Amos Joel,  whose switching device opened the way for the mobile phone industry, has died age 90.

Joel, who was an inventor, received more than 70 patents, but he was perhaps best known for No. 3,663,762, which in 1972 allowed a mobile phone user to make an uninterrupted call while moving from one cell region to another.

This gave mobile phone users the ability to wander round, drive and walk into lamp posts as they communicated. Joel tinkered with electronics from an early age. While in college, he met his wife, the former Rhoda Fenton, on a blind date and invited her to come upstairs and see his patents.

Joel spent his professional career at Bell Labs, working 43 years there until he retired in 1983. During World War II he designed circuits for early digital computers. After the war, he developed and taught a course on switching systems and circuit design and eventually designed the first automatic telephone billing equipment.