VCO and PLL Frequency Synthesizer Discrete Designs for 0.3 – 2.4 GHz Local Oscillator of a Radio Operating Over Wide Frequencies

Author (s):

  1. Dr. C. H. Vithalani, Government Engineering College, Rajkot, Gujarat, India
  2. Mehul R. Naik, Institute of Technology, Nirma University, Ahmedabad, Gujarat, India,


The transceivers used in the software defined radio require designing wideband RF hardware covering octave bands. The local oscillator of the mixer should be a wideband frequency synthesizer. Building on the theory of oscillations in the voltage controlled oscillator, the paper presents the concept of negative resistance in the transistor circuit with some inductance at the base. It also provides simulation of this concept. The functioning of the phase-locked loop and how it can be used to synthesize various frequencies in local oscillator is discussed with emphasis on design tradeoffs. Applying the theory and simulation, four different VCO circuits were designed and fabricated for the range covering 300 to 2400 MHz. These VCOs were later used in the design of wideband PLL frequency synthesizer. The results including very good phase noise performance are presented. This approach can be used to design wideband synthesizers used in software defined radio of the base stations in mobile communication.

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