University of Twente Student Theses


State of the art LC-based frequency reference

Busscher, S.G.H. (2019) State of the art LC-based frequency reference.

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Abstract:De facto standard for frequency references is the crystal-based oscillator. While having decent frequency stability (±1ppm/OC), it is let down by its cost and size. These are the reasons for switching to the LC-based cross-coupled CMOS-design which has the advantages of being cheaper and smaller, enabling on-chip implementation. However, in the 1 GHz frequency region the problem arises with the quality factor of inductors where QL << QC and therefore RL >> RC. Variances in temperature will affect the resistances the most and RL will therefore have the most influence in varying oscillation frequency as function of temperature. All the cross-coupled configurations suffer from these variations of RL so it would be interesting to investigate various LC-architectures (like the Hartley or Clapp) to check how they are affected by RL variations. The common-gate Colpitts oscillator was found out to be less affected by the parasitic resistance RL and better temperature stable (±10ppm/OC) than the widely-used cross-coupled LC-oscillator (±50ppm/OC). In this report, the frequency stability as a result of temperature variations of various common-gate oscillator designs in the 1 GHz region are calculated and simulated and compared to the common-gate Colpitts oscillator frequency stability in order to find a better performing configuration. The configurations that are tested include Hartley, Clapp and a cross-coupled LC-oscillator with extra capacitor. Furthermore, adaptations to the Colpitts design are calculated where one design has a parallel capacitor added to the inductor to tune the inductor and the other one a series resistance added to the capacitors in order to tune the QC. Results show that the Hartley, Clapp and cross-coupled +Ca are not better performing than the original Colpitts in terms of frequency stability. Both the adapted Colpitts designs however show significant improvement in the simulations when tuned right (±100ppm ∆100OC).
Item Type:Essay (Bachelor)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology
Programme:Electrical Engineering BSc (56953)
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