GB2150382A

GB2150382A - Optical signalling between elements on a circuit board

Info

Publication number: GB2150382A
Application number: GB8331834A
Authority: GB
Inventors: David John Sydney Westwood
Original assignee: Thorn Emi Ferguson Ltd
Current assignee: Thomson Multimedia Sales UK Ltd
Priority date: 1983-11-29
Filing date: 1983-11-29
Publication date: 1985-06-26

Abstract

Two printed circuit boards 1, 2 in a television receiver have electronic components 3 to 9 (namely integrated circuits 3, 6, 7, indicator 4, resistor 5, capacitor 8 and switch 9). Metallic support pins 10 of each component are soldered to copper strip 11 for connection to an external power supply. Components 3 to 9 have infra-red transmitters 12 and infra-red receivers 13 to provide data and/or control signal connection between the components. Board 2 has a light-pipe 14 of optically refractive material to allow transmission of infrared beams between boards. <IMAGE>

Description

SPECIFICATION Circuit board The present invention relates to a circuit board on which are electrical and/or electronic components, and to an assembly of such circuit boards.

At present, each printed circuit board used in a television receiver has many electrical and electronic components including integrated circuits. To manufacture such a printed circuit board, firstly all the integrated circuits and other components are inserted in the appropriate positions, generally automatically, and then the resultant unit is passed to a solder-bath at which all the necessary electrical connections are made (thereby also securely mechanically fixing all the circuits and components onto the board). Then each board has to be checked individually, usually by a person, to determine that the components have adequate electrical connections, and any faults detected must be rectified.Such rectification needs to be done by a skilled worker capable of doing careful and precise repairs; even with such handling, there is a significant risk of unintentional damage occurring to neighbouring integrated circuits and other components on the board. Moreover such repairs are time consuming.

As each integrated circuit may have between ten and thirty connections with other circuits or components, the inspection and rectification stages can be responsible for a significant portion of the overall time for manufacturing the final product of the printed circuit board and hence be a significant factor in its overall cost.

An object of the present invention is to provide a printed circuit board in which there is a significant reduction in the inspection and rectification necessary.

The present invention provides a circuit board having a plurality of electrical and/or electronic components, at least some components having means to transmit data and/or control signals in the form of coded optical signals, at least some components having means to receive the coded optical signals, each path of coded optical signals between those components having at least a portion with no transmission line or waveguide.

Thus the number of soldered electrical connections between integrated circuits and other components can be significantly reduced, thereby minimising the disadvantages relating to inspection and rectification.

In one form of the present invention, a circuit board has a plurality of electrical and electronic components including at least one integrated circuit device having means to transmit data and/or control signals in the form of coded optical signals, at least one electrical or electronic component having means to receive the coded optical signals, each path of coded optical signals between those components having at least a portion with no transmission line or waveguide.

In another form of the present invention, a circuit board has a plurality of electrical and electronic components, at least one component having means to transmit data and/or control signals in the form of coded optical signals, at least one integrated circuit device having means to receive the coded optical signals, each path of coded optical signals between those components having at least a portion with no transmission line or waveguide.

There can also be, in an assembly of circuit boards as described above, transmission of data and/or control signals between components on different boards.

Another aspect of the present invention provides an assembly of circuit boards, at least one circuit board having an electrical or electronic component with means to transmit data and/or control signals in the form of a coded optical signal, at least one circuit board having an electrical or electronic component with means to receive that coded optical signal, the path of that coded optical signal between the components having at least a portion with no transmission line or waveguide.

The term "optical signal" is used within this specification to refer to a signal with wavelenthsoin the infra-red or visible light section of the electromagnetic radiation spectrum. Thus, preferably the transmitting means is an infra-red generator and the receiving means is an infra-red receiver.

Preferably, at least some of the components are integrated circuit devices; the associated transmission means and/or receiving means may form part of the internal circuitry of these devices and hence these functions would be inherently achieved in these devices.

Preferably an electrical conductor is associated with at least one circuit board to connect at least some of the components on the board or boards to a common power supply.

Any coded optical signal from a transmission means may be passed or otherwise guided (e.g. by reflection or refraction) in any appropriate way in order that it passes to the intended receiving means.

An optical signal may be coded in any suitable way, for example by carrier wave frequency modulation. The coding may include information on the intended recipient component(s) to ensure that the signal is not used by other components; additionally or alternatively the direction of transmission of the signal, and optionally its subsequent path, is suitably controlled.

In order that the invention may more readily be understood, a description is now given, by way of example only, reference being made to the sole accompanying Figure which shows part of an assembly of printed circuit boards.

This Figure shows two printed circuit boards 1, 2 in an assembly of a number of such boards for use in a television receiver. On the boards 1 and 2 are located a number of electronic components 3 to 9, namely integrated circuits 3, 6 and 7, inductor 4, resistor 5, capacitor 8 and switch 9. Each of these components requires connection to an external power supply; thus the metallic support pins 10 of each component pass through the respective board and are soldered to a common copper strip 11 which is connected to a suitable power supply. A copper strip 11 extends the length of each board 1, 2 either in a straight line or in a curved path in order to connect all the components to a power supply; the copper strips are formed on boards 1,2 by conventional photolithographic processes.

The connections between the components 3 to 9 for carrying data andior control signals are by infra-red beams. Thus a component may have one or more infra-red transmitters 12 (shown schematically in the Figure as a white rectangular projection), for example light emitting diodes, and/or one or more infra-red receivers 13 (shown schematically in the Figure as a black concavity), for example photo diodes. The integrated circuit 3 has two infra-red transmitters, one directing an infra-red beam (representing a set of signals) to an infra-red receiver on inductor 4 and the other directing an infra-red beam (optionally representing another set of signals) to an infra-red receiver on integrated circuit 6.

The output from inductor 4 is directed by infrared transmitters to, inter alia, resistor 5 and integrated circuit 6. Whereas the components 3, 4 and 6 are in a straight line, the resistor 5 is displaced from that straight line so that it does not interfere with the infra-red beam extending directly between components 4 and 6.

integrated circuit 6 has three separate infra-red receivers, one for each of the signals from the different sources thereby enabling the signals to be used readily in different functions of the integrated circuit processing. However integrated circuit 7 has a single infra-red receiver which is common for three signals from separate sources. Thus either these three signals are used in combination or integrated circuit 7 does some separation processing before utilizing the signals individually.

Integrated circuit 7 receives infra-red beams from, inter alia, resistor 5 and integrated circuit 6, namely components on another board. Thus there can be ready connection of signals between boards.

Board 2 has a light pipe 14 of optically refractive material which enables infra-red beams, directed onto one end of it from conductor 4 and capacitor 8, to be transmitted to one or more further boards (not shown) on the other side of board 2. Clearly this pipe can be used to transmit beams in either or both ways.

The infra-red beams may be coded in any appropriate way in order to carry the information relating to the data and/or control signals. For example there may be carrier frequency modulation at different frequencies, thereby resulting in a reduction in cross-talk or other interference between beams.

The coded information contained in each infrared beam includes a portion which indicates the intended recipient component, so as to minimise the possibility of any component using or processing signals not intended for it. Focussed transmission of the infra-red beams and highly directional reception of them further reduce the possibility of such unintended use.

Any or all of the boards in an assembly may utilize serial data transmission (to minimise the number of channels and hence the number of transmitters and receivers per component) or parallel data transmission (to maximise the speed of processing), or a combination of each.

Thus an assembly of printed circuit boards can be made up, with the only soldering necessary being the electrical connection of the components to the common power rail (i.e. strip 11). This significant reduction in the number of soldering operations ensures that the manufacturing and testing processes are quicker and easier than before.

Moreover the assembly, once completed, is more reliable in operation than existing equipment. Also the use of infra-red beams provides a number of further advantages; the components are isolated between themselves against the feedback which occurs in wired circuits; any problems associated with fluctuating or badly-defined earth circuits are obviated; and radiation to aerials otherwise produced by electrical current flowing in the conductors between components is obviated (thereby reducing interference and making it harder to tap the circuit board).

In a modification to the above described assembly, those components with low power consumption are not electrically connected to a copper power rail, but are supplied with power optically.

Thus each of these components has a photovoltaic junction on its exterior, so that any light (from a light source suitably positioned in the receiver) falling on the junction is converted to electricity for powering the component.

Thus for each component supplied in this way, the total number of soldering operations necessary for an assembly is reduced. If all the components were of suitably low power consumption, then no electrical soldering at all would be necessary.

Clearly each of the components would still need to be suitably positioned on, and then mechanically secured to, the circuit board. However this can be done easily and quickly once it is not necessary to effect electrical connection.

In any form of the invention, the circuit board can be replaced by any suitable form of substrate to provide a support for the components.

Claims

1. A circuit board having a plurality of electrical and/or electronic components, at least some components having means to transmit data and/or control signals in the form of coded optical signals, at least some components having means to receive the coded optical signals, each path of coded optical signals between those components having at least a portion with no transmission line or waveguide.

2. A circuit board having a plurality of electrical and electronic components including at least one integrated circuit device having means to transmit data andlor control signals in the form of coded optical signals, at least one electrical or electronic component having means to receive the coded optical signals, each path of coded optical signals be tween those components having at least a portion with no transmission line or waveguide.

3. A circuit board having a plurality of electrical and electronic components, at least one component having means to transmit data and/or control signals in the form of coded optical signals, at least one integrated circuit device having means to receive the coded optical signals, each path of coded optical signals between those components having at least a portion with no transmission line or waveguide.

4. A circuit board according to any one of the preceding Claims, wherein the transmitting means is an infra-red generator and the receiving means is as infra-red receiver.

5. A circuit board according to any one of the preceding claims, wherein an electrical conductor connects at least some of the components to a power supply.

6. A circuit board according to any one of the preceding claims, wherein the transmitting means and/or the receiving means include means to focus the coded optical beam in one or more specific directions.

7. A circuit board according to any one of the preceding claims, comprising means to effect carrier frequency modulation and demodulation to provide coded optical signals.

8. An assembly of circuit boards comprising at least one printed circuit board as claimed in any one of claims 1 to 7, at least one circuit board in the assembly having means to transmit data and/ or control signals in the form of a coded optical signal, at least one circuit board in that assembly having means to receive that coded optical signal, the path of that coded optical signal between the circuit boards having at least a portion with no transmission line or waveguide.

9. An assembly of circuit boards, at least one circuit board having an electrical or electronic component with means to transmit data and/or control signals in the form of a coded optical signal, at least one circuit board having an electrical or electronic component with means to receive that coded optical signal, the path of that coded optical signal between the components having at least a portion with no transmission line or waveguide.

10. A circuit board substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

11. An assembly of circuit boards substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.