Browsing by Subject "Noise figure"

Now showing 1 - 5 of 5

Open Access
Bandwidth, power and noise considerations in airborne cMUTs
(IEEE, 2009-09) Şenlik, Muhammed N.; Olcum, Selim; Köymen, Hayrettin; Atalar, Abdullah
Capacitive micromachined ultrasonic transducers (cMUTs) offer wider bandwidth in air due to their low mechanical impedances. The impedance mismatch between the air and transducer decreases with the smaller device dimensions increasing the bandwidth at the expense of the degradation in the transmit power and the receive sensitivity. In this work, the bandwidth of cMUT is optimized by increasing its radiation resistance. This is done by properly choosing the size of cMUT membranes and their placement within an array. This selection not only brings an improvement in the transmitted power when it is used as a transmitter, but also improves the noise figure when it is used as a receiver. A further improvement in the noise figure is possible when the cells are clustered and connected to separate receivers. ©2009 IEEE.
Open Access
Design and optimization of a sub-1dB noise figure low noise amplifier for magnetic resonance applications using CMOS technology
(2024-12) Bal, Ayşe Rana
Low Noise Amplifiers (LNAs) are crucial components in magnetic resonance imaging (MRI) receivers, primarily designed to amplify weak signals while minimizing the added noise. They have a special requirement of having an input impedance very close to a short-circuit. This requirement assures that there is no current in the MRI coil when the LNA is connected to the coil with a quarter-wave transmission line. By eliminating the current in the coil, the risk of coupling between coils also known as mutual coupling, within an array is reduced. This thesis explores designs of sub-1dB noise figure CMOS LNAs operating at 437 MHz and 477 MHz for 10.3 T and 10.5 T MRI systems, respectively, using variations of cascode amplifier structures while addressing the challenges and advancements in CMOS RF design. The first LNA designed for a singular 10.3 T MRI coil system demonstrates a power gain of 20.54 dB, a noise figure of 0.97 dB, an input return loss of −11.70 dB, and an IIP3 of −12.26 dBm with its fully modeled design. For a 10.5 T Array MRI system, one single-ended and one differential-ended LNA is designed. The single-ended demonstrates a power gain of 18.42 dB, a noise figure of 0.42 dB, an input return loss of −0.90 dB, an output return loss of −18.03 dB, and an IIP3 of −17.12 dBm, whereas the differential-ended demonstrates a power gain of 14.76 dB, a noise figure of 0.60 dB, an input return loss of −0.94 dB, an output return loss of −18.73 dB, and an IIP3 of −14.36 dBm both with their fully modeled designs. The differential amplifier also displays a significant improvement in PSRR, making it a good choice for array MRI applications.
Open Access
An input matched X-band balanced low noise amplifier design and implementation using discrete transistors
(2015-07) Ballı, Çağdaş
X-Band, which is defined as the frequency range from 8 GHz to 12 GHz by IEEE, is used for the applications such as satellite communications, radar and space communications. These applications require an input matched, high gain and low noise amplifier as a front-end component in their receiver chains. In this work, an input matched X-Band balanced low noise amplifier is designed and implemented by using GaAs HJ-FET transistor. Measurements of the fabricated amplifier show a maximum noise figure of 1.74 dB, a minimum gain of 12.1 dB and a minimum input return loss of 11.4 dB from 8.2 GHz to 8.4 GHz.
Open Access
Noise figure of a balanced amplifier
(Institute of Electrical and Electronics Engineers, 2018) Coskun, A. A.; Atalar, Abdullah
Noise figure expression of a balanced amplifier built with lossy divider and combiner and two imperfectly noise-matched component amplifiers is derived analytically using the method of noise waves in terms of the noise parameters of the amplifiers. We present analytical expressions for the three noise parameters of the balanced amplifier. We show that a low-noise amplifier optimized to be used as a stand-alone amplifier is not the optimum choice for the component amplifiers of a balanced amplifier. The derived expressions can be used to choose or optimize the component amplifiers.
Open Access
Nonlinearity-tailored fiber laser technology for low-noise, ultra-wideband tunable femtosecond light generation
(OSA - The Optical Society, 2017) Liu, X.; Laegsgaard, J.; Iegorov, R.; Svane, A. S.; Ilday, F. Ö.; Tu, H.; Boppart, S. A.; Turchinovich, D.
The emission wavelength of a laser is physically predetermined by the gain medium used. Consequently, arbitrary wavelength generation is a fundamental challenge in the science of light. Present solutions include optical parametric generation, requiring complex optical setups and spectrally sliced supercontinuum, taking advantage of a simpler fiber technology: a fixed-wavelength pump laser pulse is converted into a spectrally very broadband output, from which the required resulting wavelength is then optically filtered. Unfortunately, this process is associated with an inherently poor noise figure, which often precludes many realistic applications of such supercontinuum sources. Here, we show that by adding only one passive optical element—a tapered photonic crystal fiber—to a fixed-wavelength femtosecond laser, one can in a very simple manner resonantly convert the laser emission wavelength into an ultra-wide and continuous range of desired wavelengths, with very low inherent noise, and without mechanical realignment of the laser. This is achieved by exploiting the double interplay of nonlinearity and chirp in the laser source and chirp and phase matching in the tapered fiber. As a first demonstration of this simple and inexpensive technology, we present a femtosecond fiber laser continuously tunable across the entire red–green–blue spectral range.