Realization of Direct Linear Relation Between Control Voltage and Resonance Frequency of the LC Voltage Controlled Oscillator

Abstract

The main problem of traditional LC ( L represents the inductance, and C represents the Capacitance) Voltage Controlled Oscillators VCOs, is the non-linearity relation between the tuning control voltage and output resonance frequency, which is caused by two following reasons: the first one is the inverse and non-linear relation between the tuning control voltage and produced capacitance of the used varactor diode in the VCO circuit, and the second is the inverse and non-linear relation between the capacitance value of the used varactor diode and the output resonance frequency. In this paper, a proposed circuit has been designed and implemented to solve this problem and realize a direct-linear relation between the tuning control voltage and output resonance frequency for the LC Voltage Controlled Oscillator that utilize the varactor diode as a voltage controlled capacitance. The proposed circuit has been realized using Logarithmic, Inverting, Ant-Logarithmic, and Difference Amplifiers, which they are characterized by their simplicity and low cost. The theoretical and practical results of testing the proposed circuit had been presented using MATLAB software package. The proposed work has been practically tested by 21 measurement points, whereas, it has exhibited stimulant results that supports the successfulness of its design and performance.

Keywords

• difference amplifier
• inverting amplifier
• logarithmic amplifier
• tuning control voltage
• varactor diode