Voltage controlled oscillator for ultra-wide band RFID reader

Abstract

Voltage controlled oscillator is inevitably the most important signal source of the wireless communication and radio frequency identification (RFID) systems. The spectral purity of a voltage controlled oscillator is a fundamental parameter that determines the low bit-error rate of the transceiver system like an RFID reader. Meanwhile, the rapidly emerging ultra-wide band (UWB) technology lacks low phase noise voltage controlled oscillators designed on the low-cost printed circuit boards rather than using the expensive monolithic microwave integrated circuits. However, most of the voltage controlled oscillators suffer from the spectral impurity due to the phase noise increased by the low quality-factor of the resonator. In this research, by using the parallel feedback topology, a voltage controlled oscillator has been designed in the UWB frequencies for an RFID reader. Phase noise has been reduced by introducing the novel technique of a coupled branch-line resonator. Further, a novel cross-coupled branch-line resonator has been designed for the phase noise reduction in the voltage controlled oscillator. To increase the tunability for the operation of voltage controlled oscillator, varactor diodes have been employed to the cross-coupled branch-line resonator. The standard process of printed circuit boards has been adopted to design the voltage controlled oscillator at the frequency of 3.228 GHz on the Taconic TLX-8 substrate. The designed voltage controlled oscillator operates within the UWB frequencies over a bandwidth of 105 MHz from the frequency of 3.125 GHz to 3.230 GHz by tuning the control voltage of varactor diodes from 0 to 16 V. Phase noise has been reduced to -136.253 dBc/Hz at 1 kHz offset frequency and -159.173 dBc/Hz at 1 MHz offset frequency. DC power consumption by the voltage controlled oscillator is only 10 mW to deliver an output power of 1.92 dBm. Figure of merit has been found as -219.35 dBc/Hz to assess the overall performance of the voltage controlled oscillator. The design occupies a small chip area of 58.5 mm × 53 mm which is compact enough for portable applications. Tuning sensitivity of the voltage controlled oscillator is about 6.18 MHz/V in an average which also shows linear-curve characteristics that are highly required for an RFID reader. Therefore, based on this research, the voltage controlled oscillator is expected to be an excellent candidate for low phase noise applications by utilizing the low-cost process of printed circuit boards.