GB2102244A - Improvements in telecommunication equipment - Google Patents

Abstract

Telecommunication equipment comprises a first adaptor circuit 1 for connection to user equipment, a second adaptor circuit 2 for connection to a telecommunication network device and optical transmission means 3 connected between the adaptor circuits 1 and 2. The optical transmission means include a first series of photodiodes 12 cooperating with a first series of phototransistors 13 for transmitting logic signals from the user equipment to the telecommunication network. A second series of photodiodes 14 cooperating with a second series of phototransistors 15 transmit logic signals from the telecommunication network to the user equipment. The optical transmission means 3 provide electrical isolation, thereby preventing a dangerously high fault signal in the user equipment reaching the telecommunication network. <IMAGE>

Description

SPECIFICATION Improvements in telecommunication equipment This invention relates to telecommunication equipment.

A telecommunication network has a large number of input/output terminals or so-called modems to which are connected various items of user equipment, such as computing machines, teleprinters, or visual display units. In normal operation of such a network, low voltage electrical signals in logic form pass through the interface between each item of user equipment and the associated telecommunication network device.

User equipment is made to comply with certain technical and safety standards, but in general less control and supervision is kept over the use and maintenance of user equipment than over the telecommunication network itself which is commonly supervised by a public utility or corporation such as, in the United Kingdom, British Telecom.

There is a risk that an abonormally high voltage developed or originating in the user equipment as a result of a fault in the operation, servicing or testing of the equipment will be passed into the telecommunication system, where it is liable to damage the system or harm workers working on the system. Hitherto, this problem has been tackled by the expedient of inserting a series fuse and parallel zener diodes, connected to protective ground, between each input/output terminal and the telecommunication device. Skilled personnel are needed to instal and maintain such fused safety devices, and there is a need for some form of electrical isolating means which can be easily fitted at the interface between each item of user equipment and the telecommunication device.

According to the invention telecommunication equipment for linking user equipment with a telecommunication network device has optical transmission means which are capable of passing logic signals at normal signal levels but which are incapable of passing electrical signals at dangerously high signal levels, in order to protect the telecommunication system, and any workers working thereon, from dangerously high fault signals which may originate in the user equipment. The optical transmission means therefore provide electrical isolation between the user equipment and the telecommunication network device, preventing the transmission to the telecommunication network of a dangerously high voltage signal.

According to another aspect, the invention provides telecommunication equipment for linking user equipment with a telecommunication network device, the telecommunication equipment comprising first adaptor means for connection to the telecommunication network device and optical transmission means connected between the first and second adaptor means, the optical transmission means comprising a first series of light emitting devices electrically connected to the first adaptor means, a second series of light emitting devices electrically connected to the second adaptor means, a first series of light sensitive devices which are electrically connected to the second adaptor means and which are sensitive to light emitted by the first series of light emitting devices, and a second series of light sensitive devices which are electrically connected to the first adaptor means and which are sensitive to light emitted by the second series of light emitting devices, logic signals at normal signal levels being passed from the first series of light emitting devices to the first series of light sensitive devices, for the transfer of normal electrical signals from the user equipment to the telecommunication network device, and logic signals at normal signal levels being passed from the second series of light emitting devices to the second series of light sensitive devices, for the transfer of normal electrical signals from the telecommunication network device to the user equipment, the light emitting devices and the light sensitive devices providing electrical isolation between the first adaptor means and the second adaptor means, whereby the telecommunication network is protected against high voltage signals originating in the user equipment.

Preferably, the light sensitive devices are bistable devices, being in one state when illuminated by the corresponding light emitting device, and being in the other state when not illuminated by the corresponding light emitting device. The light sensitive devices may be phototransistors which are in an electrically conducting state when illuminated and an electrically non-conducting state when not illuminated, the phototransistors therefore acting as switches which, even if they are switched to a conducting state by a dangerously high voltage in the user equipment acting on the light emitting device, cause the generation of a normal signal level in the output fed to the telecommunication network.

In the preferred embodiment to be described, each of the first or second light sensitive devices is connected to a corresponding logic circuit included in the second or first adaptor means, respectively, the logic circuit producing a logic output signal corresponding to that applied to the first or second adaptor means, respectively, during normal operation.

Telecommunication equipment forming a preferred embodiment of the invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagram showing the main functional blocks of the telecommunication equipment, and Figure 2 is an electrical circuit diagram of the telecommunication equipment.

As shown in Figure 1, the main functional components of the telecommunication equipment are a first adaptor circuit 1, a second adaptor circuit 2, optical transmission means 3 (or so called optical isolator) and a power source in the form of a transformer 4. User equipment such as a computer, computer terminal, teleprinter, or visual display unit, for example (such equipment normally being referred to as data terminal equipment) is linked to the first adaptor circuit 1, and the telecommunication network is linked to the second adaptor circuit 2 through data control set equipment or modem (not shown). Logic signals 5 reach the first adaptor circuit 1 from the data terminal equipment, and corresponding logic signals 6 are fed to the data control equipment and thence on to the telecommunication network.

Logic signals 7 reach the second adaptor circuit 2 from the telecommunication network via the data control equipment, and corresponding logic signals 8 are fed to the users data terminal equipment. The first adaptor circuit 1 adapts the logic signals 5 to a form suitable for supply to the optical transmission means 3, and the second adaptor circuit 2 adapts the signals from the optical transmission means 3 to a form identical to the logic signals fed to the first adaptor circuit 1.

Similarly, the second adaptor circuit 2 adapts the logic signals 7 to a form suitable for supply to the optical transmission means 3 and the first adaptor circuit 1 adapts the signals from the optical transmission means 3 to a form identical to the logic signals 7 fed to the second adaptor circuit 2. Power for the adaptor circuits 1 and 2 is supplied from the transformer 4, as indicated by the respective d.c. supplies 9 and 10.

The optical transmission means 3 has a first series of light emitting or photodiodes 1 2 cooperating with a first series of phototransistors 13, for the transmission of logic signals from the users data terminal equipment to the telecommunication network. For the transmission of logic signals from the telecommunication network to the user equipment, the optical transmission means 3 has a second series of photodiodes 14 and a cooperating second series of phototransistors 1 5. Independent control switches to the adaptor circuits 1 and 2 are shown at 16 and 17.

In the circuit diagram of Figure 2, the respective broken boundaries 1, 2 and 3 enclose the components forming the first adaptor circuit, the second adaptor circuit and the optical transmission means. The lower half of Figure 2 shows the first series of photodiodes 1 2 comprising individual photodiodes 1 2a, 1 2b . . ..

and the first series of phototransistors 1 3 comprising individual phototransistors 1 3a, 136... Each photodiode 1 2a, 126... and its associated phototransistor 1 3a, 1 3b . . . is preferably a commercially available integrated circuit.

Two of the logic signals 5 from the user equipment are connected to the first adaptor circuit 1 at terminals 1 8 and 19 respectively. The signal connected to the terminal 18 is a "transmit data" signal and the signal connected to the terminal 19 is a "request to send" signal.

Additional logic signals from the user equipment are connected tofurtherterminals (not shown) of the first adaptor circuit 1 , but all these signals are processed in a similar way by the first adaptor circuit 1 , the optical transmission means 3 and the second adaptor circuit 2. Accordingly, the processing of the "transmit data" signal on the terminal 18 will be described in detail, it being understood that the additional signals are treated in a similar manner.

The transmit data signal on the terminal 18 has the two alternative logic values of +6V or -6V, and these two values are converted by a voltage translator 20 into +5V or OV, respectively. The output of the voltage translator 20 is fed to a current amplifier 22a which produces an output current, or no output current, for the respective input of 5V or OV. The output of the current amplifier 22a drives a corresponding photodiode 1 2a which is illuminated when supplied with current from the current amplifier 22a, and not illuminated when there is zero current output from the current amplifier 22a. When energised, the photodiode 1 2a illuminates its corresponding phototransistor 1 3a the collector of which is connected to an input terminal 21 of an integrated circuit 23 in the second adaptor circuit 2.

When the transistor 13a is in its nonconducting state, it acts as a high impedance, and a voltage of 5V on a line 24 also appears on the input terminal 21 to the circuit 23. When the transistor 1 3a is rendered conductive, the voltage on the input terminal 21 to the circuit 23 falls to zero, so that a "transmit data" signal of +6V on the terminal 1 8 causes a zero voltage on the input terminal 21 of the circuit 23, whilst a transmit data signal of -6V on the terminal 18 causes a +5V signal on the terminal 21.The integrated circuit 23 is a voltage translator logic circuit and converts the input of OV on the terminal 21 to an output of +6V on a terminal 25, and an input of +5V on the terminal 21 to an output of-6V on the terminal 25, thereby ensuring that the logic signal on the terminal 25 is the same as the transmit data signal on the terminal 18.

The "request to send" logic signal of +6V or -6V on terminal 19 is fed in a similar manner through a corresponding current amplifier 22b, a corresponding photodiode 1 2b, and phototransistor 1 3b, producing a corresponding signal of +6V or -6V on the output terminal 26.

Other logic signals are fed through additional current amplifiers, photodiodes and phototransistors, as indicated by the broken lines in Figure 2.

The upper half of Figure 2 shows the second series of photodiodes 1 4a, 1 4b and the second series of phototransistors 1 Sa, 1 Sb which are provided to transfer signals from the telecommunication network to the user equipment. The arrangement is similar to that already described and shown in the lower half of Figure 2. That is to say, a "receive data" logic signal of +6V or -6V on terminal 27 is coupled through a voltage translator 28 which produces +5V or OV and which feeds a current amplifier 29a, ..... . producing an output current or no output current respectively.The current amplifier 29 powers the corresponding photodiode 14a, the output of OV or +5V from the cooperating phototransistor 15a being fed to a voltage translator 30 producing an output of +6V or -6V on a terminal 32 for connection to the user equipment. A "clear to send" logic signal on terminal 33 is fed through the diode 1 4b and transistor 1 sub, appearing as a corresponding logic signal on the terminal 34. Other logic signals are fed from the telecommunication network to the user equipment in a similar manner.

For each logic signal transferred between the user equipment and the telecommunication system, the cooperating photodiode and phototransistor provide an optical link, there being no electrical intercommunication through the optical transmission means 3 so that high voltage fault signals (e.g. of 2,200 volts) originating in the user equipment are not transferred as high voltage signals to the telecommunication network. This electrical isolation is ensured by maintaining a gap of at least 3 mm between circuitry electrically connected to the user equipment and circuitry electrically connected to the telecommunication network. The transformer 4, shown in Fiqure 1, has a single primary winding and two screened secondary windings, but a preferable arrangement is to use two separate transformers, each of a split bobbin design, for powering the respective adaptor circuits 1 and 2.

The adaptor circuits 1 and 2 and the optical transmission means are provided by circuitry on a single printed circuit board which has printed thereon a conducting ribbon serving as a safety earth. The ribbon is indicated diagrammatically at 35 in the drawing and is made as wide as possible consistent with the maintenance of the gap of at least 3 mm previously mentioned. The printed circuit board is preferably made to handle logic signals according to a telecommunications standard known as CCITT. The logic signals 5 to 8 conform to a specification known as V28 in the CCITT standard.

The voltage translators 20 and 28 operate with hysteresis so as to be able to accept a certain noise level in the signals 5 and 7 without the noise prompting the corresponding output signals 6 and 8 to change logic states.

Claims (11)

1. Telecommunication equipment for linking user equipment with a telecommunication network device, the telecommunication equipment having optical transmission means which are capable of passing logic signals at normal signal levels but which are incapable of passing electrical signals at dangerously high voltage levels, in order to protect the telecommunication system, and any workers working thereon, from dangerously high fault signals which originate in the user equipment.

2. Telecommunication equipment for linking user equipment with a telecommunication network device, the telecommunication equipment comprising first adaptor means for connection to the user equipment, second adaptor means for connection to the telecommunication network and optical transmission means connected between the first and second adaptor means, the optical transmission means comprising a first series of light emitting devices electrically connected to the first adaptor means, a second series of light emitting devices electrically connected to the second adaptor means, a first series of light sensitive devices which are electrically connected to the second adaptor means and which are sensitive to light emitted by the first series of light emitting devices and a second series of light sensitive devices which are electrically connected to the first adaptor means and which are sensitive to light emitted by the second series of light emitting devices, logic signals at normal signals levels being passed from the first series of light emitting devices to the first series of light sensitive devices, for the transfer of normal electrical signals from the user equipment to the telecommunication network device, and logic signals at normal signal levels being passed from the second series of light emitting devices to the second series of light sensitive devices, for the transfer of normal electrical signals from the telecommunication network device to the user equipment, the light emitting devices and the light sensitive devices providing electrical isolation between the first adaptor means and the second adaptor means, whereby the telecommunication network is protected against high voltage signals originating in the user equipment.

3. Telecommunication equipment according to claim 2, wherein the light sensitive devices are bistable devices, being in one state when illuminated by the corresponding light emitting device and being in the other when not illuminated by the corresponding light emitting device.

4. Telecommunication equipment according to claim 3, wherein the light sensitive devices are phototransistors which are in an electrically conducting state when illuminated and in an electrically non-conducting state when not illuminated.

5. Telecommunication equipment according to claim 3, wherein each of the first or second light sensitive devices is connected to a corresponding logic circuit included in the second or first adaptor means, respectively, the logic circuit producing logic circuit output signals corresponding to those aplied to the first or second adaptor means, respectively, during normal operation.

6. Telecommunication equipment according to claim 5, wherein the first adaptor means and the second adaptor means include voltage translator means, to which the logic signals from the user equipment are connected, and current amplifier means which are connected in series between the voltage translator means and the light emitting devices.

7. Telecommunication equipment according to claim 6, wherein the voltage translator means processes the logic signals from the user equipment with hysteresis.

8. Telecommunication equipment according to any of the preceding claims, wherein the first and second adaptor means and the optical transmission means are constituted by circuitry mounted on a common printed circuit board.

9. Telecommunication equipment according to claim 8, wherein the printed circuit board has thereon a conducting ribbon serving as a safety earth.

10. Telecommunication equipment according to any of the preceding claims, wherein the light emitting devices are photodiodes.

11. Telecommunication equipment constructed and arranged substantially as herein particularly described with reference to the accompanying drawings.