Introduction to Envelope Tracking - Cambridge Wireless

Introduction to Envelope TrackingG J WimpennySnr Director Technology, Qualcomm UK Ltd EER first proposed by Leonard Kahn in 1952 to improve efficiency of SSB transmitters ET offers similar efficiency enhancement to EER but has fewer drawbacks Technique not widely adopted for many years due to difficulty of implementation, particularly for wide bandwidth signals In the last few years the implementational issues have been overcome and ET is now widely used to improve PA efficiency in Cellular HandsetsEnvelope Tracking Historical Context2 Modern high spectral efficiency Wireless communications standards have high Peak to Average Power Ratio (PAPR) 4G/LTE, WiFi Conventional fixed supply Power Amplifier has to use supply voltage high enough to support Peak Power, but is only energy efficient at the peaks. Most of the time the voltage is much higher than needed, resulting in high PA heat dissipation In ET, the PA supply voltage is dynamically adjusted to the instantaneous amplitude of the signal, resulting in high PA efficiency at all timesEnvelope Tracking Overview3 The efficiency of a Fixed Supply PA is much lower at average Pout than at peak Pout.

• BW of Envelope path needs to be 2-3x RF bandwidth • Delay alignment between RF and Envelope paths at PA (interfaces B and C) is essential to achieve good RF linearity (ACLR / EVM). Sub-sample timing alignment ( <ns) required for wideband signals • Analogue imperfections in both Envelope and RF paths must be corrected

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