Low-Noise Cryogenic Amplifier built using Hybrid MMIC-like / TRL Technique

Övrigt konferensbidrag, 2008

HEMT cryogenic low-noise amplifiers are an important part of instrumentation: the amplifiers use as a front-end for different measurements and as IF amplifiers in heterodyne receivers. During last few years the low-noise limit has reached as low level as approximately 0.5 K/GHz for GaAs [1] and 0.25 K/GHz for InP HEMT [2]. However, besides electrical performance improvement there were not many improvements on mass and dimension side of such amplifiers as they were built based on standard TRL technology with discrete active and passive components. Mass and dimensions are also very important for real applications. When ultimate low-noise performance is placed in focus, pure MMIC technology seems to loose against design using discrete components. With this in view, pioneered work by E. F. Lauria, et. al. [3] have successfully demonstrated a design employing MMIC approach while using discrete components and based on a microstrip on Cuflon with lumped bias network. Encouraged by this work, we propose a compact design of a 4-8 GHz cryogenic low noise amplifier using a combination of standard TRL and lumped element technology to achieve both ultimate noise performance over the specified band and a very compact size. In our design, the size reduction of the amplifier is realized by selecting an alumina substrate with a high dielectric constant, (εr = 9.9), but also by taking advantage of the lumped networks in the matching and bias circuitries. Avoiding quarter wave transformers and instead use a lumped element design approach opens up for the possibilities to reach greater bandwidths and simultaneously obtain a more compact design. In order to make optimum design, we have performed extensive simulations. Each amplifier stage has been simulated in Agilent EMDS, 3D electromagnetic field simulation package, including the single layer capacitors, and then implemented in the ADS circuit simulations as an S-parameter file. Over the 4-8 GHz band, the simulations predict noise temperature, Taverage < 4.3 K, S11 < -12 dB, S22 < -15 dB, and a gain, S21 > 35 dB. The transistors selected for the design are commercial InP HEMT (HRL) chosen due to their excellent noise performance [2], but also for the very low power consumption, which is of great importance at cryogenic temperatures. All the components used in the RFsignal path and in the bias circuits are mounted with conductive epoxy. Apart from the RFsignal path, all components are interconnected via bond-wires. Fine tuning is done by adjusting the length and loop heights of the bond-wires. At the conference we plan to report results of measurement and characterization of the prototype amplifier. REFERENCES: [1] C Risacher, et. al., “Low Noise and Low Power Consumption Cryogenic Amplifiers for Onsala and Apex Telescopes”, Proceedings of Gaas 2004, October 2004, Amsterdam. [2] N. Wadefalk, et. al., “Cryogenic Wide-Band Ultra-Low Noise IF Amplifier Operating at Ultra-Low DC-Power”, IEEE Transactions on Microwave Theory and Techniques, vol. MTT- 51, no. 6 June 2003. [3] E. F. Lauria, et. al., “A 200-300 GHz SIS Mixer-Preamplifier with 8 GHz IF Bandwidth”, 2001 IEEE International Microwave Symposium, Phoenix, AZ, May 2001.