(19)

(11)

EP 0 256 075 A1

(12)

(43) Date of publication: 24.02.1988 Bulletin 1988/08 (21) Application number: 87901072.0 (22) Date of filing: 29.01.1987

(51) International Patent Classification (IPC):  H01L 31/ 0236( . ) H01L 31/ 108( . ) H01L 31/ 0352( . ) H04J 14/ 00( . ) (86) International application number: PCT/GB1987/000061 (87) International publication number: WO 1987/004862 (13.08.1987 Gazette 1987/18)

(84) Designated Contracting States: DE FR GB NL (30) Priority: 30.01.1986 GB 19860002309 08.01.1987 GB 19870000322 (71) Applicant: PA Consulting Services Limited London SW1X 7LE (GB)	(72) Inventors: SAWYERS, Craig Letchworth Hertfordshire (GB) MABBITT, Allen, William Bedford K41 8LT (GB) (74) Representative: Nash, Keith Wilfrid, et al  KEITH W. NASH & Co. Pearl Assurance House 90-92 Regent Street Cambridge CB2 1DP Cambridge CB2 1DP (GB)