Cascomp BJT Amplifier vs. traditional configurations

All transistor circuits introduce distortion. In Radio Frequency (RF) circuits, the third-order distortion components are the most important. The quest for more linear circuits has become more important with complex-modulation as used in modern cellular phone systems. Quinn’s Cascomp Amplifier, first reported in the 1970s, promises ideal linearity and can deliver close to that promise. We review the theory and address the question of why the Cascomp has not replaced other configurations in amplifiers where low distortion is important. Calculations are supported by measurements. A new, alternative variant of the Cascomp topology is introduced and compared with the existing configura-tion. We assert that the improved linearity comes at such a price in gain that it does not make sense to use the configuration in broadband RF circuits

Analysis of circuit conditions for optimum intermodulation and gain in bipolar cascomp amplifiers with non-ideal error correction

The cascoded-compensation or ‘Cascomp’ amplifier offers excellent distortion reduction and thermal distortion rejection, but has not seen widespread use because of a limited gain and increased complexity compared with other topologies. The original theory showed that with the addition of an ideal error amplifier the circuit will completely compensate distortion for suitably chosen degeneration and bias values. This research presents a new, rigorous mathematical proof for conditions of compensation. The authors further develop the proof to include the non-idealities of the error amplifier. It is shown that there exists a second bias point, not exposed by the original analysis that offers improved gain while maintaining distortion cancellation. By reducing the error amplifier degeneration resistance, one can increase a Cascomp circuit's overall gain by several dB while maintaining theoretically perfect distortion compensation. A robust bias point is proposed, which takes the advantage of this new theory by optimising circuit values resulting in a comparatively broader and deeper third-order distortion null. The proposed theory is confirmed with simulation and measurement that show agreement within the bounds of process and component error limits

Application of Nonlinear Transistor Characteristics

This research presents three works all related by the subject of third-order distortion reduction in nonlinear circuits. Each one is a novel extension to previous work in that branch of electronics literature. All three follow the procedure of presenting a novel algebraic proof and following up with simulations and/or measurements to confirm the theoretical result. The works are generally themed around nonlinear low-frequency bipolar transistor circuits. Firstly, an investigation is conducted into a well documented effect in bipolar-junction transistors (BJTs) called inherent third-order distortion nulling. This effect is shown to be a fundamental result of the transistor’s transfer junction acting upon an input signal. The proof of a single BJT emitter-follower amplifier’s inherent null is examined which is well documented in the literature. This forms the basis for a novel extension in Darlington transistors where theory suggests the third-order null occurs at double the collector current of a single BJT. Discrete measurements of a CA3083 transistor array are undertaken and compared with theory and simulation data. These measurements confirm theory with reasonable accuracy. A temperature and process variation independent bias circuit is developed to solve one issue with using third-order distortion nulling. This work is interesting in that it branches into series resistance compensation for translinear circuits and stands as a useful circuit in its own right. Using stacks of matched forward-biased semiconductor junctions which conform to translinear conditions, a bias current can be generated which theoretically removes temperature and series resistance dependence on the particular BJT used. This proves useful for the previous work in distortion nulling, but also allows direct and accurate measurement of series resistance. Again, simulation and measurement data is obtained from discrete measurements of the proposed circuit, and the results conform with theory to a reasonable degree. Lastly, this work presents the analysis of a cascoded-compensation (Cascomp) amplifier. It presents the first fully nonlinear derivation of the Cascomp’s transfer function and its associated harmonic and intermodulation distortion components. The derivation reveals an interesting characteristic in which the third-order intermodulation distortion has multiple local minima. This characteristic has not yet been presented in the literature, and allows better optimisation of Cascomp amplifiers in any application. Again, this characteristic and its potential benefits are confirmed with simulation and discrete measurements. Observations of the presented works are discussed and built upon in the last chapter. This leads to suggestions on future research topics branching on from these works

Macroinfaunal Community Composition and Biomass, and Bacterial and Viral Abundances From the Gulf of Alaska To the Canadian Archipelago: A Biodiversity Study

Hydrographic, sediment, and biological (chlorophyll a, bacteria, viruses, and macroinfauna) samples were collected on a several thousand mile long transect spanning from the Gulf of Alaska, through the Bering and Chukchi Seas, the Beaufort Sea, and into the Canadian Archipelago/Northwest Passage in the summer of 2000. Water column hydrographic parameters (temperature, salinity, and chlorophyll a), water column bacterial and viral abundances and distributions, as well as benthic measurements of sediment bacterial and viral abundances and distribution, sediment grain size, and sediment organic carbon and organic nitrogen content were measured. In addition, macroinfaunal community composition and diversity were examined. The Bering and Chukchi Seas had the highest overall mean abundances of bacterial, viral, and macroinfaunal parameters. Of all areas measured, the Beaufort Sea and Gulf of Alaska stations exhibited the lowest values, and Canadian Archipelago stations showed intermediate, varied values. Statistical analysis indicated significant positive correlations among many parameters. For example, the significant relationship between macroinfaunal diversity and sediment viral abundance suggests that Arctic benthic macroinfaunal communities may be influenced by viral parameters coincident with sediment grain size and the quantity and quality of surface-water derived primary production food supply

The Effects of Temperature and Herbicide on Development and Behaviour in Latrodectus katipo

Latrodectus katipo are a species of spider endemic to New Zealand. Latrodectus katipo numbers have markedly declined over the last 40 years. A species once common throughout New Zealand sand dunes, is now confined to a few specific areas. The cause of decline is likely due to habitat destruction and the introduction of exotic spiders and plants. Exotic spider species are displacing L. katipo in areas throughout NZ, while introduced plant species do not provide the ideal habitat for web-building. The introduction of exotic weed species has lead to herbicides being used throughout L. katipo habitat. Little research has been undertaken surrounding the effects of herbicide on behaviour. Similarly, few studies have been published on development in L. katipo. With climate change likely to impact temperatures around NZ, it is important to understand how temperature will affect development of the species in the future. This thesis aimed to examine the effects that temperature has on the development of the species, as well the effects that a glyphosate based herbicide has on L. katipo behaviour. The effects of temperature on development were determined by comparing development between three different temperature regimes (18°C, 23°C and 28°C). It was found that emergence time (duration inside egg-sac) was significantly shorter at higher temperatures. Hatching time (duration inside the egg), similarly, was found to be significantly shorter at higher temperatures. An overall negative pattern was observed, as temperature increased, hatching/emergence time decreased. Instar duration (time between moults) was found to be shorter at higher temperatures. Shorter instar duration meant that spiders at the highest temperature developed faster. The effects of herbicide on behaviour was determined by exposing individuals to a glyphosate based substrate and recording behaviour. Glyphosate is the active ingredient in most commonly used herbicide in NZ, which if found to have an effect on L. katipo could be very detrimental. Ethovision was used to compare the distance moved, velocity and activeness between herbicide exposure and control trials. Glyphosate exposure was found not to have a significant impact on any of the measured behavioural traits. Repeatability of behaviours were also analysed to determine whether there were consistent behavioural differences, representative of personality. Males were found to have high levels of repeatability across measures; however, females and juveniles did not (juveniles could not be sexed). Overall, higher temperatures were found to decrease development time, with higher temperatures leading to significantly faster emergence and hatching. These results could be a useful indicator of the effects that climate change may have on the development of the species. Faster development times could mean that L. katipo may have a greater chance at competing with introduced spiders, like Steatoda capensis. Further research needs to be conducted to determine whether there are any other detrimental physiological effects from higher temperatures. Glyphosate was found not to affect the measured behavioural traits. This is a positive finding as it suggests that herbicide use is not having a signficant impact on activity related behaviours and can therefore still be used to remove exotic plant species from L. katipo habitat, though further studies are needed to ensure that there are no negative effects of glyphosate

Testing for hepatitis C virus and pharmacy-based testing: the perceptions of people who inject drugs living in Newfoundland and Labrador

Injection drug use is the most common mode of transmission of Hepatitis C Virus (HCV) infection yet many people who inject drugs (PWID) are unaware they have the virus. A scoping review was conducted to explore the barriers and enablers to testing for HCV. This informed my qualitative study, which involved interviewing PWID to understand their experiences with HCV testing and learn what features of a pharmacy-based HCV testing program are important to them. The study produced 5 themes related to perceptions and experiences of PWID around HCV testing; ‘There are multiple reasons why testing is not being done’, ‘Feelings surrounding testing vary’, ‘Testing is important for one's own health and the impact on others’, ‘Access to and relationship with primary care providers affect testing’, and ‘There is a need for both increased awareness of testing and more testing options’. Five themes were also produced surrounding their perceptions of pharmacy-based testing; ‘Pharmacy based testing was seen to be easy’, ’The relationship with the pharmacy and pharmacist affects testing’, ‘Confidentiality would be important to attract people to testing’, ‘The fast result is often valuable’, and ‘Less invasive sample collection is appealing to some PWID’. Understanding testing preferences of PWID is important to inform policy enabling improved HCV testing in Newfoundland and Labrador

Threshold-Concept inspired eTutorials in electronics

Engagement of students in traditional engineering tutorials can be low, especially where the level of preparation varies widely across the student population. Online tutorials are a way of addressing this problem, as they offer the chance for students to work at their own pace, at their own preferred times, while staff can add and update questions, links, and hints in almost-real time. We created such a set of tutorials in an introductory electronics course, incorporating a strong Threshold-Concept focus. The tutorials were coded by one of us (Balsom) in PHP, and this allowed us to extensively and flexibly control reporting to examine student usage. We benchmarked students from year to year, introduced the eTutorials, and measured their impact. We employed surveys and interviews for additional feedback. We quantitatively and qualitatively address the question of how effective the eTutorials were in comparison with well-staffed, well-attended, conventional tutorials addressing the exact same material in the previous year. We also search for correlations between student usage and eventual grade with the aim of early detection of students requiring intervention. The cost is compared with use of commercially-available eTutorials in Physics that are used by a parallel introductory Physics course in the same school