A 20dBm outphasing class E PA with high efficiency at power back-off in 65nm CMOS technology

Abstract

-This paper presents an outphasing class E PA (OEPA) in a 65nm CMOS technology, using a pcb transmission-line based power combiner. The OEPA can provide +20dBm output power from VDD=1.25V at 1.4GHz with 61% drain efficiency (DE) and 58% power added efficiency (PAE). We introduced a technique to rotate and shift power and efficiency contours of the two branch PAs that enables more than 44dB output power dynamic range, reduces switch voltage stresses compared to conventional OEPAs and enables 41% DE and 24% PAE at 12.5dB back-off.

Outphasing Class-E Power Amplifiers: From Theory to Back-Off Efficiency Improvement

“…[5] (although the same final results for Z 1,2 were obtained). Secondly, because of the symmetry of the PA loads Z 1,2 and of the normalized output voltages contours with respect to the real axis, for all outphasing angles Vout,1 Vout,2 = 1 which proves the validity of our assumption leading to (7).…”

“…Firstly, the maximum voltage of the switches can be very high [6], [7]. Being implemented by transistors, there is a trade off between switch performance (e.g.…”

“…In [7], we presented a new technique to improve the back-off efficiency for OEPAs with load-insensitive class-E designs. Output power contours and efficiency contours of the class-E PAs on the Smith chart were shown to rotate and the power contours were shown to shift by changing just a few class-E design parameters.…”

“…Moreover, it was shown that this technique also improves the OPDR and reduces switch voltage stress at back-off. In contrast to [10], [11], in [7] we used a load-insensitive design which ideally yields 100% efficiency at (almost) 0dB and 10dB back-off levels and more than 95% efficiency between 0dB and 12dB back-off levels. Moreover, theoretically this yields an infinite OPDR without requiring to tune any parameter.…”

“…Moreover, theoretically this yields an infinite OPDR without requiring to tune any parameter. Using our technique in [7], the second compensation point can be shifted up to 20dB into back-off. This not only can improve the average efficiency of the OEPAs for modulated signals with high PAPRs, but is also promising for applications with output power control or for multi-mode (standard) PAs with different average output power levels [16]- [18].…”