### Signal Design and Figure of Merit for Green Communication Links

To achieve maximum energy efficiency in transmitters, it is known that circuit linearity must not only be compromised, it must actually be suppressed [1]. To take full advantage of the available energy efficiency in any power amplifier (PA), it is also necessary to use signals that allow PA operation at that efficiency [2]. In particular, signals that contain envelope zero crossings force PA circuit linearity and place a lower ceiling on the actually achievable energy efficiency that can be far below that available from the PA transistor [3].