Envelope tracking is one of those technologies which has a ‘moment’ every few years and then fades out of sight. It last hit the news last year when Qualcomm acquired one of its main proponents in the mobile field, the UK’s Nujira. Now Nokia has made its own acquisition in this area, buying Eta Devices. Envelope tracking (ET) is a power supply technique which increases device or base station power efficiency and bandwidth agility, by replacing the fixed DC supply voltage with high bandwidth dynamic supply voltage. This tracks the amplitude, or ‘envelope’, of the transmitted RF signal. The technique was invented in Bell Labs in 1937 and now has come home to Nokia, the new owner of the famous…