title: Application of Nonlinear Transistor Characteristics

authors: Balsom, Toby

subjects: Transistor

abstract: 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.

text: 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.

year: 2014

title: Joint effect of β-eutectoid content and heat treatment on the properties of binary Ti-Cu and Ti-Mn alloys

authors: Bolzoni, Leandro

subjects: Titanium alloys

abstract: The use of cheap alloying elements and alternative manufacturing techniques are two strategies that can be used to reduce the high cost of Ti alloys. Furthermore, heat treatments are an easy and cost effective method to tailor the mechanical behaviour by means of the modification of the microstructure. For that, this work analysed the quenching and aging heat treatment of binary Ti-Cu and Ti-Mn alloys manufactured via powder metallurgy. It is found that the post-processing solution treatment does not significantly affect the physical properties and residual porosity remains unchanged within the microstructure; however, the heat treatment changes the microconstituents. Serrated martensitic transformed β is formed in quenched Ti-Cu alloys and it is converted into a coarse lamellar or a hypoeutectoid structure as the Cu content increases with the subsequent aging treatment. Aging of the Ti-Mn alloys slightly coarsen the microstructural features where martensite or equiaxed metastable β grains are obtained after quenching. Enhancing of the mechanical behaviour is generally achieved and the solution treatment switches from improving the ductility to increasing the strength and the hardness as the amount of the alloying element increases.

text: Joint effect of β-eutectoid content and heat treatment on the properties of binary Ti-Cu and Ti-Mn alloys The use of cheap alloying elements and alternative manufacturing techniques are two strategies that can be used to reduce the high cost of Ti alloys. Furthermore, heat treatments are an easy and cost effective method to tailor the mechanical behaviour by means of the modification of the microstructure. For that, this work analysed the quenching and aging heat treatment of binary Ti-Cu and Ti-Mn alloys manufactured via powder metallurgy. It is found that the post-processing solution treatment does not significantly affect the physical properties and residual porosity remains unchanged within the microstructure; however, the heat treatment changes the microconstituents. Serrated martensitic transformed β is formed in quenched Ti-Cu alloys and it is converted into a coarse lamellar or a hypoeutectoid structure as the Cu content increases with the subsequent aging treatment. Aging of the Ti-Mn alloys slightly coarsen the microstructural features where martensite or equiaxed metastable β grains are obtained after quenching. Enhancing of the mechanical behaviour is generally achieved and the solution treatment switches from improving the ductility to increasing the strength and the hardness as the amount of the alloying element increases.

year: 2024

title: Experiences of New Zealand Māori mothers’ Engagement with health and social services post-COVID-19 2020 lockdown

authors: Barrett, Nikki Maree

subjects: Childbirth

abstract: Background: 
Despite universal provision of maternity care, Māori (Indigenous peoples of Aotearoa/New Zealand) experience significant maternal and infant health disparities compared to their dominant Pākehā (non-Māori) counterparts. This paper examined the lived realities of postnatal Māori māmā (mothers) engaging with health and social services. Enablers and barriers were identified to better understand what is required to strengthen health services’ responsiveness to Māori māmā health needs and aspirations. 

Methods: 
Underpinned by Kaupapa Māori research principles, which are grounded in Māori cultural values, emphasising self-determination, and Māori aspirations, a small cohort of 17 expectant Māori māmā were recruited from a Māori childbirth education programme to participate in a three-phase study. Phase three, the focus of this paper, involved seven semi-structured, open-ended telephone interviews with Māori māmā. A thematic analysis, underpinned by a mana wahine (authority inherent in Māori women) theoretical perspective amplified these experiences. 

Results: 
Five themes were identified that encapsulated participants’ engagement and interactions with health and social services. These themes were as follows: (1) right to enact tino rangatiratanga (autonomy) and self-achievement; (2) responsiveness of services; (3) service and system issues; (4) need for greater choice and opportunity; and (5) impact of COVID-19. 

Conclusions: 
This study privileged the voices of Māori wāhine, highlighting their experiences with a complex and often unresponsive health system. Participants valued services that enabled them to exercise tino rangatiratanga. Echoing the experiences of other Indigenous Peoples, incorporating culturally relevant practices into perinatal health services is crucial for achieving health equity and addressing disparities.

text: Experiences of New Zealand Māori mothers’ Engagement with health and social services post-COVID-19 2020 lockdown Background: 
Despite universal provision of maternity care, Māori (Indigenous peoples of Aotearoa/New Zealand) experience significant maternal and infant health disparities compared to their dominant Pākehā (non-Māori) counterparts. This paper examined the lived realities of postnatal Māori māmā (mothers) engaging with health and social services. Enablers and barriers were identified to better understand what is required to strengthen health services’ responsiveness to Māori māmā health needs and aspirations. 

Methods: 
Underpinned by Kaupapa Māori research principles, which are grounded in Māori cultural values, emphasising self-determination, and Māori aspirations, a small cohort of 17 expectant Māori māmā were recruited from a Māori childbirth education programme to participate in a three-phase study. Phase three, the focus of this paper, involved seven semi-structured, open-ended telephone interviews with Māori māmā. A thematic analysis, underpinned by a mana wahine (authority inherent in Māori women) theoretical perspective amplified these experiences. 

Results: 
Five themes were identified that encapsulated participants’ engagement and interactions with health and social services. These themes were as follows: (1) right to enact tino rangatiratanga (autonomy) and self-achievement; (2) responsiveness of services; (3) service and system issues; (4) need for greater choice and opportunity; and (5) impact of COVID-19. 

Conclusions: 
This study privileged the voices of Māori wāhine, highlighting their experiences with a complex and often unresponsive health system. Participants valued services that enabled them to exercise tino rangatiratanga. Echoing the experiences of other Indigenous Peoples, incorporating culturally relevant practices into perinatal health services is crucial for achieving health equity and addressing disparities.

year: 2025