MMICs are dimensionally small (from around 1 mm² to 10 mm²) and can be mass produced, which has allowed the proliferation of high frequency devices such as cellular phones. MMICs were originally fabricated using gallium arsenide (GaAs), a III-V compound semiconductor. It has two fundamental advantages over Silicon (Si), the traditional material for IC realisation: device (transistor) speed and a semi-insulating substrate. Both factors help with the design of high frequency circuit functions. However, the speed of Si-based technologies has gradually increased as transistor feature sizes have reduced and MMICs can now also be fabricated in Si technology. The primary advantage of Si technology is its lower fabrication cost compared with GaAs. Silicon wafer diameters are larger (typically 8" or 12" compared with 4" or 6" for GaAs) and the wafer costs are lower, contributing to a less expensive IC.
Photograph of a GaAs MMIC (a 2-18GHz upconverter)
Other III-V technologies, such as Indium Phosphide (InP), have been shown to offer superior performance to GaAs in terms of gain, higher cutoff frequency, and low noise. However they also tend to be more expensive due to smaller wafer sizes and increased material fragility.
Silicon Germanium (SiGe) is a Si-based compound semiconductor technology offering higher speed transistors than conventional Si devices but with similar cost advantages.
Gallium Nitride (GaN) is also an option for MMICs. Because GaN transistors can operate at much higher temperatures and work at much higher voltages than GaAs transistors, they make ideal power amplifiers at microwave frequencies.
Circuit Design and Device Modeling
GaAs-HBT-MMICs up to 80 GHz
Circuits for frequencies up to 80 GHz are realized using the FBH GaAs-HBT-MMIC process. The focus is on low phase-noise monolithic oscillators (VCOs). Beyond the modeling of the active device, the description of the passive elements is a key issue. Therefore, a library for coplanar elements has been developed, which covers the common discontinuities (T-junction, air bridges, ...). The models are derived by means of electromagnetic simulation and verified by measurements.
HBT modeling for GaAs and SiGe
Accurate large-signal HBT modeling is an indispensable tool for circuit design. In order to account for the specific behaviour of III-V HBTs, a new model was developed based on the GUMMEL-POON description. Two effects are most important to accurately simulate these HBTs. The first one is self-heating, the second one is the current dependence of the transit frequency, caused by high current injection into the collector.
Briefly, the FBH HBT model features:
- partition of intrinsic and extrinsic base-collector diode
- non-ideal base currents
- self-heating and thermal interaction (by a thermal port)
- current-dependence of base-collector capacitance and collector transit time
- base-emitter and base-collector break-down
- enhanced noise model: improved for 1/f range as well as for RF range of frequency
- scaling with transistor size
- unambiguous analytic parameter extraction from measurements
At the FBH, it is in routine use with in-house and commercial GaAs, InP-based, and Si/SiGe HBTs. Beyond this, it is installed already on several sites worldwide. The Verilog-A code including documentation can be downloaded subject to the following copyright information and disclaimer. Furthermore, the model is available upon request as a Design Kit for ADS, and in source code.
Fuentes: http://wapedia.mobi/en/MMIC; http://www.fbh-berlin.com/departments/microwave-department/circuit-design
--
German Martinez Duarte
CRF
No hay comentarios:
Publicar un comentario