WO1987007986A2 - Protective device against electrostatic discharges on electronic equipment in general - Google Patents

Abstract

The device consists of a combination of circuits including a first antenna circuit to pick up the electric field created by an electrostatic discharge, which sends an enabling signal, upon systematic suppression of noises on power line by means of a second circuit, to a third generating a following start signal with a desired time sequence, so that a fourth interface circuit, enabled by this start signal and galvanically connected to the equipment to be protected, is able to send a sequence of monitoring signals to the equipment, thus preventing an irregular operation of the equipment itself. Advantages: low cost, immunity up to 10 KV easily achieved, adaptability to various equipment.

Description

"PROTECTIVE DEVICE AGAINST ELECTROSTATIC

DISCHARGES ON ELECTRONIC EQUIPMENT IN GENERAL"

This invention belongs to the technical field of

protective and monitoring industrial equipment

and it refers to a protective device against

electrostatic discharges on electronic equipment

in general.

It is well known that in the field of electronic

devices protection against electronic discharges

is a factor of vital importance to be taken into

account during the design phase.

With the introduction of modern, circuit-

integration technologies such as C-MOS, MOS and

the like, it is necessary to avoid any anomalous

stress of the normal operating parameters of the

circuits, because in this case each electronic

board formed by such circuits would interpret the

anomalous stress as a particular input signal,

resulting in an output causing the corresponding

equipment to operate in an unforeseeable way and

surely bringing about negati e consequences.

To this end, var ous regulations have been passed

hich provide for the protection against

electrostatic discharges up to 4 KV as, for instance, for cash registers.

Such a protection is represented by the capacity

of the equipment - in this case the cash

registers - to carry electrostatic discharges up

to 4 KV without any anomalous operation.

Many solutions have been taken in order to

overcome these technical problems and to comply

with the legal regulations in force. A first

solution foresees the use of multi-layer printed

boards for the various electric/electronic circuits assembled thereon.

In this way, the stratigraphic structure of the

above-mentioned boards represents a fairly good

insulating and dispersive means for possible

discharges which affect the equipment itself, at

the same time they protect the circuits of the

equipment from possible stresses which could be

interpreted as ne input signals, which are

certainly anomalous and detrimental for the

equipment.

Besides, this solution involves high industrial

costs and an average time of productive

development months/man.

Anyway the practical results do not guarantee

both a stable answer to the event and the universal applicability of the solution itself to any kind

of equipment.

A second solution is represented by the dead

ground which extends on the whole board to be

protected, together with a number of quality

capacitors suitably arranged on the board i self.

In this way the circuits of the board to be

protected can be virtually insulated, thus

preventing any galvanic connection with external

signals .

Even this solution, however, has its limitations.

»

Infact the development times of the board

provided with the above-mentioned dead grounds

are long and moreover it is necessary to mount

on the board also all the required capacitors

involved by such solution.

As a consequence the production times become

longer and the corresponding costs higher and

nonetheless this cannot be considered a totally

reliable solution.

Finally, a third solution employes special

conductive paints or covering plastic materials,

ich cover the whole plate to be protected.

This solution provides an insulation coating on

the hole circuitry assembled and arranged on the boa rd .

In this way, an external signal can unlikely

enter into the circuit, here considered, without

a precise galvanic connection, hindered by such

protective solution.

In spite of this, also such a solution which, as

a rule, is the most often adopted in industry,

involves some problems.

First of all, the production process is more onerous and then the results are not always

positive.

As a matter of fact, this film coating must be

applied in the last phase of the production

process and for this reason the production time

becomes much longer and its costs much higher.

Moreover, this kind of coating can guarantee only

a certain degree of protection, since above

which, the results are uncertain.

Finally, another aspect common to all above-

mentioned solutions to be considered, is that

almost always the protection problems are tackled

only when the equipment has already been totally

assembled. As a consequence, the extra time

required to determine the best solution of the

problem hinders the actual planning completion of the equipment itself, involving high and not

controllable co ts, esDβcially in case of

variations of the equipment hardware.

The main object of this invention is to eliminate

the above-mentioned drawoacks with reference to

the systems currently used, realizing and

providing a protective device against

electrostatic discharges on electronic

equipments, in general, which is able to

guarantee a real feature improvement of

reliability, flexibility and protection

realization, which reference is made to.

Further advantages and features are attained, in

the following description according to the

present invention, by a protective device against

electrostatic discharges for electronic equipment

in general, charachterized in that it consists of

a combination of no n circuits including a first

antenna circuit to pick up the electric field

created by an electrostatic discharge, which

sends an enabling signal, upon systematic

suppression of noises on power line by means of a

second c rc , to a third circuit generating a

following start signal with a desired time

sequence, so that a fourth interface circuit, enabled by this start signal and galvaπically

connected to the equipment to be protected, can

send a seq ence of monitoring signals to this

equipment, thus preventing any irregular

operation of the equipment itself.

Further characteristics and advantages of the

invention can be gathered from the following

detailed description of a preferred, but not

exclusive, embodiment of a protective device

against electrostatic discharges on electronic

equipment in general, reference being made to the

accompanying drawing, which has a mere indicative

value and thus noπ limitative, which shows a

preliminary block diagram of the device according

to the present invention.

Referring to the figure, the number 6 indicates

the device according to the present invention, as

a whole. An antenna circuit 1, which is

fundamentally nown, acts as a sensor of an

electric field created by an electrostatic

discharge .

At each tracking this circuit 1 triggers a

monostable circuit 2 which acts as a signal

generator.

Another circuit 3, which is also known, works in parallel with the circuit 1 ,- so that no

spurious signals such as those caused by the

noises of the power line can reach the circuit 2.

Finally, trough an interface circuit 4 the device

6 can be fitted to every equipment 5 according to

a sequence of a plurality of signals 4a, 4b at

least one of which disconnects the equipment.

This structural description of the device is now

followed by a detailed analysis of its normal

operation process.

Every time an electrostatic discharge causes an

electric field, thus the antenna circuit 1 ,

acting as a sensor circuit, picks up the field

and the discharge itself and sends an enabling

signal to the monostable circuit 2.

The latter's output presents a known R-C

configuration through which the outgoing signal

can be gauged according to a time sequence

only depending on resistance and capacitance value.

In this way the signal of the antenna triggers

the monostable 2 which, according to a suitable

timing, sends its start signal to the interface

circuit 4 which adapts *he received signal to the

type of equipment 5 to be interfaced, applying

to this equipment 5 a plurality of analog and/or digital signals 4a, 4b, which cutoff the normal

operation of the equipment 5 in order to avoid a

defective operation. In short, the device 6 acts

as a controller of the equipment 5 to which it is

fitted by feeding to such equipment signals 4a,

4b, of which at least one disconnects its

essential functions, but only in the case of

irregular signals generated by an electric field.

Immediately after the tracking this disconnection

is reset, for example, through a CPU in the

equipment 5.

It is important that such disconnection takes

place only when a disturbance created by an

electric field could be sent to the circuits of

the equipment 5, so that it does not bring about

further operational problems for the operator of

the equipment.

Therefore, in order to improve the reliability of

the device 6, it is suggested to provide also the

filter 3, because it filters the disturbances

created by the noises of the supply.

In this way the invention can achieve the

proposed objects. Infact, thanks to this device 6

it is possible to safeguard the operational

integrity of any equipment 5 to which 6 is fitted, preventing through a fine filtering of

signals any defective and detrimental operation

of the equipment 5 owing to an eventual

disturbing signal, such as an electrostatic

discharge, generated by an electric field.

In so far as the illustrated embodiment, an

immunity to electrostatic discharges up to 10 KV

has been ascertained.

Moreover, this device 6 can be easily and cheaply

interfaced with any equipment, although it was

originally developed to protect the cash

registers .

Clearly, the invention is not limited to the only

embodiment described above, but various

modifications and variations are possible, both

regarding the parameters and the circuits, all

falling within the inventive concept.

Claims

1 ) Protective device against electrostatic

discharges on electronic equipment in general,

characterized in that it consists of a

combination of knowrt 'ci rcuits including a first

antenna circuit to pick up the electr c field

created by an electrostatic discharge, which

sends an enabling signal, upon sistematic suppression of noises on power line by means of a

second circuit, to a third circuit which

generates a following start signal with a desired

time sequence, so that a fourth interface

circuit, enabled by this start signal and

ςalvaπically connected to the equipment to be

protected, can send to the latter a sequence of

monitoring signals which prevent any irregular

operation of the equipment itself.

2) Protective device against electrostatic

discharges on electronic equipment in general

according to claim 1, characterized in that

said third circuit consists of a monostable

circuit. 3) Protective device against electrostatic

discharges on electronic equipment in general

according to what previously described and

illustrated for the specified objects.