group of angel investors (notably Kent Plumley), the two developed a telephony DTMF tone receiver based on Cowpland's PhD thesis. This was a major advance in the technology, since they were able to sell receivers at a fraction of the cost of competing versions, while gaining returns of 1000%. Additionally, Mitel later became a chip manufacturer with the acquisition of the Silek foundry in Bromont, Quebec. Later, the pair realized that the then-new technology of microprocessors and other semiconductor devices would make a similar change in the market for small PBXs. The SX200 PBX launched to immense success, being cheaper to purchase, quicker to install and far more functional. Mitel became one of the more successful manufacturers of small PBX systems and telecom semiconductors in the world, floating on the New York Stock Exchange in 1981. In 1985, British Telecom bought a controlling interest in Mitel. Cowpland would later form the company that became Corel, and Matthews later founded Newbridge Networks. Newbridge Networks In 1986, Matthews drove Newbridge to become a leader in the worldwide data networking industry, manufacturing data communications products, especially ATM devices and routers. In 2000 the company employed more than 6,500 employees with recorded FY 1999 revenue of $1.8 billion. Later in 2000, Newbridge was acquired by Alcatel for $7.1 billion. Matthews' personal stake in Newbridge was valued at over a billion dollars, and as a result of the transaction he became the largest single shareholder in Alcatel. Return to Mitel In 2000, he reacquired the Mitel PBX business and company name, taking it private. He has invested heavily ($600 million by 2006) in Mitel to turn it into a broadband communications company. The company has made significant investments in enterprise Voice over IP telephony technology. Mitel's manufacturing business was spun off as BreconRidge. The company acquired Intertel in April 2007. Mitel went public again in 2010. Mitel announced the purchase of Aastra Technologies in November 2013. Mitel announced the purchase of Mavenir Systems in March 2015. Mitel announced the purchase of Polycom in April 2016, however, the deal fell through and Polycom instead merged with private equity firm Siris Capital Group. In July 2017, Mitel announced they had reached a deal to buy ShoreTel for $430 million, increasing the size of the company to 4,200 employees. On 24 April 2018, the company announced it would be bought by an investor group led by Searchlight Capital