Jeremy Everard

High performance direct coupled bandpass filters on coplanar waveguide

This paper describes the design and performance of shunt inductively coupled bandpass filters implemented on an open coplanar waveguide. This new structure exhibits low radiation loss due to the removal of the capacitively coupled gaps encountered in end or edge coupled filters. Unloaded Qs greater than 540 have been achieved in unshielded single section resonators at 4 GHz on very thin substrates. These high Qs enable the design of filters with low insertion loss and good stopband rejection. Applications include low insertion loss, high and printed filters where no screening is required, low noise oscillators and superconducting filters. >

Transmission-line load-network topology for class-E power amplifiers

Class-E amplifiers are a type of switching amplifier offering very high efficiency approaching 100%. In this paper, a topology and design methodology, which could be used for a transmission-line implementation of a class-E power amplifier, is presented. A simple transmission-line class-E load network is proposed that offers combined transformation of the load resistance down to a suitable level, as well as simultaneous suppression of harmonics in the load. The load network was developed and tested with the aid of a time-domain simulator (i.e., SPICE). A microstrip layout was designed and a first prototype was built operating at 1 GHz utilizing a field-effect transistor as the switching device. A drain efficiency of 72% was measured for our prototype after tuning, although better performance can be expected with an improved switching transistor and careful tuning of the load network.

Low noise oscillators

The author describes a set of design rules which are general and can be used to produce oscillators with a very low noise performance where both additive and flicker noise are considered. Linear theories which accurately describe the noise performance of resonator-type oscillators are presented. The limits set by varactor diodes on the noise performance are described and the noise degradation caused by open-loop phase error is shown. Seven design examples are demonstrated which show close correlation with the theory.<<ETX>>

Characterization of flicker noise in GaAs MESFET's for oscillator applications

GaAs MESFET oscillators commonly exhibit increased close-to-carrier noise, which is often attributed to upconversion of flicker noise from the MESFET. To establish and quantify this effect, this paper presents an experimental system that allows the simultaneous measurement of the flicker noise on the gate and drain terminals of a GaAs-MESFET, and of the noise imposed on an RF carrier when amplified by the MESFET. The cross correlations between these parameters can thus be determined; an analytical method is shown for extracting the levels of the effective sources of flicker noise from the results, and the manner in which these affect the RF carrier. In the tests performed, it was often found that the close-to-carrier noise was related directly to the low-frequency flicker noise.

A new technique for the quasi-TEM analysis of conductor-backed coplanar waveguide structures

Numerically efficient and accurate formulae based on the spectral domain method for the analysis of conductor backed coplanar waveguide structures are presented. Quasi-TEM parameters are obtained for these waveguide structures by using piecewise linear functions to approximate the potential distribution at the air-dielectric interface. Techniques such as nonuniform discretization and bound estimation are described which demonstrate shorter computational times. Results on the characteristic impedance calculation of standard coplanar waveguide are given to demonstrate the numerical accuracy and efficiency of the method presented here. >

Measurement of the cross correlation between baseband and transposed flicker noises in a GaAs MESFET

When an RF carrier is amplified by a GaAs MESFET, amplitude modulation (AM) and phase modulation (PM) noises are imposed on the carrier. This is generally believed to be caused by transposition to the carrier frequency of the low-frequency flicker noise generated by the FET. The cross correlation between the AM and PM noises and the low-frequency noise observed on the drain of the FET is measured. While the AM noise and the low-frequency noise on the drain of the FET exhibit a high degree of correlation, the PM noise and the low-frequency drain noise are not highly correlated. The latter result may explain the limited success of oscillator phase noise reduction methods which rely on the existence of a large cross correlation between the PM and low-frequency noises.<<ETX>>

Simplified phase noise model for negative-resistance oscillators and a comparison with feedback oscillator models

This paper describes a greatly simplified model for the prediction of phase noise in oscillators which use a negative resistance as the active element. It is based on a simple circuit consisting of the parallel addition of a noise current, a negative admittance/resistance, and a parallel (Q-limited) resonant circuit. The transfer function is calculated as a forward trans-resistance (VOUT/IIN) and then converted to power. The effect of limiting is incorporated by assuming that the phase noise element of the noise floor is kT/2, i.e., -177 dBm/Hz at room temperature. The result is the same as more complex analyses, but enables a simple, clear insight into the operation of oscillators. The phase noise for a given power in the resonator appears to be lower than in feedback oscillators. The reasons for this are explained. Simulation and experimental results are included.

Ultra-Low Phase Noise Ceramic based Dielectric Resonator Oscillators

This paper describes, in general terms, the theory and design of ultra-low noise oscillators based on ceramic dielectric resonators and in particular oscillators operating at L and C band. This extends as presented in M. Sallin et al. (2003) at L band the new oscillators offer <-170dBc/Hz at 10kHz offsets with noise floors below -180dBc/Hz beyond 50kHz offset. Results at other frequencies up to 10GHz are also presented. The AM noise has been measured to be significantly below the PM noise at most offsets. To achieve this performance the amplifiers resonators and tuning elements have been extensively optimised. For example L band amplifiers produce very low residual flicker noise <-180dBc at 10kHz offset

A review of low noise oscillator. Theory and design

A large number of papers have been published on low noise oscillators, however they are usually very specific to the particular application. This paper describes a set of design rules which are general and can be used to produce oscillators with very low noise performance where both additive (thermal noise) and flicker noise are considered. Linear theories are described which accurately describe the noise performance of resonator type oscillators. The limits set by varactor diodes on the noise performance in tuneable oscillators are described and the noise degradation caused by open loop phase error is shown. Several design examples are included and these show close correlation with the theory.

Transposed gain microwave oscillators with low residual flicker noise

This paper describes the design of two low noise microwave oscillators operating at 7.6 GHz. These oscillators use room temperature sapphire resonators operating in the TE/sub 01//spl delta/ mode which demonstrate unloaded Qs of 44,000. Silicon transposed gain amplifiers are used to produce near-flicker-free gain. Oscillators with flicker noise corners around 1 kHz and a phase noise of -131 dBc/Hz at 10 kHz offset are demonstrated. This is within 5.5 dB of the theoretically predicted minimum noise. Further improvements of 30 dB are expected using related techniques.