An Area-Efficient Integrated RF Reflectometer Based on Low-Power Logarithmic Power Detector

In this article, an area-efficient radio frequency (RF) scalar reflectometer is presented. Coupled incident and reflected power waves are detected with a low-power logarithmic detector without utilizing active RF amplifiers. The differential output voltage of the power detector (PD) is converted to a digital code, which is proportional to the return loss in decibels. A current-mode successive approximation register (SAR) analog-to-digital converter (ADC) with a reference digital-to-analog converter modulated with digital-to-time conversion is adopted to minimize the area of the readout circuitry while maintaining a high linearity. The device is implemented in a 90-nm RF silicon-on-insulator (SOI) complementary metal–oxide–semiconductor (CMOS) technology, occupying a core area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${0.37}\text {mm}^{2}$</tex-math> </inline-formula>. The implemented reflectometer demonstrates a measurement error of less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${2}\text {dB}$</tex-math> </inline-formula> for load points with return loss worse than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${15}\text {dB}$</tex-math> </inline-formula> from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${900}\text {MHz}$</tex-math> </inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${2.5}\text {GHz}$</tex-math> </inline-formula>. The implemented reflectometer consumes a dc current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${190}\text {$\mu ${A}}$</tex-math> </inline-formula> from a 1.8 V supply during detection.