In this paper, a low-power zero-IF self-oscillating mixer (SOM) for a new generation of high data-rate battery-free, yet active mu RFID tag (a fully integrated RF identification tag on a single CMOS die with no external components, nor packaging) operating at millimeter-wave frequencies is proposed and demonstrated. It exploits, on one hand, the intrinsic mixing properties of an LC cross-coupled voltage-controlled oscillator, and on the other hand, the injection-locking properties in oscillators. By injection locking the SOM's natural oscillation frequency to the reader's carrier frequency (a frequency that bears information of the tag: reader-to-tag communication), it enables a direct-conversion to the baseband with no external local oscillator (LO) source (self-mixing), nor RF frequency conversion into IF frequency, therefore significantly reducing its power consumption. Up-link communication (tag-to-reader communication) is performed by up-converting the tag's data using the same SOM. Furthermore, the in-phase injected energy stabilizes the self-generated LO and enhances the SOM phase noise, resulting into a low-phase noise baseband signal. Using a standard 65-nm CMOS process, a 40-GHz zero-IF SOM was designed, fabricated, and tested. Experimental results exhibit a conversion loss of about 30 dB under -38-dBm injected RF power with a power consumption of only 280 mu W during reader-to-tag communication, and 580 mu W during tag-to-reader communication.
