Balanced Detection in Multiport Direct-Conversion Interferometric Receiver for IoT Systems

Multiport interferometric receivers are recognized for their competitive low-power and low-cost wireless sensor solutions. However, the systematically generated rectified wave components in a conventional direct-conversion interferometric receiver can saturate the receiver in a radio propagation environment comprising multichannel signals in the operating band of interest, which requires power-hungry auxiliary building blocks for compensation. In this work, a balanced detection scheme in a radio frequency/microwave interferometric receiver, for the first time, is devised and presented for implementing a differential acquisition. This method is based on the phase opposition of the local oscillator (LO) driving signal measured between a pair of Schottky diodes. The subtraction of two outputs is set to cancel unwanted rectified signals and improve the desired detected signal quality. A prototype is implemented in the 60-GHz frequency band using a miniature hybrid microwave integrated circuit fabrication process, which can be extended to any frequency band of interest and fabrication technology. The balanced detection scheme shows an excellent suppression of second-order distortions and about 6-dB conversion gain improvement of the detected signals in comparison to a conventional interferometric receiver employing a single-ended detection scheme. The demodulation of several modulated digital signals has been successfully demonstrated, which only requires about 25% of the driving signal power to have a similar error vector magnitude performance as with the single-ended detection scheme when probing an intermediate frequency detected signal.