A Fully Integrated Transformer-Coupled Power Detector With 5 GHz RF PA for WLAN 802.11ac in 40 nm CMOS

This paper introduces a fully integrated direct power detector that monitors both RF current and RF voltage to detect the RF output power of the on-chip RF PA realized in a standard 40 nm CMOS process. The RF current measurement is realized by a sense winding in the output transformer, while the RF voltage waveform measurement is performed by capacitive division of the RF output voltage. Since the RF current and the RF voltage are both acquired, this power detector accurately and continuously determines the real output power of the RF PA with a maximum inaccuracy of ±0.5 dB over a wide 32.5 dB dynamic range. This power detector was integrated together with a 5 GHz RF PA designed for the WLAN IEEE 802.11ac communication standard. The power detector is capable of performing a RF output power measurement even for an antenna impedance mismatch up to voltage standing wave ratio (VSWR) 2.8:1 with an accuracy of ±1 dB, which allows the power detector to be used in an automatic antenna-mismatch correction system to prevent performance degradation in the RF PA. Finally, since the proposed power detector can be completely incorporated inside the RF PA output transformer. It results in zero area overhead, proving a very cost effective design.