JPH09191102A - Protective circuit for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the size of a packaged semiconductor device by eliminating the need of separately installing terminals for a protective circuit in addition to the terminals required for operating the semiconductor device. SOLUTION: A protective circuit for semiconductor device is provided with a protective transistor circuit 22 constituted by arranging a plurality of transistors Tr1, Tr2,... in parallel and a base voltage generating circuit 23 constituted by connecting a plurality of diodes D1-D4 in parallel between the transistor circuit 22 and terminals 11A-11D. The emitters of the transistors Tr1, Tr2,... are connected to the corresponding terminals 11A-11D, 12A, 12B,... and a substrate voltage Vsub is commonly supplied to the collectors of the transistors Tr1, Tr2,.... The cathodes K1-K4 of the diodes D1-D4 are connected to the corresponding terminals 11A-11D and the anodes of the transistors Tr1, Tr2,... are commonly connected to the base terminals of the transistors Tr1, Tr2,... through a common contact A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device protection circuit, and is particularly suitable for reducing the input / output terminals of a CCD image sensor.

[0002]

2. Description of the Related Art Generally, in order to prevent electrostatic breakdown of a semiconductor device, a protection circuit is provided at a lead-out portion of an input / output terminal. As this protection circuit, a protection transistor circuit formed on the same chip is generally used.

Specifically, the configuration of the above protection circuit, especially CC
The configuration of the conventional protection circuit applied to the D image sensor will be described with reference to FIG.

A plurality of terminals, to which a plurality of driving voltages for driving the CCD image sensor are applied, are provided in the peripheral portion of the semiconductor substrate on which the CCD image sensor is formed. The protection circuit is connected between the two.

Of the plurality of terminals, the terminals 101A to 101D shown in FIG. 5 are used to drive a vertical transfer register for vertically transferring the signal charges accumulated in the image portion of the image sensor. The first to fourth vertical transfer pulses φV1 to φV4 are supplied from the outside, and the terminals 102A and 102B are used to drive the horizontal transfer register that sequentially transfers the signal charges transferred from the vertical transfer register to the output side. The generated first and second horizontal transfer pulses φH1 and φH2 are supplied from the outside. There are various input / output terminals of the CCD image sensor other than the above, but only the main ones are shown here and the others are omitted.

In addition, the conventional protection circuit has a plurality of npns.
Are configured by connecting transistors Tr1, Tr2, Tr3, ... In parallel, and the emitters of the transistors Tr1, Tr2, Tr3, ... Are respectively associated with the corresponding terminals 101A-101D, 102A ,.
102B ... And are connected by wiring so that a voltage Vc (= substrate voltage Vsub) is commonly supplied to each collector, and a protection voltage V _B is commonly supplied to each base. The wiring is connected as described above.

In this case, the substrate voltage Vsub is taken out from the semiconductor substrate which is the base of the image sensor, and the protective voltage V _B is provided with a separate terminal 103.
I am going to supply through 3.

According to this protection circuit, for example, when a negative surge voltage is erroneously applied to the terminal 102A to which the horizontal transfer pulse φH1 is supplied, the substrate voltage Vsub is applied to the terminal 102A through the transistor Tr5 which is in the ON state.
Since it appears in the wiring between the image sensors, a large current is prevented from flowing from the image sensor to the terminal 102A, and electrostatic breakdown of the image sensor due to the application of the negative surge voltage is avoided.

On the contrary, when a positive surge voltage is erroneously applied to the terminal 102A to which the horizontal transfer pulse φH1 is supplied, in particular, a positive surge voltage exceeding the reverse bias withstand voltage between the base and emitter of the transistor Tr5 is applied. In this case, the emitter-base of the transistor Tr5 becomes conductive, and the transistor Tr5 is turned on in a pseudo manner, so that the large current flowing through the terminal 102A does not flow to the image sensor side and the transistor Tr5 does not flow. It will flow to the substrate side through Tr5. As a result, a large current is prevented from flowing from the terminal 102A to the image sensor, and electrostatic breakdown of the image sensor due to the application of the positive surge voltage is avoided.

As described above, by using the above protection circuit, the surge voltage is erroneously detected by the terminals 101A to 101D,
Each terminal 1 even if applied to 102A, 102B ...
It is possible to prevent the image sensor connected to 01A to 101D, 102A, 102B, ...

[0011]

By the way, in the above-mentioned conventional technique, the protection voltage V _B is applied to each base terminal of the plurality of protection transistors Tr1, Tr2, Tr3, ... Although necessary, this protection voltage V _B is essentially unnecessary for the operation of the CCD image sensor.

That is, in the prior art, in order to provide the protection circuit, the terminals 101A to 101A to which the drive voltage related to the operation of the image sensor is applied as the terminals led to the outside.
In addition to 01D, 102A, 102B, ..., It is necessary to separately provide the terminal 103 to which the protection voltage V _B is applied, and as a result it is necessary to increase the number of terminals by one.

This is a great demerit particularly when manufacturing an image sensor for an endoscope, which is indispensable to be small and lightweight.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a packaging circuit without the need for providing a terminal for a protection circuit in addition to the terminals required for the operation of a semiconductor device. To provide a protection circuit for a semiconductor device, which is effective in reducing the size of the semiconductor device.

Another object of the present invention is to reduce the thickness of the camera wiring connected to an image sensor for an endoscope when the semiconductor device is applied to the image sensor for an endoscope, for example. It is to provide a protection circuit for a semiconductor device.

[0016]

A protection circuit according to the present invention relates to a semiconductor device having a protection transistor circuit for improving the electrostatic withstand voltage of the semiconductor device. The base voltage of the protection transistor circuit is obtained from a plurality of applied voltage groups applied to the terminals.

As a result, the base voltage applied to each base portion of the protection transistor circuit constituting the protection circuit is
It is obtained from a plurality of applied voltage groups applied to a plurality of terminals.

This means that, for example, only a plurality of terminals to which a voltage necessary for operating a semiconductor device and terminals to which a signal is output are led to the outside without separately providing a terminal dedicated to a protection circuit. It will be good.

Therefore, the protection circuit according to the present invention is effective in reducing the size of a packaged semiconductor device including terminals.

In the above structure, when the semiconductor device is applied to, for example, an image sensor for an endoscope, the number of external terminals of the image sensor is reduced,
It is also advantageous in reducing the thickness of the code (camera wiring) of the endoscope.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the protection circuit for a semiconductor device according to the present invention applied to a protection circuit for a CCD image sensor (hereinafter, simply referred to as a protection circuit according to the embodiment) are shown in FIGS. This will be described with reference to FIG.

Before describing the protection circuit according to this embodiment, an example of an image sensor to which the protection circuit is applied will be described with reference to FIG.

This image sensor is, for example, an interline transfer (IT) type image sensor, and as shown in the drawing, a large number of light receiving portions 1 for photoelectrically converting into an amount of electric charge according to the amount of incident light are arranged in a matrix. Further, among the plurality of light receiving units 1, a plurality of vertical transfer registers 2 common to the light receiving units 1 arranged in the column direction and an image unit (imaging unit) 3 arranged in the row direction are provided.

Further, one horizontal transfer register 4 adjacent to the image section 3 and common to a large number of vertical transfer registers 2 is provided in parallel.

Between the image part 3 and the horizontal transfer register 4, two vertical-horizontal transfers for transferring the signal charges transferred to the final stage of the vertical transfer register 2 in the image part 3 to the horizontal transfer register 4. The registers VH1 and VH2 are formed in common for the many vertical transfer registers 2 and in parallel with each other. These two vertical-
Vertical-horizontal transfer pulses φVH1 and φVH2 are supplied to the horizontal transfer registers VH1 and VH2, respectively, and these transfer pulses φVH1 and φVH are supplied.
By supplying 2, the signal charges from the vertical transfer register 2 are transferred to the horizontal transfer register 4.

An output unit 5 is connected to the final stage of the horizontal transfer register 4. The output unit 5 converts the signal charges transferred from the final stage of the horizontal transfer register 4 into an electric signal (for example, a voltage signal), for example, a charge-electric signal conversion unit including a floating diffusion or a floating gate. 6, a reset gate 7 that sweeps away the signal charge after the electric signal is converted in the charge-electrical signal converter 6 to the drain region D according to the input of the reset pulse φRG, and the charge-
It has an amplifier 8 for amplifying the electric signal from the electric signal converter 6. The power supply voltage Vdd is applied to the drain region D.

By supplying the vertical transfer pulses .phi.V1 to .phi.V4 to the image part 3, the potential distribution under each vertical transfer electrode in the image part 3 is sequentially changed, whereby the signal charges are respectively transferred to the vertical transfer registers in the image part 3. 2 is transferred in the vertical direction (on the side of the horizontal transfer register 4).

In the image section 3, the light receiving section 1
In the vertical blanking period, the signal charges stored in the first column are first read out to the vertical transfer register 2 and then transferred to the horizontal transfer register 4 side by row in the horizontal blanking period. As a result, the signal charges in the final stage of the vertical transfer register 2 are transferred to the horizontal transfer register 4 via the two vertical-horizontal transfer registers VH1 and VH2.

In the next horizontal scanning period, by applying horizontal transfer pulses φH1 and φH2 of two phases different from each other to the horizontal transfer electrodes formed by, for example, two layers of polycrystalline silicon layers formed on the horizontal transfer register 4, The signal charges are sequentially transferred to the charge-electrical signal conversion unit 6 on the output unit 5 side,
The electric signal is converted into an electric signal in the electric-electrical signal converting unit 6, and is taken out from the corresponding output terminal 9 via the amplifier 8 as the image pickup signal S.

Then, the protection circuit according to the present embodiment is
It is provided in the periphery of the semiconductor substrate on which the image sensor is formed. Specifically, as shown in FIG. 2, a plurality of terminals 11A to 11A to which a plurality of drive voltages for driving the image sensor are applied. 11D, 12A, 12B ...
The protection circuit 21 according to the present embodiment is connected between the image sensor main body and the image sensor main body.

Here, the plurality of terminals 11A to 11D,
Of the terminals 12A, 12B ..., the terminals 11A to 11D are
First to fourth vertical transfer pulses φV1 to φV used to drive the vertical transfer register 2 that vertically transfers the signal charges accumulated in the image portion 3 of the image sensor.
4 is supplied from the outside, and terminals 12A and 12B are used for driving the horizontal transfer register 4 which sequentially transfers the signal charges transferred from the vertical transfer register 2 to the output section 5 side. Transfer pulse φH1 and φH
2 is supplied from the outside. Note that CC
There are various input / output terminals of the D image sensor other than the above, but only the main ones are shown here and the others are omitted.

Then, the protection circuit 2 according to this embodiment
1 is a plurality of npn transistors Tr1, Tr2, Tr
.. are connected in parallel, and the protection transistor circuit 22 and the protection transistor circuit 22.
And a plurality of diodes D1 to D4 between the terminals 11A to 11D
And a base voltage generation circuit 23 configured by being connected in parallel with each other.

A plurality of transistors Tr1, Tr2, Tr3, ... Constituting the protection transistor circuit 22.
Are terminals 11A to 11 to which the respective emitters correspond.
Are connected to D, 12A, 12B, ... And are connected by wiring so that a voltage Vc (= substrate voltage Vsub) is commonly supplied to each collector. In this case, the substrate voltage Vsub is taken out from the semiconductor substrate which is the base of the image sensor.

In the plurality of diodes D1 to D4 constituting the base voltage generating circuit 23, the respective cathodes K1 to K4 are connected to the corresponding terminals 11A to 11D, and the respective anodes are set to the common A and through the common contact A thereof. Each transistor Tr1 in the protection transistor circuit 22
Commonly connected to the base terminals of Tr2, Tr3, ....

The first to fourth vertical transfer pulses .phi.V1 to .phi.V4 supplied to the terminals 11A to 11D are four-phase vertical transfer pulses having different phases, as shown in FIG. Is -9 [V], and the high level voltage is 0 [V].

[0036] With such a configuration, the -9 + △ V _F [V] from the low-level voltage -9 [V] as the base voltage of the transistors Tr1, Tr2, Tr3 · · · · of the vertical transfer pulse φV1~φV4 The voltage can be obtained. The reason is that the voltage level of each vertical transfer pulse φV1 to φV4 is always a low level potential of −9 [V] at any time, as shown in FIG. 3, in the case of normal transfer. , The potential at the common contact A on the anode side is
Always is because the _{-9 + △ V F [V]} . Where △
V _F is a forward bias voltage of the diodes D1 to D4, which is 0.
It is about 7 [V].

The protection circuit according to the present embodiment has the above-mentioned configuration, for example, when a negative surge voltage of −9 [V] or less is erroneously applied to the terminal 12A to which the horizontal transfer pulse φH1 is supplied, the terminal 12A is supplied. Transistor T corresponding to 12A
By turning on r5, the transistor Tr
5, the substrate voltage Vsub appears in the wiring between the terminal 12A and the image sensor, so that a large current is prevented from flowing from the image sensor to the terminal 12A, and electrostatic breakdown of the image sensor due to the application of the negative surge voltage is avoided. To be done.

Conversely, when a positive surge voltage is erroneously applied to the terminal 12A to which the horizontal transfer pulse φH1 is supplied, a positive surge voltage exceeding the reverse bias withstand voltage between the base and emitter of the transistor Tr5 is applied. In this case, since the emitter-base of the transistor Tr5 becomes conductive and the transistor Tr5 is turned on in a pseudo manner, a large current flowing through the terminal 12A does not flow to the image sensor side, and the transistor Tr5 does not flow. It will flow to the substrate side through Tr5. As a result, a large current is prevented from flowing from the terminal 12A to the image sensor, and electrostatic breakdown of the image sensor due to the application of the positive surge voltage is avoided.

As described above, in the protection circuit 21 according to this embodiment, the terminals 11A to 11D are included in the base voltage generation circuit 23 including the diodes D1 to D4.
First to fourth vertical transfer pulses φV1 to φV applied to
Since the base voltage to be supplied to the base terminals of the respective transistors Tr1, Tr2, Tr3, ... Of the protection transistor circuit 22 is generated from the voltage of No. 4, it is necessary to lead the terminal dedicated to the protection circuit to the outside. As a result, the electrostatic breakdown voltage of the CCD image sensor can be improved without increasing the number of external terminals.

Therefore, the protection circuit 2 according to this embodiment
When the image sensor provided with 1 is applied to, for example, an image sensor for an endoscope, the number of external terminals of the image sensor is reduced, so that the thickness of the endoscope code (camera wiring) is reduced. It is also advantageous in doing so.

Next, a modification of the protection circuit according to the above embodiment will be described with reference to FIG.

The protection circuit 21 according to this modification is, as shown in the figure, the protection circuit 2 according to the embodiment shown in FIG.
1 has almost the same configuration as that of the protection transistor circuit 2
2, a plurality of transistors Tr1, Tr2, Tr
3 ... Each emitter and corresponding terminals 11A to 11
Are different in that diodes DD1, DD2, DD3, ... Are inserted and connected between D, 12A, 12B ,. In this case, the diodes DD1 and DD
The direction of connection of 2, DD3 ...
The emitter side of 1, Tr2, Tr3, ... Is the anode,
The terminal side is the cathode.

These diodes DD1, DD2, DD3
By inserting and connecting ..., it becomes effective in the following cases. That is, in the normal operation state, the voltage of the anode-side common terminal A of the diodes D1 to D4 forming the base voltage generation circuit 23 and the anode side of the newly inserted diodes DD1, DD2, DD3, ... Since the electric potentials V _E of the
First to fourth vertical transfer pulses φV1 to φ applied to D
Even if any of the voltage levels of V4 drops to a negative side slightly below the specified -9 [V] due to a temperature change or the like to cause an undershoot, the corresponding transistors Tr1 to Tr4 maintain the off state. As a result, the terminal where the undershoot has occurred and the substrate are not electrically connected, and the operation of the image sensor can be stably performed.

In the above example, one diode is connected to the emitter of each transistor, but two or more diodes may be connected. In this case, the margin for undershoot increases.

In the above-mentioned embodiments and modifications, the case where the invention is applied to the CCD image sensor is shown.
The same applies to various semiconductor devices having a protection circuit.

[0046]

As described above, according to the protection circuit for a semiconductor device of the present invention, a plurality of diodes are used, and the protection transistor circuit is protected from a plurality of applied voltage groups applied to a plurality of terminals. Since the base voltage is obtained, it is not necessary to separately provide a terminal for the protection circuit in addition to the terminal required for the operation of the semiconductor device, which is effective in reducing the size of the packaged semiconductor device.

In particular, the semiconductor device may be, for example, a CCD.
When applied to an image sensor, the thickness of the camera wiring connected to the image sensor can be reduced.

[Brief description of the drawings]

FIG. 1 is a CC in which a protection circuit according to the present embodiment is provided.
It is a block diagram which shows a D image sensor.

FIG. 2 is a circuit diagram showing a configuration of a protection circuit according to the present embodiment.

FIG. 3 is a waveform diagram showing four-phase vertical transfer pulses applied to an external terminal of the image sensor.

FIG. 4 is a circuit diagram showing a configuration of a protection circuit according to a modification.

FIG. 5 is a circuit diagram showing a configuration of a protection circuit according to a conventional example.

[Explanation of symbols]

 11A to 11D Vertical transfer pulse input terminals 12A and 12B Horizontal transfer pulse input terminals 21 Protection circuit 22 Protection transistor circuit 23 Base voltage generation circuit Tr1, Tr2, Tr3 ... Transistors D1 to D4 Diodes DD1, DD2, DD3. ··· diode

Claims (5)

[Claims] 1. A semiconductor device having a protection transistor circuit for improving electrostatic breakdown voltage of a semiconductor device, comprising: a plurality of diodes; and a plurality of applied voltage groups applied to a plurality of terminals, wherein the protection transistor is provided. A protection circuit for a semiconductor device, which is configured to obtain a base voltage of the circuit. 2. The cathode portions of the plurality of diodes are respectively connected to the plurality of terminals, and the anode portion is commonly connected to the base portion of the protection transistor circuit. 2. A semiconductor device protection circuit according to 1. 3. The semiconductor device protection circuit according to claim 1, wherein the semiconductor device is a CCD image sensor. 4. The semiconductor device according to claim 3, wherein the applied voltage group applied to the plurality of terminals is a drive voltage applied to a plurality of transfer electrodes forming a vertical transfer register. Protection circuit. 5. One or a plurality of diodes are also connected to each emitter of the protection transistor circuit, and are connected to the plurality of terminals through the plurality of diodes. Item 1 to 4
A protection circuit for a semiconductor device according to claim 1.