Phase noise in microwave oscillators and amplifiers.

摘要

This thesis presents analysis and measurements of phase noise in oscillators and amplifiers. Low phase noise is an increasingly important requirement for RF circuit designers. In digital communications systems, close-in phase noise (or phase jitter in the time domain) affects the system bit-error rate. In analog communications systems, close-in phase noise can limit channel bandwidth and broadband noise reduces the signal-to-noise ratio and the system sensitivity, especially after several repeater stations. In Doppler radar applications, the oscillator phase noise can set the minimum signal level that must be returned by a target in order to be detected.;This thesis describes an experimental method for determining additive phase noise of an unmatched transistor in a stable 50O environment. The measured single-sideband phase noise is used to determine the large-signal noise figure of the device. Such characterization is used as input for the design of oscillators and power amplifiers.;Next, a design method for voltage controlled oscillators (VCOs) with simultaneous small size, low phase noise, DC power consumption and thermal drift is presented. Design steps to give good prediction of VCO phase noise and power consumption behavior are: (1) measured resonator frequency-dependent parameters; (2) transistor additive phase noise/noise figure characterization; (3) accurate tuning element model; and (4) bias-dependent model in case of an active load. It is shown that the method can be applied effectively for design of VCOs that meet requirements for challenging applications such as Chip Scale Atomic Clocks (CSAC).;The last part of the thesis is investigation of linearity in power amplifiers and its relations to phase noise. When a device is operated in saturation, it is nonlinear. Most communication systems use modulation of both amplitude (Amplitude Modulation, AM) and phase (Phase Modulation, PM) of the carrier signal, e.g. Quadrature Amplitude Modulation (QAM). The various nonlinearities of active microwave circuit result, among other effects, in AM to PM conversion. Since phase modulation is related to phase noise, additive phase noise can be expected to be related to linearity. This relationship is explored and analyzed based on extensive load/source pull measurements of output power, adjacent channel power ratio, error vector magnitude and additive phase noise at 900MHz on a HBT 1-watt class AB power amplifier.