Minimum Noise Temperature Research Articles

Optimization of Channel Structures in InP HEMT Technology for Cryogenic Low-Noise and Low-Power Operation

We report the impact from channel composition on the cryogenic low-noise performance at low dc power for a 100-nm gate-length InGaAs-InAlAs-InP high-electron mobility transistor (HEMT). Two indium (In) channel compositions, 65% and 80%, were studied by dc and RF characterization at 300 and 5 K. For the cryogenic low-noise optimization, it was important to increase the transconductance to gate–source capacitance ratio in the weak inversion region implying that a higher maximum cutoff frequency in the HEMT does not guarantee lower noise. The HEMT noise performance was obtained from noise measurements in a hybrid three-stage 4–8-GHz ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{C}$</tex-math> </inline-formula> -band) low-noise amplifier (LNA) down to 300- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> W dc power dissipation. While the HEMT LNA noise performance for both the channel compositions at 300 K was found to be comparable, the HEMT LNA at 5 K with 65% In channel showed a minimum noise temperature of 1.4 K, whereas the noise temperature in the HEMT LNA with 80% In channel HEMTs increased to 2.4 K. The difference in the noise became more pronounced at reduced dc power dissipation. The ultralow dc power of 300 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> W demonstrated for a cryogenic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{C}$</tex-math> </inline-formula> -band LNA with an average noise temperature of 2.9 K and 24-dB gain is of interest for future qubit read-out electronics at 4 K.

Impact of bandwidth on antenna‐array noise matching

This letter expands the treatments of wideband noise analysis of antenna arrays by including bandwidth effects on beam-equivalent receiver noise temperature, , and the active reflection coefficient, . The particular focus of the letter is on receiver noise decorrelation in wideband systems having noise bandwidth 1 Hz. The new analysis and simulations show increase in and the departure of from that obtained using contemporary analyses for 1 Hz. Although the paper also shows that for many applications over moderate bandwidths and close connection between the receiver and array the influence of on is not significant, the simulations of a 71-element array demonstrate that the noise decorrelation due to wide can result in tens of percent (as much as 45.5% in simulations described in this letter) increase in above the low-noise amplifier minimum noise temperature, which should be taken into account at the design stage of ultra-wide band systems, such as those under investigation by, for example, the Defense Advanced Research Project Agency (DARPA) in its wideband adaptive RF protection (WARP) program and ultra-sensitive active electronically scanned array (AESA) radars for tracking stealth objects.

A 183-GHz FMCW Transceiver Module for Wireless Fuse Applications

This paper presents the design, construction, and testing of a 183-GHz FMCW transceiver module for wireless fuse applications. The transmitter consists of a square-triangle wave converter, a Ku-band VCO, a 91.5-GHz × 2 × 3 multiplying and amplifying chain, a 10-dB multi-hole directional coupler, and a 183-GHz frequency doubler. For the multiplying chain, the generated 91.5-GHz signal power is partly coupled out by the 10-dB coupler. The coupled output power is used as local oscillator (LO) signal to pump the 183-GHz subharmonic mixer (SHM). The receiver is cascaded by a 183-GHz SHM and a low-noise immediate frequency (IF) amplifier. The measured typical output power of the 183-GHz transceiver is 48 mW and the minimum noise temperature of the receiver is 620 K at 181 GHz. At 5-mm and 10-mm detection distance, the measured signal noise ratio (SNR) of transceiver IF signal is higher than 30 dB and 17 dB at 10 KHz bandwidth, respectively. The SNR is high enough for the following signal processing.

Increasing the signal-to-noise ratio of magnetic tunnel junctions by cryogenic preamplification

Cryogenic preamplification using silicon–germanium heterojunction bipolar transistors has proven to be effective in increasing the signal-to-noise ratio of the tunnel magnetoresistance of high resistance magnetic tunnel junctions at 8 K. The magnetic tunnel junctions used have resistances greater than 1 MΩ, and the cryogenic measurement system still has sufficient bandwidth for the 1/f noise to roll off. A noise model for the system has been proposed and evaluated experimentally. The noise temperature and minimum noise temperature of the transistor used in the experiment are calculated and compared. The signal-to-noise ratio of the junction alone and the transistor-junction system is derived from the sample and circuit parameters and compared. Experimental data show a signal-to-noise ratio increase by a factor of 6.62 after adding in the cryogenic preamplifier. An increase in 1/f noise in the antiparallel state of the tunneling junction as opposed to the parallel state is also observed giving evidence of 1/f noise dependence on the magnetic state of the junction.

Hot electron heatsinks for microwave attenuators below 100 mK

We demonstrate improvements to the cooling power of broad bandwidth (10 GHz) microwave attenuators designed for operation at temperatures below 100 mK. By interleaving 9-μm thick conducting copper heatsinks in between 10-μm long, 70-nm thick resistive nichrome elements, the electrical heat generated in the nichrome elements is conducted more readily into the heatsinks, effectively decreasing the thermal resistance between the hot electrons and cold phonons. For a 20 dB attenuator mounted at 20 mK, a minimum noise temperature of Tn ∼ 50 mK was obtained for small dissipated powers (Pd&amp;lt;1 nW) in the attenuator. For higher dissipated powers, we find Tn∝Pd1/4.4, with Pd=100 nW corresponding to a noise temperature of 90 mK. This is in good agreement with thermal modeling of the system and represents nearly a factor of 20 improvement in cooling power or a factor of 1.8 reduction in Tn for the same dissipated power, when compared to a previous design without interleaved heatsinks.

The Theory of Special Noise Invariants

This paper reports a novel systematic theory of the noise invariants of two-port linear noisy networks under lossless reciprocal input and output impedance transformations. The theory clarifies the relationship between the circuit theory of linear noisy networks and the theory of four noise parameters, which are widely applied in the design of low-noise amplifiers (LNAs). In particular, we prove that the fundamental noise invariants under input and output impedance transformations are the eigenvalues of a permuted version of the noise correlation matrix and that there is no feedback operation that preserves them. Known invariants, such as the minimum equivalent noise temperature ${T}_{{N}{min}}$ and ${N}$ , may be expressed in terms of such eigenvalues. In addition, we provide a complete characterization of the four noise parameters of two-port passive dissipative networks in terms of their gain parameters and derive the condition under which the invariant ${4N}{T}_{{0}}{/}{T}_{{N}{min}}$ of passive nonreciprocal networks is lower than two. We also extend the theory of special noise invariants to LNAs with lossy input matching network. Overall, the impact of the findings emerging from the theory is highlighted through theorems, remarks, circuit examples, and studies on widespread design methodologies.

Low noise 874 GHz receivers for the International Submillimetre Airborne Radiometer (ISMAR).

We report on the development of two 874 GHz receiver channels with orthogonal polarizations for the International Submillimetre Airborne Radiometer. A spline horn antenna and dielectric lens, a Schottky diode mixer circuit, and an intermediate frequency (IF) low noise amplifier circuit were integrated in the same metallic split block housing. This resulted in a receiver mean double sideband (DSB) noise temperature of 3300 K (minimum 2770 K, maximum 3400 K), achieved at an operation temperature of 40 °C and across a 10 GHz wide IF band. A minimum DSB noise temperature of 2260 K at 20 °C was measured without the lens. Three different dielectric lens materials were tested and compared with respect to the radiation pattern and noise temperature. All three lenses were compliant in terms of radiation pattern, but one of the materials led to a reduction in noise temperature of approximately 200 K compared to the others. The loss in this lens was estimated to be 0.42 dB. The local oscillator chains have a power consumption of 24 W and consist of custom-designed Schottky diode quadruplers (5% power efficiency in operation, 8%-9% peak), commercial heterostructure barrier varactor (HBV) triplers, and power amplifiers that are pumped by using a common dielectric resonator oscillator at 36.43 GHz. Measurements of the radiation pattern showed a symmetric main beam lobe with full width half maximum <5° and side lobe levels below -20 dB. Return loss of a prototype of the spline horn and lens was measured using a network analyzer and frequency extenders to 750-1100 GHz. Time-domain analysis of the reflection coefficients shows that the reflections are below -25 dB and are dominated by the external waveguide interface.

0.3-14 and 16-28 GHz Wide-Bandwidth Cryogenic MMIC Low-Noise Amplifiers

We present two monolithic microwave integrated circuit (MMIC) cryogenic broadband low-noise amplifiers (LNAs) based on the 100 nm gate length InP high-electron mobility transistor technology for the frequency range of 0.3-14 and 16-28 GHz. The 0.3-14 GHz three-stage LNA exhibited a gain of 41.6 ± 1.4 dB and an average noise temperature of 3.5 K with a minimum noise temperature of 2.2 K at 6 GHz when cooled down to 4 K. The 16-28 GHz three-stage LNA showed a gain of 32.3 ± 1.8 dB and an average noise temperature of 6.3 K with a minimum noise temperature of 4.8 K at 20.8 GHz at the ambient temperature of 4 K. This is the first demonstration of cryogenic MMIC LNA covering the whole K-band. To the best of the authors' knowledge, the cryogenic MMIC LNAs demonstrated the state-of-the-art noise performance in the 0.3-14 and 16-28 GHz frequency range.

Two-Finger InP HEMT Design for Stable Cryogenic Operation of Ultra-Low-Noise Ka- and Q-Band LNAs

We investigate the cryogenic stability of two-finger 100-nm gate-length InP HEMTs aimed for Ka- and Q-band ultra-low noise amplifiers (LNAs). InP HEMTs with unit gate widths ranging between 30 and 50 $\mu \text{m}$ exhibit unstable cryogenic behavior with jumps in drain current and discontinuous peaks in transconductance. We also find that shorter gate length enhances the cryogenic instability. We demonstrate that the instability of two-finger transistors can be suppressed by either adding a source air bridge, connecting the back end of gates, or increasing the gate resistance. A three-stage 24–40 GHz and a four-stage 28–52-GHz monolithic microwave-integrated circuit LNA using the stabilized InP HEMTs are presented. The Ka-band amplifier achieves a minimum noise temperature of 7 K at 25.6 GHz with an average noise temperature of 10.6 K at an ambient temperature of 5.5 K. The amplifier gain is 29 dB ± 0.6 dB. The Q-band amplifier exhibits minimum noise temperature of 6.7 K at 32.8 GHz with average noise temperature of 10 K at ambient temperature of 5.5 K. The amplifier gain is 34 dB ± 0.8 dB. To our knowledge, the Ka- and Q-band amplifiers demonstrate the lowest noise temperature reported so far for InP cryogenic LNAs.

Microwave attenuators for use with quantum devices below 100 mK

To reduce the level of thermally generated electrical noise transmitted to superconducting quantum devices operating at 20 mK, we have developed thin-film microwave power attenuators operating from 1 to 10 GHz. The 20 and 30 dB attenuators are built on a quartz substrate and use 75 nm thick films of nichrome for dissipative components and 1 μm thick silver films as hot electron heat sinks. The noise temperature of the attenuators was quantified by connecting the output to a 3D cavity containing a transmon qubit and extracting the dephasing rate of the qubit as a function of temperature and dissipated power Pd in the attenuator. The minimum noise temperature Tn of the output from the 20 dB attenuator was Tn≤53 mK for no additional applied power and Tn≈120 mK when dissipating 30 nW. In the limit of large dissipated power (Pd&amp;gt;1 nW), we find Tn∝Pd1/5.4, consistent with detailed thermal modeling of heat flow in the attenuators.

Low noise terahertz MgB2 hot-electron bolometer mixers with an 11 GHz bandwidth

Terahertz (THz) hot-electron bolometer mixers reach a unique combination of low noise, wide noise bandwidth, and high operation temperature when 6 nm thick superconducting MgB2 films are used. We obtained a noise bandwidth of 11 GHz with a minimum receiver noise temperature of 930 K with a 1.63 THz Local Oscillator (LO), and a 5 K operation temperature. At 15 K and 20 K, the noise temperature is 1100 K and 1600 K, respectively. From 0.69 THz to 1.63 THz, the receiver noise increases by only 12%. Device current-voltage characteristics are identical when pumped with LOs from 0.69 THz up to 2.56 THz, and match well with IVs at elevated temperatures. Therefore, the effect of the THz waves on the mixer is totally thermal, due to absorption in the π conduction band of MgB2.

Effect of the Critical and Operational Temperatures on the Sensitivity of HEB Mixers

In this paper, we present a study of the noise and the gain of ${\hbox{MgB}}_{2}$ hot-electron bolometer mixers with different critical temperatures $(T_{c})$ and at various operation temperatures. At a local oscillator (LO) frequency of 1.63 THz the minimum input receiver noise temperature $(T_{r})$ was 700 K with a gain of $-{\hbox{18}}~{\hbox{dB}}$ for a device with a $T_{c}$ of 8.5 K. For a device with a $T_{c}$ of 22.5 K the corresponding values were 1700 K and $-{\hbox{19}}~{\hbox{dB}}$ . For the latter device the $T_{r}$ was 2150 K at a bath temperature of 12 K, which is not achievable with Nb-compound based HEB mixers. We present and compare different methods for measurements of the HEB mixer gain and the output noise.

A 520–620-GHz Schottky Receiver Front-End for Planetary Science and Remote Sensing With 1070 K–1500 K DSB Noise Temperature at Room Temperature

A state-of-the-art 520-620-GHz receiver front end working at room temperature was designed, built, and measured. The receiver front-end features a GaAs-Schottky diode-based subharmonic mixer and a 260-307-GHz doubler, both fabricated with the new LERMA-LPN Schottky process on a 4- μm-thick GaAs membrane suspended in a waveguide with metal beamleads. Small-area mesas and optimized transmission lines with low dielectric loading are used. At 295 K ambient temperature, an average of 1284 K DSB receiver noise temperature was measured over the 520-620-GHz frequency range, including the 3.5-8.5-GHz IF chain loss. A record 1130 K minimum DSB receiver noise temperature at 557 GHz was measured. At 134 K ambient temperature, an average DSB receiver noise temperature of 685 K from 538 to 600 GHz was measured when correcting for the cryostat window loss. A minimum DSB receiver noise of 585 K was measured at an RF center frequency of 540 GHz. The 520-620-GHz receiver presented in this article allows an increase in the sensitivity of the JUpiter ICy Moons Explrorer-SWI instrument of about a factor of two compared with requirements. It will allow study of the Jovian system with particular emphasis on the chemistry, meteorology, structure, and atmospheric coupling processes of Jupiter and its icy satellites, thereby providing important data for the exploration of their habitable zones.

&lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\hbox{MgB}_{2} $&lt;/tex-math&gt;&lt;/inline-formula&gt; Hot-Electron Bolometer Mixers at Terahertz Frequencies

In this paper, we compare the performance of MgB2 Hot-Electron Bolometer Mixers operating at Local Oscillator frequencies of 0.6 and 1.63 THz. The minimum noise temperatures that were obtained are 700 and 1150 K for 0.6 and 1.63 THz, respectively. The receiver noise bandwidth is of the order of 2.2-3 GHz for 10-nm-thick HEB devices with a Tc of 8.5 K. Sub-micrometer size HEBs were also fabricated with no degradation of the initial film quality when a 20-nm MgB2 film with a Tc of 22 K was used. In the direct detection mode, the maximum voltage responsivity is in the range of 1-2 kV/W at 1.63 THz and the optimal bias current is around 1/4-1/3 of the Ic at 4.2 K.

Low-Noise Amplifier Design Considerations For Use in Antenna Arrays

This work analyzes the implications of noise coupling in arrays of antennas on the design of low-noise amplifiers (LNAs). To select LNA design parameters in a manner familiar to LNA designers, the effective noise temperatures T <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sup> of LNAs are presented. The effect of beamformer coefficients and antenna coupling on T <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sup> is analyzed in a manner similar to a stand-alone LNA analysis. This leads to the proposed LNA design strategy of selecting LNA Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> near the reflection coefficient of antenna ports and selecting the largest practical |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | with a proper phase. This strategy is based on the assumption that the antenna array may be used for various beamforming and nonbeamforming applications, unknown at the time of the design. Numerical simulations of a 38- and 41-element antenna arrays show that a global search of LNA S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> and Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> , which result in the minimum average beam-equivalent receiver noise temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rec</sub> , finds nearly identical results to the proposed LNA design strategy. For a 41-element array with high antenna coupling at low frequencies, the proposed method shows as much as 80% improvement in the T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rec</sub> over conventional LNA design strategies that do not account for the intended use of the amplifier in an array.

2.7 THz Balanced Waveguide HEB Mixer

We report on the development of a waveguide-based balanced superconducting mixer for operation near 2.7 THz. The mixer employs a pair of NbN hot-electron bolometers defined on 6 μm-thick silicon substrate that follows a 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> hybrid coupler. To produce the critical structures of the coupler and waveguide embedding circuit, we have utilized silicon micromachining techniques based on deep reactive ion etching. Operating near 4.2 K bath temperature, we have measured a minimum uncorrected DSB receiver noise temperature of less than 2000 K using Callen-Welton formula and local oscillator sideband noise rejection better than 13±3 dB at 2.74 THz. The concept is suitable for building arrays, readily scalable for higher frequencies up 5 THz, and could accommodate other mixer technologies, such as room-temperature Schottky diode mixers.

Microwave noise characterization of graphene field effect transistors

The microwave noise parameters of graphene field effect transistors (GFETs) fabricated using chemical vapor deposition graphene with 1 μm gate length in the 2 to 8 GHz range are reported. The obtained minimum noise temperature (Tmin) is 210 to 610 K for the extrinsic device and 100 to 500 K for the intrinsic GFET after de-embedding the parasitic noise contribution. The GFET noise properties are discussed in relation to FET noise models and the channel carrier transport. Comparison shows that GFETs can reach similar noise levels as contemporary Si CMOS technology provided a successful gate length scaling is performed.

Considerations on the $ {{ 4 {{NT}}_{\rm o} }/{ {T}_{\rm m}}}$ Ratio and the Noise Correlation Matrix of Active and Passive Two-Port Networks

The constraint on the Wiatr–Pospieszalski (WP) parameter <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \Theta _{\rm W\!P}= {{ 4 {NT}_{\rm o} }/{ {T}_{\rm m}}}\leqslant 2$</tex></formula> , where <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$ {\hbox{N}}$</tex></formula> is the Lange invariant and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ {T}_{\rm m}$</tex></formula> the minimum equivalent noise temperature and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ {T}_{\rm o}={\hbox{290}}~ \left ( {\hbox{K}} \right )$</tex> </formula> , has been suggested as a validation tool for the characterization of active microwave devices, despite its acknowledged limitations. This paper provides a solid theoretical background on <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$ \Theta _{\rm W\!P}$</tex></formula> that is used to investigate noisy linear two-port networks. In particular, parallel feedback is discussed thoroughly in order to understand its effect on the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \Theta _{\rm W\!P}$</tex></formula> parameter and determine the conditions for which <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \Theta _{\rm W\!P}$</tex></formula> is larger or smaller than 2. A suitable expression that explains the conditions for <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$ \Theta _{\rm W\!P}$</tex></formula> of on-chip devices to be less than 2 is obtained. The theoretical results are supported by a scalable GaN device model extracted from measurements providing further insight into the noise performance of microwave devices. Finally, the investigation is applied to passive two-port networks to highlight the singular properties of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \Theta _{\rm W\!P}=2$</tex> </formula> . The broad result of this paper's investigation is that the constraint <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \Theta _{\rm W\!P}\leqslant 2$</tex> </formula> is not a property of the noise parameter matrix as the constraint <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$1\leqslant \Theta _{\rm W\!P} $</tex> </formula> is; yet, the threshold <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \Theta _{\rm W\!P}=2$</tex></formula> is demonstrated to have unique features for both active and passive two-port networks. Alternative and original demonstrations of the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$1\leqslant \Theta _{\rm W\!P} $</tex></formula> constraint are also obtained as a byproduct of the investigation.

Unified Theory of Linear Noisy Two-Ports

Network noise invariants are introduced that lead to improved noise characterization and a complete theory of linear noisy two-ports. Minimum power-added noise temperature and minimum cold load temperature are identified as network noise invariants under lossless embedding. Associated invariant equations provide explicit relations between all known and new network invariants. From these equations, an invariant under lossless embedding is identified that defines network noise-gain coupling in the most basic terms of noise correlation, minimum noise temperature, and complex nonreciprocal gain. A noise correlation parameter q is formally introduced that is invariant to lossless input and/or output transformation. Conditions and bounds are established, and it is shown that q ≈ 2 for low-noise active devices. An exact expression for the q parameter of a minimum noise cascade network is given in terms of constituent device invariants. From a systems point of view, the cascade q parameter represents source impedance noise sensitivity. A lower bound on cascade q is determined by device invariants minimum power-added noise temperature and minimum cold load temperature. It is shown that the cascade q lower bound is realized by simultaneous noise and power match.

Gate-to-Drain Capacitance Dependent Model for Noise Performance Evaluation of InAlAs/InGaAs Double-gate HEMT

In the present work, the effect of the gate-to-drain capacitance (C<SUB>gd</SUB> on the noise performance of a symmetric tied-gate In <SUB>0.52</SUB>AI <SUB>0.48</SUB>As/In <SUB>0.53</SUB>Ga <SUB>0.47</SUB>As double-gate HEMT is studied using an accurate charge control based approach. An analytical expression for the gate-to-drain capacitance is obtained. In terms of the intrinsic noise sources and the admittance parameters (Y <SUB>11</SUB> and Y <SUB>21</SUB> which are obtained incorporating the effect of C <SUB>gd</SUB>, the various noise performance parameters including the Minimum noise figure and the Minimum Noise Temperature are evaluated. The inclusion of gate-to-drain capacitance is observed to cause significant reduction in the Minimum Noise figure and Minimum Noise Temperature especially at low values of drain voltage, thereby, predicting better noise performance for the device.