Comment on “On the Double-Inflection Characteristic of the Continuous-Wave AM/AM in Class-F−1 Power Amplifiers” [Dec 18 1131-1133]

Sharma et al. [1] analyzed the phenomenon of double gain compression in harmonically tuned PAs for the first time. The phenomenon of double inflection point and the research are very novel. The formula is very complete, and the content is very popular. However, when we referred to it, we found a wrong equation. The expression in [1, eq. (11)] is as follows: \begin{align*} {P_{{\mathrm{out,inflection1}}}}=&\frac {\mu _{1}^{2}}{{2{Z_{2L}}}} \\=&\frac {{{V_{dd}}}}{{2{Z_{2L}}\left |{ {\frac {1}{2}{g_{m2}} + \frac {3}{2}{g_{m3}}{V_{B}}} }\right |}}\\&\times \left ({\vphantom {\frac {{{V_{dd}}}}{{\left |{ {\frac {1}{2}{g_{m2}} + \frac {3}{2}{g_{m3}}{V_{B}}} }\right |{Z_{2L}}}}} {g_{m1}} + 2{g_{m2}}{V_{B}} + 3{g_{m3}}V_{B}^{2} }\right . \\&\qquad \left .{+\, \frac {3}{4}{g_{m3}}\frac {{{V_{dd}}}}{{\left |{ {\frac {1}{2}{g_{m2}} + \frac {3}{2}{g_{m3}}{V_{B}}} }\right |{Z_{2L}}}} }\right )^{2}{Z_{1L}}.\end{align*}