The oscillator in communication and measurement systems, be they radio, coaxial cable, microwave, satellite, radar or optical fibre, defines the reference signal onto which modulation is coded and later demodulated. The flicker and phase noise in such oscillators are central in setting the ultimate systems performance limits of modern communications, radar and timing systems. These oscillators are therefore required to be of the highest quality for the particular application as they provide the reference for data modulation and demodulation. . | Fundamentals of RF Circuit Design with Low Noise Oscillators. Jeremy Everard Copyright 2001 John Wiley Sons Ltd ISBNs 0-471-49793-2 Hardback 0-470-84175-3 Electronic 4 Low Noise Oscillators Introduction The oscillator in communication and measurement systems be they radio coaxial cable microwave satellite radar or optical fibre defines the reference signal onto which modulation is coded and later demodulated. The flicker and phase noise in such oscillators are central in setting the ultimate systems performance limits of modern communications radar and timing systems. These oscillators are therefore required to be of the highest quality for the particular application as they provide the reference for data modulation and demodulation. The chapter describes to a large extent a linear theory for low noise oscillators and shows which parameters explicitly affect the noise performance. From these analyses equations are produced which accurately describe oscillator performance usually to within 0 to 2dB of the theory. It will show that there are optimum coupling coefficients between the resonator and the amplifier to obtain low noise and that this optimum is dependent on the definitions of the oscillator parameters. The factors covered are 1. The noise figure and also source impedance seen by the amplifier . 2. The unloaded Q the resonator coupling coefficient and hence QJQ0 and closed loop gain. 3. The effect of coupling power out of the oscillator. 4. The loop amplifier input and output impedances and definitions of power in the oscillator. 5. Tuning effects including the varactor Q and loss resistance and the coupling coefficient of the varactor. 6. The open loop phase shift error prior to loop closure. 180 Fundamentals of RF Circuit Design Optimisation of parameters using a linear analytical theory is of course much easier than non-linear theories. The chapter then includes eight design examples which use inductor capacitor surface acoustic wave SAW transmission
