GB2153165A

GB2153165A - Connector assembly

Info

Publication number: GB2153165A
Application number: GB08401497A
Authority: GB
Inventors: Robert Stanley Welch
Original assignee: AVX Corp
Current assignee: Kyocera Avx Components Corp
Priority date: 1984-01-20
Filing date: 1984-01-20
Publication date: 1985-08-14
Also published as: GB8401497D0; FR2558661A1; DE3426369A1; JPS60154482A

Abstract

A connector assembly includes a capacitive/inductive RF filter (L,C1,C2) formed of at least one disc (10,11) of capacitive material juxtaposed with at least one disc (12) of inductive ferrite material and at least one disc (13) of a surge suppression material capable of providing a low resistance path (R) to ground when the applied voltage level exceeds a predetermined threshold value. The disc (13) may be a metal oxide varistor material which also has capacitive characteristics. <IMAGE>

Description

SPECIFICATION Connector assembly This invention relates to a connector assembly including a filter for filtering out RF interference signals to ground.

It is known to provide in such a connector assembly, an RF filter including one or more capacitors and at least one inductor of ferrite material arranged such as to filter to ground any spurious or undesirable RF signals which might otherwise pass through the connector.

It is an object of the present invention to provide a connector assembly including an RF filter employing capacitive and inductive elements and including additionally means for suppressing voltage surges by providing a low resistance path for the high voltage energy.

According to the present invention there is provided a connector assembly including an RF filter employing at least one capacitive element and at least one inductive element wholly or in part of ferritic material characterised in that additionally at least one element of a voltage responsive resistive material is introduced into the assembly to suppress voltage surges by providing a low resistance path for the high voltage energy.

In a preferred embodiment of the invention the connector assembly includes a discoidal filter comprising at least one capacitive disc and at least one ferrite disc and further including at least one disc of a material capable of suppressing voltage surges e.g. metal oxide varistor material.

According to another aspect of the invention the surge suppression material forms part of the dielectric material of the capacitor.

The invention will now be described by way of example only with particular reference to the accompanying drawings wherein: Figure 1 shows a discoidal array consisting of discs of capacitive, inductive and voltage responsive resistive material; Figure 2 is an equivalent circuit of the array of Fig. 1; Figure 3 is a schematic showing various constructions of discoidal arrays of the connector assembly and Figure 4 is a graph showing the typical characteristics of the material used for the surge suppression part of the connector assembly.

Referring to Fig. 1, the outer discs 10 and 11 of the filter are capacitive. One inner disc 1 2 is a ferrite layer. Intermediate outer capacitive disc 10 and ferrite disc 1 2 there is located a surge suppression disc 1 3 of resistive material, hereinafter described more fully.

A central conductor 1 4 extends through the array of discs 10, 11, 12, 13.

Each capacitive disc 10, 11 is made from films of ceramic tape over which are printed films of precious metal such as Ag/Pd. The tapes are printed to give a desired circuit configuration pressed at several tons per square inch and fired in a furnace at about 1 300 C. in Fig. 2, there is shown an equivalent electrical circuit of the array of Fig. 1 in which the central conductor 14 is shown as AB, the two capacitive discs as C1, C2, the inductive ferrite discs as L and the disc of resistive material as R.

The ferrite layer may be a lossy material especially to provide RF signal suppression, it will have for example the general formula MFe2O4 where M is any one of the metals Ni, Cu, Mn, Mg, Zn, Fe and it may be cut from a sintered block or pressed and drilled in the unsintered state to form a disc.

It is to understood that the connector assembly of the invention may have any number and arrangement of capacitive ferrite and resistive discs. In Fig. 3 discoidal arrays may be arranged as shown, made up of one or more capacitive discs 10, 11, one or more inductive ferrite discs 1 2 and one or more discs 1 3 of varistor material. The discs are separated axially of the filter for ease of illustration only.

The connector when assembled may comprise any number of layers of capacitive and inductive and surge suppression voltage responsive resistive arrays, that may be assembled in any sequence, and the arrays may have any values of capacitance and inductance. The frequency response and equivalent circuit will then be modified accordingly.

The surge suppressor discs 1 3 are included in the connector assembly to protect cables and associated equipment from over-voltage conditions produced by for instance electromagnetic pulses or lighting strikes, by providing a low resistance path for the high voltage energy.

Such a function is produced by materials wherein the resistance to current flow is reduced when the applied voltage level exceeds a certain threshold value; materials which exhibit this property including metal oxide varistor materials (e.g. zinc oxide based materials, or magnesium oxide based materials) silicon carbide, titanate based materials etc.

Typical voltage/current characteristics of such surge suppression materials are shown in Fig. 5.

Such varistor materials comprise fine particles e.g. zinc oxide pressed or otherwise combined with certain additives and sintered at high temperatures to provide solid parts.

These parts can also be made using the electrode/mechanical configurations used for forming multilayer ceramic discoidal capacitor arrays.

Metal oxide varistor materials have a current/voltage characteristic expressed by: I = KVt where V is the voltage applied across a pair of electrodes I is the current flowing between the electrodes K is a constant depending on: physical dimensions of the part its material composition the process used in making the part a is a constant for a given range of current and is a measure of the non-linearity of the I/V characteristic.

The voltage-dependent characteristic is a result of a large number of crystal contacts forming a complicated network of series and parallel resistors.

This non-linear bulk phenomenon is bidirectional, and the voltage limiting effect is practically instantaneous. Heat generation and absorption is uniformly distributed throughout the material, and the heat conductivity is good to dissipate heat generated.

The dielectric constant of the varistor material depends on the ingredient mix, sintering temperature etc., and is typically in the range 600-1800 for a zinc oxide, bismuth oxide mix. A part constructed with the mechanical/ electrode geometry of a discoidal capacitor array has both surge suppression and capacitance characteristics at the same time. The capacitance characteristics at the same time.

The capacitance characteristics of interest are for signals lower than the effective "clipping" voltage of the surge suppression.

Effective clipping voltages depend on formulation, process etc., and range from a few volts to the kilovolt level.

The connector assembly comprising the discoidal filter and surge suppressor of the invention offers a construction that is less costly to manufacture and assemble than that of presently known constructions and also gives an electrical component superior in efficiency of operation to said known constructions.

Claims

1. A connector assembly including an RF filter employing at least one capacitive element and at least one inductive element wholly or in part of ferritic material characterised in that additionally, at least one element of a voltage responsive resistive material capable of suppressing voltage surges is introduced into the assembly to provide a low resistance path for the high voltage energy.

2. A connector assembly as claimed in claim 1 wherein the capacitive, inductive and resistive elements each comprise a disc assembled in juxtaposition to form a discoidal array.

3. A connector assembly as claimed in claim 1 wherein said at least one surge suppression element is formed of a material capable of reducing its resistance to current flow whe the applied voltage level exceeds predetermined threshold value, such as to provide a low resistance path to ground for the high viltage energy.

4. A connector assembly as claimed in claim 3 wherein said material is a metal oxide varistor material e.g. zinc oxide based material or magnesium oxide based material.

5. A connector assembly as claimed in claim 3 wherein said material is silicon carbide or a titanate based material.

6. A connector assembly including an RF filter employing at least one capacitive element and at least one inductive element wholly or in part of ferritic material characterised in that the dielectric material of the said at least one capacitive element includes a voltage responsive resistance material capable of suppressing voltage surges to provide a low resistance path for the high voltage energy.

7. A connector assembly substantially as hereinbefore described with reference to and as shown in the accompanying drawings.