8
Oscillators
This chapter presents the principles of oscillator design, including start-up and steady-state operation conditions, noise and stability of oscillations, basic oscillator configurations using lumped and transmission-line elements, and simplified equation-based oscillator analyses and optimum design techniques. An immittance design approach is introduced and applied to the series and parallel feedback oscillators, including circuit design and simulation aspects. Voltage-controlled oscillators (VCOs) and their varactor tuning range and linearity for different oscillator configurations are discussed. Finally, the basic circuits and operation principles of crystal and dielectric resonator oscillators are given.
8.1 OSCILLATOR OPERATION PRINCIPLES
8.1.1 Steady-State Operation Mode
A simple feedback oscillator model is shown in Figure 8.1(a) where an oscillator circuit is decomposed into a forward nonlinear network and a feedback linear network, both of which are two-port networks. Figure 8.1(b) shows an example of a transformer-coupled metal-oxide-semiconductor field-effect transistor (MOSFET) oscillator without bias circuit to illustrate common features of the feedback oscillator. Because an oscillator is an autonomous circuit, electronic noise in the active device or power supply turn-on transient leads to the self-excitation of the oscillations. This provides the initial oscillation build-up. As the oscillation amplitude grows, the active device displays larger nonlinearity ...
