JPS6154468A - Semiconductor device - Google Patents

Abstract

PURPOSE:To prevent an internal circuit from breaking when performing operation different from normal operation by interposing a clamping circuit between an external terminal and an internal circuit. CONSTITUTION:When a voltage of, for example, about 10-15V is applied to the external terminal, gate-source voltages of transistors (TR) of a voltage decision circuit rises above a threshold voltage and those TRs turn on. A positive voltage is developed at an output node N and a testing circuit 8 is actuated to perform specific testing operation, etc. In this case, the TR5 of the voltage clamping circuit 4 is cut off when the gate of a TR3 rises up to a level Vcc-Vth even if the voltage at an external terminal 1 rises above Vcc, thereby preventing the high voltage at the external terminal 1 from being applied to the input TR3 directly. At this time, the voltage applied between the drain and gate of the TR5 is the difference voltage between the plus voltage applied to the external terminal 1 and Vcc, so the gate dielectric strength is the same with the TR3 and there is no gate destruction occurring.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a semiconductor device, and particularly relates to a method for applying a voltage or current outside the normal usage range from the outside in order to cause a semiconductor device to operate differently from its normal operation for testing or other purposes. The present invention relates to a semiconductor device provided with means for accurately securing an internal circuit when applying voltage.

(Prior Art) Conventionally, in a semiconductor device such as a semiconductor memory device, a voltage outside the normal operating range is applied to an external terminal, and this voltage is detected by a detection circuit provided inside the device. Actions are being taken. For example, erasable programmable read-only memory (EP)
In a ROM (ROM), it is possible to clear all bits of memory cells by applying a voltage higher than the signal voltage in normal logic operation to a certain external terminal.

However, in such conventional semiconductor devices, if you try to use an external terminal connected to an internal circuit part with a low input withstand voltage, if a voltage outside the normal usage range is applied to the external terminal, normal operation will not be possible. This had the disadvantage that the internal circuitry used for this purpose was destroyed. In particular, if a voltage higher than the power supply voltage during normal use is applied for a relatively long time as a voltage outside the normal usage range, the dirt insulation film of the input transistor of the internal circuit may be destroyed.
Due to these inconveniences, there has been a problem in that such external terminals cannot be used to change the operating mode by applying a high voltage.

(Problems to be Solved by the Invention) The purpose of the present invention is to solve the problems in the conventional form of the prelude,
In semiconductor devices that operate differently from normal operation by applying voltages and currents that are outside the normal operating range, this method is based on the concept of inserting a clamp circuit between the external terminal and the internal circuit. The purpose is to prevent damage to the internal circuit when performing different operations.

(Means for Solving the Problem) In order to solve the above-mentioned problem, the present invention provides a voltage determination circuit that determines whether the voltage at the external terminal is outside the normal usage range, and a voltage determination circuit that determines whether the voltage at the external terminal is outside the normal usage range. It is equipped with a clamp circuit that is inserted between the external terminal and the circuit and prevents the external terminal voltage from being directly applied to the internal circuit when the external terminal voltage is outside the normal usage range. A semiconductor device is provided which is characterized in that it performs an operation different from normal operation when the voltage is outside the usable range.

(Function) With the above-described configuration, when a voltage higher than the power supply voltage in normal use is applied to the external terminal for testing, testing, or other purposes, the voltage at the external terminal is directly controlled by the clamp circuit. Since no voltage is applied to the internal circuit, destruction of the internal circuit is accurately prevented.

(Embodiment) Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings. The accompanying drawings show a circuit of an input section of a semiconductor device according to an embodiment of the present invention. In the circuit shown in the same figure,
A voltage clamp circuit 4 is connected between the external terminal 1 and the terminal of the input transistor 3 of the internal circuit 2 for normal operation. The voltage clamp circuit 4 is, for example, an MIS
It has a transistor 5, and its source and drain are respectively connected to the external terminal 1 and the dart of the input MIS (MIS) lannoster 3. MIS) The dart of the transistor 5 is connected to a 5V power supply VCC, for example. In addition, the external terminal 1 has MIS transistor rows connected in series between the diagnostic external terminal and the ground.
A voltage determination circuit having a depletion type transistor 7 connected in parallel to the MIS transistor 5-n is connected to the output node N1 of the voltage determination circuit. Test circuit 8
is connected. Each transistor 6- of the voltage determination circuit
1.6-2°..., 6-n have their drains connected to f-), and the depletion type MIS transistors have their darts connected to their sources. Note that the test circuit 8 is not limited to a circuit that tests the operation of an internal circuit, but may be a circuit that clears all memory cells of a storage device, for example.

With the circuit described above, when a voltage in the normal use range close to the range from the voltage of the power supply VCC to the ground voltage is applied to the external terminal 1, the transistor 5 of the voltage clamp circuit 4 is turned on, and the external The voltage at terminal 1 is applied almost unchanged to input transistor 3, and normal operation is performed. Note that the transistor 6-1 of the voltage determination circuit
, 6-2.

. . , 6-n are selected so that they are all cut off when a voltage within the normal use range is applied to the external terminal 1. Therefore, the output N of the voltage determination circuit
1 is at a low level, and the test circuit 8 is not activated.

On the other hand, when a voltage of, for example, about 10 to 15' is applied to the external terminal 1, the transistors 6-1, 6-2. ..., 6-n, each f-) source voltage becomes equal to or higher than the threshold voltage, and these transistors are turned on. As a result, a positive voltage is generated at the output node N1, the test circuit 8 is activated, and a predetermined test operation is performed. In this case, the transistor 5 of the voltage clamp circuit 4 maintains the f-) voltage of the transistor 3 even if the voltage at the external terminal 1 exceeds vcc. c - level of vth (
When vth rises to the threshold value of transistor 5), it is cut off, thus preventing the high voltage at external terminal 1 from being directly applied to input transistor 3. At this time, the voltage applied between the drain of transistor 5 (external terminal 1 side) and dart is the difference voltage between the positive voltage applied to external terminal 1 and vcc, so even if the dart breakdown voltage is the same as transistor 3, dart breakdown will occur. does not occur.

In the above, we have explained the case where a voltage outside the normal use range of the external terminal IK is used for tests, etc. However, when conducting tests, etc., it is also possible to run the normal use @ supination current to the external terminal 1. That is clear. Note that the depletion transistor 7 in the above-described circuit is provided to ensure that the voltage at the output node N1 of the voltage determination circuit reaches the ground potential when the voltage at the external terminal 1 is within the normal use range.

(Effects of the Invention) As described above, according to the present invention, when a voltage or current outside the normal usage range is applied to an external terminal to perform an operation different from the normal operation, the internal circuit is affected by overvoltage or overvoltage. Application of the FtL current is prevented, and destruction of the internal circuit is precisely prevented.

[Brief explanation of the drawing]

The accompanying drawing is a block circuit diagram showing an input section of a semiconductor device according to an embodiment of the present invention. 1: External terminal, 2: Internal circuit, 3: Input transistor,
4: Voltage flag circuit, 5.6-1゜6-2, -,
6-n: MIS transistor, 7: depression type MIS transistor, 8: test circuit.

Claims (1)

[Claims] A voltage judgment circuit that determines whether the voltage at the external terminal is outside the normal usage range, and an external terminal that is inserted between the external terminal and the internal circuit to determine if the voltage at the external terminal is outside the normal usage range. 1. A semiconductor device comprising a clamp circuit that prevents a voltage from being directly applied to an internal circuit, and performing an operation different from normal operation when a voltage at an external terminal is outside a normal use range.