Successive Approximation RF Reflectometer for Antenna Tuning in Cellular Handheld Devices

A radio-frequency (RF) scalar reflectometer detecting a load return loss value by successively attenuating the forward-coupled RF power until it reaches the level of reverse-coupled RF power is presented in this paper. The device operates at cellular frequencies between 690 and 2700 MHz and covers voltage standing wave ratios range up to 20:1. The monolithically integrated device comprising an RF core, an analog-to-digital converter, a power regulation unit, and a serial communication interface occupies a die area of 850×850 μm
²
in 130-nm CMOS technology and consumes a maximum supply current of 400 μA from a 2.8 V supply during detection. The device does not require frequency and temperature calibration when operating in scalar mode. A method for operating the same integrated circuit (IC) in vector detection mode is briefly introduced. The target application for the presented reflectometer IC is impedance sensing in antenna tuning RF front-ends.