Even circuit designers who are experienced with low noise design can find it difficult to explain how noise is quantified and analyzed.
I will explain the formal methods of quantifying noise and illustrate their use in the design of a variety of common RF circuits. For linear time-invariant circuits such as small-signal amplifiers, noise transfer functions play a key role. For time-varying circuits such as passive mixers and LC oscillators, noise is in many cases injected in discrete time. Methods for the design continue to evolve towards greater simplicity, and I will present some of them.
There is seldom a noise optimum in these circuits. It is usually a tradeoff, as I will show, between noise, large-signal linearity, and power dissipation.
Millimeter Wave mobile communication (5G and beyond) has been associated with much lower radiation power and much shorter communication range. Millimeter Wavelengths suffer from very strong attenuation in water-rich substances limiting penetration into biological objects (e.g., human and animal bodies and plants) to just a few millimeters. Deeper inside the body the intensity is negligible making for greater safety compared to early mobile standards (3G and 4G). However, the safety of millimeter-wave radiation for 5G and beyond remains a public concern.
This Technical Lecture aims to comprehensively review the relevant electromagnetic fundamentals underlying the wave-matter interaction involved in any eventual health hazard which might be associated with millimeter-wave radiation. Basic related aspects include the following:
•Direct health hazards must involve either chemical reactions or thermal/mechanical destruction of cells/tissues. This must be accompanied by energy transfer from the electromagnetic wave to the biological substances.
•Indirect hazards include overloading the biological mechanisms involved in the body thermoregulation.
•Thermal effects involve rise of temperature, an increase in the magnitude of atomic/molecular lattice vibrations.Chemical reactions (e.g., burning) will only occur if the temperature increase exceeds a certain limit. Otherwise, the rise is reversible, regulated to steady state by the blood circulation within the body.
•Non-ionizing waves are wavelengths that are much larger than the atomic/molecular scale, a continuous spatial distribution of the wave is an adequate mathematical representation. The wave power-density is described by the Poynting vector, and the power transfer from the wave to the biological substances can be calculated with high precision using the concept of constitutive parameters (conductivity, permittivity, and permeability). Millimeter Waves and even Tera-Hertz Waves belong to this category.
•Ionizing radiation has wavelengths comparable to the interatomic or intermolecular spaces and an electromagnetic wave quantization approach makes sense. Wave-matter interactions can be explained using the discrete representation of the waves, photons, which are ensembles of energy packages highly localized in time and space. A single photon carries energy proportional to its frequency which, e.g., can be fully transferred to and result in electrical destruction of a molecular bond. Ionizing radiation only occurs at frequencies much higher than that of ultraviolet light and therefore is not applicable to the millimeter-wave case.
•Use of a photon representation to describe Millimeter Waves would require the photon spatial extent to be of the same order of magnitude as the wavelength and a photon collision would necessarily involve millions of atoms/ molecules (as if swimming in it). A single chemical bond could not absorb the entire photon energy
The microwave and RF design engineer always seeks to develop a design that will meet specifications the first time that the circuit is fabricated. To do so requires that as many elements and phenomenon as possible associated with the control devices and circuit be accurately modeled. In the case of the microwave and RF semiconductor control circuits, accurate modeling of the solid-state control components over frequency, voltage, current and power is key to successful control system design. This talk will cover material that will provide the RF and microwave design engineer insight into the physical operation and modeling of PIN diodes and field-effect transistors (FETs) as control components and their use in microwave and RF control circuits. The talk will cover basic RF and microwave control circuits for reconfigurable electronics, and then focus on linear and nonlinear models for PIN diode, MESFET and MOSFET control elements to implement these circuits. The talk will conclude with control circuit examples using these models for use in reconfigurable RF and microwave electronics.