. 3 in order to avoid damage due to an excessive voltage from the DUT.
[0005]
In the case of protecting the input of the amplifier AMP in the circuit as shown in FIG. 3, the positive clamp voltage V _{CLMP +} and the negative clamp voltage V _CLMP− to be clamped are applied to the diodes D3 and D4, so that the positive clamp voltage is applied to the input of the amplifier AMP. It is possible to prevent a voltage exceeding V _{CLMP +} and the negative clamp voltage V _CLMP− from being input. In the case of such a clamp circuit, the clamped voltage range is {(V _{CLMP +} ) + VD 3} or more and {(V _CLMP− ) −VD 4} or less if the voltage drop of the diode D 3 is VD 3 and the voltage drop VD 4 of the diode D 4. It becomes.
[0006]
[Problems to be solved by the invention]
However, in the conventional input protection device described with reference to FIG. 2, since a plurality of measurement circuits are selected by the switch circuit, the input of the unselected signal path is in an open state. In general, in a signal processing circuit such as a measurement circuit, the input leakage current of the next stage exists in the input section, and when the input is in an open state, this leakage current is integrated into the stray capacitance of the substrate and the input potential rises. (Or descends) and eventually reaches a potential that saturates the signal processing circuit.
[0007]
When the signal processing circuit is saturated, various problems may occur. For example, when the signal processing circuit is an amplifier having a load resistor connected to the output thereof, when the input is saturated, a large voltage is generated at the output, and a large current flows through the load resistor therefrom. This current is the power supply current of the amplifier, and the sum of the currents of all the pins becomes wasteful power consumption of the entire system.
[0008]
One method for preventing this is to provide a switch structure between the switch circuit and the signal processing circuit that applies a potential to the input that does not saturate the signal processing circuit when the signal processing path is not selected. As mentioned above, this method requires the number of switch structures obtained by multiplying the number of all output pins of the DUT by the number of signal paths, resulting in an increase in the number of parts and an increase in cost, and a reduction in the size of the entire system. The problem that it becomes difficult occurs.
[0009]
In addition, when the leakage current at the input of the signal processing circuit is relatively small, the input is a resistor whose (leakage current) × (resistance value) is large enough to suppress unnecessary power consumption of the signal processing circuit. There is a method of connecting to the ground potential. However, when the signal processing circuit needs to exhibit a large input resistance with respect to the DUT, there is a problem that the input resistance of the signal processing circuit is lowered by the resistance. .
[0010]
The present invention solves the above problems, and provides an input protection circuit capable of reducing the size of the device itself and preventing saturation of a signal processing circuit whose input is in an open state. For the purpose.
[0011]
[Means for Solving the Problems]
In order to achieve such an object, according to the first aspect of the present invention, a plurality of measurement circuits are connected to the output pins of the large-scale integrated circuit to be tested, and the output pins are connected to the measurement circuit corresponding to the test purpose. In an input protection device of an LSI test system that selectively inputs an output signal,
A switch circuit that is inserted into the signal input path of the measurement circuit and selectively inputs the output signal of the output pin to the plurality of measurement circuits by a signal switching signal;
A first diode in which an anode is connected to each of the signal input paths of the plurality of measurement circuits and a positive clamp voltage is applied to the cathode, and a negative clamp voltage is connected to the anode in each of the signal input paths. A clamp circuit constituted by an applied second diode ;
A clamp voltage switching unit for switching the voltage of the clamp voltage ;
With
The clamp voltage switching unit is
A clamp voltage necessary for input protection of the measurement circuit is applied to the clamp circuit of the signal input path through which the output signal of the output pin is input via the switch circuit, and the output signal of the output pin is the switch It blocked by circuit to the clamp circuit of the signal path becomes open, and is characterized in applying a clamping voltage to avoid saturation of the input potential of the measurement circuit.
[0022]
1 is different from the conventional example of FIG. 2 in that clamp voltage switching portions U1 and U2 are provided. The clamp voltage switching unit U1 generates a positive clamp voltage (VA _{CLMP +} ) and a negative clamp voltage (VA _CLMP- ) to be applied to the first and second diodes connected to the signal path A, and the clamp voltage switching unit U2 A positive clamp voltage (VB _{CLMP +} ) and a negative clamp voltage (VB _CLMP− ) applied to the first and second diodes connected to the signal path B are generated.
[0023]
In the figure, for example, when the signal path A is selected, a control signal for turning on the switch circuits SWA1 to SWA3 is output from the on / off control unit 10 to each switch circuit as in the conventional example, and the switch circuit SWB1 from the control unit 20 A control signal for turning off SWB3 is output to each switch circuit. As a result, the output of each output pin is input to the measurement circuit connected to the signal path A. At this time, the clamp voltage switching unit U1 simultaneously protects the signal processing circuit connected to the signal path A against the input from the DUT to the first and second diodes connected to the signal path A (positive clamp voltage ( VA _{CLMP +} ) and a negative clamp voltage (VB _CLMP− ) are applied, and the clamp voltage switching unit U2 is adjusted to a value that does not saturate the signal processing circuit in the first and second diodes connected to the signal path B. _Apply clamp voltage (VB _{CLMP +} ) and negative clamp voltage (VB _CLMP- ).
[0024]
Similarly, when the signal path B is selected, a control signal for turning off the switch circuits SWA1 to SWA3 is output from the on / off control unit 10 to each switch circuit, and the switch circuit SWB1 to SWB3 is turned on from the control unit 20. A control signal is output to each switch circuit. As a result, the output of each output pin is input to the measurement circuit connected to the signal path B. At the same time, the clamp voltage switching unit U1 simultaneously adjusts the positive clamp voltage (VA _{CLMP +} ) and the negative clamp voltage (VB) adjusted so that the signal processing circuit does not saturate the first and second diodes connected to the signal path A. _CLMP- ) is applied, and the clamp voltage switching unit U2 is connected to the first and second diodes connected to the signal path B to protect the signal processing circuit connected to the signal path A against the input from the DUT. _Apply clamp voltage (VB _{CLMP +} ) and negative clamp voltage (VB _CLMP- ).
[0025]
Here, the positive clamp voltage and the negative clamp voltage adjusted to values that do not saturate the signal processing circuit described above are values obtained by sufficiently narrowing the voltage range of the positive clamp voltage and the negative clamp voltage. By setting a clamp voltage in a sufficiently narrow range for the first and second diodes, a clamp circuit with a narrowed voltage range even if the input potential of the signal processing circuit changes due to an input leakage current in the signal path This limits the voltage changeable range and avoids saturation in the signal path. Therefore, such an operation can prevent saturation of the signal processing circuit whose input is in an open state.
[0026]
In addition to the input protection circuit described above, there is a configuration as shown in FIG. In the figure, an input terminal is connected to a fixed contact of a switch circuit RL1 using a relay, for example, and a movable contact of the switch circuit RL1 is connected to an input terminal of an electronic circuit such as an amplifier AMP. The switch circuit RL1 is turned on / off by a signal cutoff signal CLR output from the overvoltage detection unit U10.
[0027]
The anode of a diode D11 is connected to the movable contact of the switch circuit RL1, and the cathode of the diode D11 is connected to the emitter of a transistor Q1 having a positive clamp voltage VCLMP + applied to its base.
[0028]
The collector of the transistor Q1 is connected to the cathode of a Zener diode D13, and the anode of the Zener diode D13 is connected to the ground potential. A resistor R11 is connected in parallel to the Zener diode D13.
[0029]
The movable contact of the switch circuit RL1 is connected to the cathode of a diode D12, and the anode of the diode D12 is connected to the emitter of a transistor Q2 having a negative clamp voltage V _CLMP− applied to the base.
[0030]
The anode of a Zener diode D14 is connected to the collector of the transistor Q2, and the cathode of the Zener diode D14 is connected to the ground potential. Further, a resistor R12 is connected in parallel to the Zener diode D14.
[0031]
Furthermore, the cathode potential V + of the Zener diode D13 and the anode potential V− of the Zener diode D14 output the signal cutoff signal CLR and output an interrupt signal to the control circuit CPU and an RST terminal that inputs a reset signal. Is input to the overvoltage detection unit U10.
[0032]
In the circuit having such a configuration, when an input signal Vin having a potential exceeding the positive clamp voltage V _{CLMP +} or the negative clamp voltage V _CLMP− is applied from the input terminal, the transistor Q1 or Q2 is turned on, and the overvoltage detection unit U10 Is changed to the Zener voltage of the Zener diode D13 or the Zener diode D14. The overvoltage detection unit U10 detects this, turns off the switch circuit RL1, and outputs an interrupt signal to the control circuit CPU to request error processing.
[0033]
In the control circuit CPU, after the switch circuit RL1 is turned off by the above-described operation, when the internal signal determines that the input signal Vin has returned to the normal voltage range, the control circuit CPU outputs a reset signal to the overvoltage detection unit U10, and again The switch circuit RL1 is turned on and signal processing is resumed. By the operation described above, the input protection circuit can automatically return from the overvoltage protection state to the normal state.
[0034]
The above description merely shows a specific preferred embodiment for the purpose of explanation and illustration of the present invention. Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.
[0035]
【The invention's effect】
As is apparent from the above description, the present invention has the following effects. In the first aspect of the present invention, the input protection device according to the present invention is a signal processing circuit in which the input is opened by simply remodeling the conventional input protection circuit by adding a clamp voltage switching circuit. Saturation can be prevented. Further, since the clamp voltage switching circuit can be realized with a simple electronic circuit, the input protection device can be miniaturized and manufactured at low cost.
[0038]
By using a general-purpose electromagnetic switch (relay) for the switch circuit (RL1) , it is possible to manufacture the switch circuit at a low cost and easily in an electronic circuit that requires a large current to flow. It is possible to correspond to. Also, parts procurement is easy.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an input protection circuit according to the present invention.
FIG. 2 is a configuration diagram illustrating an example of a conventional input protection circuit.
FIG. 3 is a configuration diagram illustrating an example of a clamp circuit of a conventional input protection circuit.
FIG. 4 is a block diagram showing another embodiment of the input protection circuit according to the present invention.
[Explanation of symbols]
1 Input terminal 10, 20 ON / OFF control unit U1, U2 Clamp voltage switching circuit SWA1, SWA2, SWA3, SWB1, SWB2, SWB3, RL1 Switch circuit AMP Electronic circuit D11, D12 Diode D13, D14 Zener diode Q1, Q2 Transistors R11, R12 Resistor U10 Overvoltage detector CPU control circuit

Claims (1)

In an input protection device for an LSI test system in which a plurality of measurement circuits are connected to an output pin of a large-scale integrated circuit to be tested, and an output signal of the output pin is selectively input to a measurement circuit corresponding to a test purpose.
A switch circuit that is inserted into the signal input path of the measurement circuit and selectively inputs the output signal of the output pin to the plurality of measurement circuits by a signal switching signal;
A first diode in which an anode is connected to each of the signal input paths of the plurality of measurement circuits and a positive clamp voltage is applied to the cathode; and a cathode is connected to each of the signal input paths and a negative clamp voltage is applied to the anode. A clamp circuit constituted by an applied second diode;
A clamp voltage switching unit for switching the voltage of the clamp voltage;
With
The clamp voltage switching unit is
A clamp voltage necessary for input protection of the measurement circuit is applied to the clamp circuit of the signal input path through which the output signal of the output pin is input via the switch circuit, and the output signal of the output pin is the switch An input protection device, wherein a clamp voltage for avoiding saturation of an input potential of the measurement circuit is applied to the clamp circuit in a signal path that is cut open by a circuit.

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