Low Phase Noise Voltage Control Oscillator using Cross-Coupled Structure

The voltage controlled oscillator (VCO) is an oscillator that its oscillation frequency is adjustable within a given frequency range by DC voltage change mechanism imposedon at least one element contributed in closed loop. It should be noted that the use of single oscillator circuits which are able togenerate several separate local frequencies is highly desired in existing multiband front-ends, e.g. advanced cellular mobile technologies. The economy of the single wide-range VCOwould be extended further if same concept applied in the design of mixers as well as in LNAs and RF filters [ ]. On theother hand, high electron mobility transistors (HMTs) offer the highest operating frequency, lowest noise and lowest powerconsumption of any current millimeter wave transistor. These excellences have been spearheaded by processing improvements in epitaxial materials, Short gate lengths usinge-beam lithography and Monolithic millimeter-wave integrated circuit (MMIC) processing advances with repeatability and low parasitic. Therefore, due to the aforementioned features of HEMT technology, it has been driven to military and commercial. [ ]. There are manyresearches involving in VCO design based on the current technologies. In Ref. [ ] An HBT based dual band VCO using resonant mode switching operating above GHz is implemented. This method, however, requires the use of transistors to act as current sources. This introduces anothersource of /f noise in the VCO [ ] which is already a big issue in HEMT based designs. Dual band VCO’s operating at frequencies less than GHz are reported [ ] -[ ] using switched resonators, however the switch capacitance was in parallel with the resonator, limiting the channel width and thusthe switch resistance. However, the higher flicker noise corner frequency of HEMTs compared to CMOS and HBT deviceslimits the HEMT oscillators’ phase noise characteristics. Whereas, the AlGaN/GaN HEMT oscillators are also showing low phase noise reported in Ref. [ ] with – dBc/Hz phase noise at MHz offset and in Ref. [ ] with – dBc/Hz phase noise at MHz offset, which can compete against with its moremature counterparts. In this work a HEMT-based VCO at GHz designed and analyzed. Among the HEMT, CMOS and HBT fabricationcurrent technologies, the HEMT are selected because of its better performance as earlier mentioned. The cross-coupled topology is used as the basic structure of proposed design. The simulated results are good enough in term of noise phase and frequency bandwidth comparable to related works