Abstract
The recently introduced Zero-IF self-oscillating mixers (SOMs) enable a direct frequency conversion, of interest for the implementation of compact and low consumption radio frequency identification (RFID) tags, among other applications. In previous works, the Zero-IF SOM is placed in only one of the terminals of the wireless link, the other one being based on a conventional scheme. In this article, a system made up of two wirelessly locked Zero-IF SOMs, operating as a frequency upconverter and downconverter, will be analyzed to evaluate its potential for low-cost short-range communications. A complete formulation describing the system under antenna and propagation effects will be presented, which, as a particular case, is able to predict the behavior of the previously proposed Zero-IF SOM, locked by an independent signal. The formulation based on oscillator models extracted from harmonic balance allows deriving design criteria for an optimum and robust performance and can predict the maximum communication range, as well as the stability properties and phase-noise behavior. The operation under modulated conditions is analyzed with a novel envelope-transient formulation, accounting for the time differentiation caused by the propagation effects. The methods have been applied to a system of two Zero-IF SOMs operating at 900 MHz.
Highlights
Z ERO-IF self-oscillating mixers (SOMs), proposed in [1] and [2], enable a direct frequency conversion that avoids the need for both an oscillator and a mixer
In comparison with conventional implementations, they reduce the power consumption and size, which is of general interest for compact transmitters and receivers, such as those required for radio frequency identification (RFID) and sensor systems [3]
In the RFID system proposed in [1], the Zero-IF SOM, placed in the tag, is injection locked by the carrier transmitted by the reader
Summary
Z ERO-IF self-oscillating mixers (SOMs), proposed in [1] and [2], enable a direct frequency conversion that avoids the need for both an oscillator and a mixer. A complete formulation describing the system under antenna and propagation effects will be derived, which, as a particular case, is able to predict the behavior of the previously proposed Zero-IF SOM [1], [2], locked by an independent signal. As will be shown here, the mutually injection-locked operation can be maintained up to distances of several meters with a conventional oscillator design using a single transistor per SOM and low-gain antennas Note that for this initial proof of concept, two transistor-based SOMs will be considered, though other devices, such as the tunnel diodes recently proposed in [13] and [14], can be more convenient to reduce consumption, size, and cost.
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