An electronically tuneable inductance with extended frequency range
The extension of the usable frequency range of an electronically tuneable inductance circuit is investigated. By means of numerical and analytical studies, the transistor-internal reverse transfer capacitance can be identified as a frequency-limiting element, which must be minimised. This is achieved by circuitry-wise compensation of the capacitive effect by introducing an additional inductance. The concept is verified through measurements of the practical implementation and shows an extension of the frequency range by two octaves throughout the VHF range, which proves beneficial for applications such as broadband matched and tuneable transmission lines, amplifier circuits, oscillators, or filters.
Implementation of an Electronically Tuneable, Transistor-based, Passive, Symmetric RF Inductance
The concept of an electrically tuneable inductance based on a transistor circuit is introduced. Even though it incorporates an active circuit, passive, reciprocal behaviour is displayed at the output terminals. The resulting inductance value is tuneable through a variation of the biasing condition, constant for a wide frequency range, and it can be used in either series or parallel circuit configuration. Guidelines for the design of the circuit are presented and used to successfully simulate, build and measure the tuneable inductance. The inductance circuit is a promising approach to closing a long-existing gap, and thereby providing new possibilities of circuit design, e.g., in terms of miniaturisation through integrated circuits. It can prove beneficial for numerous applications, such as broadband matched and tuneable transmission lines, amplifier circuits, oscillators, or filters.
Passive reciprocal transistor-based RF tuneable inductances
Where unused frequency bands become scarce, their resourceful handling is essential. Consequential, to enable best use of various frequency bands with a single device, the need for reconfigurability emerges. Complementary to already existing technologies, a novel transistor-based circuit is introduced that makes passive, reciprocal, electronic reactive tuning possible. Ultimately, a tuneable inductance was chosen as an example for reactance circuits due to its outstanding relevance for modern, reconfigurable circuit design. The general development process of the inductance circuit is outlined through an abstracted process overview. It enables a broad understanding of the challenges and possibilities of this approach. Also, by extensive circuit analysis with ideal and non-ideal element values, the gap between numerical simulation and guidelines for practical implementation can be narrowed. From the resulting analytic expression, the key figures of an electronic tuneable inductance are derived, namely the range of inductive tuning, the quality factor and the achievable frequency range. These values enable the circuit designer to set up a reasonable starting point for developing a tuneable inductance circuit and gives the means to estimate its unprecedented, passive output behaviour.